A lightweight steel surface hardening atomic layer deposition process

Abstract

This invention discloses an atomic layer deposition process for surface hardening of lightweight steel, relating to the fields of material surface engineering and atomic layer deposition technology. The process includes: cleaning and drying a lightweight steel substrate; performing in-situ activation treatment on the heated surface of the lightweight steel substrate to form an activated surface; forming a transition layer on the activated surface using atomic layer deposition, wherein the transition layer is formed through multiple sets of transition deposition cycles; by performing in-situ activation treatment on the lightweight steel substrate and combining it with atomic layer deposition, a titanium-oxygen-nitrogen transition layer with a compositional gradient is constructed. Simultaneously, in the main hardened layer, an alternating intercalation structure of titanium nitride and oxides is introduced, along with surface sealing and densification treatment, achieving a continuous transition of the film from the substrate to the hardened layer and multi-level synergistic strengthening. This effectively balances the stability of the interface structure and the density of the film, improving the adhesion between the film and the substrate, as well as the overall wear resistance and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the fields of material surface engineering and atomic layer deposition technology, and in particular to an atomic layer deposition process for surface hardening of lightweight steel. Background Technology

[0002] With the increasing demands on structural material performance in fields such as automotive lightweighting, rail transportation, and high-end equipment manufacturing, lightweight high-strength steel (such as Si-Mn-Al series steel) is gradually becoming an important material system to replace traditional steel.

[0003] While ensuring high strength, this type of steel achieves a reduction in density through alloy design, resulting in a good specific strength advantage. In recent years, hard coatings based on plasma-enhanced atomic layer deposition (PEALD) (such as TiN, Al2O3, etc.) have shown good potential in improving the surface hardness and wear resistance of materials, and are gradually being applied to the surface modification of high-performance steels.

[0004] However, existing surface hardening technologies based on atomic layer deposition still face a core problem in practical applications, especially in terms of film-substrate interface bonding, gradient structure design, and the compactness of composite hardened layers. Specifically, the following issues are observed: traditional PVD coatings have poor step coverage and are prone to forming pores at microscopic defects or complex curved surfaces, leading to stress concentration at the interface and a decrease in adhesion; CVD processes typically require high temperatures, which can easily cause softening or grain coarsening of the lightweight steel matrix, and residual reaction byproducts can affect coating purity and corrosion resistance; although the diffusion layer formed by nitriding / carburizing is tightly bonded, the hardness gradient control precision is limited, and brittle phases are easily generated under high loads or alternating stresses, reducing toughness. Summary of the Invention

[0005] This invention provides an atomic layer deposition process for surface hardening of lightweight steel, comprising: S1. The lightweight steel substrate is cleaned and dried. The treated lightweight steel substrate is placed in the atomic layer deposition reaction chamber. The atomic layer deposition reaction chamber is evacuated to a vacuum under inert gas protection. The treated lightweight steel substrate is then heated to the deposition temperature. S2. Perform in-situ activation treatment on the heated lightweight steel substrate to form an activated surface; S3. A titanium-oxygen-nitrogen transition layer is formed on the activated surface by atomic layer deposition, wherein the titanium-oxygen-nitrogen transition layer is formed through multiple sets of transition deposition cycles; Each transition deposition cycle includes a metal precursor subcycle, an oxygen-containing reaction subcycle, and a nitrogen-containing reaction subcycle. Along the deposition direction perpendicular to the surface of the lightweight steel substrate, the proportion of the number of oxygen-containing reaction subcycles to the total number of subcycles in each transition deposition cycle decreases from one group to the next, while the proportion of the number of nitrogen-containing reaction subcycles to the total number of subcycles in each group increases from one group to the next. S4. An atomic layer deposition method is used to form the main hardening layer on the surface of the titanium-oxygen-nitrogen transition layer. The main hardening layer is a TiN / Al2O3 intercalated composite structure, which is formed by multiple hardening deposition cycles. Each set of hardening deposition cycles includes 5 to 30 titanium nitride deposition sub-cycles and 1 to 10 oxide intercalation deposition sub-cycles; S5. A surface sealing layer is formed on the surface of the main hardened layer, and the resulting film layer is densified to form a lightweight steel surface composite hardened layer.

[0006] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel described in this invention, wherein the in-situ activation treatment in S2 is plasma activation or ozone activation.

[0007] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel according to the present invention, wherein: in S3 and / or S4, at least a portion of the deposition cycles are performed sequentially in the following manner: The process involves introducing a precursor, purging with an inert gas, introducing reactants or performing plasma treatment, and then purging with an inert gas again.

[0008] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel according to the present invention, wherein at least part of the titanium nitride deposition sub-cycle in S4 adopts plasma-enhanced atomic layer deposition.

[0009] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel according to the present invention, wherein: the titanium nitride deposition sub-cycle step in S4 includes: The process involves introducing a titanium-containing precursor, purging with inert gas, treating with hydrogen plasma, purging with inert gas again, treating with nitrogen plasma or ammonia plasma, and purging with inert gas again.

[0010] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel according to the present invention, wherein: between S2 and S3, an interface layer is formed on the activated surface by atomic layer deposition. The interface layer is aluminum oxide with a thickness of 1–10 nm.

[0011] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel described in this invention, the titanium-oxygen-nitrogen transition layer has a thickness of 5-50 nm, and its oxygen content decreases in a stepwise manner and its nitrogen content increases in a stepwise manner along the deposition direction.

[0012] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel according to the present invention, the total thickness of the main hardening layer is 20-200 nm. The thickness of the oxide intercalation layer formed by the oxide intercalation deposition subcycle is 0.1–3 nm.

[0013] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel according to the present invention, the surface sealing layer is alumina with a thickness of 1-20 nm, and the densification treatment is at least one of the following: (1) Keep warm at 100-350℃ for 5-120 minutes; (2) Nitrogen plasma was used for treatment for 10 to 300 seconds.

[0014] As a preferred embodiment of the atomic layer deposition process for surface hardening of lightweight steel as described in this invention, the lightweight steel substrate is Si-Mn-Al lightweight high-strength steel.

[0015] The beneficial effects of this invention are as follows: by performing in-situ activation treatment on the lightweight steel substrate and combining it with atomic layer deposition, a titanium-oxygen-nitrogen transition layer with a compositional gradient is constructed. At the same time, in the main hardened layer, an alternating intercalation structure of titanium nitride and oxide is introduced. Combined with surface sealing and densification treatment, a continuous transition of the film layer from the substrate to the hardened layer and multi-level synergistic reinforcement are achieved. This effectively balances the stability of the interface structure and the density of the film layer, improving the bonding force between the film layer and the substrate and the overall wear resistance and corrosion resistance. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of the atomic layer deposition process for surface hardening of lightweight steel in Example 1; Figure 2 This is a schematic diagram of the composite hardening layer structure in Example 1; Figure 3 This is a schematic diagram of the compositional gradient changes in the transition layer in Example 1; Figure 4This is a schematic diagram of the main hardening layer intercalation structure in Example 1. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings and Tables 1-5.

[0019] Example 1 This invention provides an atomic layer deposition process for surface hardening of lightweight steel, comprising the following steps: S1. The lightweight steel substrate is cleaned and dried. The treated lightweight steel substrate is placed in the atomic layer deposition reaction chamber. The atomic layer deposition reaction chamber is evacuated to a vacuum under inert gas protection. The treated lightweight steel substrate is then heated to the deposition temperature. S2. Perform in-situ activation treatment on the heated lightweight steel substrate to form an activated surface; S3. A titanium-oxygen-nitrogen transition layer is formed on the activated surface by atomic layer deposition, wherein the titanium-oxygen-nitrogen transition layer is formed through multiple sets of transition deposition cycles; Each transition deposition cycle includes a metal precursor subcycle, an oxygen-containing reaction subcycle, and a nitrogen-containing reaction subcycle. Along the deposition direction perpendicular to the surface of the lightweight steel substrate, the proportion of the number of oxygen-containing reaction subcycles to the total number of subcycles in each transition deposition cycle decreases from one group to the next, while the proportion of the number of nitrogen-containing reaction subcycles to the total number of subcycles in each group increases from one group to the next. S4. An atomic layer deposition method is used to form the main hardening layer on the surface of the titanium-oxygen-nitrogen transition layer. The main hardening layer is a TiN / Al2O3 intercalated composite structure, which is formed by multiple hardening deposition cycles. Each set of hardening deposition cycles includes 5 to 30 titanium nitride deposition sub-cycles and 1 to 10 oxide intercalation deposition sub-cycles; S5. A surface sealing layer is formed on the surface of the main hardened layer, and the resulting film layer is densified to form a lightweight steel surface composite hardened layer. The surface sealing layer is aluminum oxide with a thickness of 1-20 nm. The densification treatment is carried out at 100-350℃ for 5-120 min or by nitrogen plasma treatment for 10-300 s.

[0020] This embodiment provides a specific implementation method for forming a composite hardening layer on the surface of lightweight steel. The implementation method includes: pre-treating the lightweight steel substrate; in-situ activation of the pre-treated substrate surface; and forming a transition layer on the activated surface. A primary hardened layer is formed on the surface of the transition layer; A surface sealing layer is formed on the surface of the main hardened layer and densification treatment is performed to obtain a composite hardened layer with surface strengthening effect on the surface of lightweight steel.

[0021] To facilitate the verification of the feasibility of this solution, this embodiment selects lightweight high-strength steel for the locking tooth plate of the new energy vehicle seat slide rail as the simulated application object.

[0022] These types of parts are subjected to contact loads, local sliding friction, and the effects of condensation and chlorine-containing media in actual use. They require high surface hardness and wear resistance, as well as good bonding stability and corrosion resistance between the film layer and the steel substrate. Therefore, they are suitable as the verification scenario for this embodiment.

[0023] The lightweight steel matrix used in this embodiment is Si-Mn-Al lightweight high-strength steel with a plate thickness of 1.2mm and a sample cut into 30mm×20mm pieces. First, the substrate is cleaned and dried to remove surface oil, particulate contaminants, and adsorbed water. Specifically, the sample was first placed in an alkaline cleaning solution at 55°C and ultrasonically degreased for 8 minutes, then rinsed twice with deionized water, and then ultrasonically cleaned in acetone and anhydrous ethanol for 5 minutes each, and finally dried in hot air at 80°C for 15 minutes. This step effectively reduces the adverse effects of surface contamination on subsequent deposition uniformity and interfacial bonding.

[0024] After pretreatment, the sample was loaded into the atomic layer deposition reaction chamber, evacuated to 40 Pa under nitrogen protection, and the substrate was heated to 250 °C and held for 20 min to allow the sample to reach a stable deposition temperature. Subsequently, the substrate surface was activated in situ to improve surface reactivity and enhance subsequent nucleation.

[0025] In the specific execution of this embodiment, the activation step uses Ar / H2 mixed plasma treatment, wherein the Ar flow rate is 120 sccm, the H2 flow rate is 30 sccm, the plasma power is 180W, and the treatment time is 90s; After adopting this activation method, weakly adsorbed impurities and unstable surface layers on the substrate surface can be further removed, while the surface reactivity can be improved, which is beneficial to the continuous nucleation of the subsequent transition layer.

[0026] A transition layer is formed on the activated surface, which serves to mitigate the interfacial mismatch between the lightweight steel substrate and the upper hardened layer, and reduce the risk of local delamination caused by abrupt interlayer changes. In the specific implementation of this embodiment, the transition layer adopts a titanium-oxygen-nitrogen transition layer, and through multiple sets of transition deposition cycles, it is made to have a higher oxygen content on the side near the substrate and a higher nitrogen content on the side near the main hardening layer, thereby forming a transition structure that gradually changes along the deposition direction; The metal precursor used in the transition layer is tetrakis(dimethylamino)titanium, the oxygen-containing reactant is water vapor, and the nitrogen-containing reactant is ammonia plasma. In this embodiment, a total of 8 groups of transition deposition cycles are set up. The ratio of oxygen-containing reaction sub-cycles to nitrogen-containing reaction sub-cycles in each group is as follows: Group G1 12:3, Group G2 11:4, Group G3 10:5, Group G4 9:6, Group G5 8:7, Group G6 7:8, Group G7 6:9, Group G8 5:10. The thickness of the resulting transition layer is approximately 11.9 nm. Within each transitional deposition cycle group, the metal precursor subcycle is always executed first, followed by deposition in an alternating manner according to the preset ratio of oxygen-containing to nitrogen-containing subcycles. Specifically, for cases where the number of oxygen-containing subcycles is greater than that of nitrogen-containing subcycles (such as group G1), oxygen-containing and nitrogen-containing subcycles are first performed alternately until all nitrogen-containing subcycles are completed, and then the remaining oxygen-containing subcycles are executed. If the number of nitrogen-containing subcycles is greater than that of oxygen-containing subcycles (such as in group G8), they are performed alternately first. After the oxygen-containing subcycles are completed, the remaining nitrogen-containing subcycles are then executed. When the number of both is equal, they are performed alternately. An inert gas purging step is inserted between all sub-cycles to ensure the self-limiting reaction characteristics of atomic layer deposition; The above setup helps improve the chemical and structural bonding between the steel substrate and the upper film layer, and provides a stable foundation for the continuous deposition of the main hardening layer.

[0027] After the transition layer is formed, the main hardening layer is formed on its surface; The main hardening layer is the main structure for surface strengthening in this embodiment, and it mainly plays the role of improving surface hardness, reducing wear, and improving service stability. In the specific implementation of this embodiment, the main hardening layer adopts a TiN / Al2O3 intercalation composite structure and is formed through multiple hardening deposition cycles. The TiN sub-cycle is carried out by plasma-enhanced atomic layer deposition, and the Al2O3 intercalation is formed by alternating reaction of aluminum source precursor and water vapor. In this embodiment, the main hardened layer adopts a TiN / Al2O3 intercalation composite structure, which is formed through multiple hardening deposition cycles, wherein the oxide intercalation is Al2O3.

[0028] The main hardening layer consists of 22 hardening deposition cycles, each including 18 titanium nitride deposition sub-cycles and 2 oxide intercalation deposition sub-cycles.

[0029] TiN sub-cycles are performed using plasma-enhanced atomic layer deposition, following the sequence of "TDMAT introduction, inert gas purging, hydrogen plasma treatment, inert gas purging again, ammonia plasma treatment, and inert gas purging again". Al2O3 intercalation is formed through an alternating reaction of TMA and water vapor. After deposition with the above parameters, the thickness of the resulting main hardened layer is approximately 39.6 nm.

[0030] This intercalation composite structure helps to reduce the possibility of continuous defect propagation while ensuring the hardening effect, thereby improving the overall stability of the film under frictional load.

[0031] In the specific preparation of this embodiment, after obtaining the main hardened layer, the surface of the film layer is further treated to improve the sealing degree and environmental stability of the outer surface of the film layer. Specifically, an Al2O3 surface sealing layer with a thickness of approximately 3.1 nm is formed on the surface of the main hardened layer; then, a densification treatment is performed using N2 plasma at a temperature of 160 W × 120 s.

[0032] This treatment method can further reduce open defects and localized connectivity defects on the film surface, slow down the rate at which corrosive media penetrate into the film, and help improve the stability of the composite hardened layer in humid and salt spray environments.

[0033] This treatment method can further reduce open defects and localized connectivity defects on the film surface, slow down the rate at which corrosive media penetrate into the film, and help improve the stability of the composite hardened layer in humid and salt spray environments. After the above steps, a composite hardened layer with a total thickness of approximately 54.6 nm is formed on the surface of the lightweight steel. The results of its layer thickness composition, surface roughness, and critical scratch load are shown in Table 4, F1.

[0034] The obtained samples were subjected to structural and performance tests. The structural characterization results showed that the obtained composite hardening layer continuously covered the surface of the lightweight steel, the interlayer interface was clear, and obvious compositional transition characteristics could be observed in the transition layer region. This indicates that the process route of this embodiment can stably establish a hierarchical structure from the matrix to the main hardening layer in the actual preparation process. The relevant structural results are shown in F1 of Table 4. Performance test results show that the nanohardness of the sample in this embodiment is 16.7 GPa, the steady-state friction coefficient is 0.39, and the wear rate is 1.46 × 10⁻⁶. -6 mm 3 ·N -1 ·m -1 The corrosion current density is 0.13 μA·cm.-2 After 72 hours of salt spray, the rust area was 0.4%, and the relevant results are shown in Table 5, F1. The above results demonstrate that the composite hardened layer formed in this embodiment can simultaneously achieve good wear resistance and corrosion resistance under conditions of relatively low total film thickness.

[0035] As can be further seen from the aforementioned comparative examples, the sample obtained in this embodiment has significant advantages over the comparative examples that do not use a layered composite structure in terms of scratch critical load, wear rate, and corrosion current density. This indicates that this embodiment does not rely on a single hard film layer to achieve surface strengthening, but achieves a balance of stability, wear resistance, and corrosion resistance through the synergistic effect of substrate surface activation, transition layer buffering, main hardened layer strengthening, and surface integrity improvement.

[0036] The above results show that, by pretreating and surface-activating the lightweight steel substrate, a transition layer, a main hardening layer, and a surface sealing layer are sequentially formed on its surface and then densified, a composite hardening layer with good wear resistance and corrosion resistance can be obtained under conditions of lower total film thickness. The process path of this implementation method is clear, the resulting film structure is well-defined, and the relevant performance results can reflect the improvement effect of this process on the surface strengthening of lightweight steel.

[0037] Example 2 The lightweight steel surface hardening atomic layer deposition process corresponding to this embodiment, and its further limitation on the deposition conditions of the main hardening layer, are an implementation method formed by strengthening the deposition conditions of the titanium nitride sub-cycle in the main hardening layer based on the lightweight steel surface composite hardening layer preparation process in Example 1. The overall process route of this embodiment is the same as that of embodiment 1, and still includes substrate pretreatment, surface activation, formation of transition layer, formation of main hardening layer, formation of surface sealing layer and subsequent densification treatment; Unlike Example 1, this example enhances the plasma-enhanced atomic layer deposition conditions of the TiN sub-cycle in the main hardened layer to further improve the compactness of the TiN layer, reduce residual defects, and improve the hardness, wear resistance, and environmental stability of the composite hardened layer.

[0038] The lightweight steel matrix, simulated application scenario, sample size, matrix cleaning and drying methods, vacuuming and heating conditions after mounting, and in-situ activation method used in this embodiment are all the same as in Example 1. That is, the lightweight steel matrix is ​​Si-Mn-Al lightweight high-strength steel, and the sample can be a 30mm×20mm plate sample with a thickness of 1.2mm; The cleaning and drying process, the conditions of evacuating the reaction chamber to 40 Pa and heating it to 250°C for 20 min, and the steps of in-situ activation using Ar / H2 mixed plasma are all the same as in Example 1, and will not be repeated here.

[0039] When forming a transition layer on the activated surface, this embodiment also uses a titanium-oxygen-nitrogen gradient transition layer, and its construction concept is the same as that in Embodiment 1. That is, through multiple sets of transition deposition cycles, the oxygen content in the transition layer decreases stepwise and the nitrogen content increases stepwise in the direction away from the steel substrate surface, so as to form a gradual buffer zone of composition and structure between the steel substrate and the subsequent main hardening layer.

[0040] The metal precursor, oxygen-containing reactant, and nitrogen-containing reactant used in the transition layer are the same as in Example 1, and each group of transition deposition cycles includes a metal precursor sub-cycle, an oxygen-containing reactant sub-cycle, and a nitrogen-containing reactant sub-cycle.

[0041] In this embodiment, a total of 8 transition deposition cycles are set up. The ratio of oxygen-containing reaction subcycles to nitrogen-containing reaction subcycles in each group is 12:3, 11:4, 10:5, 9:6, 8:7, 7:8, 6:9 and 5:10, respectively. The thickness of the resulting transition layer is approximately 12.1 nm.

[0042] The core difference between this embodiment and Embodiment 1 lies in the deposition conditions of the TiN sub-cycle in the main hardening layer.

[0043] The main hardened layer still adopts a TiN / Al2O3 intercalation composite structure. A total of 22 hardening deposition cycles were set up, each including 18 TiN sub-cycles and 2 Al2O3 intercalation deposition sub-cycles. The thickness of the obtained main hardened layer is about 40.8 nm.

[0044] The Al2O3 intercalation can be formed in the same way as in Example 1, that is, atomic layer deposition is still performed using TMA and water vapor. The function of this intercalation is still to interrupt the continuous columnar growth of the TiN layer, suppress the propagation of through defects, and improve the crack resistance of the main hardened layer. Therefore, it is not repeated as a major change point in this example.

[0045] Compared with Example 1, the TiN sub-cycle in this example is still carried out in the order of "introducing TDMAT, inert gas purging, hydrogen plasma treatment, inert gas purging again, ammonia plasma treatment, and inert gas purging again", but enhanced PEALD conditions are used. Specifically, the TDMAT pulse time is maintained at 0.20s, and the pre- and post-purge times remain at 8s, 6s, and 8s, respectively. Unlike Example 1, this example increases the hydrogen plasma treatment time from 4s to 6s, the ammonia plasma treatment time from 7s to 10s, and increases the ammonia plasma power from the conditions of Example 1 to 240W, while maintaining the hydrogen plasma power at 180W. The working pressure during the plasma treatment stage is controlled between 55Pa and 65Pa.

[0046] With the above-mentioned enhanced PEALD conditions, the residual ligands of titanium-containing precursors adsorbed on the surface can be removed more fully, and the surface active sites can also complete the nitridation reaction more fully under the action of ammonia plasma, thereby making the obtained TiN sublayer more compact and with lower impurity residue.

[0047] In this embodiment, the Al2O3 intercalation deposition method in each hardening deposition cycle is the same as in Example 1, and will not be described again. After deposition according to the cycle group number and sub-cycle parameters shown in F2 of Table 3, the thickness of the main hardened layer is approximately 40.8 nm.

[0048] The results show that under enhanced PEALD conditions, the TiN sublayer is formed more fully, the overall structure of the main hardened layer is more compact, and the thickness can provide effective hardening without significantly increasing internal stress due to excessive film thickness.

[0049] After the main hardening layer is formed, this embodiment continues to form an Al2O3 surface sealing layer on its surface and performs N2 plasma densification treatment; The surface sealing layer is approximately 3.0 nm thick, and the densification treatment conditions are 160 W × 120 s. After this step, a composite hardened layer with a total thickness of approximately 55.9 nm is formed on the surface of the lightweight steel.

[0050] Performance test results show that the nanohardness of sample F2 in Table 5 is 17.4 GPa, the steady-state friction coefficient is 0.37, and the wear rate is 1.24 × 10⁻⁶. -6 mm 3 ·N -1 ·m -1 The corrosion current density is 0.11 μA·cm. -2 After 72 hours of salt spray, the rust area was 0.3%. Compared to Example 1, Example 2, with only a slight increase in total film thickness, showed further improvement in nanohardness, a further decrease in the coefficient of friction and wear rate, and enhanced corrosion resistance. This indicates that the performance improvement in Example 2 mainly stems from the improvement in TiN sublayer quality brought about by the enhanced PEALD, rather than from changes in the structure of the transition layer, intercalation layer, or surface sealing layer.

[0051] Combining Tables 4 and 5, it can also be seen that the critical scratch load of Example 2 is higher than that of Example 1, indicating that under the premise that the overall structure of the main hardened layer remains unchanged, the TiN sublayer formed by the enhanced PEALD has better interface quality and overall mechanical compatibility with adjacent intercalation layers and adjacent sublayers. Compared with Comparative Example C4, which uses thermal ALD to form TiN, Example 2 has significant advantages in terms of nanohardness, wear rate, and corrosion current density. This indicates that in the composite hardening layer system of the present invention, the stepwise treatment with hydrogen plasma and ammonia plasma, and the appropriate enhancement of the treatment intensity, are beneficial to further exert the hardening and densification effects of the TiN layer.

[0052] The above results indicate that, based on Example 1, enhancing the PEALD treatment conditions of the TiN subcycle is beneficial to further improve the TiN sublayer formation quality, thereby improving the hardness, wear resistance, and corrosion resistance of the composite hardened layer.

[0053] Example 3 The process described in this embodiment, and its further limitation on setting an interface layer between the substrate and the transition layer, is an implementation method formed by further setting an interface layer between the substrate and the transition layer based on the preparation process of the lightweight steel surface composite hardening layer in Embodiment 1. The overall process route of this embodiment is basically the same as that of Embodiment 1, except that: after the lightweight steel substrate has completed surface activation, the transition layer is not directly formed, but an interface layer is first formed on the surface of the substrate, and then a transition layer, a main hardening layer, and a surface sealing layer are formed on the surface of the interface layer and densification treatment is performed. By introducing an interface layer, the initial nucleation uniformity and interface integrity can be further improved, thereby enhancing the adhesion stability and corrosion resistance of the composite hardened layer.

[0054] The simulated application scenario in this embodiment can remain consistent with that in Embodiment 1, that is, using Si-Mn-Al lightweight high-strength steel for the locking tooth plate of the new energy vehicle seat slide rail as the simulated application object.

[0055] The matrix material, sample size, cleaning and degreasing steps, deionized water rinsing steps, organic solvent ultrasonic cleaning steps, hot air drying steps, slide loading and vacuuming conditions, and heating and heat preservation conditions used are all the same as in Example 1, and will not be repeated here.

[0056] In other words, this embodiment is based on the substrate pretreatment and initial deposition conditions that have been fully disclosed in Example 1, and only the initial structure of the film layer is further optimized. Therefore, the same content will not be repeated.

[0057] After the substrate is cleaned, dried, and placed into the atomic layer deposition reaction chamber, in-situ activation treatment is performed in the same reaction chamber. This activation method is the same as in Example 1, using Ar / H2 mixed plasma to activate the substrate surface to remove residual adsorbates and improve surface reactivity. After activation, this example does not immediately form a titanium-oxygen-nitrogen gradient transition layer; instead, an Al2O3 interface layer is first formed on the activated lightweight steel surface. The purpose of this interface layer is to provide a continuous, uniform, and chemically stable initial covering layer before the gradient transition layer, thereby improving the initial nucleation consistency of the lightweight steel surface, especially in areas with uneven local structure, micro-undulations, and potential surface defects, and reducing the local reaction differences and interface discontinuities that may occur when subsequent multilayer structures are directly established on the steel surface.

[0058] The interface layer is formed by atomic layer deposition, preferably using trimethylaluminum (TMA) as the aluminum source and water vapor as the reactant. The deposition is carried out in a cycle of "TMA introduction - inert gas purging - water vapor introduction - inert gas purging again". Specifically, the TMA pulse time can be controlled to 0.05s, the water vapor pulse time can be controlled to 0.05s, and the nitrogen purging time between each step can be controlled to 8s. In this embodiment, the number of interface layer deposition cycles is controlled to make the thickness of the resulting interface layer approximately 2.5 nm, and the thickness result corresponds to F3 in Table 4; By controlling the thickness of the interface layer within this range, it is possible to ensure that it forms a basic continuous coverage on the steel surface, while also preventing the interface layer from weakening the necessary component buffering effect between the subsequent transition layer and the substrate due to excessive thickness. In other words, the interface layer in this embodiment does not replace the gradient transition layer, but is located between the steel substrate and the gradient transition layer, playing an auxiliary role in improving the integrity of the initial interface.

[0059] After the interface layer is formed, a titanium-oxygen-nitrogen gradient transition layer is formed on the surface of the interface layer. The formation concept, basic deposition path, and working mechanism of this transition layer are the same as in Example 1. That is, through multiple sets of transition deposition cycles, the oxygen content in the transition layer gradually decreases in the direction away from the steel substrate surface, while the nitrogen content gradually increases, thereby constructing a gradient composition transition region between the subsequent main hardening layer and the substrate. Since an Al2O3 interface layer has been set in this embodiment, the side of the transition layer near the substrate is actually in contact with this interface layer. Under this condition, the relatively high oxygen content reaction characteristics in the first part of the transition layer can form a good connection with the interface layer, while the gradually increasing nitrogen content reaction characteristics in the latter part of the transition layer are conducive to establishing a smoother structural transition with the subsequent TiN main hardening layer.

[0060] The metal precursor, oxygen-containing reactant, and nitrogen-containing reactant used in the transition layer are the same as in Example 1, and each group of transition deposition cycles includes a metal precursor sub-cycle, an oxygen-containing reactant sub-cycle, and a nitrogen-containing reactant sub-cycle. In this embodiment, a total of 8 transition deposition cycles were set up. The ratio of oxygen-containing reaction subcycles to nitrogen-containing reaction subcycles in each group was 12:3, 11:4, 10:5, 9:6, 8:7, 7:8, 6:9 and 5:10, respectively, and the thickness of the resulting transition layer was approximately 11.8 nm.

[0061] The execution order of each sub-loop is the same as in Example 1, and will not be repeated here. After this step, a titanium-oxygen-nitrogen gradient transition layer with a thickness of approximately 11.8 nm is formed. The thickness and gradient characterization results are shown in Table 4, F3.

[0062] After the transition layer is formed, the main hardening layer is formed on its surface. In this embodiment, the main hardening layer still adopts a TiN / Al2O3 intercalation composite structure, and its overall design, execution path and technical purpose are the same as those in Example 1.

[0063] The main hardened layer still adopts the TiNAl2O3 intercalation composite structure, with a total of 22 hardening deposition cycles. Each cycle includes 18 TiN sub-cycles and 2 Al2O3 intercalation deposition sub-cycles, and the thickness of the obtained main hardened layer is about 39.2 nm. The TiN sub-cycle is still carried out using the PEALD method, and is completed in the following order: "Introduction of TDMAT, inert gas purging, hydrogen plasma treatment, inert gas purging again, ammonia plasma treatment, and inert gas purging again". The Al2O3 intercalation is still formed through alternating deposition of TMA and water vapor. The function of this intercalation is still to interrupt the continuous columnar growth trend of TiN, inhibit the penetration of internal defects and the continuous propagation of cracks. Since the main change in this embodiment is in the interface layer, the composition and formation mechanism of the main hardening layer will not be repeated.

[0064] After executing the procedure according to the parameters shown in F3 of Table 3, the thickness of the main hardened layer is approximately 39.2 nm.

[0065] After the main hardening layer is formed, this embodiment continues to form an Al2O3 surface sealing layer on its surface and performs N2 plasma densification treatment. The process and execution method of this part can be consistent with that of Example 1. The thickness of the surface sealing layer is about 3.1 nm, and the densification treatment conditions are 160 W × 120 s.

[0066] The surface sealing layer is mainly used to seal open defects and tiny pinholes on the outermost layer of the main hardened layer. Subsequent N2 plasma densification treatment further compacts the surface structure, reduces the connectivity of surface defects, and improves the environmental stability of the film layer. After the above steps, this embodiment forms a composite hardened layer with a total thickness of approximately 56.6 nm on the surface of lightweight steel. The thickness composition, surface roughness, scratch critical load, and gradient characteristics are shown in Table 4, F3.

[0067] As shown in F3 of Table 4, the interface layer thickness of the sample in this embodiment is about 2.5 nm, the surface roughness Ra is 19.9 nm, the critical scratch load Lc2 is 35.0 N, and an obvious O / N step gradient can still be observed by XPS depth analysis.

[0068] This indicates that the transition layer and the main hardening layer were not negatively affected after the interface layer was applied; on the contrary, they were improved in terms of interface integrity and surface uniformity. Table 5, F3, further shows that the nanohardness of the sample in this embodiment is 17.0 GPa, the steady-state friction coefficient is 0.38, and the wear rate is 1.31 × 10⁻⁶. -6 mm 3 ·N -1 ·m -1 The corrosion current density is 0.09 μA·cm. -2 After 72 hours of salt spray, the rust area was 0.2%; The above results show that, by adding an interface layer, this embodiment not only did not weaken the hardening effect of the main hardening layer, but also further improved the film layer in terms of adhesion, wear resistance and corrosion resistance.

[0069] Comparing this embodiment with Embodiment 1, it can be seen that the two are generally consistent in terms of transition layer, main hardening layer, surface sealing layer and subsequent densification treatment. The main difference is that this embodiment adds an Al2O3 interface layer located between the substrate and the transition layer. As can be seen from the data in Tables 4 and 5, the critical scratch load in this embodiment is higher than that in Example 1, the surface roughness is slightly reduced, and the corrosion current density and the rust area after salt spray are further decreased. This indicates that the introduction of the interface layer is beneficial to improving the initial coverage quality of the substrate surface and the stability of the interlayer interface, especially in reducing the adverse effects of local interface defects on the overall performance of the subsequent composite film layer. In other words, the interface layer in this embodiment is not a simple, optional additional layer, but an important means of optimizing the initial interface state of the steel surface, which makes the foundation for the construction of the subsequent gradient transition layer and the main hardening layer more stable.

[0070] Further comparison with the aforementioned comparative examples C1, C2, C3 and C4 shows that this embodiment still maintains the overall advantages of the composite hierarchical structure of the present invention.

[0071] Compared with C1, which lacks a transition layer, intercalation layer and surface sealing layer, this embodiment has significantly improved adhesion stability, hardness, wear resistance and corrosion resistance, indicating that the layered composite design of the present invention plays a decisive role. Compared to C2, which only retains the transition layer but lacks the intercalation layer and the surface sealing layer, this embodiment further demonstrates the synergistic gain of the intercalation layer and the surface sealing layer; Compared to C3, which omits the surface sealing layer, this embodiment has a more significant advantage in corrosion resistance, demonstrating that a complete hierarchical system is particularly important for environmental stability. Compared to C4, which uses thermal ALD to form TiN, this embodiment shows that the TiN main hardening layer formed by PEALD, in combination with the interface layer and the gradient transition layer, can further improve the overall performance of the entire composite hardening layer.

[0072] In summary, based on the overall technical approach of Example 1, this embodiment discloses an implementation method that can further improve the initial interface integrity, enhance the film bonding stability, and improve corrosion resistance by setting a thin Al2O3 interface layer between the lightweight steel substrate and the titanium-oxygen-nitrogen gradient transition layer.

[0073] The formation method of this interface layer is clear, the parameters are executable, the connection relationship with the subsequent transition layer and the main hardening layer is clear, and the final composite hardening layer has a clear structure and excellent performance. Therefore, this setting is beneficial to improving the interface bonding state and enhancing the stability of the film layer.

[0074] The above results show that adding an Al2O3 interface layer based on Example 1 is beneficial to further improve the initial interface state and enhance the bonding stability and corrosion resistance of the composite hardened layer.

[0075] Example 4 The process and its variations regarding densification are based on the lightweight steel surface composite hardening layer preparation process of Example 1, with the subsequent densification path replaced. The overall hierarchical structure of this embodiment is the same as that of Example 1, still forming a transition layer, a main hardening layer, and a surface sealing layer on the surface of the lightweight steel; Unlike Example 1, after the main hardening layer and the surface closed structure are formed, this example does not use plasma densification. Instead, it uses controlled heat treatment to perform subsequent densification and structural stabilization treatment on the resulting composite hardening layer, in order to verify the feasibility and process compatibility of the composite hardening layer system under alternative post-processing paths.

[0076] When forming a transition layer on the activated surface, this embodiment still uses a titanium-oxygen-nitrogen gradient transition layer. Its formation principle and function are the same as in Embodiment 1. That is, by setting a relatively high oxygen-containing reaction characteristic on the side closer to the steel substrate and a relatively high nitrogen-containing reaction characteristic on the side closer to the main hardening layer, the oxygen content in the transition layer decreases stepwise and the nitrogen content increases stepwise in the direction away from the substrate, so as to form a buffer zone with continuous compositional change between the steel substrate and the main hardening layer.

[0077] In this embodiment, a total of 8 transition deposition cycles were set up. The ratio of oxygen-containing reaction subcycles to nitrogen-containing reaction subcycles in each group was 12:3, 11:4, 10:5, 9:6, 8:7, 7:8, 6:9 and 5:10, respectively, and the thickness of the resulting transition layer was approximately 11.7 nm.

[0078] After the transition layer is formed, the main hardened layer is formed on its surface.

[0079] In this embodiment, the main hardening layer still adopts a TiN / Al2O3 intercalation composite structure. The overall concept is the same as in Example 1, that is, multiple TiN sublayers provide the main hardening effect, and the periodic introduction of ultrathin Al2O3 intercalation inhibits defect penetration and continuous crack propagation.

[0080] A total of 22 hardening deposition cycles were set up, each including 18 TiN sub-cycles and 2 Al2O3 intercalation deposition sub-cycles, and the thickness of the main hardened layer was approximately 39.4 nm.

[0081] After the main hardened layer is formed, this embodiment continues to form an Al2O3 surface sealing layer on its surface.

[0082] The surface sealing layer is an Al2O3 surface sealing layer with a thickness of approximately 3.0 nm; The process remains consistent with Example 1, serving to seal open defects and pinholes on the outermost surface of the main hardened layer, reducing the possibility of rapid penetration of external corrosive media into the film. Unlike Example 1, this example does not employ N2 plasma for low-temperature densification after the surface sealing layer is formed. Instead, it uses controlled heat treatment for densification of the resulting composite hardened layer. Specifically, the sample with the completed surface sealing layer deposition is kept in a low-oxygen environment under an inert atmosphere, and the temperature is raised to 280°C, held for 40 minutes, and then cooled in the furnace to below 120°C before being removed from the furnace.

[0083] The heat treatment process is preferably carried out in a nitrogen atmosphere, and the atmosphere flow rate is maintained sufficiently to suppress the backflow of outside air, so as to avoid significant secondary oxidation on the film surface during the heat treatment process.

[0084] The purpose of using heat treatment for densification in this embodiment is not to simply replace plasma post-treatment, but to utilize controlled temperature conditions to further adjust the metastable structure inside the composite hardened layer, promote the shrinkage of local loose regions, and improve the stability of the interlayer interfaces. For the TiN sublayer and Al2O3 intercalation in the main hardened layer, appropriate heat treatment helps to reduce the local non-ideal structures and weak bonding regions remaining during the deposition process; For surface sealing layers, heat treatment helps improve their coverage integrity and surface stability. Since the heat treatment temperature is controlled at 280℃, it remains within the acceptable range for surface treatment of lightweight steel and will not significantly damage the original microstructure of the substrate. The above results show that, while keeping the basic structure of the transition layer, the main hardening layer and the surface sealing layer unchanged, replacing the subsequent densification step with controlled heat treatment can still yield a composite hardening layer with good adhesion stability, wear resistance and corrosion resistance.

[0085] Further comparison of this embodiment with Embodiment 1 reveals that, under similar overall film structure and thickness, Embodiment 4 exhibits slightly inferior nanohardness, friction coefficient, wear rate, and corrosion current density compared to Embodiment 1.

[0086] This indicates that in the system of the present invention, N2 plasma densification still has a stronger effect on further compacting the surface structure, reducing open defects and improving near-surface densification; but at the same time, the performance of this embodiment is still significantly better than that of the comparative sample that lacks a transition layer, intercalation layer or surface sealing layer, indicating that even if heat treatment densification is used, as long as the core structural system of "gradient transition layer - intercalation main hardening layer - surface sealing layer" is retained, the comprehensive performance that is significantly better than that of a simple single-layer hardened film can still be obtained.

[0087] For example, compared with the aforementioned comparative example C1, the scratch critical load of this embodiment is significantly higher, and the wear rate and corrosion current density are significantly lower, indicating that the synergistic effect of the transition layer, intercalation layer and surface sealing layer is still the key to determining the performance of the composite hardened layer. Compared with Comparative Example C3, this embodiment still has a significant advantage in corrosion resistance, indicating that the surface sealing layer, in combination with subsequent heat treatment, can effectively improve the surface integrity. Compared with Comparative Example C4, which uses thermal ALD to form TiN, the hardness and wear resistance of this embodiment are still superior, indicating that the formation of TiN sublayers using the PEALD method is still of great significance in ensuring the quality of the main hardened layer.

[0088] Therefore, it can be seen that the beneficial effect of this embodiment is to prove that, under the overall technical route of the present invention, even if the post-processing is replaced by controlled heat treatment instead of plasma densification, a composite hardened layer with good performance can still be obtained, thereby broadening the process applicability window of the present invention.

[0089] In summary, based on the overall structural design of Example 1, this embodiment replaces the subsequent densification step with controlled heat treatment densification instead of N2 plasma treatment, disclosing another executable and industrially feasible post-processing path. This implementation requires simple equipment and is suitable for surface treatment production lines that lack plasma post-processing modules but possess controlled heat treatment conditions. Simultaneously, its processing temperature remains controlled within a range that does not significantly affect the microstructure of the lightweight steel matrix, thus possessing clear feasibility and engineering value.

[0090] Example 5 The process and its variations regarding the activation method in this embodiment are based on the preparation process of the lightweight steel surface composite hardening layer in Example 1, and the implementation method is formed by replacing the activation method of the substrate surface.

[0091] The overall process route of this embodiment is the same as that of embodiment 1, and still includes substrate pretreatment, surface activation, formation of transition layer, formation of main hardening layer, formation of surface sealing layer and subsequent densification treatment; Unlike Example 1, this example does not use Ar / H2 mixed plasma activation, but instead uses ozone activation to verify that a composite hardened layer with clear layers and good performance can still be stably constructed on the surface of lightweight steel under different activation paths.

[0092] The simulated application scenario, matrix material, and sample form in this embodiment are the same as in Example 1.

[0093] That is, the Si-Mn-Al series lightweight high-strength steel used for locking tooth plates of new energy vehicle seat slide rails is still selected as the simulation object, and the sample size can be 30mm×20mm, with a substrate thickness of 1.2mm.

[0094] The substrate pretreatment steps can also be the same as in Example 1, that is, first, the substrate is ultrasonically degreased with an alkaline cleaning solution, then rinsed with deionized water, ultrasonically cleaned with acetone, ultrasonically cleaned with anhydrous ethanol, and dried with hot air in sequence. After that, the substrate is placed in the atomic layer deposition reaction chamber, vacuumed to 40 Pa under nitrogen protection, and heated to 250°C and kept at that temperature for 20 min.

[0095] Since the above steps are the same as those in Example 1, and their purpose is to remove surface contaminants, adsorbed water and weakly bound impurities, and to establish stable deposition temperature conditions, they will not be repeated.

[0096] Unlike Example 1, this example does not use Ar / H2 mixed plasma to activate the substrate surface in situ, but instead uses ozone activation.

[0097] Specifically, after the substrate reaches 250°C and stabilizes, an ozone / oxygen mixture is introduced into the reaction chamber. The total gas flow rate is controlled at 100 sccm, the ozone concentration is controlled at 80 mg / L to 100 mg / L, and the chamber pressure during the activation phase is controlled at 55 Pa to 65 Pa. Three rounds of ozone activation are performed using a pulsed exposure method. Each round includes: introducing the ozone / oxygen mixture for 15 seconds, maintaining exposure for 20 seconds, followed by purging with nitrogen for 30 seconds. After three rounds of activation, nitrogen gas is introduced for a stable purging for 60 seconds. Using the above ozone activation method, residual organic contaminants and some weakly bonded surface layers on the steel surface can be removed. Furthermore, ozone's strong oxidizing activity enables a more uniform and reactive surface state on the substrate, thereby improving the continuity and consistency of the initial nucleation of the subsequent transition layer.

[0098] Compared to plasma activation, ozone activation equipment has relatively lower requirements and does not have an ion bombardment effect, making it suitable for some deposition systems that are more sensitive to surface damage or do not have a plasma module.

[0099] On the ozone-activated surface, this embodiment still first forms a titanium-oxygen-nitrogen gradient transition layer. The basic concept, working mechanism and deposition path of this transition layer can be consistent with that of Embodiment 1. That is, through multiple sets of transition deposition cycles, the oxygen content in the transition layer gradually decreases in the direction away from the steel substrate surface, and the nitrogen content gradually increases, thereby constructing a gradient composition buffer zone between the steel substrate and the subsequent main hardening layer.

[0100] The metal precursor used in the transition layer is still tetrakis(dimethylamino)titanium TDMAT, the oxygen-containing reactant is water vapor, and the nitrogen-containing reactant is ammonia plasma. Eight transition deposition cycles were set up, with the ratio of oxygen-containing to nitrogen-containing subcycles in each cycle being 12:3, 11:4, 10:5, 9:6, 8:7, 7:8, 6:9, and 5:10, respectively. The resulting transition layer thickness was approximately 11.5 nm. Each transition deposition cycle included a metal precursor subcycle, an oxygen-containing subcycle, and a nitrogen-containing subcycle.

[0101] This indicates that ozone activation does not disrupt the formation logic of the subsequent gradient transition layer, and the transition layer can still be stably established.

[0102] After the transition layer is formed, the main hardened layer is formed on its surface.

[0103] In this embodiment, the main hardening layer still adopts a TiN / Al2O3 intercalation composite structure. Its overall design, deposition sequence and mechanism of action are consistent with those of Example 1, and will not be described again.

[0104] A total of 22 hardening deposition cycles were set up, each including 18 TiN sub-cycles and 2 Al2O3 intercalation deposition sub-cycles. The thickness of the main hardened layer was approximately 39.1 nm. The TiN sub-cycles were still performed using the standard PEALD method.

[0105] The purpose of setting this surface sealing layer and subsequent densification treatment is still to seal open defects on the surface of the main hardened layer, improve surface integrity, and reduce the intrusion rate of external corrosive media. After the above treatment, a composite hardened layer with a total thickness of approximately 53.7 nm is formed on the surface of the lightweight steel in this embodiment. The structural characterization results, such as its thickness composition, surface roughness, and scratch critical load, are shown in Table 4, F5.

[0106] As shown in F5 of Table 4, the surface roughness Ra of the sample in this embodiment is 22.0 nm, the critical scratch load Lc2 is 30.4 N, and XPS depth analysis still shows that there is an obvious O / N step gradient in the transition layer region.

[0107] This demonstrates that although ozone was used instead of surface plasma activation in this embodiment, the resulting film still maintained good continuity and interlayer stability.

[0108] Table 5, F5 shows that the nanohardness of the sample in this embodiment is 16.3 GPa, the steady-state friction coefficient is 0.41, and the wear rate is 1.59 × 10⁻⁶. -6 mm 3 ·N -1 ·m -1 The corrosion current density is 0.15 μA·cm. -2 After 72 hours of salt spray, the rust area was 0.6%.

[0109] The above results show that the composite hardened layer formed in this embodiment can significantly improve the wear resistance and corrosion resistance of the lightweight steel surface, indicating that this embodiment is clearly feasible.

[0110] Comparing this embodiment with Embodiment 1, it can be seen that they are basically the same in terms of the transition layer, main hardening layer, surface sealing layer, and subsequent densification process. The main difference lies in the in-situ activation method of the substrate surface. Embodiment 1 uses Ar / H2 plasma activation, while this embodiment uses ozone activation.

[0111] As can be seen from the data in Tables 4 and 5, the critical scratch load, nanohardness, coefficient of friction, wear rate, and corrosion current density of this embodiment are all slightly inferior to those of Example 1.

[0112] This indicates that in the system of the present invention, Ar / H2 plasma activation still has a better effect on improving the surface reactivity of the substrate, improving initial nucleation and enhancing interlayer bonding; however, at the same time, the performance of this embodiment is still significantly better than that of the simple monolayer TiN scheme and several comparative examples lacking key hierarchical structures, indicating that ozone activation can still meet the implementation requirements of the present invention.

[0113] Furthermore, compared with the aforementioned comparative example C1, this embodiment retains the gradient transition layer, the TiN / Al2O3 intercalation composite main hardening layer, and the surface sealing layer. Therefore, its scratch critical load is significantly improved, and its wear rate and corrosion current density are significantly reduced, indicating that the composite layered structure of the present invention is still the decisive factor for performance improvement. Compared with Comparative Example C2, this embodiment not only has better bonding performance, but also further improved wear resistance and corrosion resistance, indicating that the intercalation and surface sealing layer still make significant contributions to film integrity and environmental stability. Compared with Comparative Example C4, the nano-hardness and wear resistance of this embodiment are still superior, indicating that as long as the TiN in the main hardened layer is formed by PEALD, even if the activation method is changed to ozone, the present invention is still superior to the method of forming TiN by thermal ALD.

[0114] Therefore, the significance of this embodiment is not to achieve higher peak performance than that of Embodiment 1, but to demonstrate that the present invention has an alternative path in activation process that can be adapted to different equipment conditions and process boundaries.

[0115] In summary, this embodiment maintains the overall technical approach of Embodiment 1, but replaces the in-situ activation of the substrate surface with ozone activation instead of Ar / H2 plasma activation, and provides clear and executable ozone activation parameters.

[0116] The ozone generation and delivery conditions required for this embodiment are available in the field. The processing temperature is still controlled within the range suitable for the surface treatment of lightweight steel. Subsequent transition layer, main hardening layer, surface sealing layer and densification treatment can be stably implemented. The resulting film still has good bonding performance, wear resistance and corrosion resistance. The above results show that, under ozone activation conditions, the subsequent transition layer, main hardening layer, surface sealing layer and densification treatment can still be stably implemented, thereby obtaining a composite hardening layer with good bonding performance, wear resistance and corrosion resistance on the surface of lightweight steel.

[0117] Example 6 This embodiment, along with its further limitations on parameter ranges, is an implementation method formed by simultaneously expanding the transition layer thickness, the number of deposition cycles for the main hardening layer, the intercalation density, and the surface treatment intensity based on the lightweight steel surface composite hardening layer preparation process in Embodiment 1. The overall technical route of this embodiment is the same as in Embodiment 1, but by increasing the number of deposition cycles for the transition layer, increasing the number of cycle groups for the main hardening layer, and appropriately enhancing the surface sealing layer and subsequent densification treatment intensity, the resulting composite hardening layer maintains a stable hierarchical structure while further verifying the feasibility and engineering scale-up adaptability of this scheme under conditions of a wider parameter window and larger film thickness.

[0118] The simulated application scenario, matrix material, sample size, matrix pretreatment method, vacuuming and heating conditions, and in-situ activation method used in this embodiment are all the same as in Example 1. That is, Si-Mn-Al lightweight high-strength steel for the locking tooth plate of the new energy vehicle seat slide rail is still selected as the simulation object, and the sample size can be 30mm×20mm with a matrix thickness of 1.2mm; Before deposition, the substrate is subjected to ultrasonic degreasing with alkaline cleaning solution, rinsing with deionized water, ultrasonic cleaning with acetone and anhydrous ethanol, and hot air drying. After being loaded into the atomic layer deposition reaction chamber, the substrate is evacuated to 40 Pa under nitrogen protection and heated to 250 °C and held for 20 min. Subsequently, in-situ activation was performed using Ar / H2 mixed plasma. Since the above steps are consistent with those in Example 1, and their function remains to provide a clean, stable, and highly reactive initial surface, they will not be repeated in this example.

[0119] On the activated surface, this embodiment still first forms a titanium-oxygen-nitrogen gradient transition layer. However, compared with Example 1, the transition layer no longer uses 8 sets of transition deposition cycles, but instead uses 10 sets of transition deposition cycles to form a thicker and smoother compositional transition region. The overall concept of the transition layer is the same as in Example 1. By setting a higher proportion of oxygen-containing reactive sub-cycles on the side closer to the lightweight steel substrate and a higher proportion of nitrogen-containing reactive sub-cycles on the side closer to the main hardening layer, the oxygen content in the transition layer gradually decreases and the nitrogen content gradually increases in the direction away from the substrate surface, thereby further reducing the abrupt change in interface composition between the substrate and the main hardening layer.

[0120] In this embodiment, the metal precursor used in the transition layer is still tetrakis(dimethylamino)titanium TDMAT, the oxygen-containing reactant is still water vapor, and the nitrogen-containing reactant is still ammonia plasma. In this embodiment, a total of 10 transition deposition cycles were set up. The ratio of oxygen-containing reaction subcycles to nitrogen-containing reaction subcycles in each group was 13:2, 12:3, 11:4, 10:5, 9:6, 8:7, 7:8, 6:9, 5:10, and 4:11, respectively, resulting in a transition layer thickness of approximately 18.4 nm. Each transition deposition cycle group included a metal precursor subcycle, an oxygen-containing reaction subcycle, and a nitrogen-containing reaction subcycle.

[0121] Compared to Example 1, this example adds two subsequent sets of transition deposition cycles, further extending the gradient transition range. The nitrogen-containing reaction characteristics of the latter transition set are more pronounced, allowing the transition layer closer to the main hardened layer to transition more fully to the nitride structure. The execution order of various sub-cycles remains the same as in Example 1, and will not be repeated here.

[0122] After this step, a titanium-oxygen-nitrogen gradient transition layer with a thickness of approximately 18.4 nm is formed. The structural characterization results are shown in Table 4, F6. This setting indicates that the transition layer of the present invention is not limited to a thin fixed thickness. As long as the gradual change concept of gradually decreasing oxygen content and gradually increasing nitrogen content is still followed, a transition structure with good bonding promotion effect can be formed.

[0123] After the transition layer is formed, the main hardening layer is formed on its surface. In this embodiment, the main hardening layer still adopts the TiN / Al2O3 intercalation composite structure. However, compared with Example 1, this embodiment further increases the total amount of hardening deposition cycles and the number of TiN and intercalation configurations in each group to verify the feasibility of the present invention under the condition of a thicker main hardening layer.

[0124] A total of 26 hardening deposition cycles were set up, each including 22 TiN sub-cycles and 3 Al2O3 intercalation deposition sub-cycles, and the thickness of the main hardened layer was approximately 63.2 nm.

[0125] Compared with Example 1, this example increases the number of hardening deposition cycle groups from a lower level to 26 groups, the number of TiN sub-cycles in each group to 22, and the number of oxide intercalation sub-cycles in each group to 3.

[0126] The purpose of adopting the above settings is to increase the total thickness of the main hardening layer while increasing the frequency of intercalation, thereby avoiding the problems of internal stress concentration, columnar defect extension, and easier penetration of local cracks caused by an excessively thick main hardening layer.

[0127] In other words, this embodiment does not simply pursue "thickening" of the film layer, but rather maintains the structural stability and crack resistance of the main hardening layer by increasing the intercalation density while expanding the film thickness. After deposition according to the parameters shown in F6 in Table 3, a main hardening layer with a thickness of about 63.2 nm is formed. Although this thickness is significantly higher than that in Example 1, it can still be precisely controlled by the number of atomic layer deposition cycles, and the entire main hardening layer still has clear layered composite characteristics.

[0128] After the main hardening layer is formed, this embodiment continues to form an Al2O3 surface sealing layer on its surface and performs plasma densification treatment.

[0129] Compared with Example 1, this example appropriately increases the thickness of the surface sealing layer and correspondingly enhances the post-processing intensity to match the thicker transition layer and main hardening layer structure.

[0130] The surface sealing layer is an Al2O3 surface sealing layer with a thickness of approximately 4.5 nm; Subsequent densification was carried out using N2 plasma at a temperature of 180W for 150s.

[0131] Subsequently, N2 plasma was used for densification treatment, and the treatment intensity was correspondingly increased. The reason for this setting is that as the overall film thickness increases, the number of open defects on the surface and their connection length may also increase accordingly. Therefore, a thicker surface sealing layer and a stronger subsequent densification effect are needed to more fully seal and compact the surface and near-surface area of ​​the main hardened layer to ensure that the film layer still has good environmental stability under thicker conditions. After this step, a composite hardened layer with a total thickness of approximately 86.1 nm was formed on the surface of the lightweight steel in this embodiment. Its thickness composition, surface roughness, scratch critical load, and gradient structure characterization results are shown in Table 4, F6.

[0132] Table 4, F6, shows that the surface roughness Ra of the sample obtained in this embodiment is 24.1 nm, the critical scratch load Lc2 is 34.4 N, and XPS depth analysis still shows a significant O / N step gradient. This indicates that even with a significant increase in the thickness of the transition layer and the main hardened layer, the gradient transition structure and intercalation composite structure constructed in this invention can still be effectively established, and the interlayer structure does not become uncontrolled or significantly unstable due to the increase in film thickness. Table 5, F6, shows that the nanohardness of the sample in this embodiment is 17.1 GPa, the steady-state friction coefficient is 0.36, and the wear rate is 1.18 × 10⁻⁶. -6 mm 3 ·N -1 ·m -1 The corrosion current density is 0.12 μA·cm. -2 After 72 hours of salt spray, the rust area was 0.3%.

[0133] These results demonstrate that, despite the expansion of the parameter window and a significant increase in film thickness, this embodiment still maintains excellent mechanical, tribological, and corrosion resistance properties.

[0134] Comparing this embodiment with Embodiment 1, it can be seen that the total film thickness of Embodiment 6 is significantly increased, but its critical scratch load remains at a high level. The nano-hardness, wear resistance, and corrosion resistance do not deteriorate significantly due to the increase in thickness; on the contrary, they are further improved in terms of wear rate and friction coefficient. This shows that the solution of the present invention does not depend on a single thin film layer configuration to be successful. Rather, after expanding the parameter range of the transition layer and the main hardening layer, the overall performance of the film layer can still be maintained through the synergistic effect of gradient transition, intercalation segmentation, and surface sealing.

[0135] Compared with Comparative Example C1, this embodiment shows significant improvements in bonding performance, hardness, wear resistance and corrosion resistance, indicating that even if the thickness of a single-layer TiN solution varies, it is difficult to achieve the comprehensive effect brought by the multi-layer composite structure of this invention. Compared with Comparative Example C2, this embodiment further demonstrates that with only a transition layer and lacking intercalation and surface sealing layers, it is impossible to obtain sufficiently stable overall performance under thicker film conditions; Compared with Comparative Example C3, this embodiment exhibits better corrosion resistance, indicating that the surface sealing layer plays a more important role under the condition of a thicker main hardening layer. Compared to Comparative Example C4, this embodiment demonstrates that using PEALD to form TiN, supplemented by intercalation and enhanced densification, helps maintain a high-quality main hardened layer over a wider film thickness range.

[0136] The beneficial effect of this embodiment is not simply to increase the film thickness, but to demonstrate that the core technical route of the present invention has a wide range of applicable parameters.

[0137] Specifically, on the one hand, by increasing the number of transition deposition cycles, the compositional transition between the steel substrate and the main hardened layer becomes smoother, which is beneficial to maintaining good adhesion stability under thicker film conditions. On the other hand, by increasing the number of TiN sub-cycles and intercalation sub-cycles in the main hardening layer, the total thickness can be increased while continuing to suppress crack penetration and continuous defect propagation. Furthermore, by appropriately increasing the thickness of the surface sealing layer and enhancing the densification treatment intensity, the corrosion risk caused by surface open defects under thicker film conditions is further reduced. Therefore, this embodiment demonstrates the stability and scalability of the present invention's solution even within a wider process window.

[0138] In summary, this embodiment, based on the overall structural design of Embodiment 1, discloses an implementation method suitable for constructing thicker composite hardened layers by increasing the number of transition layer cycle groups, increasing the number of main hardened layer deposition cycles, increasing the intercalation density, thickening the surface sealing layer, and enhancing subsequent densification treatment. The equipment, precursors, reactants, and processing conditions used in this embodiment are all available in the art, with clearly defined parameter settings and a clear execution path, enabling the stable formation of thicker and higher-performance composite hardened layers on the surface of lightweight steel. The above results show that, under the conditions of increasing the number of transition layer cycles, increasing the number of main hardening layer deposition cycles, increasing the intercalation density, and enhancing the strength of the surface sealing layer and subsequent densification treatment, it is still possible to stably form a thick and high-performance composite hardening layer on the surface of lightweight steel.

[0139] The tables used in Examples 1-6 above are as follows: Table 1: Overall Process Configuration for Each Sample Sample number Activation method Should I set the interface layer? Transition layer type Main hardening layer type TiN formation method Should a surface sealing layer be set? densification method Scheme Features F1 <![CDATA[Ar / H2 plasma activation]]> no Titanium-oxygen-nitrogen gradient transition layer <![CDATA[TiN / Al2O3 intercalated composite layer]]> Standard PEALD yes N2 plasma densification Basic complete solution F2 <![CDATA[Ar / H2 plasma activation]]> no Titanium-oxygen-nitrogen gradient transition layer <![CDATA[TiN / Al2O3 intercalated composite layer]]> Enhanced PEALD yes N2 plasma densification Enhancing the compactness of TiN subcycles F3 <![CDATA[Ar / H2 plasma activation]]> <![CDATA[Yes, Al2O3 interface layer]]> Titanium-oxygen-nitrogen gradient transition layer <![CDATA[TiN / Al2O3 intercalated composite layer]]> Standard PEALD yes N2 plasma densification Introducing an interface layer to improve integration F4 <![CDATA[Ar / H2 plasma activation]]> no Titanium-oxygen-nitrogen gradient transition layer <![CDATA[TiN / Al2O3 intercalated composite layer]]> Standard PEALD yes Heat treatment densification Verification of alternative densification pathways F5 Ozone activation no Titanium-oxygen-nitrogen gradient transition layer <![CDATA[TiN / Al2O3 intercalated composite layer]]> Standard PEALD yes N2 plasma densification Validating alternative activation pathways F6 <![CDATA[Ar / H2 plasma activation]]> no Titanium-oxygen-nitrogen gradient transition layer <![CDATA[TiN / Al2O3 intercalated composite layer]]> Standard PEALD yes N2 plasma densification Verify wider parameter window C1 <![CDATA[Ar / H2 plasma activation]]> no none Single TiN layer Standard PEALD no N2 plasma densification No transition layer, no intercalation layer, no sealing layer C2 <![CDATA[Ar / H2 plasma activation]]> no Titanium-oxygen-nitrogen gradient transition layer Single TiN layer Standard PEALD no N2 plasma densification Only retain the transition layer C3 <![CDATA[Ar / H2 plasma activation]]> no Titanium-oxygen-nitrogen gradient transition layer <![CDATA[TiN / Al2O3 intercalated composite layer]]> Standard PEALD no N2 plasma densification Only remove the surface sealing layer C4 <![CDATA[Ar / H2 plasma activation]]> no Titanium-oxygen-nitrogen gradient transition layer <![CDATA[TiN / Al2O3 intercalated composite layer]]> Hot ALD yes N2 plasma densification Only change the TiN formation mode Table 2: Deposition parameters of the transition layer in each sample Sample number Number of transitional sedimentary cycles G1 O:N G2 O:N G3 O:N G4 O:N G5 O:N G6 O:N G7 O:N G8 O:N G9 O:N G10 O:N transition layer thickness / nm F1 8 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 — — 11.9 F2 8 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 — — 12.1 F3 8 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 — — 11.8 F4 8 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 — — 11.7 F5 8 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 — — 11.5 F6 10 13:02 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 4:11 18.4 C2 8 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 — — 11.6 C3 8 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 — — 11.8 C4 8 12:03 11:04 10:05 9:06 8:07 7:08 6:09 5:10 — — 11.7 Table 3: Main hardened layer, surface sealing layer and densification parameters in each sample Sample number Hardened deposition cycle number Number of TiN sub-loops per group Number of oxide intercalation subcycles per group Intercalation materials TiN deposition method Main hardened layer thickness / nm Surface sealing layer material Surface sealing layer thickness / nm densification method F1 22 18 2 <![CDATA[Al2O3]]> Standard PEALD 39.6 <![CDATA[Al2O3]]> 3.1 N2 plasma, 160W × 120s F2 22 18 2 <![CDATA[Al2O3]]> Enhanced PEALD 40.8 <![CDATA[Al2O3]]> 3 N2 plasma, 160W × 120s F3 22 18 2 <![CDATA[Al2O3]]> Standard PEALD 39.2 <![CDATA[Al2O3]]> 3.1 N2 plasma, 160W × 120s F4 22 18 2 <![CDATA[Al2O3]]> Standard PEALD 39.4 <![CDATA[Al2O3]]> 3 Heat treatment at 280℃ for 40 minutes F5 22 18 2 <![CDATA[Al2O3]]> Standard PEALD 39.1 <![CDATA[Al2O3]]> 3.1 N2 plasma, 160W × 120s F6 26 22 3 <![CDATA[Al2O3]]> Standard PEALD 63.2 <![CDATA[Al2O3]]> 4.5 N2 plasma, 180W × 150s C1 22 20 0 — Standard PEALD 43.2 — — N2 plasma, 160W × 120s C2 22 20 0 — Standard PEALD 39.1 — — N2 plasma, 160W × 120s C3 22 18 2 <![CDATA[Al2O3]]> Standard PEALD 39.4 — — N2 plasma, 160W × 120s C4 22 18 2 <![CDATA[Al2O3]]> Hot ALD 38.9 <![CDATA[Al2O3]]> 3 N2 plasma, 160W × 120s Table 4: Characterization results of film structure of each sample Sample number Interface layer thickness / nm transition layer thickness / nm Main hardened layer thickness / nm Surface sealing layer thickness / nm Total thickness / nm Surface roughness Ra / nm Scratch critical load Lc2 / N Does XPS display the O / N step gradient? F1 — 11.9 39.6 3.1 54.6 21.4 31.8 yes F2 — 12.1 40.8 3 55.9 20.6 33.7 yes F3 2.5 11.8 39.2 3.1 56.6 19.9 35 yes F4 — 11.7 39.4 3 54.1 22.3 30.7 yes F5 — 11.5 39.1 3.1 53.7 22 30.4 yes F6 — 18.4 63.2 4.5 86.1 24.1 34.4 yes C1 — — 43.2 — 43.2 28.7 15.4 no C2 — 11.6 39.1 — 50.7 26.1 22.9 yes C3 — 11.8 39.4 — 51.2 23.8 28.1 yes C4 — 11.7 38.9 3 53.6 24.6 26.7 yes Table 5: Performance Test Results of Each Sample Sample number Nanohardness / GPa steady-state friction coefficient <![CDATA[Wear rate / (×10 - 6 mm 3 ·N -1 ·m -1 )]]> <![CDATA[Corrosion current density / μA·cm -2 > 72h salt spray corrosion area / % Result Features F1 16.7 0.39 1.46 0.13 0.4 A complete basic solution with balanced overall performance. F2 17.4 0.37 1.24 0.11 0.3 The compactness of TiN is further improved. F3 17 0.38 1.31 0.09 0.2 Bonding strength and corrosion resistance are further improved. F4 16.1 0.42 1.67 0.16 0.5 Thermal densification is feasible, but slightly less so than plasma densification. F5 16.3 0.41 1.59 0.15 0.6 Ozone activation is feasible, but its performance is slightly lower than that of plasma activation. F6 17.1 0.36 1.18 0.12 0.3 Excellent performance is maintained even after the parameter window is expanded. C1 12.1 0.58 5.92 0.86 7.8 Lacking a key hierarchical structure, it has the worst performance. C2 13.5 0.51 3.84 0.49 4.6 With only a transition layer, performance is improved but not sufficient. C3 16.1 0.43 1.98 0.27 1.9 The corrosion resistance decreased significantly after the surface sealing layer was removed. C4 15 0.47 2.36 0.31 1.4 TiN formed by thermal ALD has insufficient density. It should be noted that the Ar / H2 mixed plasma activation used in this invention is only an exemplary implementation. Those skilled in the art will understand that other reducing plasmas (such as pure H2 plasma and N2 / H2 mixed plasma) can also remove surface adsorbates and improve surface reactivity, thereby obtaining similar activation effects. These variations are all within the protection scope of this invention. The “step-like decrease” or “step-like increase” in this invention refers to the following: during the deposition of the titanium-oxygen-nitrogen transition layer, the transition layer is divided into multiple deposition groups along the direction away from the surface of the lightweight steel substrate. The oxygen content (or nitrogen content) within each deposition group remains basically uniform, while the oxygen content (or nitrogen content) between adjacent deposition groups undergoes a step-like change. In embodiments of the present invention, each deposition group corresponds to a set of transition deposition cycles. By gradually reducing the proportion of oxygen-containing reaction sub-cycles and gradually increasing the proportion of nitrogen-containing reaction sub-cycles, a stepwise decrease in oxygen content and a stepwise increase in nitrogen content are achieved.

[0140] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An atomic layer deposition process for surface hardening of lightweight steel, characterized in that, include: S1. The lightweight steel substrate is cleaned and dried. The treated lightweight steel substrate is placed in the atomic layer deposition reaction chamber. The atomic layer deposition reaction chamber is evacuated to a vacuum under inert gas protection. The treated lightweight steel substrate is then heated to the deposition temperature. S2. Perform in-situ activation treatment on the heated lightweight steel substrate to form an activated surface; S3. A titanium-oxygen-nitrogen transition layer is formed on the activated surface by atomic layer deposition, wherein the titanium-oxygen-nitrogen transition layer is formed through multiple sets of transition deposition cycles; Each transition deposition cycle includes a metal precursor subcycle, an oxygen-containing reaction subcycle, and a nitrogen-containing reaction subcycle. Along the deposition direction perpendicular to the surface of the lightweight steel substrate, the proportion of the number of oxygen-containing reaction subcycles to the total number of subcycles in each transition deposition cycle decreases from one group to the next, while the proportion of the number of nitrogen-containing reaction subcycles to the total number of subcycles in each group increases from one group to the next. S4. An atomic layer deposition method is used to form the main hardening layer on the surface of the titanium-oxygen-nitrogen transition layer. The main hardening layer is a TiN / Al2O3 intercalated composite structure, which is formed by multiple hardening deposition cycles. Each set of hardening deposition cycles includes 5 to 30 titanium nitride deposition sub-cycles and 1 to 10 oxide intercalation deposition sub-cycles; S5. A surface sealing layer is formed on the surface of the main hardened layer, and the resulting film layer is densified to form a lightweight steel surface composite hardened layer. The surface sealing layer is aluminum oxide with a thickness of 1-20 nm, and the densification treatment is performed by holding at 100-350°C for 5-120 min or by using nitrogen plasma for 10-300 s.

2. The atomic layer deposition process for surface hardening of lightweight steel as described in claim 1, characterized in that: The in-situ activation treatment in S2 is either Ar / H2 mixed plasma activation or ozone activation.

3. The atomic layer deposition process for surface hardening of lightweight steel as described in claim 1, characterized in that, In S3 and / or S4, at least a portion of the deposition cycle is performed sequentially in the following manner: The process involves introducing a precursor, purging with an inert gas, introducing reactants or performing plasma treatment, and then purging with an inert gas again.

4. The atomic layer deposition process for surface hardening of lightweight steel as described in claim 1, characterized in that: At least a portion of the titanium nitride deposition sub-cycle in S4 employs plasma-enhanced atomic layer deposition.

5. The atomic layer deposition process for surface hardening of lightweight steel as described in claim 1 or 4, characterized in that, The titanium nitride deposition sub-cycle step in S4 includes: The process involves introducing a titanium-containing precursor, purging with inert gas, treating with hydrogen plasma, purging with inert gas again, treating with nitrogen plasma or ammonia plasma, and purging with inert gas again.

6. The atomic layer deposition process for surface hardening of lightweight steel as described in claim 1, characterized in that: Between S2 and S3, an interface layer is formed on the activated surface by atomic layer deposition. The interface layer is aluminum oxide with a thickness of 1–10 nm.

7. The atomic layer deposition process for surface hardening of lightweight steel as described in claim 1, characterized in that: The thickness of the titanium-oxygen-nitrogen transition layer is 5–50 nm, and along the deposition direction, its oxygen content decreases in a stepwise manner while its nitrogen content increases in a stepwise manner.

8. The atomic layer deposition process for surface hardening of lightweight steel as described in claim 1, characterized in that: The total thickness of the main hardened layer is 20–200 nm; The thickness of the oxide intercalation layer formed by the oxide intercalation deposition subcycle is 0.1–3 nm.

9. The atomic layer deposition process for surface hardening of lightweight steel as described in claim 1, characterized in that, The lightweight steel matrix is ​​Si-Mn-Al series lightweight high-strength steel.

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