Chemical vapor deposition process for a piston rod surface

Abstract

The application discloses a chemical vapor deposition process for a piston rod surface and belongs to the field of chemical vapor deposition. The process comprises the following steps: inductively quenching and tempering a piston rod base body to form a gradient quench-hardened layer distributed along a radial direction on the surface of the piston rod base body; finely grinding and polishing the gradient quench-hardened layer and controlling the last surface layer removal amount so that part of the quench-hardened structure interface and residual compressive stress of the outer surface of the gradient quench-hardened layer are reserved to obtain a surface to be deposited; and controlling the last removal state of the outer surface of the gradient quench-hardened layer and reserving part of the quench-hardened structure interface and residual compressive stress so that a carbon-based deposition phase can grow along the quench-hardened structure interface first, thereby solving the problems of insufficient combination continuity and poor interface stability between a deposition layer and a base body of an existing piston rod surface.

Description

Technical Field

[0001] This invention relates to the field of chemical vapor deposition technology, and more specifically, to a chemical vapor deposition process for piston rod surfaces. Background Technology

[0002] The piston rod is a key moving component in a hydraulic cylinder. During operation, its outer surface needs to slide back and forth with the seals for extended periods, while also enduring multiple forces including hydraulic loads, friction and wear, external corrosive media, and localized surface impacts. Therefore, the hardness, wear resistance, corrosion resistance, and stability of the piston rod surface with the seals directly affect the service life, sealing performance, and operational reliability of the hydraulic cylinder. Current hydraulic cylinder technical standards impose high requirements on the surface roughness, straightness, and plating performance of the piston rod sliding surface. The surface roughness is typically Ra 0.16μm to 0.63μm, and for higher precision requirements, Ra can be no greater than 0.1μm to 0.2μm. Furthermore, the piston rod sliding surface is usually hard chrome plated. When the plating wears off locally, forming longitudinal scratches, it is often necessary to remove the old plating and re-chrome plate and polish. The chrome plating thickness is typically around 0.03mm to 0.05mm.

[0003] In existing production processes, piston rods are typically first surface hardened or medium-frequency hardened, followed by grinding, polishing, and surface protection treatment. Relevant work standards clearly state that the determination of the surface hardening length is usually based on HRC51 as the dividing point. In the polishing stage, to meet the requirements of subsequent surface treatment and sealing sliding, 320-grit, 400-grit, 600-grit, and 800-grit grinding wheels or flap wheels are often used in sequence. It is required that the surface roughness Ra of the polished surface before plating be controlled within 0.2, and the surface roughness Ra of the polished surface after plating be controlled between 0.05 and 0.2, and Rmr is not less than 65%.

[0004] However, the existing technologies mentioned above still have significant shortcomings. On the one hand, the surface protection of existing piston rods usually uses hard chrome plating as the main wear-resistant and corrosion-resistant layer. Although this type of surface layer can meet the requirements of use under normal working conditions, under long-term reciprocating sliding, local impact or corrosive media, local wear, micro-crack propagation or plating peeling may still occur. Once longitudinal scratches are formed on the sliding surface of the piston rod, the risk of external oil leakage at the seal will be significantly increased, and repairs will be required by means of deplating, replating and repolishing, resulting in high maintenance costs.

[0005] On the other hand, existing processes do not adequately utilize the correlation between the microstructure of the piston rod substrate surface and the subsequent formation of the protective surface layer. Existing heat treatment processes are mainly used to obtain a certain hardening depth and surface hardness, and polishing processes are mainly used to improve surface roughness. The formation of the subsequent protective surface layer is usually treated as an independent step, and the influence of the microstructure interface, residual compressive stress and its spatial distribution retained on the surface of the gradient hardened layer on the nucleation, growth continuity and interface bonding state of the subsequent deposited layer has not been fully considered.

[0006] This means that existing surface treatment methods still have room for improvement in terms of film uniformity, interfacial bonding stability, and functional allocation of the film layer along its thickness. Summary of the Invention

[0007] To address the problems mentioned in the background section, the present invention provides the following technical solution: The chemical vapor deposition process on the piston rod surface includes: induction hardening and tempering the piston rod substrate to form a radially distributed gradient hardened layer on the piston rod substrate surface; The gradient hardened layer is finely ground and polished, and the amount of surface layer removed in the final stage is controlled so that some hardened structure interface and residual compressive stress are retained on the outer surface of the gradient hardened layer to obtain the surface to be deposited. The piston rod with the surface to be deposited is fed into the vacuum deposition chamber, where it undergoes degassing and plasma activation treatment in sequence. Carbon-containing precursor gas, hydrogen-containing gas, and inert gas are introduced into the vacuum deposition chamber. Initial deposition is performed using a first pulse bias voltage while the piston rod is rotating, so that the carbon-based deposition phase preferentially grows along the partially hardened microstructure interface and forms a carbon-based bonding layer on the surface to be deposited. Under the condition of continuous vacuum, a continuously varying second pulse bias is used, and the flow ratio of the carbon-containing precursor gas, the hydrogen-containing gas and the inert gas is adjusted simultaneously, so that a carbon-based support layer and a carbon-based working layer are continuously formed on the outer side of the carbon-based bonding layer along the thickness direction, so as to form a carbon-based gradient film layer generated by the surface microstructure of the gradient hardened layer. The carbon-based gradient film is stabilized. Furthermore, during the fine grinding and polishing of the gradient hardened layer, the final surface layer removal amount is controlled to be 2% to 12% of the depth of the gradient hardened layer, and the surface to be deposited meets the following conditions: The surface roughness Ra is 0.08 μm to 0.16 μm, the surface residual compressive stress is 200 MPa to 800 MPa, and the exposed area of ​​the hardened structure interface uniformly distributed along the piston rod axis accounts for 10% to 35% of the total area of ​​the surface to be deposited.

[0008] Furthermore, the degassing treatment is performed at a temperature of 160°C to 230°C for a time of 40 min to 70 min; The plasma activation treatment includes a pre-activation stage performed under the inert gas atmosphere and an interface preferential activation stage performed under the mixed atmosphere of hydrogen-containing gas and the inert gas, wherein the substrate bias voltage of the pre-activation stage is 250V to 450V and the treatment time is 2min to 6min. The interface preferential activation stage uses a pulse bias voltage with a peak value gradually decreasing from 350V to 500V to 120V to 220V, and the processing time is 3min to 10min. The initial deposition includes a selective nucleation stage and a continuous film formation stage performed sequentially. In the preferred nucleation stage, the flow ratio of the hydrogen-containing gas to the carbon-containing precursor gas is 4:1 to 7:1, and the time is 1 min to 4 min. In the continuous film-forming stage, the flow ratio of the hydrogen-containing gas to the carbon-containing precursor gas is 2:1 to 4:1, and the time is 4 min to 12 min, so that the carbon-based bonding layer continuously spreads from the hardened structure interface to the surrounding area, and the thickness of the carbon-based bonding layer is 0.3 μm to 1.2 μm.

[0009] Furthermore, the second pulse bias voltage and the flow ratio of the hydrogen-containing gas to the carbon-containing precursor gas are adjusted in a continuously variable manner using reverse coupling. In this process, the peak value of the second pulse bias voltage continuously decreases from 450V to 800V to 150V to 350V, the duty cycle continuously decreases from 25% to 45% to 10% to 25%, and the flow ratio of the hydrogen-containing gas to the carbon-containing precursor gas continuously increases from 1:1 to 3:1 to 3:1 to 6:1. The first part of the main deposition stage lasts from 10 to 40 minutes to form the carbon-based support layer on the outside of the carbon-based bonding layer, and the second part of the main deposition stage lasts from 5 to 20 minutes to form the carbon-based working layer on the outside of the carbon-based support layer. Furthermore, a continuous transition zone of 30s to 180s is provided between the front section and the rear section to prevent abrupt interface formation between the carbon-based support layer and the carbon-based working layer.

[0010] Furthermore, the stabilization process includes the following steps: After stopping the supply of the carbon-containing precursor gas, the supply of the hydrogen-containing gas and the inert gas continues, and the substrate bias voltage is reduced to 20% to 60% of the peak value of the second pulse bias voltage. The substrate temperature is controlled at 120°C to 220°C, and the treatment lasts for 5 to 30 minutes. In the first stage of the stabilization process, the flow ratio of the hydrogen-containing gas to the inert gas is 1:1 to 4:1, and in the second stage of the stabilization process, the flow ratio of the hydrogen-containing gas to the inert gas is 1:2 to 1:6.

[0011] Furthermore, after the stabilization treatment is completed, the carbon-based gradient film layer satisfies the following relationship: The thickness of the carbon-based support layer accounts for 55% to 85% of the total thickness of the carbon-based gradient film layer, the thickness of the carbon-based working layer accounts for 15% to 45% of the total thickness of the carbon-based gradient film layer, the nanoindentation hardness of the carbon-based support layer is 18 GPa to 35 GPa, the nanoindentation hardness of the carbon-based working layer is 10 GPa to 22 GPa, and the hydrogen content continuously increases along the direction from the carbon-based support layer to the carbon-based working layer.

[0012] Furthermore, the proportion of the exposed area of ​​the hardened structure interface to the total area of ​​the surface to be deposited satisfies the following correspondence with the duration of the preferred nucleation stage and the peak value of the second pulse bias: When the ratio is 10% to 20%, the duration of the preferred nucleation stage is 3 to 4 minutes, and the peak value of the second pulse bias is 650V to 800V. When the ratio is 20% to 35%, the duration of the preferred nucleation stage is 1 min to 3 min, and the peak value of the second pulse bias is 450V to 650V. This allows the carbon-based bonding layer to form a continuous nucleation zone along the interface of the hardened structure and to continuously spread to the surrounding area.

[0013] In summary, the present invention has the following beneficial effects: By controlling the final removal state of the outer surface of the gradient hardened layer and retaining part of the hardened structure interface and residual compressive stress, the carbon-based deposited phase can preferentially grow along the hardened structure interface, thereby solving the problems of insufficient continuity of bonding between the existing piston rod surface deposited layer and the substrate and poor interface stability.

[0014] By continuously adjusting the deposition bias and the ratio of reactive gas flow rate under constant vacuum conditions, a carbon-based support layer and a carbon-based working layer are continuously formed on the outer side of the carbon-based bonding layer along the thickness direction, thereby solving the problems of existing piston rod surface film layers having single function, obvious interlayer abrupt changes, and difficulty in simultaneously taking into account load-bearing and low shear characteristics.

[0015] By implementing a phased stabilization treatment after the main deposition and adjusting the nucleation time and the initial parameters of the main deposition according to the exposure state of the tissue interface on the surface to be deposited, the resulting carbon-based gradient film has good structural stability and process adaptability. This solves the problems of insufficient nucleation, excessive nucleation in local areas, and easy peeling failure in later use under the existing fixed parameter deposition method. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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 flow chart of the chemical vapor deposition process for the piston rod surface of the present invention; Figure 2 This is a schematic diagram of the structure of the piston rod surface microstructure guiding the formation of a carbon-based gradient film according to the present invention; Figure 3 This is a schematic diagram showing the relationship between the exposed ratio of the hardened tissue interface and the film formation parameters according to the present invention. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 The following is in conjunction with the appendix Figure 1-3 The present invention will be described in further detail below.

[0020] Please see Figure 1-3 The present invention provides a technical solution: a chemical vapor deposition process for the surface of a piston rod, including induction hardening and tempering of the piston rod substrate to form a radially distributed gradient hardened layer on the surface of the piston rod substrate; The gradient hardened layer is finely ground and polished, and the amount of surface layer removed in the final stage is controlled so that some hardened structure interface and residual compressive stress are retained on the outer surface of the gradient hardened layer, thus obtaining the surface to be deposited. A piston rod with the surface to be deposited is fed into a vacuum deposition chamber, where it undergoes degassing and plasma activation treatments in sequence. Carbon-containing precursor gas, hydrogen-containing gas and inert gas are introduced into the vacuum deposition chamber. Initial deposition is performed using the first pulse bias voltage while the piston rod is rotating, so that the carbon-based deposition phase preferentially grows along the partially hardened microstructure interface and forms a carbon-based bonding layer on the surface to be deposited. Under the condition of continuous vacuum, a continuously varying second pulse bias voltage is used, and the flow ratio of carbon-containing precursor gas, hydrogen-containing gas and inert gas is adjusted simultaneously to continuously form a carbon-based support layer and a carbon-based working layer along the thickness direction on the outer side of the carbon-based bonding layer, so as to form a carbon-based gradient film layer generated by the surface microstructure of the gradient hardened layer. Stabilization treatment of carbon-based gradient films; In this embodiment: 45 steel is selected as the piston rod base. The total length of the piston rod is 620mm, the outer diameter of the working section is 45mm, and the length of the sealing sliding section is 360mm. After rough turning and semi-finish turning of the blank, a machining allowance of 0.45mm to 0.55mm is reserved on one side, followed by induction hardening and tempering. Induction hardening adopts medium-frequency induction heating, with an induction frequency of 28kHz to 35kHz, an output power of 85kW to 105kW, a workpiece rotation speed of 180r / min to 260r / min, a radial gap between the induction coil and the outer surface of the workpiece controlled at 4.5mm to 5.5mm, an axial scanning speed of 4.0mm / s to 6.5mm / s, and a quenching cooling medium of 8% to 10% by volume quenching liquid, with a liquid temperature controlled at 24℃ to 32℃. Tempering is performed immediately after quenching, with a tempering temperature of 200℃ to 230℃ and a holding time of 60min to 100min, followed by natural cooling to room temperature. After processing, a gradient hardened layer with a depth of 2.6 mm to 2.9 mm is formed on the surface of the piston rod working section, with a surface hardness of HRC54 to 58 and a hardness of not less than HRC51 at a position 2.5 mm from the surface.

[0021] After heat treatment, the material undergoes fine grinding and polishing. The fine grinding stage uses an external cylindrical grinder with grinding wheel grits of 320 mesh and 600 mesh, and a single feed rate controlled from 0.005 mm to 0.015 mm. The polishing stage uses a single-head polishing machine with flap wheels of 320 mesh, 400 mesh, 600 mesh, and 800 mesh, with the spindle speed controlled at 1410 r / min, continuously moving from the threaded end to the working section. The final surface layer removal is controlled to be 0.11 mm to 0.18 mm, representing 4.2% to 6.7% of the gradient hardened layer depth. After treatment, the surface roughness Ra of the working section is 0.09 μm to 0.13 μm. To confirm the surface condition, witness rods were prepared simultaneously under the same process conditions. The surface of the witness rods was lightly etched with 4% nitric acid alcohol for 6 to 8 seconds, and 20 images were collected equidistantly along the axial direction under a 500x metallographic microscope. The exposed area on the surface at the boundary between the tempered martensite transition zone and the high-hardness martensite zone was defined as the hardened microstructure interface exposure zone. The percentage of its projected area was calculated using image analysis software, and the percentage was found to be 18.6% to 24.3%. At the same time, the piston rod working section was tested using the sin²ψ method at the front, middle, and rear positions using an X-ray residual stress tester, and the surface residual compressive stress was measured to be -362 MPa to -475 MPa, thus obtaining the surface to be deposited.

[0022] After ultrasonically cleaning the piston rod sequentially with a weak alkaline degreasing solution, deionized water, and anhydrous ethanol, it was placed into the plasma chemical vapor deposition chamber, and the substrate vacuum was evacuated to a value better than 5 × 10⁻⁶. -3 The temperature was increased to 185°C to 205°C and held for 50 to 60 minutes to complete degassing. Subsequently, plasma activation was performed. First, pre-activation was conducted in an argon atmosphere with a chamber pressure of 60 to 80 Pa and a substrate bias voltage of 320 to 380 V for 4 to 5 minutes. Then, a mixed atmosphere of hydrogen and argon was used, with a hydrogen flow rate of 180 to 240 sccm and an argon flow rate of 80 to 120 sccm, a chamber pressure of 28 to 40 Pa, and a pulsed bias voltage with a peak value gradually decreasing from 420 V to 180 V for 5 to 7 minutes to improve the surface activity of the exposed hardened microstructure interface area.

[0023] Within 10 seconds after activation, the initial deposition stage begins, using acetylene as the carbon-containing precursor gas, hydrogen as the hydrogen-containing gas, and argon as the inert gas. Preferred nucleation is performed first, with acetylene flow rates of 35 to 50 sccm, hydrogen flow rates of 180 to 260 sccm, and argon flow rates of 120 to 160 sccm. The hydrogen to acetylene flow ratio is controlled at 4.5:1 to 6:1. The first pulse bias peak value is 520V to 620V, the duty cycle is 20% to 28%, and the frequency is 3. The process was carried out at 0 kHz to 45 kHz for 2 to 3 minutes. Subsequently, continuous film deposition was initiated, with the acetylene flow rate increased to 60 sccm to 85 sccm, the hydrogen flow rate adjusted to 150 sccm to 220 sccm, and the hydrogen to acetylene flow ratio controlled at 2.5:1 to 3.5:1. The peak value of the first pulse bias was adjusted to 420 V to 500 V and lasted for 6 to 9 minutes. After the initial deposition was completed, a carbon-based bonding layer with a thickness of 0.55 μm to 0.82 μm was formed on the surface to be deposited.

[0024] The main deposition stage begins under continuous vacuum conditions. The main deposition employs a continuous linkage adjustment of the second pulse bias voltage and the gas flow rate ratio. Within the first 20 to 26 minutes, the peak value of the second pulse bias voltage is continuously reduced from 720V to 360V, and the duty cycle is continuously reduced from 38% to 24%. Simultaneously, the hydrogen to acetylene flow rate ratio is continuously increased from 1.6:1 to 2.8:1 to form a carbon-based support layer. A 90-second continuous transition zone is then established. Within the next 7 to 10 minutes, the peak value of the second pulse bias voltage is further reduced to 220V to 260V, the duty cycle is reduced to 14% to 18%, and the hydrogen to acetylene flow rate ratio is further increased to 4.0:1 to 5.0:1 to form a carbon-based working layer. Throughout the entire deposition process, the piston rod rotation speed was controlled at 220 r / min to 280 r / min, the revolution speed was controlled at 18 r / min to 25 r / min, and the substrate temperature was maintained at 170℃ to 210℃, ultimately obtaining a carbon-based gradient film with a total thickness of 4.3 μm to 5.6 μm.

[0025] After the main deposition is completed, a stabilization treatment is performed. First, acetylene supply is stopped, while hydrogen and argon continue to be supplied. The substrate bias voltage is reduced to 35% to 45% of the peak value of the second pulse bias voltage, and the substrate temperature is controlled at 150℃ to 180℃. The initial stabilization period lasts 6 to 8 minutes, with the hydrogen to argon flow ratio controlled at 2:1 to 3:1. The subsequent stabilization period lasts 8 to 12 minutes, with the hydrogen to argon flow ratio adjusted to 1:3 to 1:4. This treatment yields a structurally stable carbon-based gradient film.

[0026] The obtained piston rod was inspected, and the total film thickness measured by cross-sectional SEM was 4.9 μm, of which the carbon-based support layer was 3.2 μm thick and the carbon-based working layer was 1.7 μm thick. Nanoindentation testing was used; the nanoindentation hardness of the carbon-based support layer was 26.8 GPa, and that of the carbon-based working layer was 15.4 GPa. Scratch testing was used to evaluate the adhesion state, and the critical failure load Lc2 was 57 N to 64 N. Verification was performed using a reciprocating sealing test bench with a test pressure of 14 MPa, a stroke of 250 mm, a frequency of 2.5 Hz, and a hydraulic oil temperature of 55℃ to 60℃, for a cumulative reciprocating cycle of 1.0 × 10⁻⁶. 6 After the test, no film peeling or penetrating longitudinal scratches were observed in the working section. The average wear depth was 0.72 μm and the external leakage was 6.1 mL. This indicates that by controlling the surface retention state of the gradient hardened layer and implementing activation, initial deposition, main deposition and stabilization treatments on this basis, a carbon-based gradient film with stable adhesion, continuous interlayer transition and suitable for sealing reciprocating sliding conditions can be obtained.

[0027] The specific experimental results are as follows: Table 1: Key Process Parameters and Test Results project Parameters or results matrix material 45 steel Total length of piston rod 620mm outer diameter of working section 45mm Induction frequency 28kHz to 35kHz Output power 85kW to 105kW Coil-workpiece gap 4.5mm to 5.5mm Scan speed 4.0 mm / s to 6.5 mm / s Quenching fluid concentration 8% to 10% Quenching fluid temperature 24℃ to 32℃ Tempering temperature 200℃ to 230℃ tempering time 60 min to 100 min Gradient hardened layer depth 2.6mm to 2.9mm Surface hardness HRC54 to 58 Final surface removal amount 0.11mm to 0.18mm Surface roughness Ra 0.09μm to 0.13μm Percentage of exposed area of ​​hardened tissue interface 18.6% to 24.3% Surface residual compressive stress -362MPa to -475MPa Degassing temperature 185℃ to 205℃ Degassing time 50 to 60 minutes Pre-activated bias 320V to 380V Pre-activation time 4 to 5 minutes Mixed gas activation bias 420V gradually reduced to 180V Activation time of mixed gas 5 to 7 minutes Preferred nucleation stage time 2min to 3min Continuous film formation stage time 6 min to 9 min carbon-based bonding layer thickness 0.55μm to 0.82μm The main sedimentation period 20 to 26 minutes Continuous transition time 90s After the main sedimentation period 7 to 10 minutes Total thickness of carbon-based gradient film 4.3μm to 5.6μm carbon-based support layer thickness 2.7μm to 3.6μm carbon-based working layer thickness 1.2μm to 1.9μm Stabilization temperature 150℃ to 180℃ Stabilization some time ago 6 to 8 minutes After stabilization 8 to 12 minutes Support layer nano-indentation hardness 26.8 GPa Working layer nano-indentation hardness 15.4 GPa <![CDATA[Critical failure load of scratch Lc2]]> 57N to 64N Number of cycles <![CDATA[1.0×10 6 Next Average wear depth 0.72μm External leakage 6.1mL

[0028] Example 2 like Figure 1-3 As shown, when performing fine grinding and polishing on the gradient hardened layer, the final surface layer removal amount is controlled to be 2% to 12% of the gradient hardened layer depth, and the surface to be deposited meets the following conditions: The surface roughness Ra is 0.08 μm to 0.16 μm, the surface residual compressive stress is 200 MPa to 800 MPa, and the exposed area of ​​the hardened microstructure interface uniformly distributed along the piston rod axis accounts for 10% to 35% of the total surface area to be deposited; The degassing treatment temperature is 160℃ to 230℃, and the time is 40 min to 70 min; The plasma activation treatment includes a pre-activation stage carried out in an inert gas atmosphere and an interface preferential activation stage carried out in a mixed atmosphere of hydrogen gas and inert gas. The substrate bias voltage of the pre-activation stage is 250V to 450V, and the treatment time is 2min to 6min. The interface optimization activation stage uses a pulse bias voltage with a peak value gradually decreasing from 350V to 500V to 120V to 220V, and the processing time is 3min to 10min. Initial deposition consists of a selective nucleation stage and a continuous film formation stage, which proceed sequentially. In the selective nucleation stage, the flow ratio of hydrogen-containing gas to carbon-containing precursor gas is 4:1 to 7:1, and the time is 1 min to 4 min. In the continuous film-forming stage, the flow ratio of hydrogen-containing gas to carbon-containing precursor gas is 2:1 to 4:1, and the time is 4 min to 12 min, so that the carbon-based bonding layer can be continuously spread from the hardened microstructure interface to the surrounding area, and the thickness of the carbon-based bonding layer is 0.3 μm to 1.2 μm.

[0029] In this embodiment: After forming the gradient hardened layer in Example 1, the working section of the piston rod is finely ground and polished to obtain a surface suitable for subsequent preferential activation and initial deposition. The piston rod substrate is made of 45 steel, the outer diameter of the working section is 45 mm, and the length of the working section is 360 mm. After heat treatment, the depth of the gradient hardened layer is controlled to be approximately 2.7 mm, and the surface hardness of the working section is HRC55 to 58.

[0030] Fine grinding is performed in two passes using an external cylindrical grinding machine. The first pass uses a 320-grit grinding wheel with a single feed rate of 0.012 mm to 0.018 mm, and the second pass uses a 600-grit grinding wheel with a single feed rate of 0.004 mm to 0.008 mm. Polishing is performed using a single-head polishing machine with flap wheels of 320, 400, 600, and 800 grit in sequence. The spindle speed is controlled at 1410 r / min. Polishing paste is applied to the workpiece starting from the thread end and the workpiece moves continuously along the axial direction. The final surface layer removal is controlled at 0.13 mm, accounting for 4.8% of the gradient hardened layer depth. After processing, the surface roughness Ra of the surface to be deposited is 0.11 μm, which meets the accuracy range corresponding to the company's existing sliding surface and polishing standards.

[0031] To confirm the surface condition after the final surface layer removal, three witness rods were prepared simultaneously under the same material and heat treatment conditions. The surface of the witness rods was lightly etched with 4% nitric acid alcohol for 7 seconds. Twenty images were collected equidistantly along the axial direction under a 500x metallographic microscope. The exposed area of ​​the tempered martensite transition zone and the high-hardness martensite zone on the surface was defined as the hardened microstructure interface exposure area. The area ratio was calculated using image analysis software and found to be 22.4%. At the same time, an X-ray residual stress tester was used to test the sin²ψ method at one point each at the front, middle and rear of the piston rod working section. The surface residual compressive stress was measured to be -418MPa. Through the above treatment, a surface to be deposited with low roughness, residual compressive stress and a certain proportion of hardened microstructure interface exposure was obtained.

[0032] The piston rod was then ultrasonically cleaned sequentially in a 2% (w / w) weak alkaline degreasing solution, deionized water, and anhydrous ethanol for 10 min, 5 min, and 8 min, respectively. After drying, it was placed into the plasma chemical vapor deposition chamber. The chamber was evacuated to a substrate vacuum better than 5 × 10⁻⁶. -3 After Pa, the temperature is raised to 195℃ and held for 55 minutes to complete the degassing process.

[0033] After degassing, plasma activation treatment is performed. First, pre-activation is carried out in an argon atmosphere with an argon flow rate of 160 sccm, a chamber pressure of 72 Pa, a substrate bias voltage of 340 V, and a treatment time of 4 min. This is used to remove the weak bonding layer and processing residues on the surface. Then, the atmosphere is switched to a mixed atmosphere of hydrogen and argon for interface activation. The hydrogen flow rate is 210 sccm, the argon flow rate is 100 sccm, the chamber pressure is 34 Pa, and the peak pulse bias voltage is gradually reduced from 460 V to 180 V. The treatment time is 6 min. This stage allows the exposed hardened structure interface region on the surface to be deposited to preferentially obtain higher surface activity, providing conditions for the directional nucleation of the subsequent carbon-based deposition phase.

[0034] Within 8 seconds after interface activation, the initial deposition process begins. Acetylene is used as the carbon-containing precursor gas, hydrogen as the hydrogen-containing gas, and argon as the inert gas. Preferred nucleation is performed first, with an acetylene flow rate of 42 sccm, a hydrogen flow rate of 220 sccm, and an argon flow rate of 130 sccm. The hydrogen to acetylene flow rate ratio is 5.2:1. The first pulse bias peak value is 560 V, the duty cycle is 24%, the frequency is 38 kHz, and the duration is 2 min. Then, continuous film deposition is performed, with the acetylene flow rate increased to 72 sccm, the hydrogen flow rate adjusted to 190 sccm, the hydrogen to acetylene flow rate ratio is 2.6:1, and the first pulse bias peak value adjusted to 450 V. The duration is 7 min. After the initial deposition is completed, a carbon-based bonding layer with a thickness of 0.68 μm is formed on the surface to be deposited.

[0035] To verify whether this implementation process achieved the technical objective of preferential growth along the interface of the hardened structure, a witness film of the same material was placed simultaneously in the cavity and cross-sectional SEM observation was performed on the witness film. At the junction of the bonding layer and the substrate, a continuous nucleation zone preferentially growing along the original interface exposed area can be seen, which then spreads to the surrounding area. No large-area isolated island-like non-connected areas were seen, indicating that there is a clear correspondence between the above-mentioned surface control steps to be deposited and the activation and initial deposition steps, and it is not a simple surface cleaning plus conventional film formation.

[0036] Table 2: Key parameters of the surface to be deposited and the initial deposition project Parameters or results matrix material 45 steel outer diameter of working section 45mm Working section length 360mm Gradient hardened layer depth Approximately 2.7mm Surface hardness of working section HRC55 to 58 Final surface removal amount 0.13mm The proportion of the final surface layer removal to the depth of the hardened layer 4.8% Surface roughness Ra to be deposited 0.11μm Percentage of exposed area of ​​hardened tissue interface 22.4% Surface residual compressive stress -418MPa Degassing temperature 195℃ Degassing time 55min Pre-activated atmosphere Argon Pre-activation pressure 72Pa Pre-activated matrix bias 340V Pre-activation time 4min Interface activation atmosphere hydrogen + argon Interface activation pressure 34Pa Interface activation bias peak 460V gradually reduced to 180V Interface activation time 6min acetylene flow rate during the optimal nucleation stage 42sccm Hydrogen flow rate during the optimal nucleation stage 220sccm Argon flow rate during the optimal nucleation stage 130sccm The optimal hydrogen / acetylene flow ratio during the nucleation stage 5.2:1 Preferred nucleation stage bias peak 560V Duty cycle of the optimal nucleation stage 24% Frequency of the optimal nucleation stage 38kHz Preferred nucleation stage time 2min Acetylene flow rate during continuous film formation stage 72sccm Hydrogen flow rate during continuous film formation stage 190sccm Hydrogen / acetylene flow ratio during continuous film formation stage 2.6:1 Peak bias voltage during continuous film formation stage 450V Continuous film formation stage time 7min carbon-based bonding layer thickness 0.68μm

[0037] Example 3 like Figure 1-3 As shown, the second pulse bias voltage and the flow ratio of hydrogen-containing gas to carbon-containing precursor gas are continuously adjusted by reverse coupling. Among them, the peak value of the second pulse bias voltage decreased continuously from 450V to 800V to 150V to 350V, the duty cycle decreased continuously from 25% to 45% to 10% to 25%, and the flow ratio of hydrogen-containing gas to carbon-containing precursor gas increased continuously from 1:1 to 3:1 to 3:1 to 6:1. The first part of the main deposition stage lasts 10 to 40 minutes to form a carbon-based support layer on the outside of the carbon-based bonding layer, and the second part of the main deposition stage lasts 5 to 20 minutes to form a carbon-based working layer on the outside of the carbon-based support layer. Furthermore, a continuous transition zone of 30s to 180s is set between the front and rear sections to prevent abrupt interface formation between the carbon-based support layer and the carbon-based working layer. In this embodiment, after the formation of the surface to be deposited, interface activation and initial deposition are completed in Example 2, a continuously covered carbon-based bonding layer has been formed on the piston rod surface. In order to obtain a carbon-based gradient film layer with continuously changing properties from the inside to the outside on the outside of the carbon-based bonding layer, the main body deposition is carried out under the condition of not opening and closing the vacuum.

[0038] At the start of the main deposition, acetylene is still used as the carbon-containing precursor gas, hydrogen as the hydrogen-containing gas, and argon as the inert gas in the deposition chamber. The piston rod maintains a linkage between rotation and revolution, with the rotation speed controlled at 240 r / min and the revolution speed controlled at 20 r / min. The matrix temperature is controlled at 185℃ to 195℃, and the chamber pressure is maintained at 26 Pa to 34 Pa.

[0039] The pre-deposition stage employed high bias voltage and low hydrogen-to-carbon ratio deposition conditions. Specifically, the peak value of the second pulse bias voltage was continuously reduced from 720V to 410V, the duty cycle was continuously reduced from 36% to 26%, and the hydrogen-to-acetylene flow ratio was continuously increased from 1.7:1 to 2.7:1. This pre-deposition stage lasted for 22 minutes. During this stage, the acetylene flow rate was gradually adjusted from 92 sccm to 78 sccm, the hydrogen flow rate was gradually adjusted from 156 sccm to 210 sccm, and the argon flow rate was maintained between 120 sccm and 150 sccm. After the pre-deposition stage was completed, a relatively thick carbon-based support layer was formed on the outside of the carbon-based bonding layer.

[0040] After the first phase ends, without interrupting the discharge and gas supply, a continuous transition zone is set up, which lasts for 90 seconds. During this period, the peak value of the second pulse bias voltage continues to decrease from 410V to 300V, the duty cycle decreases from 26% to 20%, and the flow ratio of hydrogen to acetylene increases from 2.7:1 to 3.6:1. The purpose of this transition zone is to smoothly transition the high load-bearing layer formed in the first phase to the low shear layer formed in the second phase, avoiding the formation of abrupt interfaces in the film thickness direction.

[0041] The main deposition stage employs relatively low bias voltage and a high hydrogen-to-carbon ratio. Specifically, the peak value of the second pulse bias is further reduced from 300V to 240V, the duty cycle is further reduced from 20% to 15%, and the hydrogen-to-acetylene flow ratio is increased from 3.6:1 to 4.6:1. This stage lasts for 8 minutes, during which the acetylene flow rate is controlled at 48 sccm to 58 sccm, the hydrogen flow rate at 220 sccm to 250 sccm, and the argon flow rate at 100 sccm to 130 sccm. After the main deposition stage is completed, a carbon-based working layer is formed outside the carbon-based support layer.

[0042] After the main deposition was completed, the witness film placed in the cavity was observed using a cross-sectional scanning electron microscope. The results showed that there was no clear straight interface between the bonding layer, the support layer and the working layer. The support layer and the working layer only showed a gray-scale gradient area in the thickness direction. Further segmented testing was carried out along the thickness direction of the film by nanoindentation. The hardness of the middle region near the carbon-based bonding layer was 24.6 GPa to 27.3 GPa, and the hardness of the region near the outermost surface was 13.8 GPa to 16.5 GPa. This indicates that the main deposition stage was not a simple superposition to form two discrete films, but rather a film structure that continuously changed from the high load-bearing region to the low shear region through the continuous linkage adjustment of the second pulse bias voltage and the hydrogen-carbon ratio.

[0043] Raman spectroscopy was used to test different thicknesses of the cross section. The D and G peak areas were relatively low near the carbon-based support layer and relatively high near the carbon-based working layer. This indicates that the outer surface layer formed in the later stage of the main deposition has a higher proportion of low-shear carbon phase. Combined with the results of cross-sectional morphology and hardness changes, it can be confirmed that there is a clear process correspondence between the front section, the continuous transition zone and the rear section in the main deposition stage, and a carbon-based gradient film with continuous structural changes can be obtained.

[0044] To facilitate implementation by those skilled in the art, the key parameters of the main deposition stage and the resulting film are listed in Table 3.

[0045] Table 3: Key parameters and film results of the main deposition stage in Example 3 project Parameters or results Base temperature 185℃ to 195℃ cavity pressure 26Pa to 34Pa Piston rod rotation speed 240r / min Piston rod revolution speed 20r / min Pre-deposition time 22min Changes in peak bias voltage 720V continuously dropped to 410V Changes in duty cycle in the first segment The percentage dropped from 36% to 26%. Changes in the initial hydrogen / acetylene flow ratio The ratio rose from 1.7:1 to 2.7:1. Front-end acetylene flow The 92 sccm was gradually adjusted to 78 sccm. front-end hydrogen flow rate The initial value was gradually adjusted from 156 sccm to 210 sccm. front-end argon flow rate 120 sccm to 150 sccm Continuous transition time 90s Transition region bias peak variation 410V down to 300V Changes in duty cycle in the transition zone 26% to 20% Changes in the hydrogen / acetylene flow ratio in the transition zone The ratio increased from 2.7:1 to 3.6:1. Post-deposition time 8min Changes in peak bias voltage in the later stage 300V down to 240V Duty cycle change in the latter part 20% to 15% Changes in the hydrogen / acetylene flow ratio in the later stage The ratio increased from 3.6:1 to 4.6:1. Post-stage acetylene flow 48 sccm to 58 sccm Post-stage hydrogen flow rate 220 sccm to 250 sccm Argon flow rate in the later stage 100 sccm to 130 sccm Carbon-based support layer hardness 24.6 GPa to 27.3 GPa Carbon-based working layer hardness 13.8 GPa to 16.5 GPa Cross-sectional interface state No abrupt linear interface was observed; the interface gradually changed in the thickness direction.

[0046] Example 4 like Figure 1-3 As shown, the stabilization process includes the following steps: After stopping the introduction of carbon-containing precursor gas, continue to introduce hydrogen-containing gas and inert gas, reduce the matrix bias voltage to 20% to 60% of the peak value of the second pulse bias voltage, control the matrix temperature to 120℃ to 220℃, and process for 5 min to 30 min. In the first stage of stabilization treatment, the flow ratio of hydrogen gas to inert gas is 1:1 to 4:1, and in the second stage of stabilization treatment, the flow ratio of hydrogen gas to inert gas is 1:2 to 1:6. After stabilization, the carbon-based gradient film layer satisfies the following relationship: The thickness of the carbon-based support layer accounts for 55% to 85% of the total thickness of the carbon-based gradient film, the thickness of the carbon-based working layer accounts for 15% to 45% of the total thickness of the carbon-based gradient film, the nanoindentation hardness of the carbon-based support layer is 18 GPa to 35 GPa, the nanoindentation hardness of the carbon-based working layer is 10 GPa to 22 GPa, and the hydrogen content continuously increases along the direction from the carbon-based support layer to the carbon-based working layer. In this embodiment, after the main body deposition is completed in Example 3, a continuous carbon-based gradient film layer has been formed on the surface of the piston rod. In order to further reduce the internal stress of the outer layer, stabilize the surface state of the carbon-based working layer, and maintain the integrity of the load-bearing structure of the carbon-based support layer, the obtained film layer is stabilized.

[0047] At the start of the stabilization process, acetylene supply was stopped, while hydrogen and argon continued to flow. The piston rod maintained its rotation and revolution in tandem, with the rotation speed controlled at 220 to 260 r / min and the revolution speed at 18 to 22 r / min. The chamber pressure was maintained at 24 to 30 Pa. The substrate bias voltage was further reduced from the peak value of the second pulse bias voltage at the end of the main deposition to approximately 40% of its peak value, and the substrate temperature was controlled at 165°C to 175°C.

[0048] The stabilization treatment is divided into a pre-treatment stage and a post-treatment stage. The pre-treatment stage lasts for 7 minutes, with a hydrogen flow rate of 180 to 210 sccm and an argon flow rate of 80 to 100 sccm, and the hydrogen to argon flow rate ratio is controlled at 2.1:1 to 2.4:1. This stage is mainly used to release the deposition internal stress on the surface of the carbon-based working layer and to restabilize the outermost carbon phase. The post-treatment stage lasts for 10 minutes, with the hydrogen flow rate reduced to 70 to 90 sccm and the argon flow rate increased to 230 to 270 sccm, and the hydrogen to argon flow rate ratio controlled at 1:3.0 to 1:3.4. After the post-treatment is completed, the discharge is stopped, and the workpiece is held at the same temperature for another 3 minutes before being cooled to below 80°C in the furnace and then removed.

[0049] To confirm the structure and performance of the stabilized membrane, witness sheets were placed simultaneously in the same batch, and the witness sheets and piston rod body were tested.

[0050] The film thickness was measured using a cross-sectional scanning electron microscope. Three positions (front, middle, and back) along the thickness direction were selected on the cross-section of the witness sheet, and each position was measured three times and the average value was taken. The results showed that the total thickness of the carbon-based gradient film was 4.8 μm, the thickness of the carbon-based support layer near the substrate was 3.3 μm, accounting for 68.8% of the total thickness, and the thickness of the carbon-based working layer near the outermost surface was 1.5 μm, accounting for 31.2% of the total thickness.

[0051] Nanoindentation hardness was tested using witness films from the same batch. Samples were taken along the thickness direction of the film at the middle of the carbon-based support layer and the middle of the carbon-based working layer, with 5 points tested in each region. After removing outliers, the average value was taken. The results showed that the nanoindentation hardness of the carbon-based support layer was 26.4 GPa, and the nanoindentation hardness of the carbon-based working layer was 15.7 GPa. This indicates that after stabilization treatment, the film still maintains the structural characteristic of decreasing hardness from the inside to the outside, with the inner layer serving as the load-bearing layer and the outer layer being more suitable for low-shear contact conditions.

[0052] The variation of hydrogen content along the thickness direction was tested using the time-of-flight elastic recoil detection method. The witness films from the same batch were divided into five equal-thickness regions along the film thickness direction, designated as region A, region B, region C, region D, and region E, from the side closest to the carbon-based support layer towards the carbon-based working layer. The test results showed that the hydrogen atom contents in each region were 18.4 at%, 19.7 at%, 21.6 at%, 24.3 at%, and 27.1 at%, respectively, indicating that the hydrogen content gradually increased along the direction from the carbon-based support layer to the carbon-based working layer, without any sudden drop or reverse fluctuation.

[0053] To further verify the effect of stabilization treatment on improving the film state, a comparison was made between similar test films before and after stabilization treatment. The unstabilized sample showed a high density of fine particle defects on the outermost layer, and the G peak in the Raman spectrum had a large full width at half maximum (FWHM). After stabilization treatment, the particle defects on the outermost layer were significantly reduced, and the G peak position shifted slightly towards lower wavenumbers, indicating that the carbon phase structure of the outer layer tended to be stable. A reciprocating friction pre-run test was conducted on the piston rod body, running for 1.5 × 10⁻⁶ hours under a loading pressure of 12 MPa, a frequency of 2 Hz, and a reciprocating stroke of 200 mm. 5 Subsequently, no localized peeling or through-type longitudinal cracks were observed in the working section.

[0054] In summary, this embodiment discloses the specific gas system, bias adjustment method, temperature and time window for stabilization treatment, and discloses the total thickness of the film after stabilization treatment, the ratio of the thickness of the support layer to the working layer, the hardness of each layer, and the changes in hydrogen content along the thickness direction. Based on this, those skilled in the art can directly implement the above technical solution and can verify the obtained film through cross-sectional morphology, nanoindentation, and hydrogen content depth analysis.

[0055] Table 4. Stabilization treatment parameters and film results in Example 4 project Parameters or results Piston rod rotation speed 220r / min to 260r / min Piston rod revolution speed 18 r / min to 22 r / min cavity pressure 24Pa to 30Pa Base temperature 165℃ to 175℃ Stabilized bias Approximately 40% of the peak value at the end of the main deposition phase. Stabilization some time ago 7min Stabilization of hydrogen flow rate 180 sccm to 210 sccm Argon flow rate before stabilization 80 sccm to 100 sccm Stabilization front hydrogen / argon flow ratio 2.1:1 to 2.4:1 After stabilization 10min Hydrogen flow rate after stabilization 70 sccm to 90 sccm Argon flow rate after stabilization 230 sccm to 270 sccm Hydrogen / argon flow ratio in the stabilization stage 1:3.0 to 1:3.4 Total thickness of carbon-based gradient film 4.8μm carbon-based support layer thickness 3.3μm Carbon-based support layer thickness percentage 68.8% carbon-based working layer thickness 1.5μm Carbon-based working layer thickness percentage 31.2% Carbon-based support layer nano-indentation hardness 26.4 GPa Carbon-based working layer nano-indentation hardness 15.7 GPa Hydrogen content in area A 18.4 at% Hydrogen content in area B 19.7at% Hydrogen content in region C 21.6at% Hydrogen content in region D 24.3at% Hydrogen content in region E 27.1at%

[0056] Example 5 like Figure 1-3 As shown, the proportion of the exposed area of ​​the hardened structure interface to the total area of ​​the surface to be deposited satisfies the following correspondence with the duration of the preferred nucleation stage and the peak value of the second pulse bias: When the ratio is 10% to 20%, the duration of the preferential nucleation stage is 3 to 4 minutes, and the peak value of the second pulse bias voltage is 650V to 800V. When the ratio is 20% to 35%, the duration of the preferential nucleation stage is 1 min to 3 min, and the peak value of the second pulse bias voltage is 450V to 650V. This allows the carbon-based bonding layer to form a continuous nucleation zone along the interface of the hardened structure and to continuously spread to the surrounding area; In this embodiment, after the surface to be deposited is formed and its surface state is detected in Example 2, different preferred nucleation times and main deposition initiation bias are applied to piston rods with different hardened structure interface exposure area ratios to verify the influence of the correspondence between the three on the formation state of the continuous nucleation zone of the carbon-based bonding layer.

[0057] In this embodiment, six piston rod blanks of the same material, size, and heat treatment regime were selected. All blanks used 45 steel as the base material, with a working section outer diameter of 45 mm and a working section length of 360 mm. The induction hardening and tempering regimes were the same as in Example 1, and the gradient hardened layer depth was controlled between 2.6 mm and 2.9 mm after quenching. Subsequently, by adjusting the amount removed during the final grinding and polishing, different proportions of the hardened microstructure interface exposed area were formed in each group of samples, specifically divided into groups A, B, and C. The proportion of the hardened microstructure interface exposed area in group A was controlled between 10% and 20%, in group B between 20% and 35%, and group C was used as a deviation group to verify the film formation state under mismatched parameters.

[0058] The method for detecting the proportion of the exposed area of ​​the hardened microstructure interface was the same as in Example 2. Specifically, witness rods were prepared simultaneously under the same process conditions as the piston rod. The surface of the witness rods was lightly etched with 4% nitric acid alcohol for 6 to 8 seconds. Twenty images were collected equidistantly along the axial direction under a 500x metallographic microscope. The exposed area of ​​the tempered martensite transition zone and the high-hardness martensite zone on the surface was defined as the exposed area of ​​the hardened microstructure interface. Image analysis software was used to calculate the proportion of this area to the total area of ​​the surface to be deposited. The average proportions were 16.3% for group A, 27.8% for group B, and 28.1% for group C.

[0059] After activation, the A group samples were treated with a parameter combination of longer preferred nucleation time and higher initial value of the second pulse bias voltage. Specifically, the preferred nucleation stage lasted 3.5 min, and the first pulse bias voltage and gas flow rate conditions were the same as in Example 2. When entering the main deposition stage, the initial value of the second pulse bias voltage peak was set to 720V, and then the bias voltage was gradually reduced and the hydrogen to acetylene flow rate ratio was increased in the continuous linkage manner of Example 3. The B group samples were treated with a parameter combination of shorter preferred nucleation time and lower initial value of the second pulse bias voltage. Specifically, the preferred nucleation stage lasted 2.0 min, and the initial value of the second pulse bias voltage peak in the main deposition stage was set to 560V. The subsequent continuous adjustment method was the same as in Example 3. Although the C group samples had a similar proportion of hardened tissue interface exposed area as the B group, the parameters of the A group were deliberately used, i.e., the preferred nucleation stage lasted 3.5 min and the initial value of the second pulse bias voltage peak was 720V, to serve as a deviation group for comparison.

[0060] To determine whether a continuous nucleation zone formed along the hardened microstructure interface in the carbon-based bonding layer, witness slices were placed simultaneously in each deposition batch corresponding to each sample group. After deposition, the witness slices were observed using a combination of surface SEM and cross-sectional SEM. Surface SEM was used to observe the island-like connectivity of the initial nucleation region, while cross-sectional SEM was used to observe the continuous coverage at the interface between the bonding layer and the matrix. The proportion of the length of the continuously connected carbon-based nucleation region along the original hardened microstructure interface to the total interface length within the observation field was defined as the continuous nucleation zone coverage.

[0061] The test results show that, under the condition of 16.3% interface exposure, with a preferred nucleation time of 3.5 min and a main deposition initiation bias of 720V, the continuous nucleation zone coverage of Group A samples was 91.4%, and the density of uncovered isolated areas was 0.7 nuclei / mm. Under the condition of 27.8% interface exposure, with a preferred nucleation time of 2.0 min and a main deposition initiation bias of 560V, the continuous nucleation zone coverage of Group B samples was 93.1%, and the density of uncovered isolated areas was 0.5 nuclei / mm. In contrast, although the interface exposure of Group C samples was 28.1%, a longer preferred nucleation time and a higher main deposition initiation bias resulted in a decrease in the continuous nucleation zone coverage to 76.8% and an increase in the density of uncovered isolated areas to 2.6 nuclei / mm. In some local areas, the coexistence of nucleation zones with excessively thick bonding layers and adjacent weak zones was observed.

[0062] To further verify the impact of this correspondence on the subsequent film integrity, scratch tests and short-range reciprocating friction pre-tests were conducted on samples from groups A, B, and C. The scratch test results showed that the critical failure loads Lc2 for groups A and B were 61.2 N and 62.7 N, respectively, while that for group C was 48.9 N. The short-range reciprocating friction pre-test was conducted at a pressure of 12 MPa, a frequency of 2 Hz, and a stroke of 200 mm, with a range of 1.0 × 10⁻⁶. 5 In the second instance, no local peeling was observed in the working sections of samples from groups A and B, while samples from group C showed localized micro-peeling approximately 55 mm from the threaded end. These results indicate that when the exposed area of ​​the hardened structure interface falls within different ranges, the duration of the preferential nucleation stage and the initial value of the second pulse bias peak need to be adjusted accordingly to ensure that the carbon-based bonding layer forms a continuous nucleation band along the hardened structure interface and continuously spreads to the surrounding area.

[0063] Based on the above implementation results, those skilled in the art can clearly obtain the following implementation rules: when the proportion of the exposed area of ​​the hardened structure interface in the surface to be deposited is low, the duration of the preferential nucleation stage should be appropriately extended and the initial bias voltage of the main deposition stage should be increased to enhance the preferential nucleation effect of the limited exposed area; when the proportion of the exposed area of ​​the hardened structure interface is high, the duration of the preferential nucleation stage should be shortened accordingly and the initial bias voltage of the main deposition stage should be reduced to avoid local excessive concentration of nucleation leading to uneven subsequent spreading. In this way, the defined parameter correspondence can be realized, and it can be verified by the coverage of the continuous nucleation zone, the density of the uncovered isolated area, and the subsequent attachment state.

[0064] Table 5: Correspondence and Results between the Exposed Area Percentage of Hardened Microstructure Interface and Film Formation Parameters Group Percentage of exposed area of ​​hardened tissue interface Duration of the optimal nucleation stage The starting value of the second pulse bias peak Continuous nucleation zone coverage Density of uncovered isolated areas <![CDATA[Critical failure load of scratch Lc2]]> Group A 16.3% 3.5min 720V 91.4% 0.7 pieces / mm 61.2N Group B 27.8% 2.0min 560V 93.1% 0.5 pieces / mm 62.7N Group C Deviation Group 28.1% 3.5min 720V 76.8% 2.6 pieces / mm 48.9N In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0065] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A chemical vapor deposition process for the surface of a piston rod, characterized in that, include: The piston rod substrate is subjected to induction hardening and tempering to form a radially distributed gradient hardened layer on the surface of the piston rod substrate; The gradient hardened layer is finely ground and polished, and the amount of surface layer removed in the final stage is controlled so that some hardened structure interface and residual compressive stress are retained on the outer surface of the gradient hardened layer to obtain the surface to be deposited. The piston rod with the surface to be deposited is fed into the vacuum deposition chamber, where it undergoes degassing and plasma activation treatment in sequence. Carbon-containing precursor gas, hydrogen-containing gas, and inert gas are introduced into the vacuum deposition chamber. Initial deposition is performed using a first pulse bias voltage while the piston rod is rotating, so that the carbon-based deposition phase preferentially grows along the partially hardened microstructure interface and forms a carbon-based bonding layer on the surface to be deposited. Under the condition of continuous vacuum, a continuously varying second pulse bias is used, and the flow ratio of the carbon-containing precursor gas, the hydrogen-containing gas and the inert gas is adjusted simultaneously, so that a carbon-based support layer and a carbon-based working layer are continuously formed on the outer side of the carbon-based bonding layer along the thickness direction, so as to form a carbon-based gradient film layer generated by the surface microstructure of the gradient hardened layer. The carbon-based gradient film is stabilized.

2. The chemical vapor deposition process for the piston rod surface according to claim 1, characterized in that, When performing fine grinding and polishing on the gradient hardened layer, the final surface layer removal amount is controlled to be 2% to 12% of the depth of the gradient hardened layer, and the surface to be deposited meets the following conditions: The surface roughness Ra is 0.08 μm to 0.16 μm, the surface residual compressive stress is 200 MPa to 800 MPa, and the exposed area of ​​the hardened structure interface uniformly distributed along the piston rod axis accounts for 10% to 35% of the total area of ​​the surface to be deposited.

3. The chemical vapor deposition process for the piston rod surface according to claim 2, characterized in that, The degassing treatment is performed at a temperature of 160°C to 230°C for a time of 40 min to 70 min. The plasma activation treatment includes a pre-activation stage performed under the inert gas atmosphere and an interface preferential activation stage performed under the mixed atmosphere of hydrogen-containing gas and the inert gas, wherein the substrate bias voltage of the pre-activation stage is 250V to 450V and the treatment time is 2min to 6min. The interface preferential activation stage uses a pulse bias voltage with a peak value gradually decreasing from 350V to 500V to 120V to 220V, and the processing time is 3min to 10min. The initial deposition includes a selective nucleation stage and a continuous film formation stage performed sequentially. In the preferred nucleation stage, the flow ratio of the hydrogen-containing gas to the carbon-containing precursor gas is 4:1 to 7:1, and the time is 1 min to 4 min. In the continuous film-forming stage, the flow ratio of the hydrogen-containing gas to the carbon-containing precursor gas is 2:1 to 4:1, and the time is 4 min to 12 min, so that the carbon-based bonding layer continuously spreads from the hardened structure interface to the surrounding area, and the thickness of the carbon-based bonding layer is 0.3 μm to 1.2 μm.

4. The chemical vapor deposition process for the piston rod surface according to claim 3, characterized in that, The second pulse bias voltage and the flow ratio of the hydrogen-containing gas to the carbon-containing precursor gas are continuously adjusted by reverse coupling. In this process, the peak value of the second pulse bias voltage continuously decreases from 450V to 800V to 150V to 350V, the duty cycle continuously decreases from 25% to 45% to 10% to 25%, and the flow ratio of the hydrogen-containing gas to the carbon-containing precursor gas continuously increases from 1:1 to 3:1 to 3:1 to 6:

1. The first part of the main deposition stage lasts from 10 to 40 minutes to form the carbon-based support layer on the outside of the carbon-based bonding layer, and the second part of the main deposition stage lasts from 5 to 20 minutes to form the carbon-based working layer on the outside of the carbon-based support layer. Furthermore, a continuous transition zone of 30s to 180s is provided between the front section and the rear section to prevent abrupt interface formation between the carbon-based support layer and the carbon-based working layer.

5. The chemical vapor deposition process for the piston rod surface according to claim 4, characterized in that, The stabilization process includes the following steps: After stopping the supply of the carbon-containing precursor gas, the supply of the hydrogen-containing gas and the inert gas continues, and the substrate bias voltage is reduced to 20% to 60% of the peak value of the second pulse bias voltage. The substrate temperature is controlled at 120°C to 220°C, and the treatment lasts for 5 to 30 minutes. In the first stage of the stabilization process, the flow ratio of the hydrogen-containing gas to the inert gas is 1:1 to 4:1, and in the second stage of the stabilization process, the flow ratio of the hydrogen-containing gas to the inert gas is 1:2 to 1:

6.

6. The chemical vapor deposition process for the piston rod surface according to claim 5, characterized in that, After the stabilization treatment is completed, the carbon-based gradient film layer satisfies the following relationship: The thickness of the carbon-based support layer accounts for 55% to 85% of the total thickness of the carbon-based gradient film layer, the thickness of the carbon-based working layer accounts for 15% to 45% of the total thickness of the carbon-based gradient film layer, the nanoindentation hardness of the carbon-based support layer is 18 GPa to 35 GPa, the nanoindentation hardness of the carbon-based working layer is 10 GPa to 22 GPa, and the hydrogen content continuously increases along the direction from the carbon-based support layer to the carbon-based working layer.

7. The chemical vapor deposition process for the piston rod surface according to claim 6, characterized in that, The proportion of the exposed area of ​​the hardened structure interface to the total area of ​​the surface to be deposited satisfies the following correspondence with the duration of the preferred nucleation stage and the peak value of the second pulse bias: When the ratio is 10% to 20%, the duration of the preferred nucleation stage is 3 to 4 minutes, and the peak value of the second pulse bias is 650V to 800V. When the ratio is 20% to 35%, the duration of the preferred nucleation stage is 1 min to 3 min, and the peak value of the second pulse bias is 450V to 650V. This allows the carbon-based bonding layer to form a continuous nucleation zone along the interface of the hardened structure and to continuously spread to the surrounding area.

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