A heat treatment method for regulating the precipitation behavior of nickel-titanium alloy

Abstract

The present invention provides a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy, which is used to regulate the precipitation behavior of nickel-titanium alloy, including the size of the precipitated phase and the distribution of the precipitated phase at the grain boundary and in the grain, and includes the following steps: step S1, coating the nickel-titanium alloy with a coating material and performing annealing treatment; step S2, removing the coating material and performing direct current aging to complete the regulation of the precipitation behavior of the nickel-titanium alloy. The nickel-titanium alloy obtained by the heat treatment method for regulating the precipitation behavior of the nickel-titanium alloy of the present invention has a variety of precipitation effects.

Description

Technical Field

[0001] The invention belongs to the field of shape memory alloy process treatment, and in particular relates to a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy. Background Art

[0002] Nickel-rich nickel-titanium alloys are widely used in biomedicine and civil engineering due to their functional properties (superelasticity and shape memory). Their functional properties are derived from the reversible thermoelastic martensitic transformation. The precipitated phase in nickel-titanium alloys can produce a microscopic strain field in the matrix and affect the nickel content of the matrix, which is an important factor affecting the martensitic transformation of nickel-titanium alloys. However, since grain boundaries promote non-uniform nucleation, the precipitated phases currently tend to aggregate at the grain boundaries, resulting in segregation, that is, dense distribution at the grain boundaries. The single distribution pattern limits the regulation effect on the martensitic transformation of nickel-titanium alloys and hinders the further application of nickel-titanium alloys.

[0003] There are currently some reports on the precipitation behavior of nickel-titanium alloys, including: (1) direct aging produces a preferential segregation effect at grain boundaries, but this direct aging method cannot regulate the distribution of the precipitated phase; (2) cyclic loading introduces dislocations, so that the precipitated phase precipitates preferentially at the dislocations. Although this method can make the precipitated phase precipitate uniformly, it requires loading and unloading cycles, which is not applicable to irregularly shaped, or semi-finished or finished nickel-titanium alloy parts. Summary of the invention

[0004] The present invention is made to solve the above-mentioned problems, and its purpose is to provide a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy.

[0005] The present invention provides a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy, which is used to regulate the precipitation behavior of nickel-titanium alloy, including the size of the precipitated phase and the distribution of the precipitated phase at the grain boundary and in the grain, and has the following characteristics, including the following steps: step S1, coating the nickel-titanium alloy with a coating material and performing annealing treatment;

[0006] Step S2, after removing the coating material and performing direct current aging, the precipitation behavior of the nickel-titanium alloy is regulated.

[0007] The heat treatment method for regulating the precipitation behavior of nickel-titanium alloy provided by the present invention may also have the following characteristics: wherein the coating material is non-nickel-titanium alloy, including steel, stainless steel, glass and copper.

[0008] The heat treatment method for regulating the precipitation behavior of nickel-titanium alloy provided by the present invention may also have the following characteristics: wherein, in step S1, when annealing is performed, 1000°C ≤ annealing temperature < melting points of the coating material and the nickel-titanium alloy, and annealing time ≥ 30 min.

[0009] The heat treatment method for regulating the precipitation behavior of nickel-titanium alloy provided by the present invention may also have the following characteristics: wherein, in step S2, when direct current aging is performed, 5A / mm 2 ≤Aging current density≤15A / mm 2 , aging time ≥30min.

[0010] The present invention also provides a nickel-titanium alloy, which is obtained by the above-mentioned heat treatment method for regulating the precipitation behavior of the nickel-titanium alloy, and has the following characteristics: the precipitation effect of the nickel-titanium alloy includes: a precipitate phase with uniform size and uniform distribution at the grain boundary and within the grain, a precipitate phase with small and dense size at the grain boundary but large and sparse size within the crystal, or a precipitate phase with large and sparse size at the grain boundary but small and dense size within the crystal.

[0011] The nickel-titanium alloy provided by the present invention may also have the following characteristics: wherein the types of precipitated phases include Ni4Ti3, Ni3Ti2 and Ni3Ti.

[0012] Functions and Effects of the Invention

[0013] According to a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy involved in the present invention, first, the nickel-titanium alloy is coated with different materials and annealed. During the high-temperature annealing process, the elements of the coating material diffuse into the nickel-titanium alloy, and then the coating material is removed and DC aging is performed. The precipitation behavior of the nickel-titanium alloy is affected by the coupling effect of the coating element diffusion and the current aging, and then the precipitation behavior of the nickel-titanium alloy is regulated. The distribution of the precipitated phase at the grain boundary and in the crystal and the size of the precipitated phase can be successfully regulated to obtain a nickel-titanium alloy with multiple precipitation effects. Therefore, a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy of the present invention can solve the problem of the single precipitation behavior of the existing nickel-titanium alloy. Compared with the traditional method, the method of the present invention breaks through the constraint of the grain boundary promoting non-uniform nucleation on the precipitation behavior of the nickel-titanium alloy, and has the advantages of low cost and environmental protection, and has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a process flow diagram of a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy according to the present invention;

[0015] Figure 2 is a diagram showing the precipitation effect of nickel-titanium alloy after annealing and direct current aging using different coating materials in an embodiment of the present invention;

[0016] Figure 3 It is a schematic diagram of the evolution of the average length and average thickness of the precipitated phase with the distance between the region and the grain boundary after annealing and direct current aging using different coating materials in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] Figure 1 It is a schematic diagram of the process flow of a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy according to the present invention.

[0018] like Figure 1 As shown, a heat treatment method for regulating the precipitation behavior of nickel-titanium alloy of the present invention is used to regulate the precipitation behavior of nickel-titanium alloy, including the size of the precipitated phase and the distribution of the precipitated phase at the grain boundary and in the grain, comprising the following steps:

[0019] Step S1, coating the nickel-titanium alloy with a coating material and performing annealing treatment.

[0020] The cladding materials are non-nickel-titanium alloys, including steel, stainless steel, glass and copper.

[0021] In step S1, when annealing is performed, 1000°C ≤ annealing temperature < melting points of the coating material and the nickel-titanium alloy, and annealing time ≥ 30 min.

[0022] Step S2, after removing the coating material and performing direct current aging, the precipitation behavior of the nickel-titanium alloy is regulated.

[0023] In step S2, when DC aging is performed, 5A / mm 2 ≤Aging current density≤15A / mm 2 , aging time ≥30min.

[0024] The precipitation effects of the nickel-titanium alloy obtained by the heat treatment method for regulating the precipitation behavior of the nickel-titanium alloy of the present invention include but are not limited to the following three types: precipitation phases with uniform size and uniform distribution at grain boundaries and within grains, precipitation phases with small and dense size at grain boundaries but large and sparse size within the crystals, or precipitation phases with large and sparse size at grain boundaries but small and dense size within the crystals.

[0025] The types of precipitated phases include Ni4Ti3, Ni3Ti2 and Ni3Ti.

[0026] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments and the accompanying drawings specifically illustrate a heat treatment method for regulating the precipitation behavior of nickel-titanium alloys of the present invention.

[0027] <Example>

[0028] In this embodiment, a glass tube with an outer diameter of 3 mm and an inner diameter of 1.1 mm, a 304 stainless steel tube and a copper tube are used as coating materials, respectively, and a nickel-titanium alloy wire with a diameter of 1 mm is coated and annealed, and then DC aging is performed after removal, as follows:

[0029] A heat treatment method for regulating the precipitation behavior of nickel-titanium alloy in this embodiment includes the following steps:

[0030] Step S1, coating the nickel-titanium alloy with a coating material and performing annealing treatment.

[0031] In this embodiment, the specific operation of step S1 is as follows: a glass tube, a 304 stainless steel tube, and a copper tube are respectively put on a nickel-titanium alloy wire with a diameter of 1 mm, the nickel-titanium alloy wire is coated, and the three coated samples are annealed at 1000° C. for 30 minutes, and then water quenched.

[0032] Step S2, after removing the coating material and performing direct current aging, the precipitation behavior of the nickel-titanium alloy is regulated.

[0033] In this embodiment, the specific operation of step S2 is as follows: the glass tube, 304 stainless steel tube, and copper tube are removed, and the corresponding three nickel-titanium alloy wire samples are subjected to a current density of 10.2 A / mm 2 , DC aging for 2 hours, and air cooling to room temperature after power off.

[0034] After completing the regulation of the precipitation behavior of the nickel-titanium alloy, the precipitation phase of the treated nickel-titanium alloy wire was observed by scanning electron microscopy. Figure 2 This is a diagram showing the precipitation effect of nickel-titanium alloy after annealing and direct current aging using different coating materials in an embodiment of the present invention.

[0035] Figure 2 In the figure, (a), (b), and (c) are respectively the precipitation effect diagrams of nickel-titanium alloy after annealing and DC aging when glass tube, copper tube, and stainless steel tube are used as the coating materials. The upper diagram is the SEM image of the precipitation phase, and the lower diagram is the schematic diagram of the precipitation phase. Figure 2 As shown, Figure 2 Where d is the length of the precipitated phase and t is the thickness of the precipitated phase. Figure 2 In the figure, dashed lines equidistant from the grain boundary are drawn to divide the grains into different regions, and L is the distance from the grain boundary.

[0036] The average length d of the precipitated phase in different regions is calculated respectively. mean and the average thickness t mean get Figure 3 . Figure 3 It is a schematic diagram of the evolution of the average length and average thickness of the precipitated phase with the distance between the region and the grain boundary after annealing and direct current aging using different coating materials in an embodiment of the present invention. Figure 3 In the figure, (a), (b), and (c) are schematic diagrams showing the evolution of the average length and average thickness of the precipitated phase of the nickel-titanium alloy as the distance between the region and the grain boundary after annealing and direct current aging when glass tube, copper tube, and stainless steel tube are used as the cladding materials, respectively. Figure 3 The relationship between the length and thickness of the precipitated phase and the distance between the region and the grain boundary is quantitatively expressed.

[0037] like Figure 2 and Figure 3 As shown, using glass tube as the coating material, the precipitation effect after annealing and DC aging is: the precipitated phase is small in size (length about 400nm, thickness about 70nm) and dense near the grain boundary, and the precipitated phase in the crystal (far away from the grain boundary area) is large in size (length about 2.3μm, thickness about 160nm) and sparse.

[0038] The copper tube is used as the cladding material. After annealing and direct current aging, the effect is: the precipitated phase is evenly distributed in the grain boundary grains and has uniform size (length of about 950nm and thickness of about 95nm).

[0039] Stainless steel tube is used as the coating material. After annealing and DC aging, the precipitation effect is as follows: the precipitated phase is large in size (about 2.1 μm in length and about 250 nm in thickness) and sparse at the grain boundary, while the precipitated phase is small in size (about 160 nm in length and about 60 nm in thickness) and dense within the grain.

[0040] In summary, the method for regulating the precipitation behavior of nickel-titanium alloy of the present invention does not require additional mechanical treatment methods such as loading. By using different coating materials to coat nickel-titanium alloy for annealing and combining with direct current aging, the distribution of precipitated phases at grain boundaries and within grains and the size of precipitated phases can be successfully regulated. The method has the advantages of low cost, high efficiency, energy saving, low cost, and environmental protection, and has high industrial utilization value.

[0041] Functions and Effects of the Embodiments

[0042] According to the heat treatment method for regulating the precipitation behavior of nickel-titanium alloy involved in this embodiment, the nickel-titanium alloy is first coated with different materials and annealed. During the high-temperature annealing process, the elements of the coating material diffuse into the nickel-titanium alloy, and then the coating material is removed and DC aging is performed. The precipitation behavior of the nickel-titanium alloy is affected by the coupling effect of the coating element diffusion and current aging, and then the precipitation behavior of the nickel-titanium alloy is regulated. The distribution of the precipitated phase at the grain boundary and in the crystal and the size of the precipitated phase can be successfully regulated to obtain a nickel-titanium alloy with multiple precipitation effects. Therefore, the heat treatment method for regulating the precipitation behavior of the nickel-titanium alloy in this embodiment can solve the problem of the single precipitation behavior of the existing nickel-titanium alloy. Compared with the traditional method, the method of this embodiment breaks through the constraint of the grain boundary promoting non-uniform nucleation on the precipitation behavior of the nickel-titanium alloy, and has the advantages of low cost and environmental protection, and has a good application prospect.

[0043] The above-mentioned embodiments are preferred examples of the present invention and are not intended to limit the protection scope of the present invention.

Claims

1. A heat treatment method for regulating the precipitation behavior of nickel-titanium alloy, which is used to regulate the precipitation behavior of nickel-titanium alloy, including the size of the precipitated phase and the distribution of the precipitated phase at the grain boundary and within the grain, characterized in that: The following steps are involved: Step S1, coating the nickel-titanium alloy with a coating material and performing annealing treatment; Step S2, after removing the coating material and performing direct current aging, the precipitation behavior of the nickel-titanium alloy is regulated. In step S1, when annealing is performed, 1000°C ≤ annealing temperature < melting point of the coating material and the nickel-titanium alloy, and annealing time ≥ 30 min. In step S2, when DC aging is performed, 5 A / mm 2 ≤Aging current density≤15 A / mm 2 , aging time ≥30min.

2. The heat treatment method for regulating the precipitation behavior of nickel-titanium alloy according to claim 1, characterized in that: in, The coating material is non-nickel-titanium alloy.

3. The heat treatment method for regulating the precipitation behavior of nickel-titanium alloy according to claim 1, characterized in that: in, The cladding materials include stainless steel, glass and copper.

4. A nickel-titanium alloy obtained by the heat treatment method for regulating the precipitation behavior of a nickel-titanium alloy according to any one of claims 1 to 3, characterized in that: The precipitation effects of the nickel-titanium alloy include: precipitation phases with uniform size and uniform distribution at grain boundaries and within grains, precipitation phases with small and dense size at grain boundaries but large and sparse size within grains, or precipitation phases with large and sparse size at grain boundaries but small and dense size within grains.

5. The nickel-titanium alloy according to claim 4, characterized in that: in, The types of precipitated phases include Ni4Ti3, Ni3Ti2 and Ni3Ti.

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