A cold spray solid-state additive manufacturing method of a niticu alloy

Abstract

The present application relates to the technical field of additive manufacturing, and particularly relates to a cold spraying solid-state additive preparation method of NiTiCu alloy, which comprises the following steps: mechanically mixing Ti powder, Ni powder and Cu powder according to preset mass percentages to obtain mixed powder; drying the mixed powder; depositing the dried mixed powder on a Ti substrate by using a cold spraying process to prepare a NiTiCu deposit; performing solid-state diffusion alloying treatment on the NiTiCu deposit below a NiTi eutectic temperature to obtain a NiTiCu alloy blank; heating the NiTiCu alloy blank to above the NiTi eutectic temperature for high-temperature solid solution treatment, quenching to room temperature, and then heating to a set temperature for low-temperature aging treatment to obtain the NiTiCu alloy. The purpose of the cold spraying solid-state additive preparation method of the NiTiCu alloy is to solve the problems of large superelasticity hysteresis and poor thermal cycle stability in additive manufacturing of the NiTiCu alloy.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, specifically to a method for preparing NiTiCu alloy using cold spray solid additive manufacturing. Background Technology

[0002] Shape memory alloys (SMAs) are alloys that, when deformed appropriately at a certain temperature and then subjected to a further temperature change, can return to their original shape. They mainly include three categories: NiTi-based, Cu-based, and Fe-based alloys. NiTi alloys not only possess excellent shape memory and superelasticity effects, but also exhibit good damping properties, corrosion resistance, and low stiffness. Therefore, NiTi alloys are among the most promising shape memory alloys and are widely used in aerospace, microelectromechanical systems (MEMS), and medical fields.

[0003] Traditional processing methods for NiTi alloys mainly include melting and casting, powder metallurgy, and fused additive manufacturing. Melting and casting, along with subsequent hot and cold working processes (such as forging, cooling, and hot rolling), easily introduce more impurities such as C, O, and N, while also suffering from problems like component segregation, high impurity content, and low processing efficiency. Powder metallurgy can alleviate the problems of component segregation and coarse grains associated with melting and casting, but the process is relatively complex, high-temperature sintering is difficult, porosity is large, and complex mold structures are expensive. In recent years, researchers have conducted research on fused additive manufacturing to prepare NiTi shape memory alloy parts with complex structures, but processing defects such as porosity, cracks, and surface spheroidization easily occur during the melting and forming process. Excessive Ni evaporation occurs during the material melting process, increasing the martensitic transformation initiation temperature and latent heat of phase transformation in NiTi shape memory alloys. Furthermore, due to the layer-by-layer deposition characteristic, the complex heating-cooling cycle leads to differences in composition and phase composition in different parts of the fused additive formed part, making it difficult to effectively control the uniformity of the workpiece's microstructure, and also resulting in large hyperelastic hysteresis and poor thermal cycling stability.

[0004] Therefore, the inventors provide a method for preparing NiTiCu alloy by cold spraying solid additive manufacturing. Summary of the Invention

[0005] (1) Technical problems to be solved This invention provides a cold-spray solid additive manufacturing method for NiTiCu alloys, which solves the technical problems of large hyperelastic hysteresis and poor thermal cycling stability in NiTiCu alloy additive manufacturing.

[0006] (2) Technical solution This invention provides a method for cold-spraying solid additive manufacturing of NiTiCu alloys, comprising the following steps: Ti powder, Ni powder and Cu powder are mechanically mixed according to a preset mass percentage to obtain a mixed powder; The mixed powder is then dried. The dried mixed powder was deposited onto a Ti substrate using a cold spraying process to prepare a NiTiCu deposit. The NiTiCu deposit is subjected to solid-state diffusion alloying treatment below the NiTi eutectic temperature to obtain a NiTiCu alloy billet. The NiTiCu alloy billet is heated to above the NiTi eutectic temperature for high-temperature solution treatment, quenched to room temperature, and then heated to a set temperature for low-temperature aging treatment to obtain the NiTiCu alloy.

[0007] Furthermore, the Ti powder has a particle size of 5–30 μm, the Ni powder has a particle size of 5–40 μm, and the Cu powder has a particle size of 5–40 μm.

[0008] Furthermore, before drying the mixed powder, the process further includes: The mixed powder is processed using a powder mixer, and then processed using a high-energy ball mill.

[0009] Further, the drying process of the mixed powder specifically includes: The mixed powder is heated to 100-120°C in an oven and kept at that temperature for 2-3 hours.

[0010] Furthermore, the parameters of the cold spraying process include: the flow rate of the working gas is 80-100 m³ / h. 3 The working pressure is 3.8–4.2 MPa, the heating temperature of the working gas is 550–700℃, the powder feeding speed is 1–3 rpm, and the carrier gas flow rate is 3–6 m³ / h. 3 / h, spraying distance is 20-30mm, spray gun moving speed is 100-400mm / s, and scanning interval is 0.5-2mm.

[0011] Furthermore, the thickness of the NiTiCu deposit is 0.5–1 mm.

[0012] Furthermore, the pressure for solid-state diffusion alloying treatment is 1×10⁻⁶. -3 ~5×10 -3 Pa, keep warm for 1-3 hours.

[0013] Furthermore, the pressure for high-temperature solution treatment is 1×10⁻⁶. -3 ~5×10 -3 Pa, keep warm for 0.5 to 1.5 hours.

[0014] Furthermore, the set temperature is 350–500°C.

[0015] Furthermore, the preset mass percentage is: 40-50 wt% Ti powder, 30-40 wt% Ni powder, and 10-20 wt% Cu powder.

[0016] (3) Beneficial effects In summary, this invention, by adding copper (Cu partially replacing Ni) to NiTi alloys, reduces the sensitivity of the martensitic transformation initiation temperature Ms to compositional changes and aging treatments, narrows the transformation hysteresis width, and thus enables NiTiCu shape memory alloys to exhibit smaller transformation hysteresis. It also improves the alloy's thermal cycling stability, suppresses R-phase transformation, and consequently enhances its fatigue and damping properties. Furthermore, the addition of Cu promotes subsequent cold spraying preparation of NiTiCu deposits. Simultaneously, solid-state diffusion alloying below the eutectic temperature reduces the melting and solidification process of the NiTiCu alloy, avoids porosity caused by solidification shrinkage, and improves the density of the NiTiCu alloy. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention 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.

[0018] Figure 1 This is a schematic flowchart of a cold-spray solid additive manufacturing method for NiTiCu alloy provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a solid-state diffusion heat treatment process provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a high-temperature solution treatment followed by a low-temperature aging heat treatment process provided in an embodiment of the present invention. Detailed Implementation

[0019] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention, that is, the present invention is not limited to the described embodiments.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] This invention provides a method for cold-spraying solid additive manufacturing of NiTiCu alloys, see [link to relevant documentation]. Figure 1 The method may include the following steps: S100. Ti powder, Ni powder and Cu powder are mechanically mixed according to a preset mass percentage to obtain a mixed powder.

[0022] Specifically, the particle size of Ti powder is 5–30 μm, Ni powder is 5–40 μm, and Cu powder is 5–40 μm, with weight percentages of 40–50 wt% for Ti powder, 30–40 wt% for Ni powder, and 10–20 wt% for Cu powder. Adding copper (Cu partially replacing Ni) to the NiTi alloy reduces the sensitivity of its martensitic transformation initiation temperature Ms to compositional changes and aging treatment, narrows the transformation hysteresis width, and results in a smaller transformation hysteresis (5–10 °C) in the NiTiCu shape memory alloy. It also improves the alloy's thermal cycling stability, suppresses R-phase transformation, and thus enhances its fatigue and damping properties. Furthermore, the addition of Cu promotes the subsequent cold spraying preparation of NiTiCu deposits.

[0023] S200, Dry the mixed powder.

[0024] Specifically, the mixed powder is heated to 100–120°C in an oven and held at that temperature for 2–3 hours to remove moisture and keep the powder dry. Furthermore, before drying, the powder is treated with a three-dimensional powder mixer (20–40 Hz) for 0.5–1 hour, followed by high-energy ball milling (800–1200 rpm) for 36–48 hours to further promote homogenization of the mixed powder.

[0025] S300: A cold spraying process is used to deposit the dried mixed powder onto a Ti substrate to prepare a NiTiCu deposit.

[0026] Specifically, the parameters for the cold spray coating process include: a working gas flow rate of 80–100 m³ / h. 3 The working pressure is 3.8–4.2 MPa, the heating temperature of the working gas is 550–700℃, the powder feeding speed is 1–3 rpm, and the carrier gas flow rate is 3–6 m³ / h. 3 The spraying speed is 100–400 mm / s, the spray gun moving speed is 100–400 mm / s, and the scanning interval is 0.5–2 mm. The thickness of the NiTiCu deposit is 0.5–1 mm. The cold spraying process generates intense plastic deformation, increasing the dislocation density within the material and the number of grain boundaries during alloy formation. This lowers the phase transformation barrier, which is beneficial for NiTiCu alloying and also refines the grain size. Grain refinement helps stabilize the critical stresses for martensitic and reverse phase transformations, minimizing their changes after multiple cycles. This improves the shape recovery capability of the alloy after repeated phase transformation cycles, extending the service life of the shape memory alloy.

[0027] S400. The NiTiCu deposit is subjected to solid-state diffusion alloying treatment below the NiTi eutectic temperature to obtain a NiTiCu alloy billet.

[0028] Specifically, the Ti substrate is removed, and the NiTiCu deposit is solid-state diffusion alloyed below the NiTi eutectic temperature (942℃), followed by vacuum heat treatment (1×10⁻⁶). -3 ~5×10 -3 Pa), hold at this temperature for 1–3 hours to obtain a NiTiCu alloy billet. (See also...) Figure 2 In the figure, 1 represents the heating stage (10℃ / min), 2 represents the solid-state diffusion stage, and 3 represents the furnace cooling stage. It can be seen that solid-state diffusion alloying below the NiTi eutectic temperature reduces the melting and solidification process of NiTiCu alloy, avoids porosity caused by solidification shrinkage, and improves the density of NiTiCu alloy.

[0029] S500: Heat the NiTiCu alloy billet to above the NiTi eutectic temperature for high-temperature solution treatment, quench it to room temperature, and then heat it to a set temperature for low-temperature aging treatment to obtain the NiTiCu alloy.

[0030] Specifically, the NiTi alloy billet is heated to above the NiTi eutectic temperature (942℃) for high-temperature solution treatment, followed by vacuum heat treatment (1×10⁻⁶). -3 ~5×10 -3 After holding at this temperature for 0.5–1.5 h, quenching to room temperature, and then heating to 350–500 °C for low-temperature aging treatment for 1–3 h, a NiTiCu alloy is finally obtained. (See also...) Figure 3 In the figure, 1 represents the heating stage (10℃ / min), 2 represents the high-temperature solution treatment stage, 3 represents the quenching stage, 4 represents the heating stage (10℃ / min), 5 represents the low-temperature aging stage, and 6 represents the furnace cooling stage. It can be seen that the secondary high-temperature solution treatment promotes the homogenization of various elements, eliminates defects caused by the severe plastic deformation due to cold spraying, and improves the uniformity of the NiTiCu alloy. The low-temperature aging treatment at 350–500℃ promotes the uniform precipitation of the Ni4Ti3 phase, enhances the critical stress for plastic deformation of the alloy matrix, inhibits the occurrence of plastic deformation, and thus improves the superelasticity of the NiTiCu alloy.

[0031] Example 1 1. Pure titanium (Ti) powder with a particle size of 5-30 μm, pure Ni powder with a particle size of 5-40 μm, and pure copper (Cu) powder with a particle size of 5-40 μm are mechanically mixed together, with weight percentages of 45 wt%, 38 wt%, and 17 wt%, respectively.

[0032] 2. After processing the powder with a three-dimensional powder mixer at 40 Hz for 0.5 h, the mixed powder is then processed with a high-energy ball mill at 1200 rpm for 40 h to further promote the homogenization of the mixed powder.

[0033] 3. Heat the mixed powder to 110±10℃ in an oven and keep it at that temperature for 2 hours to remove moisture from the powder and keep it dry.

[0034] 4. A 100×100×1mm NiTiCu deposit was prepared by depositing NiTiCu mixed powder onto a Ti substrate using a cold spraying process. The cold spraying parameters were: N2 working gas flow rate, 90m³ / h. 3 / h, maximum working pressure up to 4.0MPa, maximum working gas heating temperature up to 600±10℃; powder feeding speed 2 rpm, carrier gas 4m³ / min 3 / h, spraying distance 25mm, spray gun moving speed 300mm / s, scanning interval 1mm.

[0035] 5. Remove the substrate, and perform solid-state diffusion alloying of the deposited material below the NiTi eutectic temperature (930±10℃), followed by vacuum heat treatment (vacuum degree, 5×10). -3 Pa), hold for 2 hours to obtain NiTiCu alloy billet.

[0036] 6. Heat the NiTiCu alloy billet to above the NiTi eutectic temperature (955±10℃) for high-temperature solution treatment, followed by vacuum heat treatment (vacuum degree, 5×10). -3 After holding at 400±10℃ for 1 hour and quenching to room temperature, the temperature is raised to 400±10℃ for low-temperature aging treatment for 2 hours to finally obtain NiTiCu shape memory alloy.

[0037] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0038] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art without departing from the scope of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A method for cold-spraying solid additive manufacturing of NiTiCu alloy, characterized in that, The method includes the following steps: Ti powder, Ni powder and Cu powder are mechanically mixed according to a preset mass percentage to obtain a mixed powder; The mixed powder is then dried. The dried mixed powder was deposited onto a Ti substrate using a cold spraying process to prepare a NiTiCu deposit. The NiTiCu deposit is subjected to solid-state diffusion alloying treatment below the NiTi eutectic temperature to obtain a NiTiCu alloy billet. The NiTiCu alloy billet is heated to above the NiTi eutectic temperature for high-temperature solution treatment, quenched to room temperature, and then heated to a set temperature for low-temperature aging treatment to obtain the NiTiCu alloy.

2. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, The Ti powder has a particle size of 5–30 μm, the Ni powder has a particle size of 5–40 μm, and the Cu powder has a particle size of 5–40 μm.

3. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, Before drying the mixed powder, the process further includes: The mixed powder is processed using a powder mixer, and then processed using a high-energy ball mill.

4. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, The process of drying the mixed powder specifically involves: The mixed powder is heated to 100-120°C in an oven and kept at that temperature for 2-3 hours.

5. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, The parameters of the cold spraying process include: the flow rate of the working gas is 80-100 m³ / h. 3 The working pressure is 3.8–4.2 MPa, the heating temperature of the working gas is 550–700℃, the powder feeding speed is 1–3 rpm, and the carrier gas flow rate is 3–6 m³ / h. 3 / h, spraying distance is 20-30mm, spray gun moving speed is 100-400mm / s, and scanning interval is 0.5-2mm.

6. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, The thickness of the NiTiCu deposit is 0.5–1 mm.

7. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, The pressure for solid-state diffusion alloying is 1×10 -3 ~5×10 -3 Pa, keep warm for 1-3 hours.

8. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, The pressure of high-temperature solution treatment is 1×10 -3 ~5×10 -3 Pa, keep warm for 0.5 to 1.5 hours.

9. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, The set temperature is 350–500°C.

10. The method for preparing NiTiCu alloy by cold spraying solid additive manufacturing according to claim 1, characterized in that, The preset mass percentages are: 40-50 wt% Ti powder, 30-40 wt% Ni powder, and 10-20 wt% Cu powder.

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