High-strength Ni-Co-Mn-Ti shape memory alloy and preparation method thereof

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a preparation method and application of Ni-Co-Mn-Ti shape memory alloy. The preparation method comprises the following steps that 1, raw materials are weighed according to the element molar ratio of Ni: Co: Mn: Ti = 37: 13: 34.5: 15.5, an ingot is formed through electric arc melting, and then homogenizing annealing treatment is conducted; step 2, mechanically crushing the annealed alloy ingot into small blocks, grinding the small blocks into alloy powder, and then performing stress relief annealing; 3, the alloy powder obtained after stress relief annealing is placed in a graphite mold, and then the graphite mold is placed in a spark plasma sintering device to be sintered; and 4, carrying out annealing heat treatment on the sintered body alloy sample. According to the preparation method of Ni-Co-Mn-Ti, a complex and time-consuming preparation process is not needed, that is, the powder alloy is directly used as the parent alloy for sintering, the alloy preparation cost is remarkably reduced, and the compression strength of the alloy is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and particularly relates to a preparation method and application of a Ni-Co-Mn-Ti shape memory alloy. Background Art

[0002] Ni-Mn-based ferromagnetic shape memory alloy is a new type of multifunctional material that has been widely studied in recent years. This type of alloy can induce a primary martensitic phase transformation by applying stress. Among them, a full d-group Ni-Co-Mn-Ti alloy has been shown to have a significant elastocaloric effect. Therefore, Ni-Co-Mn-Ti alloy has considerable refrigeration potential.

[0003] For Ni-Co-Mn-Ti alloy, excellent mechanical properties are a prerequisite for testing its elastic and thermal properties. However, the mechanical properties of the alloy prepared by the commonly used arc melting method are relatively poor. Although the use of single crystal furnace and directional solidification technology can improve the mechanical properties of this type of alloy, the preparation process of these two technologies is complicated and the preparation cost is high.

[0004] In contrast, spark plasma sintering technology has the advantages of simple preparation process, less time consumption and low cost. Studies have shown that alloys prepared using plasma spark sintering technology have excellent mechanical properties. However, there are few reports on the preparation of shape memory alloys using plasma spark sintering technology. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a high-strength Ni-Co-Mn-Ti shape memory alloy and a preparation method thereof. The alloy is a high-strength Ni-Co-Mn-Ti shape memory alloy with stress-induced primary martensitic phase transformation behavior prepared by spark plasma sintering (SPS) technology, which solves the key brittleness problem of the alloy, and the alloy can be processed into parts of a desired shape to achieve its specific function.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] One aspect of the present invention provides a method for preparing a high-strength Ni-Co-Mn-Ti alloy, the method comprising the following steps:

[0008] Step 1, preparation of polycrystalline parent alloy:

[0009] The raw materials were weighed according to the molar ratio of the elements Ni:Co:Mn:Ti=37:13:34.5:15.5, arc-melted into ingots, and then homogenized annealed at 950°C for 48h;

[0010] Step 2, powder preparation and pretreatment:

[0011] The annealed alloy ingot is mechanically crushed into small pieces and ground into alloy powder, and then stress relief annealing is carried out. The annealing temperature is 600 °C and the annealing time is 6 h;

[0012] Step 3, sintering:

[0013] The alloy powder after stress relief annealing is placed in a graphite mold, and then placed in a spark plasma sintering device for sintering. The sintering temperature is 950 °C, the sintering pressure is 50 MPa, and the sintering time is 15 - 30 min. After sintering is completed, the sintered alloy sample is taken out after cooling and reserved;

[0014] Step 4, post-treatment:

[0015] The sintered alloy sample is subjected to annealing heat treatment. The heat treatment temperature is 950 °C and the heat treatment time is 24 h.

[0016] In the above technical solution, further, in step 1, the purities of Ni, Co, Mn, and Ti are all ≥ 99.9 wt.%.

[0017] In the above technical solution, further, in step 2, the particle size of the alloy powder is d, 0 < d ≤ 150 μm, preferably 0 < d ≤ 48 μm.

[0018] In the above technical solution, further, in step 3, the diameter of the graphite mold is 15 mm.

[0019] On the other hand, the present invention provides a Ni-Co-Mn-Ti shape memory alloy prepared by the above preparation method.

[0020] In the above technical solution, further, the fracture strain of the alloy is 19% - 27%, and the fracture strength is 1532 - 2005 MPa.

[0021] In the above technical solution, further, the isothermal elastocaloric adiabatic temperature change of the alloy is 21.5 - 34.2 K.

[0022] The present invention also provides an application of the above Ni-Co-Mn-Ti shape memory alloy in the preparation of components for elastocaloric refrigeration.

[0023] The beneficial effects of the present invention are:

[0024] 1. The Ni-Co-Mn-Ti alloy of the present invention overcomes the deficiency of large brittleness of the alloy.

[0025] 2. The preparation method of Ni-Co-Mn-Ti of the present invention does not require a complicated and time-consuming preparation process, that is, the powder alloy is directly used as the parent alloy for sintering, which significantly reduces the cost of alloy preparation.

[0026] 3. The Ni-Co-Mn-Ti alloy of the present invention refines the grain size of the alloy and improves the compressive strength of the alloy by regulating the sintering process parameters.

[0027] 4. The Ni-Co-Mn-Ti alloy of the present invention strengthens the elastic-thermal effect of the alloy under the premise of high strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Ni prepared in Example 1-3 37 Co 13 Mn 33.5 Ti 15.5 Alloy compressive strength curve;

[0029] Figure 2 Ni prepared in Example 1 and Examples 4-6 37 Co 13 Mn 33.5 Ti 15.5 Alloy compressive strength curve;

[0030] Figure 3 Ni prepared in Example 1-3 37 Co 13 Mn 33.5 Ti 15.5 Adiabatic temperature variation diagram of the elasto-caloric effect of the alloy;

[0031] Figure 4 Ni prepared in Example 1 and Examples 4-6 37 Co 13 Mn 33.5 Ti 15.5 Diagram of adiabatic temperature variation of the elastocaloric effect of an alloy. DETAILED DESCRIPTION

[0032] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0033] In the following examples, the purity of each element is Ni: 99.9wt.%, Co: 99.9wt.%, Mn: 99.9wt.%, and Ti: 99.99wt.%.

[0034] In the following examples, the models of the arc melting furnace and the SPS sintering furnace are DHL-400 and SPS-3.20MK-IV respectively.

[0035] Example 1

[0036] In this example, a Ni-Co-Mn-Ti alloy was prepared by spark plasma sintering. The sum of the molar amounts of the alloying elements was 100, and the molar ratio of the elements was Ni:Co:Mn:Ti = 37:13:34.5:15.5;

[0037] Step 1, preparation of polycrystalline parent alloy:

[0038] According to the elemental composition of the alloy, the raw materials were proportioned. First, the atomic percentages were converted into mass percentages, and Ni, Co, Mn, and Ti were weighed respectively. The proportioned raw materials were repeatedly melted by arc melting 4 times to obtain a button-shaped ingot with uniform composition. The button-shaped ingot was subjected to homogenization annealing treatment, the annealing temperature was 950 °C, and the annealing time was 48 h;

[0039] Step 2, powder preparation and pretreatment:

[0040] The annealed alloy ingot was mechanically crushed into small pieces and ground into alloy powder with a particle size d of 0 < d ≤ 48 μm using mechanical grinding equipment, and then stress relief annealing was carried out at 600 °C for 6 h;

[0041] Step 3, sintering:

[0042] According to the size of the graphite mold and the density of the as-cast alloy, the mass of the alloy powder added was calculated, and then the mold was loaded according to the sintering requirements. The diameter of the graphite mold was 15 mm and the height was 10 mm. Subsequently, it was placed in a spark plasma sintering device and sintered at 950 °C for 20 min, and the sintering pressure was 50 MPa. After sintering was completed, the sintered alloy sample was taken out after cooling and reserved;

[0043] Step 4, post-treatment:

[0044] The sintered alloy sample was subjected to annealing heat treatment at 950 °C for 24 h.

[0045] The alloy in this example was tested for mechanical properties: the fracture strength of the alloy with a sintering time of 20 min reached 2005 MPa, and the fracture strain reached 27%. This example was tested for elastocaloric properties: the elastocaloric adiabatic temperature change of the alloy with a sintering time of 20 min was 34.2 K under the condition of a rate of 0.28 s -1 The alloy in this example can be machined into any shape and applied to solid-state refrigeration devices.

[0046] Example 2

[0047] The preparation method of the Ni-Co-Mn-Ti alloy was the same as that in Example 1, except that in Step 2, 48 μm < d ≤ 74 μm.

[0048] Example 3

[0049] The preparation method of Ni-Co-Mn-Ti alloy is the same as that of Example 1, except that in step 2, 74 μm <d≤150μm。

[0050] Compression strength curves of sintered alloys with different alloy powder particle sizes in Example 1-3. Figure 1 It can be seen that the sintered target alloys all have extremely high strength, which is significantly higher than the strength of the cast alloys, especially when the alloy powder particle size is less than 48μm, the compressive strength of the alloy reaches 2005MPa.

[0051] Figure 3 is the adiabatic temperature change during the loading process of the sintered alloys of different alloy powder particle sizes in Examples 1-3, Figure 3 It can be seen that the adiabatic temperature change of the elastocaloric effect increases with the decrease of the alloy powder particle size, that is, reducing the alloy powder particle size is beneficial to improving the elastocaloric effect.

[0052] Example 4

[0053] The preparation method of the Ni-Co-Mn-Ti alloy is the same as that in Example 1, except that in step 3, the sintering time is 15 minutes.

[0054] Example 5

[0055] The preparation method of the Ni-Co-Mn-Ti alloy is the same as that in Example 1, except that in step 3, the sintering time is 25 minutes.

[0056] Example 6

[0057] The preparation method of the Ni-Co-Mn-Ti alloy is the same as that in Example 1, except that in step 3, the sintering time is 30 minutes.

[0058] Figure 2 is the compressive strength curve of different sintering times of Example 1 and Examples 4-6, Figure 2 It can be seen that when the particle size of the alloy powder is fixed, the sintering time has little effect on the compressive strength of the sintered alloy.

[0059] Figure 4 is the adiabatic temperature change during the loading process of the sintered alloys of Example 1 and Examples 4-6 with different sintering times, Figure 4 It can be seen that when the particle size of the alloy powder is fixed, the sintering time has little effect on the adiabatic temperature change of the caloric effect of the sintered alloy.

[0060] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the implementation methods. The protection scope of the present invention shall be subject to the scope defined in the claims. Other different forms of changes or modifications may be made based on the above description. Obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing a high-strength Ni-Co-Mn-Ti shape memory alloy, characterized in that: The method comprises the following steps: Step 1, preparation of polycrystalline parent alloy: The raw materials were weighed according to the molar ratio of the elements Ni:Co:Mn:Ti=37:13:34.5:15.5, arc-melted into ingots, and then homogenized annealed at 950°C for 48h; Step 2, powder preparation and pretreatment: The annealed alloy ingot was mechanically broken into small pieces and ground into alloy powder, and then stress relief annealing was performed at 600°C for 6 hours. Step 3, sintering: The alloy powder after stress relief annealing is placed in a graphite mold, and then placed in a spark plasma sintering device for sintering at a sintering temperature of 950°C, a sintering pressure of 50MPa, and a sintering time of 15 to 30min. After sintering is completed and cooled, the sintered alloy sample is taken out for standby use; Step 4, post-processing: The sintered alloy sample was subjected to annealing heat treatment at a temperature of 950°C and a heat treatment time of 24 h.

2. The preparation method according to claim 1, characterized in that: In step 1, the purity of Ni, Co, Mn and Ti is ≥99.9wt.%.

3. The preparation method according to claim 1, characterized in that: In step 2, the particle size of the alloy powder is d,0 <d≤150μm。 4. The preparation method according to claim 1, characterized in that: In step 3, the diameter of the graphite mold is 15 mm.

5. A Ni-Co-Mn-Ti shape memory alloy prepared by the preparation method according to any one of claims 1 to 4.

6. The Ni-Co-Mn-Ti shape memory alloy according to claim 5, characterized in that: The fracture strain of the alloy is 19% to 27%, and the fracture strength is 1532 to 2005 MPa.

7. The Ni-Co-Mn-Ti shape memory alloy according to claim 5, characterized in that: The isothermal elastic adiabatic temperature change of the alloy is 21.5-34.2K.

8. Use of the Ni-Co-Mn-Ti shape memory alloy according to any one of claims 5 to 7 in the preparation of elastic-caloric refrigeration parts.

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