CN113684389B

CN113684389B - Method for improving superelasticity of Co-Ni-Al magnetic memory alloy by controlling gamma phase distribution

Info

Publication number: CN113684389B
Application number: CN202110937070.XA
Authority: CN
Inventors: 董桂馥; 孙广云; 薛照国; 刘慧孜
Original assignee: Dalian University
Current assignee: Dalian University
Priority date: 2021-08-16
Filing date: 2021-08-16
Publication date: 2022-07-29
Anticipated expiration: 2041-08-16
Also published as: CN113684389A

Abstract

The invention belongs to the field of magnetic memory alloys, and discloses a method for improving the superelasticity of a Co-Ni-Al magnetic memory alloy by controlling gamma phase distribution. The invention adopts a method combining mechanical powder metallurgy and hot-pressing sintering to prepare the Co-Ni-Al ferromagnetic shape memory alloy, and the distribution of gamma phase in the alloy is controlled by changing the heat treatment temperature, so that the comprehensive performance of the alloy is improved, and the idea is expanded for the application of the shape memory alloy. The super-elastic Co-Ni-Al ferromagnetic shape memory alloy is prepared by the following steps: the material is taken according to the atomic percentage, mixed evenly and sintered to obtain the Co-Ni-Al ferromagnetic shape memory alloy, and the distribution of the gamma phase in the alloy is controlled by changing the heat treatment temperature so as to improve the comprehensive performance of the alloy. The magnetic shape memory alloy Co-Ni-Al prepared by the invention has the advantages of good toughness, high strength, super elasticity and the like.

Description

Method for improving superelasticity of Co-Ni-Al magnetic memory alloy by controlling gamma phase distribution

Technical Field

The invention belongs to the field of magnetic memory alloys, and particularly relates to a method for improving the superelasticity of a Co-Ni-Al magnetic memory alloy by controlling gamma phase distribution.

Background

The shape memory alloy which generates shape change by martensite phase change along with temperature change can generate larger recovery strain, has output stress as high as hundreds of megapascals, and has been widely applied in the fields of aerospace, medical engineering, mechanical power and the like. Magnetic shape memory alloys are a new type of shape memory material. Not only has the thermo-elastic shape memory effect of the traditional shape memory alloy controlled by a temperature field, but also has the magnetic memory effect controlled by a magnetic field. Therefore, the alloy has the comprehensive characteristics of large recovery strain, large output stress, high response frequency and accurate control, and can play an important role in the fields of high-power underwater sonars, micro-shifters, vibration and noise control, linear motors, microwave devices, robots and the like. Magnetic-driven shape memory alloys have both the advantages of high response frequency and large output strain, and have been receiving great attention in recent years. Magnetically driven shape memory effects are currently found in many alloys, mainly including: Ni-Mn-Ga, Ni-Fe-Ga, Fe-Pd, Fe-Pt, Ni-Mn-Al, Co-Ni-Ga, Co-Ni-Al, and Ni-Mn-X (X ═ In, Sn, Sb) alloys, and the like. Among them, Ni-Mn-Ga is the first to be found and is also the most potential magnetic drive shape memory alloy. The magnetic induced strain is derived from the rearrangement of martensite twin crystal variants driven by an external magnetic field, the maximum magnetic induced strain can reach 10 percent, but the output stress is limited by the anisotropic property of magnetocrystalline and is only a few MPa; another type is represented by Ni — Mn — X (X ═ In, Sn, Sb) alloys, the magnetically induced strain of which is due to reverse phase transformation of the magnetic martensite under the action of an external magnetic field, the mechanism is that the alloy deforms In the martensite state, and is placed at an ambient temperature slightly lower than the martensite reverse phase transformation start temperature (As), a magnetic field is applied to the alloy to lower the As temperature, and when the As temperature is lowered below the ambient temperature, the martensite reverse phase transformation can occur without changing the ambient temperature, and the deformation is recovered. But the mechanical properties of the intrinsically brittle alloy are improved at the expense of losing its thermal elasticity and magnetic properties. So far, the Co-Ni-Al alloy has attracted more attention.

As an intelligent material, the Co-Ni-Al magnetic control shape memory alloy is a material basis for future national defense and various high-tech fields. Meanwhile, the super-elasticity of the alloy has great application prospect in mobile phone communication, medical treatment and life, and has low price and great economic and social benefits.

As the Co-Ni-Al alloy has a beta + gamma two-phase coexistence region in a wide range, the as-cast solidification structure is generally a beta matrix and a beta + gamma eutectic crystal. Wherein the beta phase is a high-temperature parent phase with an ordered body-centered cubic B2 structure, and the gamma phase is a plastic phase with an unordered face-centered cubic structure. Meanwhile, the phase transition temperature of the Co-Ni-Al alloy is extremely sensitive to the heat treatment condition, and the martensite phase transition temperature and the Curie temperature can be changed in a wider range by changing the heat treatment process, so that the Co-Ni-Al alloy is a high-temperature shape memory alloy with great potential. While the gamma phase is a soft phase which can improve the mechanical properties of the alloy, it is particularly attractive that the size, volume fraction and distribution of the gamma phase can be controlled by a heat treatment process.

Disclosure of Invention

In order to solve the problems of large brittleness and poor machining performance of the conventional magnetic memory alloy, the Co-Ni-Al magnetic memory alloy is successfully prepared by adopting a method combining mechanical powder metallurgy and hot-pressing sintering, and the gamma phase distribution in the Co-Ni-Al magnetic memory alloy is controlled by utilizing a heat treatment process, so that the shape memory effect and the superelasticity of the Co-Ni-Al polycrystalline alloy are further improved.

The above purpose of the invention is realized by the following technical scheme:

a method for improving the superelasticity of Co-Ni-Al magnetic memory alloy by controlling the distribution of gamma phase comprises the following steps:

step S1: respectively taking nickel powder, cobalt powder and aluminum powder as raw materials according to atomic percentage;

step S2: uniformly mixing the raw materials in the step S1 through a stirrer;

step S3: pouring the uniformly mixed raw materials in the step S2 into a self-designed high-strength graphite forming die;

step S4: pressing the forming die in the step S3 by using a universal testing machine to make the powdery raw material into a cuboid style;

step S5: sintering the forming mold of the step S4 in a hot isostatic sintering furnace together with the pattern;

step S6: cooling the sample prepared in the step S5 to room temperature along with the furnace, and taking out the sample to obtain the super-elastic Co-Ni-Al magnetic memory alloy;

step S7: super elastic Co-N obtained in step S6Mechanically polishing the i-Al magnetic memory alloy to remove surface impurities, cleaning with acetone, and sealing in vacuum degree of 10 ^-4 Carrying out heat preservation homogenization treatment in a quartz tube of Torr, wherein the heat preservation temperature range is 800-1300 ℃, and obtaining the highly ordered Co-Ni-Al magnetic memory alloy.

Further, the nickel powder, the cobalt powder and the aluminum powder in step S1 have a purity of 99.95% and a particle size of 300 meshes, and are prepared according to an atomic percentage of 35: 34: 31 configuration;

Further, in the step S2, the rotating speed of the stirrer is 200r/min-500r/min, and the stirring time is 2-3 h;

further, the universal tester is pressurized to 4-50MPa in step S4, and the powder is pressed into a cuboid shape with the diameter of 15 x 25mm by maintaining the pressure for 10-15 min;

further, the temperature of the hot isostatic pressing sintering furnace in the step S5 is 800-1000 ℃, and the time is 40-60 min;

further, the pressure of the universal tester is 30MPa in step S4, the temperature of the hot isostatic pressing sintering furnace is 800 ℃ in step S5, after the powder is pressed into a cuboid shape with the diameter of 15 × 15 × 25mm in the hot forging process of step S4, the cuboid shape is turned over for 90 degrees along the major axis, after the powder is pressed, the cuboid shape is turned over for 90 degrees along the minor axis again, the powder is subjected to hot forging forming on the sample in three different directions, and the grain orientation of the sample is changed because the stress state of the material is changed.

Further, the heat preservation homogenization treatment in step S7 specifically includes: the super elastic Co-Ni-Al magnetic memory alloy obtained in step S6 is mechanically polished to remove surface impurities, cleaned by acetone, cut into 6 pieces with the same size, and sealed in a vacuum degree of 10 ^- ⁴ In a quartz tube of Torr, each sample is subjected to homogenization treatment at a holding temperature of 800 ℃ or 900 ℃ or 1000 ℃ or 1100 ℃ or 1200 ℃ or 1300 ℃ for 5 hours, respectively, and each sample is taken out and quenched into water to obtain a high degree of order.

Compared with the prior art, the invention has the beneficial effects that:

the method combines mechanical powder metallurgy and hot-pressing sintering to prepare the Co-Ni-Al ferromagnetic shape memory alloy, and the distribution of a gamma phase in the alloy is controlled by changing the heat treatment temperature, so that the comprehensive performance of the alloy is improved, and the idea is expanded for the application of the shape memory alloy. The magnetic shape memory alloy Co-Ni-Al prepared by the invention has the advantages of good toughness, high strength, super elasticity and the like.

1. The fracture strength of the Co-Ni-Al alloy sample subjected to heat preservation treatment at 1300 ℃ prepared by the invention is 1350Mpa, which is improved by about 1.5 times compared with the existing Co-Ni-Al alloy;

2. the fracture strain of the alloy prepared by the invention is tested, and the result shows that the fracture strain of the Co-Ni-Al alloy subjected to heat preservation treatment at 1300 ℃ prepared by the invention is 16.6 percent, which is 6.6 percent higher than that of the existing Co-Ni-Al alloy, and the toughness of the Co-Ni-Al alloy prepared by the invention is high.

3. The size and the number of gamma phases of the Co-Ni-Al alloy prepared by the invention are gradually reduced along with the rise of the heat treatment temperature.

4. The shape recovery rate of the Co-Ni-Al alloy prepared by the method is over 90 percent, and is improved by 50 percent compared with other methods.

Drawings

The invention is further illustrated with reference to the following figures and examples.

FIG. 1 is a microstructure morphology diagram of Co-Ni-Al alloy after heat treatment at different temperatures, wherein the treatment temperature and time of each sample are respectively as follows: (a)1300 ℃/5 h; (b)1200 ℃/5 h; (c)1100 ℃/5 h; (d)1000 ℃/5 h; (e)900 ℃/5 h; (f)800 ℃/5 h;

FIG. 2 is a room temperature XRd diffraction pattern of Co-Ni-Al alloy after different heat treatment processes, and the treatment temperature and time of each sample are respectively as follows: (a)1300 ℃/5 h; (b)1200 ℃/5 h; (c)1100 ℃/5 h; (d)1000 ℃/5 h; (e)900 ℃/5 h; (f)800 ℃/5 h;

FIG. 3 is a graph of the room temperature compressive stress strain of a Co-Ni-Al magnetic memory alloy with a heat treatment process;

FIG. 4 shows the shape memory effect of Co-Ni-Al alloy after heat treatment at different temperatures, wherein the treatment temperature and time for each sample are as follows: (a)1000 ℃/5 h; (b)1100 ℃/5 h; (c)1200 ℃/5 h; (d)1300 ℃ for 5 h.

Detailed Description

The invention is described in more detail below with reference to specific examples, without limiting the scope of the invention. Unless otherwise specified, the experimental methods adopted by the invention are all conventional methods, and experimental equipment, materials, reagents and the like used in the experimental method can be obtained from commercial sources.

The invention successfully prepares the Co-Ni-Al magnetic memory alloy by adopting a method combining mechanical powder metallurgy and hot-pressing sintering, controls the gamma phase distribution in the Co-Ni-Al magnetic memory alloy by utilizing a heat treatment process, further improves the shape memory effect and the superelasticity of the Co-Ni-Al polycrystalline alloy, enriches a Co-Ni-Al base magnetic control shape memory alloy system, and endows the Co-Ni-Al polycrystalline alloy with good shape memory effect so as to obtain the high-performance Co-Ni-Al magnetic shape memory alloy.

The equipment used is a universal testing machine of WDW-50 type and a vacuum hot-pressing sintering furnace ZT-40-20Y.

Example 1

Taking nickel powder, cobalt powder and aluminum powder with the purity of 99.95 percent and the granularity of 300 meshes as raw materials according to atomic percent, and mixing the raw materials according to the weight ratio of 35: 34: 31, stirring the metal powder for 2 hours by using 500r/min in a stirrer to uniformly mix the metal powder, then putting the mixture into a self-designed mould, pressing the mould by using a clamping mould on a universal testing machine, pressing the powder into a cuboid shape with the diameter of 15 multiplied by 25mm by pressurizing to 30MPa pressure and maintaining the pressure for 10 minutes, then placing the cuboid shape and a self-designed mould together in a hot isostatic sintering furnace for hot-pressing sintering molding, then turning over 90 degrees along the major axis for pressing sintering, finally turning over 90 degrees along the minor axis for pressing sintering again, and (3) carrying out hot forging molding on the sample in three different directions, wherein the hot forging temperature is 800 ℃, the liquid forging pressure is 30MPa, the heat preservation time in each direction is 20-40 minutes, and sintering is carried out by the sintering process, so that the Co-Ni-Al magnetic memory alloy with uniform grain size is obtained.

Removing surface impurities from the Co-Ni-Al magnetic memory alloy through mechanical polishing, cleaning the Co-Ni-Al magnetic memory alloy with acetone, sealing the Co-Ni-Al magnetic memory alloy into a quartz tube with the vacuum degree of 10-4Torr, respectively carrying out homogenization treatment of heat preservation at 800 ℃ for 5 hours, heat preservation at 900 ℃ for 5 hours, heat preservation at 1000 ℃ for 5 hours, heat preservation at 1100 ℃ for 5 hours, heat preservation at 1200 ℃ for 5 hours and heat preservation at 1300 ℃ for 5 hours, and taking out and quenching the Co-Ni-Al magnetic memory alloy into water to obtain high order degree. Finally, the highly ordered Co-Ni-Al magnetic memory alloy is obtained.

Example 2

The present embodiment differs from embodiment 1 in that: the incubation time was changed to 60 minutes, and the procedure of example 1 was otherwise the same.

Example 3

The present embodiment differs from embodiment 1 in that: the same procedure as in example 1 was repeated except that the hot forging temperature was changed to 900 ℃.

The Co-Ni-Al magnetic memory alloy prepared in example 1 was subjected to the texture morphology test, and the test results are shown in FIG. 1. FIG. 1 shows that 6 sets of homogenization treatments were performed on Co-Ni-Al alloys at different temperatures, and the six sets of temperatures were set as follows: 1300 ℃, 1200 ℃, 1100 ℃, 1000 ℃, 900 ℃ and 800 ℃ and preserving the heat for 5 hours to obtain the appearance of the optical microstructure after heat treatment. As can be seen from fig. 1, the amount of the gamma phase in the alloy gradually increases and the size gradually decreases as the heat treatment temperature decreases. When the heat treatment temperature is 1300 ℃, a fine γ phase is observed at the grain boundary position of the alloy, and the γ phase is hardly observed in the crystal, as shown in fig. 1 (a). When the heat treatment temperature is 1200 ℃, a γ phase having a size much larger than that of fig. 1(a) can be observed at the grain boundary position of the alloy, and also, the γ phase is hardly observed in the crystal, as shown in fig. 1 (b). When the heat treatment temperature is 1100 ℃, the size of the gamma phase at the grain boundary position of the alloy is almost equivalent to that of fig. 1(b), and at this time, discontinuous gamma phases with different sizes and different intervals appear in the crystal grains of the alloy, and the gamma phase is dispersed among martensite laths in the crystal grains, as shown in fig. 1 (c). When the heat treatment temperature is 1000 ℃, the size of the gamma phase at the grain boundary position of the alloy is almost equivalent to that of fig. 1(b), the number of the gamma phase in the crystal grain of the alloy is obviously increased compared with that of fig. 1(c), the interval between the gamma phases is reduced, the size of the gamma phase is slightly reduced, and the gamma phase is dispersed among martensite laths in the crystal grain, as shown in fig. 1 (d).

In addition, as is apparent from fig. 1(a) - (d), the alloy mainly exhibits a lath martensite shape. And continuously reducing the heat treatment temperature, gradually increasing the number of gamma phases, wherein the gamma phases are fine particles and are dispersed in the crystal grains, and the martensite laths in the matrix are hardly observed at the moment, so that the alloy matrix is deduced to be in an austenite state at the moment. It is known that the change of the solid solubility curve of an alloy causes the equilibrium concentration of some elements in different phases of the alloy to change, so that the number of equilibrium phases changes, and the change of the phase composition is completed by the migration of each atomic position. Therefore, the change of the microstructure morphology of the Co-Ni-Al alloy can be related to the solid solubility of elements in the Co-Ni-Al alloy, the heating temperature and the cooling mode, so that the gamma phase of the Co-Ni-Al alloy is changed after heat treatment at different temperatures.

Example 1 Co-Ni-Al magnetic memory alloys were prepared and tested for their texture structures, and the results are shown in FIG. 2. Fig. 2 is a room temperature Xrd diffraction pattern of the Co-Ni-Al alloy after being treated by different heat treatment processes, and it is clear from the figure that the intensity of the diffraction peak in the vicinity of 43 ° gradually increases with the decrease of the heat treatment temperature, and the peak is almost the strongest peak of the diffraction peaks of the alloy when the heat treatment temperature is 1100 °. In addition, when the heat treatment temperature is 1300 ℃ and 1200 ℃, the alloy has diffraction peaks around 20 ℃, the intensity of the diffraction peaks is gradually increased along with the reduction of the heat treatment temperature, and the diffraction peaks at the positions are supposed to be processed by different heat treatment temperatures, and the alloy matrix is gradually transformed from a martensite phase to an austenite phase. Meanwhile, when the heat treatment temperature is 1100 ℃, the diffraction peak near 63 ℃ disappears, the diffraction peak near 80 ℃ appears, the diffraction peak near 80 ℃ gradually decreases with the decrease of the heat treatment temperature, and the diffraction peak disappears when the heat treatment temperature is 800 ℃, which indicates that a new phase appears when the heat treatment temperature is 1100 ℃, and the structure of the specific phase needs to be continuously researched.

The fracture strength of the Co-Ni-Al magnetic memory alloy prepared in the embodiment 1 is improved by about 1.5 times compared with the Co-Ni-Al magnetic memory alloy smelted by a smelting furnace, and the fracture strain is improved by more than about 30 percent compared with the Co-Ni-Al magnetic memory alloy. The mechanical system performance of the Co — Ni — Al magnetic memory alloy obtained in this example was tested, and the results are shown in fig. 3. As the heat treatment temperature increases, the fracture strength of the Co-Ni-Al alloy gradually increases, and the fracture strain also gradually increases. From the results of fig. 1 and 2, it can be seen that the amount and size of the γ phase in the alloy gradually decrease with the increase of the heat treatment temperature, and the mechanical properties of the alloy are significantly improved. The increase in the fracture strength of the alloy is presumably due to the fact that the gamma phase acts as a dispersion strengthening in the second alloy. Meanwhile, the gamma phase is a soft phase, which plays an obvious role in improving the plasticity of the alloy.

The Co-Ni-Al magnetic memory alloy prepared in example 1 was subjected to a superelasticity test at room temperature, and the Co-Ni-Al magnetic memory alloy was used as a study object at room temperature, and was deformed by 2% of deformation, respectively, and the results are shown in fig. 4 below. FIG. 4 is a strain recovery characteristic curve of Co-Ni-Al magnetic memory alloy after 2% cold deformation, all the compressed alloys are heated to above Af temperature and kept for 1 minute. It can be seen from the figure that the shape memory effect of the alloy tends to decrease and then increase with the increase of the heat treatment temperature, and the shape memory effect of the alloy is the minimum when the heat treatment temperature is 1200 ℃, and the area of the graph surrounded by the strain recovery characteristic curve is the maximum, which indicates that the energy consumed by the deformed alloy is the highest. The shape memory effect of the alloy is almost equivalent at heat treatment temperatures of 1000 c and 1300 c, but the strength of the alloy is higher when the heat treatment temperature is 1300 c.

There may be two reasons why Co-Ni-Al alloys exhibit good one-way shape memory after cold deformation. On one hand, with the increase of the deformation amount, the critical sliding stress of the alloy is improved, so that the alloy is not easy to generate plastic deformation, and the one-way memory effect is improved. On the other hand, stress-induced martensite occurs during compressive deformation of the alloy, which may be beneficial for the one-way memory effect. Whether other changes occur in the structure of the alloy at this stage is further investigated.

It can be seen from FIG. 4 that the super-elasticity of the Co-Ni-Al magnetic memory alloy prepared in example 1 is significantly improved.

The foregoing is merely a preferred embodiment of the invention and is not intended to represent the full scope of possible implementations of the invention. It should be noted that, for those skilled in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be construed as the protection scope of the present invention.

Claims

1. A method for improving the superelasticity of Co-Ni-Al magnetic memory alloy by controlling the distribution of gamma phase is characterized by comprising the following steps:

Step S2: uniformly mixing the raw materials in the step S1 through a stirrer;

step S7: the super elastic Co-Ni-Al magnetic memory alloy obtained in step S6 is mechanically polished to remove surface impurities, cleaned by acetone and sealed in a vacuum degree of 10 ^-4 Carrying out heat preservation homogenization treatment in a quartz tube of Torr, wherein the heat preservation temperature range is 800-1300 ℃, and obtaining the highly ordered Co-Ni-Al magnetic memory alloy;

the pressure of the universal testing machine in the step S4 is 30MPa, the temperature of the hot isostatic pressing sintering furnace in the step S5 is 800 ℃, after the powder is pressed into a cuboid shape with the diameter of 15 multiplied by 25mm in the step S4 hot forging process, the cuboid shape is turned over by 90 degrees along the major axis, after the powder is pressed, the cuboid shape is turned over by 90 degrees along the minor axis again, the powder hot forging forming is carried out on the sample in three different directions, and the grain orientation of the sample is changed because the stress state of the material is changed.

2. The method as claimed in claim 1, wherein the nickel powder, the cobalt powder and the aluminum powder in step S1 have a purity of 99.95% and a particle size of 300 meshes, and the percentage by atom is 35: 34: 31 proportional configuration.

3. The method as claimed in claim 1, wherein the rotation speed of the stirrer is 200r/min to 500r/min and the stirring time is 2 to 3 hours in step S2.

4. The method of claim 1, wherein the universal tester is pressurized to 4-50MPa in step S4, and the powder is pressed into a rectangular parallelepiped shape with a diameter of 15X 25mm under a pressure of 10-15 min.

5. The method as claimed in claim 1, wherein the temperature of the sintering furnace is 800-1000 ℃ and the time is 40-60min in step S5.

6. The method for improving the superelasticity of the Co-Ni-Al magnetic memory alloy by controlling the distribution of the gamma phase as claimed in claim 1, wherein the heat-preserving homogenization treatment in step S7 is specifically as follows: the super elastic Co-Ni-Al magnetic memory alloy obtained in step S6 is mechanically polished to remove surface impurities, cleaned by acetone, cut into 6 pieces with the same size, and sealed in a vacuum degree of 10 ^-4 In a quartz tube of Torr, each sample is subjected to homogenization treatment at a holding temperature of 800 ℃ or 900 ℃ or 1000 ℃ or 1100 ℃ or 1200 ℃ or 1300 ℃ for 5 hours, respectively, and each sample is taken out and quenched into water to obtain a high degree of order.