Heat treatment method for regulating and controlling interface and functional performance of heterostructure

Abstract

The invention discloses a heat treatment method for regulating and controlling a heterostructure interface and functional performance, and belongs to the technical field of metal additive manufacturing and composite material post-treatment, two-stage heat treatment is adopted, and the heat treatment method comprises the steps that a sedimentary state SS / Cu / NiTi heterogeneous alloy component is placed in a heat treatment device; first-stage heat treatment: heating to 480 + / -20 DEG C at a heating rate of 5-10 DEG C / min, and preserving heat for 90 + / -30 minutes to realize interface passivation and copper layer recrystallization; second-stage heat treatment: continuously heating to 650 + / -30 DEG C at the heating rate of 5-15 DEG C / min, and preserving heat for 30 + / -10 minutes to realize structure homogenization and stress relief; and after the heat treatment is finished, cooling to below 100 DEG C along with the furnace at a slow cooling rate of 10-30 DEG C / min, and discharging. According to the method, the brittle intermetallic compound can be effectively spheroidized, the residual stress is reduced, and the mechanical property and the interface toughness of the component are cooperatively improved.

Description

Technical Field

[0001] This invention relates to the fields of metal additive manufacturing and composite material post-processing technology, and in particular to a heat treatment method for controlling the interface and functional properties of heterogeneous structures. Background Technology

[0002] Arc-fused additive manufacturing technology, especially CMT (Cold Metal Transfer), offers a new approach to metallurgical bonding of heterogeneous material structures due to its low heat input and stable process. This technology can be used to integrate NiTi alloys with shape memory effect, pure copper with high thermal and electrical conductivity, and 316L stainless steel with excellent strength and corrosion resistance to create intelligent composite components that combine sensing, actuation, heat transfer, and load-bearing functions, showing broad application prospects in aerospace, biomedicine, and other fields.

[0003] However, regardless of whether CMT technology or other traditional processes are used to fabricate such multi-material components, the following systemic technical challenges are faced, which severely restrict their practical application: 1. Brittle failure due to poor interfacial metallurgical compatibility: In the NiTi-Cu and Cu-316L interfacial regions, multi-component systems readily form continuously distributed brittle intermetallic compounds during rapid non-equilibrium solidification in the molten pool. These brittle phases become microcrack initiations when the component is under stress, and they propagate rapidly, leading to early brittle fracture at the interface and a sharp decline in the ductility and reliability of the component.

[0004] 2. The Inherent Contradictions in the Synergistic Regulation of Multi-Material Properties: The optimal performance of the three materials constituting this heterogeneous component depends on conflicting or even contradictory heat treatment pathways. For example, the phase transformation behavior of NiTi shape memory alloys is extremely sensitive to heat treatment regimes; pure copper requires recrystallization to restore its plasticity, but grain coarsening must be avoided; 316L stainless steel requires stress relief and prevention of harmful phase precipitation. Existing standard heat treatment schemes designed for single materials (such as solution treatment, aging, or annealing) often optimize the performance of one material while impairing the performance of another when applied to this multi-material system, failing to achieve synergistic optimization of overall performance.

[0005] 3. The interplay of inherent defects in additive manufacturing and interface problems: Although the low heat input characteristics of CMT technology suppress interface reactions to some extent, its layer-by-layer deposition manufacturing characteristics inevitably introduce significant residual stress and microstructure inhomogeneity. These residual stresses, combined with the inherently brittle interfaces, further exacerbate the risk of interface cracking, making it difficult for deposited components to directly meet the mechanical and functional reliability requirements of practical applications.

[0006] Therefore, those skilled in the art urgently need a specially designed post-heat treatment process that is not a simple superposition of existing heat treatment methods, but can fundamentally and synergistically solve the three major problems of interface brittleness, performance mismatch and complex residual stress, thereby achieving the key leap from "manufacturable" to "high performance and applicability" of SS / Cu / NiTi multi-material components. Summary of the Invention

[0007] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a heat treatment method for controlling the interface and functional performance of heterogeneous structures, aiming to synergistically solve the three major problems of interface brittleness, performance mismatch and complex residual stress.

[0008] According to one aspect of the present invention, a heat treatment method for regulating the interface and functional properties of heterogeneous structures is provided. The heat treatment method employs a two-stage heat treatment, comprising: placing a deposited heterogeneous alloy component in a heat treatment apparatus, wherein the deposited heterogeneous alloy component is a multilayer heterogeneous component formed by layer-by-layer deposition of 316L stainless steel, pure copper, and nickel-titanium shape memory alloy using arc-wire additive manufacturing technology; a first-stage heat treatment: heating to 480±20℃ at a heating rate of 5~10℃ / min and holding at that temperature for 90±30 minutes to achieve interface passivation and copper layer recrystallization; a second-stage heat treatment: continuing to heat to 650±30℃ at a heating rate of 5~15℃ / min and holding at that temperature for 30±10 minutes to achieve microstructure homogenization and stress relief; after the heat treatment, cooling in the furnace to below 100℃ at a slow cooling rate of 10~30℃ / min before removing from the furnace.

[0009] Optionally, the heat treatment apparatus is a vacuum heat treatment furnace or an atmosphere-protected furnace.

[0010] Optionally, after placing the deposited hetero alloy component in a heat treatment apparatus, the deposited hetero alloy component is covered with dry sand to prevent oxidation.

[0011] Optionally, the holding temperature for the first stage of heat treatment is 480°C.

[0012] Optionally, the holding temperature for the second stage of heat treatment is 650°C.

[0013] The beneficial effects of this invention are: Creative improvement of interface properties: The first stage, "interface passivation" at 480℃, cleverly utilizes the spheroidization phenomenon of brittle intermetallic compounds at subcritical temperatures, transforming the columnar intermetallic compounds at the Ti / Cu heterostructure into spherical shapes. The second stage, maintaining the temperature at 650℃, further provides sufficient kinetic conditions for the spheroidization of the intermetallic compounds, causing the sharp lamellars to break apart. Through precise temperature control in these two stages, the continuous, sharp, brittle intermetallic compounds at the interface are spheroidized into discontinuous particles. This structural transformation improves the structural bonding strength and elongation at fracture of the heterostructure.

[0014] Effective elimination of residual stress: Extremely slow cooling eliminates the "secondary damage" of thermal stress to the brittle interface, minimizing and relaxing internal stresses caused by differences in the thermal expansion coefficients of the constituent materials. This protects the brittle interface, which has already undergone spheroidization and passivation treatment, preventing cracking during cooling. This specific cooling regime, combined with the aforementioned second-stage heat treatment holding regime, constitutes a complete and inseparable technical solution to the problem of brittle fracture at multi-material interfaces, effectively improving the interfacial toughness, mechanical properties, and crack propagation resistance of dissimilar alloy components. Attached Figure Description

[0015] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic flowchart of a heat treatment method for regulating the interface and functional performance of heterogeneous structures in an embodiment. Figure 2 This is a SEM image of the SS / Cu / NiTi interface that has not been processed by the method of this invention; Figure 3 This is a SEM image of the SS / Cu / NiTi interface after processing by the method of this invention. Detailed Implementation

[0016] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of them. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present application. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present application can be combined with each other.

[0017] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0018] This invention provides a heat treatment method for controlling the interface and functional properties of heterogeneous structures, applicable to multilayer heterogeneous components (SS / Cu / NiTi heterogeneous components) formed by layer-by-layer deposition of 316L stainless steel, pure copper, and nickel-titanium shape memory alloy using arc-wire additive manufacturing technology. Figure 1 It includes the following steps: S1, the deposited SS / Cu / NiTi hetero alloy component is placed in a heat treatment apparatus and covered with dry sand to prevent oxidation; The heat treatment device is specifically a vacuum heat treatment furnace or an atmosphere protection furnace.

[0019] S2, First stage heat treatment - interface passivation and Cu layer recrystallization; Heating to the first characteristic temperature T1 at a heating rate of v1 = 5~10℃ / min, and holding at that temperature for a time t1, where T1 = 480±20℃ and t1 = 90±30 minutes.

[0020] At the first characteristic temperature of the first stage, brittle intermetallic compounds are transformed from a continuous network spheroids into discontinuous granules through the Oswald ripening mechanism.

[0021] S3, Second Stage Heat Treatment – ​​Homogenization and Stress Relief; Continue heating at a heating rate of v2 = 5~15℃ / min to the second characteristic temperature T2, and hold at that temperature for a time t2, where T2 = 650±30℃ and t2 = 30±10 minutes.

[0022] S4. After heat treatment, the furnace is cooled to below 100°C with the furnace at a slow cooling rate of 10~30°C / min.

[0023] It should be noted that this invention is not a simple superposition of existing heat treatment methods, but rather a series heat treatment path designed based on a deep understanding of the reaction mechanism of multi-material interfaces: "low-temperature interface engineering (first-stage heat treatment) → medium-temperature microstructure optimization (second-stage heat treatment)". Through the special effect of "passivating" the Cu / NiTi interface in specific temperature ranges of 480℃ and 650℃, the intermetallic compounds are effectively spheroidized, thereby enhancing the bonding strength of the Cu / NiTi interface.

[0024] The mechanism and function of the first stage heat treatment (480±20℃) is as follows: This temperature range is higher than the typical recrystallization temperature of pure copper (about 200~300℃), which can ensure that the Cu layer is fully recrystallized and softened, releasing its work hardening, while avoiding excessive grain growth. Holding at this temperature range can cause the initial thin-layer brittle phase formed during CMT to undergo Oswald ripening, that is, the fine and continuous compound layer breaks and spheroidizes into discontinuous granules, thereby achieving the "passivation" treatment of the interface and significantly improving the interface toughness and crack propagation resistance.

[0025] The mechanism and function of the second-stage heat treatment (650±30℃) are as follows: This stage provides sufficient kinetic conditions for the spheroidization of intermetallic compounds, and the Oswald ripening process proceeds very rapidly, allowing the sharp lamellar structure to melt and coarsen. At the same time, this temperature can effectively promote atomic diffusion, achieve homogenization of the microstructure, and significantly eliminate residual stress caused by the differences in the thermal expansion coefficients of the various component materials.

[0026] After heat treatment, the mechanism and function of the slow cooling stage are as follows: a specific slow cooling rate (10~30℃ / min) can eliminate and relax thermal stress to the greatest extent and avoid damage to the brittle interface that has been spheroidized and passivated by the "secondary thermal shock" during the cooling process.

[0027] The effectiveness of the method of the present invention is verified by observing the microstructure and testing the mechanical properties of the processed components.

[0028] Microscopic tissue observation, such as Figure 2 and Figure 3 As shown, the microstructure at the Cu / NiTi interface before and after heat treatment is revealed. The brittle phase at the interface is significantly spheroidized, and the originally sharp and continuous intermetallic compounds are accelerated to break apart and spheroidize into discontinuous particles.

[0029] Mechanical property data are shown in Table 1: Table 1 Mechanical properties of samples in the deposited state and in the state after furnace cooling to room temperature heat treatment.

[0030] In the table, the deposited state refers to the SS / Cu / NiTi hetero alloy before the application of the method of the present invention, and the heat-treated state refers to the SS / Cu / NiTi hetero alloy after the application of the method of the present invention.

[0031] As shown in Table 1, after treatment by the method of the present invention, the room temperature tensile strength of the SS / Cu / NiTi hetero alloy reaches 257 MPa and the elongation reaches 1.05%, and both the ultimate tensile strength and elongation are effectively improved.

[0032] In summary, the method of this invention successfully achieves synergistic control of the interface and functional performance of heterogeneous structures.

[0033] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0034] The steps in the method of this invention can be adjusted, combined, or deleted according to actual needs. The technical features can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the embodiments are described. However, as long as the combinations of these technical features do not contradict each other, they should all be considered within the scope of this invention.

[0035] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A heat treatment method for controlling the interface and functional properties of heterogeneous structures, characterized in that, The heat treatment method employs a two-stage heat treatment process, including: The deposited heterogeneous alloy component is placed in a heat treatment device. The deposited heterogeneous alloy component is a multilayer heterogeneous component formed by layer-by-layer deposition of 316L stainless steel, pure copper and nickel-titanium shape memory alloy through electric arc wire additive manufacturing technology. First stage heat treatment: Heat to 480±20℃ at a heating rate of 5~10℃ / min and hold for 90±30 minutes to achieve interface passivation and copper layer recrystallization. The second stage of heat treatment: continue heating to 650±30℃ at a heating rate of 5~15℃ / min, and hold for 30±10 minutes to achieve tissue homogenization and stress relief; After heat treatment, the furnace is cooled to below 100°C at a slow cooling rate of 10~30°C / min before being removed from the furnace.

2. The heat treatment method according to claim 1, characterized in that, The heat treatment device is a vacuum heat treatment furnace or an atmosphere protection furnace.

3. The heat treatment method according to claim 1, characterized in that, After the deposited hetero alloy component is placed in a heat treatment apparatus, it is covered with dry sand to prevent oxidation.

4. The heat treatment method according to claim 1, characterized in that, The holding temperature for the first stage of heat treatment is 480℃.

5. The heat treatment method according to claim 1, characterized in that, The holding temperature for the second stage of heat treatment is 650℃.

Images