A method for improving the strength and plasticity of Ni-Mn-Ga alloy

Abstract

The present invention discloses a method for improving the strength and plasticity of Ni-Mn-Ga alloy, which relates to the technical field of alloys. The present invention comprises the following steps: smelting Ni and Ga metals to obtain Ni-Ga alloy; then adding Mn and carbon for smelting treatment to obtain Ni-Mn-Ga-C alloy rods; finally, cutting the Ni-Mn-Ga-C alloy rods and subjecting them to directional solidification treatment using a seed crystal method to obtain a strong and plastic Ni-Mn-Ga-C alloy. The present invention is achieved by doping carbon and adopting an austenitic orientation. <110> A The seed crystals in the direction of the seed are directional solidified, which significantly improves the strength and plasticity of the Ni-Mn-Ga alloy.

Description

Technical Field

[0001] The invention belongs to the technical field of alloys, and in particular relates to a method for improving the strength and plasticity of a Ni-Mn-Ga alloy. Background Art

[0002] Shape memory alloys (SMAs), or alloys with a "memory" effect, are widely used in fields such as clinical medicine, automotive engineering, and aerospace. These alloys can be found in artificial joints, endoscopes, satellite antennas, automatic dryers, steam drain valves, and overcurrent protectors. They are also found in everyday applications such as electronic stoves, eyeglass frames, and mobile phone antennas. With the emergence and continued development of SMAs, they have attracted significant attention in intelligent material systems and hold broad application prospects.

[0003] Ni-Mn-Ga shape memory alloy, a new type of ferromagnetic shape memory alloy, is a new intelligent material that combines thermoelastic martensitic transformation with ferromagnetic transition. It combines the advantages of traditional alloys, such as high output strain (~10%), with a higher magnetostrictive response frequency (~kHz), perfectly integrating a magnetic field drive mechanism with the shape memory effect. This has led to its widespread application as a sensing-actuating material.

[0004] At present, the disadvantages of Ni-Mn-Ga alloys such as high brittleness and low strength have greatly restricted the application and development of the alloy. Therefore, how to improve the strength of Ni-Mn-Ga alloys, reduce the brittleness of Ni-Mn-Ga alloys, and maintain or even improve the thermal recovery of the alloy has become the main research direction of Ni-Mn-Ga alloys. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for improving the strength and plasticity of Ni-Mn-Ga alloy, which is specifically achieved according to the following technical solutions:

[0006] A method for improving the strength and plasticity of a Ni-Mn-Ga alloy comprises the following steps:

[0007] Step 1: remove impurities from Ni, Mn and Ga metal raw materials and dry them for later use;

[0008] Step 2: Follow Ni 54 Mn 26 Ga 20 The atomic ratio of Ni, Mn and Ga in the alloy is weighed, and the weighed Ni and Ga are placed in a crucible and placed in a melting furnace, and then vacuum arc melting is performed to obtain a melted Ni-Ga alloy;

[0009] Step 3, adding weighed Mn and carbon blocks to the Ni-Ga alloy, then smelting the alloy in an induction melting furnace, and suction casting the smelted alloy to obtain a Ni-Mn-Ga-C alloy rod, wherein the atomic ratio of carbon in the alloy rod is 0.1%;

[0010] Step 4: Cut the Ni-Mn-Ga-C alloy rod and then perform a seed crystal orientation solidification process to obtain a strong plastic Ni-Mn-Ga-C alloy. The orientation of the seed crystal is austenite. <110> A direction.

[0011] Preferably, the impurity removal method of Ni and Ga in step 1 is to use mechanical polishing to remove the metal surface oxide layer and impurities;

[0012] The Mn impurity removal method comprises first cleaning the Mn with a solution consisting of nitric acid-hydrofluoric acid-water in a volume ratio of 20:5:75 to remove the oxide layer on the surface of the Mn; then placing the Mn in anhydrous ethanol for ultrasonic impurity removal, and finally drying the Mn.

[0013] Preferably, the vacuum arc melting in step 2 is first vacuumed to a vacuum degree of -0.05 MPa, and then the melting current is adjusted to 200 A after arcing to remove residual oxygen, and then the current is adjusted to 270 A to 300 A for repeated melting.

[0014] Preferably, the vacuum arc melting in step 2 is performed four times at a current of 270A to 300A, with each melting time being 1 minute. After a single melting, the alloy ingot needs to be turned over.

[0015] Preferably, in step S3, the alloy ingot that has been repeatedly melted in the induction melting furnace until there is no carbon residue on the surface is subjected to suction casting, wherein the arc current during the suction casting process is 350A, and after the alloy ingot is completely melted, the suction casting switch is turned on to use the pressure difference to perform suction casting, and the alloy is suction cast into an alloy rod with a diameter of 8 mm.

[0016] Preferably, step 4 is to cut the Ni—Mn—Ga—C alloy rod into alloy rods with a diameter of 3 mm.

[0017] Preferably, step 4 is to physically bond the cut alloy rod to a seed crystal of the same diameter and 3-4 mm in length, wherein the seed crystal is located at the bottom of the alloy rod, and then place it in a heating furnace for heating and melting treatment, wherein the heating temperature is not less than 1450°C and the holding time is not less than 30 min; start the directional solidification pulling device, carry out directional solidification at a directional solidification growth rate of 10 μm / s, and naturally cool to room temperature after directional solidification for 120 mm.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention is to smelt Ni and Ga metals to obtain Ni-Ga alloy; then add Mn and carbon for smelting treatment to obtain Ni-Mn-Ga-C alloy rods; finally, cut the Ni-Mn-Ga-C alloy rods and perform seed crystal method orientation solidification treatment to obtain strong plasticity Ni-Mn-Ga-C alloy. <110> A The directional solidification of seed crystals in the direction of the molten metal is performed, significantly improving the strength and plasticity of the Ni-Mn-Ga alloy. The highly plastic Ni-Mn-Ga-C alloy prepared by the present invention not only maintains the phase structure and thermal recovery of the original alloy, but also improves the mechanical properties of the alloy. The compressive fracture strength of the highly plastic Ni-Mn-Ga-C alloy of the present invention is increased by nearly two times, and the strain is increased by three times. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a process flow chart of the present invention;

[0021] Figure 2 Schematic diagram of directional solidification of the present invention;

[0022] Figure 3 For Comparative Example 1 (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 Alloy and Comparative Example 2Ni 54 Mn 26 Ga 20 XRD spectrum of the alloy;

[0023] Figure 4 for (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 - <110> A Alloy, (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 Alloy, Ni 54 Mn 26 Ga 20 - <110> A Alloy and Ni 54 Mn 26 Ga 20 Compressive stress-strain curves of the alloys;

[0024] Figure 5(a) is Ni 54 Mn 26 Ga 20 The thermal recovery of the alloy after twinning, (b) is (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 - <110> A The thermal recovery of the alloy after twinning, (c) is Ni 54 Mn 26 Ga 20 The thermal recovery of the alloy at a compressive strain of 10% and (d) (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 - <110> A Thermal recovery of the alloy at a compressive strain of 10%;

[0025] Figure 6 for (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 - <110> A alloy cross-section orientation imaging (a) and magnified image (b), and (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 - <110> Metallographic image of alloy A (c) and enlarged image (d). DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to specific embodiments.

[0027] Example 1

[0028] A (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 - <110> The preparation method of alloy A includes the following specific steps:

[0029] Step 1: remove impurities from Ni, Mn and Ga metal raw materials and dry them for later use;

[0030] Step 2: Follow Ni 54 Mn 26 Ga 20The atomic ratio of Ni, Mn and Ga in the alloy is weighed, and the weighed Ni and Ga are placed in a crucible and placed in a melting furnace, and then vacuum arc melting is performed to obtain a melted Ni-Ga alloy;

[0031] Step 3: Add weighed Mn and carbon blocks to the Ni-Ga alloy, then smelt it in an induction melting furnace, and perform suction casting on the smelted alloy to obtain (Ni-Ga) with a diameter of 8 mm. 54 Mn 26 Ga 20 ) 99.9 C 0.1 alloy rods;

[0032] Step 4: 54 Mn 26 Ga 20 ) 99.9 C 0.1 The alloy rods are cut into 3mm diameter alloy rods, and then the seed crystal method is used for directional solidification to obtain strong plasticity (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 - <110> A alloy, the seed crystal is oriented austenite <110> A direction.

[0033] The impurity removal method of Ni and Ga in step 1 of the present invention is to use a mechanical polishing method to remove the metal surface oxide layer and impurities;

[0034] The Mn impurity removal method comprises first cleaning the Mn with a solution consisting of nitric acid-hydrofluoric acid-water in a volume ratio of 20:5:75 to remove the oxide layer on the surface of the Mn; then placing the Mn in anhydrous ethanol for ultrasonic impurity removal, and finally drying the Mn.

[0035] The vacuum arc melting described in step 2 of the present invention is to first perform a vacuum treatment to make the vacuum degree -0.05MPa, then adjust the melting current to 200A after arcing, perform melting to remove residual oxygen, and then adjust the current to 280A for repeated melting treatment.

[0036] The vacuum arc melting in step 2 of the present invention is performed four times at a current of 280A, with each melting time being 1 minute. After a single melting, the alloy ingot needs to be turned over.

[0037] In step S3 of the present invention, the alloy ingot that has been repeatedly melted in the induction melting furnace until there is no carbon residue on the surface is subjected to suction casting treatment, wherein the arc current during the suction casting treatment is 350A. After the alloy ingot is completely melted, the suction casting switch is turned on and the pressure difference is used to perform suction casting, and the alloy is suction cast into an alloy rod with a diameter of 8 mm.

[0038] Step 4 of the present invention is to physically bond the cut alloy rod to a seed crystal of the same diameter and 3 mm in length, wherein the seed crystal is located at the bottom of the alloy rod, and then place it in a heating furnace for heating and melting treatment, wherein the heating temperature is 1450°C and the holding time is 60 min; start the directional solidification pulling device, carry out directional solidification at a directional solidification growth rate of 10 μm / s, and naturally cool to room temperature after directional solidification for 120 mm.

[0039] Comparative Example 1

[0040] A (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 The preparation method of the alloy includes the following specific steps:

[0041] Step 1: Prepare (Ni) with a diameter of 8 mm according to steps 1-3 of Example 1. 54 Mn 26 Ga 20 ) 99.9 C 0.1 alloy rods;

[0042] Step 2: 54 Mn 26 Ga 20 ) 99.9 C 0.1 The alloy rod is cut into 3mm diameter alloy rods, and then subjected to directional solidification treatment to obtain a (Ni 54 Mn 26 Ga 20 ) 99.9 C 0.1 The alloy is directional solidified by placing the cut alloy rod in a heating furnace for heating and melting treatment, wherein the heating temperature is 1450°C and the holding time is 60 minutes; starting a directional solidification pulling device, performing directional solidification at a directional solidification growth rate of 10 μm / s, and naturally cooling to room temperature after directional solidification for 120 mm.

[0043] Comparative Example 2

[0044] A Ni 54 Mn 26 Ga 20 The preparation method of the alloy includes the following specific steps:

[0045] Step 1: remove impurities from Ni, Mn and Ga metal raw materials and dry them for later use;

[0046] Step 2: Follow Ni 54 Mn 26 Ga20 The atomic ratio of Ni, Mn and Ga in the alloy is weighed, and the weighed Ni and Ga are placed in a crucible and placed in a melting furnace, and then vacuum arc melting is performed to obtain a melted Ni-Ga alloy;

[0047] Step 3: Add weighed Mn to the Ni-Ga alloy and smelt it in an induction melting furnace. The smelted alloy is suction-casted (the suction-casting method is the same as that in Example 1) to obtain a Ni-Ga alloy with a diameter of 8 mm. 54 Mn 26 Ga 20 alloy rods;

[0048] Step 4: Prepare Ni 54 Mn 26 Ga 20 The alloy rod was subjected to directional solidification treatment according to the method of step 2 of Example 1 to obtain a Ni 54 Mn 26 Ga 20 alloy.

[0049] Comparative Example 3

[0050] A Ni 54 Mn 26 Ga 20 - <110> A The preparation method of the alloy includes the following specific steps:

[0051] Step 1: Obtain Ni with a diameter of 8 mm according to steps 1-3 of comparative example 1. 54 Mn 26 Ga 20 alloy rods;

[0052] Step 2: Ni 54 Mn 26 Ga 20 The alloy rod was subjected to the seed crystal method for directional solidification according to step 4 of Example 1 to obtain Ni 54 Mn 26 Ga 20 - <110> A alloy.

[0053] from Figures 1-6 It can be seen that the present invention performs carbon doping and seed crystal method directional solidification treatment on the Ni-Mn-Ga alloy, which does not change the phase composition of the alloy, and all of them are non-modulated tetragonal martensite phase. At the same time, it does not damage the thermal recovery of the alloy, and well preserves the shape memory effect of the alloy.

[0054] The present invention compares the presence or absence of carbon doping and finds that the strength and plasticity of the Ni-Mn-Ga directional solidification alloy prepared by carbon doping are better than those of the Ni-Mn-Ga master alloy without carbon doping. <110> The strength and ductility of alloys produced by directionally solidifying with A-oriented seed crystals are superior to those produced without the seed crystal method. Ni-Mn-Ga-C alloys produced by coupling carbon doping with the seed crystal method exhibit even higher strength and ductility than Ni-Mn-Ga directionally solidified alloys without carbon doping and without the seed crystal method, thus improving the strength and ductility of the alloy.

[0055] It should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and may have other variations. All variations directly or indirectly derived from the present disclosure by those skilled in the art should be considered to be within the scope of protection of the present invention.

Claims

1. A method for improving the strength and plasticity of Ni-Mn-Ga alloy, characterized in that: The following steps are involved: Step 1: remove impurities from Ni, Mn and Ga metal raw materials and dry them for later use; Step 2: Follow Ni 54 Mn 26 Ga 20 The atomic ratio of Ni, Mn and Ga in the alloy is weighed, and the weighed Ni and Ga are placed in a crucible and placed in a melting furnace, and then vacuum arc melting is performed to obtain a melted Ni-Ga alloy; Step 3, adding weighed Mn and carbon blocks to the Ni-Ga alloy, then smelting the alloy in an induction melting furnace, and suction casting the smelted alloy to obtain a Ni-Mn-Ga-C alloy rod, wherein the atomic ratio of carbon in the alloy rod is 0.1%; Step 4: Cut the Ni-Mn-Ga-C alloy rod and then perform a seed crystal orientation solidification treatment to obtain a strong plastic Ni-Mn-Ga-C alloy. The orientation of the seed crystal is austenite. <110> A direction; Step 4 is to physically bond the cut alloy rod to a seed crystal of the same diameter and 3-4 mm in length, wherein the seed crystal is located at the bottom of the alloy rod, and then place it in a heating furnace for heating and melting treatment, wherein the heating temperature is not less than 1450°C and the holding time is not less than 30 minutes; start the directional solidification pulling device, carry out directional solidification at a directional solidification growth rate of 10 μm / s, and naturally cool to room temperature after directional solidification of 120 mm.

2. The method for improving the strength and plasticity of Ni-Mn-Ga alloy according to claim 1, characterized in that: The impurity removal method of Ni and Ga in step 1 is to use mechanical polishing to remove the oxide layer and impurities on the metal surface; The Mn impurity removal method comprises first cleaning the Mn with a solution consisting of nitric acid-hydrofluoric acid-water in a volume ratio of 20:5:75 to remove the oxide layer on the surface of the Mn; then placing the Mn in anhydrous ethanol for ultrasonic impurity removal, and finally drying the Mn.

3. The method for improving the strength and plasticity of Ni-Mn-Ga alloy according to claim 1, characterized in that: In step 2, the vacuum arc melting is first performed by vacuuming to a vacuum degree of -0.05 MPa, and then the melting current is adjusted to 200 A after the arc is struck to perform melting to remove residual oxygen, and then the current is adjusted to 270 A to 300 A for repeated melting.

4. The method for improving the strength and plasticity of Ni-Mn-Ga alloy according to claim 3, characterized in that: The vacuum arc melting in step 2 is performed four times at a current of 270A to 300A, with each melting time being 1 minute. After a single melting, the alloy ingot needs to be turned over.

5. The method for improving the strength and plasticity of Ni-Mn-Ga alloy according to claim 1, characterized in that: In step 3, the alloy ingot that has been repeatedly melted in the induction melting furnace until there is no carbon residue on the surface is subjected to suction casting. The arc current during the suction casting process is 350A. After the alloy ingot is completely melted, the suction casting switch is turned on and the pressure difference is used for suction casting to form an alloy rod with a diameter of 8 mm.

6. The method for improving the strength and plasticity of Ni-Mn-Ga alloy according to claim 1, characterized in that: Step 4 is to cut the Ni—Mn—Ga—C alloy rod into alloy rods with a diameter of 3 mm.

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