Composite Hf-free semi-Heusler alloy thermoelectric material and preparation method and application thereof

Abstract

The invention provides a composite Hf-free semi-Heusler alloy thermoelectric material as well as a preparation method and application thereof. The chemical composition of the composite Hf-free semi-Heusler alloy thermoelectric material is x wt% of Cu-ZrCoSb0. 8Sn0. 2, wherein 0 < x < = 2.0, and x is mass fraction. The preparation method of the composite Hf-free semi-Heusler alloy thermoelectric material comprises the following steps: weighing Zr particles, Co particles, Sb particles and Sn particles according to the chemical composition, and smelting in a protective atmosphere to obtain an alloy ingot; and crushing the alloy ingot, mixing the crushed alloy ingot with Cu powder, grinding, and sintering to obtain the composite Hf-free semi-Heusler alloy thermoelectric material. The composite Hf-free semi-Heusler alloy thermoelectric material provided by the invention has a relatively high thermoelectric figure of merit while maintaining relatively low cost, and shows good application prospects and large-scale popularization potential in the field of high-temperature power generation.

Description

Technical Field

[0001] The present invention relates to thermoelectric material technology, in particular to a composite Hf-free semi-Heusler alloy thermoelectric material, a preparation method and application thereof. Background Art

[0002] High-temperature semi-Heusler thermoelectric materials have important application value in radioisotope generators of deep space probes due to their excellent thermoelectric and mechanical properties in the medium and high temperature range. However, the performance optimization of semi-Heusler thermoelectric materials depends on expensive elements such as Hf, and due to the large melting point difference between the components, various elements have always existed in the system, which seriously affects the thermoelectric performance of the material. The performance of thermoelectric materials is determined by the dimensionless thermoelectric figure of merit (zT), zT = S 2 σT / κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. From this formula, we can see that to increase zT, we need to increase the power factor and reduce the thermal conductivity. The electronic configuration of semi-Heusler thermoelectric materials is similar to that of the Zintl phase. By controlling segregation, electron transport and phonon scattering can be effectively manipulated, thereby enhancing the thermoelectric figure of merit. Summary of the Invention

[0003] The purpose of the present invention is to address the problems existing in traditional high-temperature semi-Heusler thermoelectric materials and propose a composite Hf-free semi-Heusler alloy thermoelectric material. The degree of Zr element segregation in this thermoelectric material can be adjusted by regulating the process route. The composite Hf-free semi-Heusler alloy thermoelectric material of the present invention has a high thermoelectric figure of merit while maintaining a low cost, and has good application prospects and large-scale promotion potential in the field of high-temperature power generation.

[0004] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "composed of", "composed of", etc. and similar meanings.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a composite Hf-free semi-Heusler alloy thermoelectric material with a chemical composition of x wt% Cu-ZrCoSb 0.8 Sn 0.2 ; Wherein, 0<x≤2.0, x is the mass fraction.

[0006] Furthermore, the composite Hf-free semi-Heusler alloy thermoelectric material has an electrical conductivity of 2-5 10 at 973K. 4 Sm -1 , Seebeck coefficient is 240-280μV K -1 , thermal conductivity is 3-5W m -1 K -1, and the final thermoelectric figure of merit is 0.6-0.8.

[0007] Another object of the present invention is to disclose a method for preparing a composite Hf-free semi-Heusler alloy thermoelectric material, comprising the following steps:

[0008] (1) weighing Zr particles, Co particles, Sb particles, and Sn particles according to the chemical composition of the composite Hf-free semi-Heusler alloy thermoelectric material, and smelting them in a protective atmosphere to obtain an alloy ingot;

[0009] (2) The alloy ingot is crushed and mixed with Cu powder, and then ground and sintered to obtain the composite Hf-free semi-Heusler alloy thermoelectric material.

[0010] Furthermore, in step (1), the molar ratio of the Zr particles, Co particles, Sb particles and Sn particles is 1.0:1.0:0.8:0.2.

[0011] Furthermore, the smelting in step (1) is magnetic levitation smelting.

[0012] Furthermore, the smelting in step (1) includes a heating and melting stage and a heat preservation stage; the heating rate in the heating and melting stage is 30-35°C / s, and the time is based on the melting of all the raw materials; the temperature in the heat preservation stage is 1900-2000°C, and the heat preservation time is 20-40s.

[0013] Furthermore, the smelting is performed three times or more in step (1).

[0014] Furthermore, in step (2), the alloy ingot is crushed to a particle size of 1 to 3 mm.

[0015] Furthermore, the Cu powder in step (2) is Cu nanopowder.

[0016] Furthermore, the mass ratio of the Cu nanopowder to the crushed alloy ingot is 0.005 to 0.02:1; specifically, it can be 0.005:1, 0.01:1, or 0.02:1.

[0017] Furthermore, the grinding speed in step (2) is 300-700 rpm, and the grinding time is 10-16 h.

[0018] Furthermore, the target particle size of the grinding in step (2) is 300 to 700 nm.

[0019] Furthermore, the sintering in step (2) is hot pressing sintering.

[0020] Furthermore, the hot pressing sintering in step (2) is performed at a temperature of 900 to 1200° C., a pressure of 20 to 60 MPa, and a holding time of 40 to 70 minutes.

[0021] Furthermore, the mixture needs to be heated after grinding in step (2) and before sintering;

[0022] When the sintering temperature is 900-1200°C, the heating is as follows: heating to 280-330°C at a rate of 15-20°C / min, then heating to 900-1000°C at a rate of 12-15°C / min; and then heating to 1000-1200°C at a rate of 5-7°C / min.

[0023] Another object of the present invention is to disclose an application of a composite Hf-free semi-Heusler alloy thermoelectric material in the field of deep space exploration.

[0024] The composite Hf-free semi-Heusler alloy thermoelectric material of the present invention has the following advantages compared with the prior art:

[0025] 1) The composite Hf-free semi-Heusler alloy thermoelectric material provided by the present invention improves the thermoelectric performance of the semi-Heusler alloy to between 0.6 and 0.8 by adjusting the content of Cu nanopowder, thereby expanding the application range of the material. It is suitable for use in extreme environments such as deep space exploration and has potential application value for supplementary power generation.

[0026] The present invention effectively controls the degree of element segregation within the material by adjusting the particle composite process and the composite content of nanoparticles. Compared with the original sample, the micron-level Zr segregation significantly increases the Seebeck coefficient to 240-290 μV K without significantly affecting the conductivity. -1 At the same time, the grain boundary phase formed by Cu and other elements at the grain boundary promotes phonon scattering and reduces thermal conductivity to 3-4W m -1 K -1 between.

[0027] The composite Hf-free semi-Heusler alloy thermoelectric material provided by the present invention has a high thermoelectric figure of merit while maintaining a low cost, and has potential application value in high-temperature power generation.

[0028] 2) The preparation method of the composite Hf-free semi-Heusler alloy thermoelectric material of the present invention has simple and scientific steps, and can control the size of the precipitated phase, thereby adjusting the thermoelectric performance.

[0029] 3) The Zr segregation control method proposed in the present invention can be used in conjunction with other performance control methods (such as vacancy engineering, band engineering, etc.) to further enhance the thermoelectric figure of merit. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The electrical conductivity diagrams of the Hf-free composite semi-Heusler alloy thermoelectric materials of Examples 1 to 3 and the thermoelectric materials of Comparative Examples 1 to 4;

[0031] Figure 2 This is a diagram of the Seebeck coefficients of the composite Hf-free semi-Heusler alloy thermoelectric materials of Examples 1 to 3 and the thermoelectric materials of Comparative Examples 1 to 4;

[0032] Figure 3 The power factor diagrams of the Hf-free composite semi-Heusler alloy thermoelectric materials of Examples 1 to 3 and the thermoelectric materials of Comparative Examples 1 to 4;

[0033] Figure 4 Thermal conductivity diagrams of the Hf-free composite semi-Heusler alloy thermoelectric materials of Examples 1 to 3 and the thermoelectric materials of Comparative Examples 1 to 4;

[0034] Figure 5 The thermoelectric figure of merit of the composite Hf-free semi-Heusler alloy thermoelectric materials of Examples 1 to 3 and the thermoelectric materials of Comparative Examples 1 to 4;

[0035] Figure 6 EPMA element distribution diagrams of the composite Hf-free semi-Heusler alloy thermoelectric material of Example 2 and the thermoelectric material of Comparative Example 3; wherein a is the EPMA element distribution diagram of Comparative Example 3, and b is the EPMA element distribution diagram of Example 2;

[0036] Figure 7 This is the element distribution diagram at the grain boundary of the Hf-free composite semi-Heusler alloy thermoelectric material in Example 2 under TEM. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the following examples. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0038] Unless otherwise stated, the units used in this specification are international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0039] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0040] In this specification, the numerical range expressed using "above" or "below" means a numerical range including the number.

[0041] In this specification, the use of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0042] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0043] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 15-25°C.

[0044] In this manual, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0045] The present invention provides a composite Hf-free semi-Heusler alloy thermoelectric material, the chemical composition of which is x wt% Cu-ZrCoSb 0.8 Sn 0.2 ; Wherein, 0<x≤2.0, x is the mass fraction.

[0046] In the present invention, in the composite Hf-free semi-Heusler alloy thermoelectric material, the value range of x is preferably 0<x≤2.0, and specifically can be 0.25, 0.5, 1.0, 1.5 or 2.0.

[0047] The present invention also provides a method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material described in the above scheme, comprising the following steps:

[0048] (1) smelting raw materials in a protective atmosphere according to the chemical composition of the composite Hf-free semi-Heusler alloy thermoelectric material to obtain an alloy ingot;

[0049] (2) The alloy ingot is crushed, ground, and sintered in sequence to obtain the composite Hf-free semi-Heusler alloy thermoelectric material.

[0050] According to the chemical composition of the composite Hf-free semi-Heusler alloy thermoelectric material, raw materials are smelted in a protective atmosphere to produce an alloy ingot. In the present invention, the raw materials preferably include Zr particles, Co particles, Sb particles, Sn particles, and Cu nanopowder. The sources of the Zr, Co, Sb, Sn, and Cu nanopowder are not particularly limited, and commercially available products familiar to those skilled in the art can be used.

[0051] In the present invention, the molar ratio of the Zr particles to the Co particles is preferably 1.0:1.

[0052] In the present invention, the molar ratio of the Zr particles to the Sb particles is preferably 1.0:0.8.

[0053] In the present invention, the molar ratio of the Zr particles to the Sn particles is preferably 1.0:0.2.

[0054] In the present invention, the molar ratio of the Cu nanopowder to the crushed and smelted ingot is 0.005 to 0.02:1; specifically, it can be 0.005:1, 0.01:1, or 0.02:1.

[0055] In a specific embodiment of the present invention, the Zr particles are preferably metallic Zr with a purity of preferably 99.95%; the Co particles are preferably metallic Co with a purity of preferably 99.98%; the Sb particles are preferably metallic Sb with a purity of preferably 99.999%; the Sn particles are preferably metallic Sn with a purity of preferably 99.99%. The Cu powder is preferably nano-Cu powder.

[0056] In the present invention, the protective atmosphere is preferably argon; the purity of the argon is preferably above 99.99%, specifically 99.99%, 99.992%, 99.994%, 99.996% or 99.999%.

[0057] In the present invention, the smelting preferably includes magnetic levitation smelting; the smelting preferably includes a heating and melting stage and a holding stage; the heating rate in the heating and melting stage is preferably 30-35°C / s, specifically 30°C / s, 31°C / s, 32°C / s, 33°C / s, 34°C / s or 35°C / s, and the time is based on the melting of all raw materials; the temperature in the holding stage is preferably 1900-2000°C, specifically 1900°C, 1920°C, 1950°C, 1980°C or 2000°C, and the holding time is preferably 20-40s, specifically 20s, 25s, 30s, 35s or 40s.

[0058] In the present invention, the smelting is preferably performed three times or more, specifically three times, four times, five times or six times; and the smelting equipment is preferably a suspension smelting furnace.

[0059] In the present invention, the smelting preferably further includes cooling; the final temperature of the cooling is preferably room temperature; the cooling rate of the cooling is preferably 55 to 60°C / s, specifically 55°C / s, 56°C / s, 57°C / s, 58°C / s, 59°C / s or 60°C / s.

[0060] After obtaining the alloy ingot, the present invention sequentially crushes, grinds, and sinters the ingot to obtain the Hf-free composite semi-Heusler alloy thermoelectric material. In the present invention, the crushing preferably includes mechanical crushing; the crushing equipment is preferably a tablet press; and the target particle size of the crushed material is preferably 1 to 3 mm, specifically 1 mm, 2 mm, or 3 mm.

[0061] In the present invention, the grinding speed is preferably 300-700 rpm, specifically 300 rpm, 400 rpm, 500 rpm, 600 rpm or 700 rpm, and the grinding time is preferably 10-16 h, specifically 10 h, 12 h, 14 h or 16 h.

[0062] In the present invention, the grinding preferably includes ball milling; the ball milling preferably includes wet ball milling; the medium of the wet ball milling is preferably anhydrous ethanol; the grinding balls used in the ball milling are preferably tungsten carbide balls; the ball-to-material ratio of the ball milling is preferably 15 to 20:1, specifically 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1.

[0063] In the present invention, the target particle size of the milled particles is preferably 300 nm to 700 nm, and specifically may be 300 nm, 400 nm, 500 nm, 600 nm or 700 nm.

[0064] In the present invention, the sintering preferably includes hot pressing sintering; the sintering temperature is preferably 900-1200°C, specifically 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, or 1200°C; the pressure is preferably 20-60 MPa, specifically 20 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, or 60 MPa; the holding time is preferably 40-70 min, specifically 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, or 70 min; and the sintering is preferably performed in a graphite mold. The present invention can make the alloy interior denser and reduce porosity within the alloy through sintering.

[0065] In the present invention, the sintering process preferably also includes heating before sintering; when the sintering temperature is 900-1200°C, the heating process is preferably: heating to 280-330°C at a rate of 15-20°C / min, and then heating to 900-1000°C at a rate of 12-16°C / min; then heating to 1000-1200°C at a rate of 5-7°C / min; when the sintering temperature is 1000-1200°C, the heating process is more preferably: heating to 300°C at a rate of 15°C / min, and then heating to 1000°C at a rate of 14°C / min, and finally heating to 1100°C at a rate of 6°C / min.

[0066] In order to further illustrate the present invention, the scheme of the present invention is described in detail below with reference to the accompanying drawings and embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0067] Example 1

[0068] This embodiment discloses a composite Hf-free semi-Heusler alloy thermoelectric material, the chemical composition of which is 2.0wt% Cu-ZrCoSb 0.8 Sn 0.2 , numbered as M x=2.0.

[0069] The preparation method of the composite Hf-free semi-Heusler alloy thermoelectric material includes the following steps: weighing 6.7248 g of Zr metal particles, 4.3444 g of Co metal particles, 7.1806 g of Sb metal particles, and 1.7502 g of Sn metal particles, wherein the molar ratio of the Zr particles, the Co particles, the Sb particles, and the Sn particles is 1.0:1.0:0.8:0.2.

[0070] The above raw materials were loaded into the crucible of the suspension melting furnace, heated to a molten state at a heating rate of 30°C / s in an argon (purity 99.99%) atmosphere, maintained at the corresponding temperature for 30s, and then cooled to room temperature at a rate of 60°C / s. The crucible was repeatedly turned over and melted for a total of 3 times to obtain an alloy ingot.

[0071] The alloy ingot was mechanically crushed and mixed with 0.4 g of nano Cu powder for wet ball milling. The mass ratio of nano Cu powder to the mechanically crushed alloy ingot was 0.02:1. The wet ball milling conditions were as follows: the medium was anhydrous ethanol, the rotation speed was 500 rpm, the wet milling time was 12 h, and the powder particle size after wet milling was 300-700 nm. The powder obtained by wet milling was placed in a graphite mold and sintered by hot pressing to obtain 2.0 wt% Cu-ZrCoSb 0.8 Sn 0.2 The hot pressing sintering was performed by heating the temperature to 300°C at a rate of 15°C / min, then to 1000°C at a rate of 14°C / min, and finally to 1100°C at a rate of 6°C / min. The sintering temperature was 1100°C, the sintering pressure was 40 MPa, and the sintering time was 60 min.

[0072] Example 2

[0073] This embodiment discloses a composite Hf-free semi-Heusler alloy thermoelectric material, the chemical composition of which is 1.0wt% Cu-ZrCoSb 0.8 Sn 0.2 , numbered M x = 1.0, the preparation method is the same as that of Example 1, except that: 0.2g of nano Cu powder is weighed, and the mass ratio of nano Cu powder to the mechanically crushed alloy ingot is 0.01:1. Finally, 1.0wt% Cu-ZrCoSb 0.8 Sn 0.2 .

[0074] Example 3

[0075] This embodiment discloses a composite Hf-free semi-Heusler alloy thermoelectric material, the chemical composition of which is 0.5wt% Cu-ZrCoSb 0.8 Sn 0.2, numbered M x = 0.5, the preparation method is the same as that of Example 1, except that: 0.1g of nano Cu powder is weighed, and the mass ratio of nano Cu powder to the mechanically crushed alloy ingot is 0.005:1. Finally, 0.5wt% Cu-ZrCoSb 0.8 Sn 0.2 .

[0076] Comparative Example 1

[0077] This comparative example prepares a thermoelectric material whose chemical composition is ZrCoSb 0.8 Sn 0.2 , numbered as x=0, and the preparation method was the same as that of Example 1, except that no Cu nanopowder was added for wet ball milling.

[0078] Comparative Example 2

[0079] This comparative example prepares a thermoelectric material whose chemical composition is 2.0wt% Cu-ZrCoSb 0.8 Sn 0.2 , numbered as sub-M x=2.0. The material composition and preparation method are basically the same as those in Example 1, except that: Cu nanopowder is added in the form of ball-free mixing for 30 minutes after the ball milling is completed.

[0080] Comparative Example 3

[0081] This comparative example prepares a thermoelectric material whose chemical composition is 1.0 wt% Cu-ZrCoSb 0.8 Sn 0.2 , numbered as sub-M x=1.0. The material composition and preparation method are basically the same as those in Example 2, except that: Cu nanopowder is added in the form of ball-free mixing for 30 minutes after the ball milling is completed.

[0082] Comparative Example 4

[0083] This comparative example prepares a thermoelectric material whose chemical composition is 0.5wt% Cu-ZrCoSb 0.8 Sn 0.2 , numbered as sub-M x=0.5. The material composition and preparation method are basically the same as those in Example 3, except that: Cu nanopowder is added in the form of ball-free mixing for 30 minutes after the ball milling is completed.

[0084] The composite Hf-free semi-Heusler alloy thermoelectric materials of Examples 1-3 and the thermoelectric materials of Comparative Examples 1-4 were tested, and the test methods and test results are as follows:

[0085] Performance Testing

[0086] The electrical performance test of the Hf-free semi-Heusler alloy composite thermoelectric materials of Examples 1 to 3 and the thermoelectric materials of Comparative Examples 1 to 4 was conducted using the LSR-3 electrical performance test system. The test curves of the electrical conductivity are shown in FIG. Figure 1 As shown, the test curve of Seebeck coefficient is as follows Figure 2 As shown, the test curve of power factor is as follows Figure 3 As shown. Figures 1 to 3 It can be seen that compared with the submicron-level Zr segregation, the conductivity of the sample with micron-level Zr segregation is slightly reduced, while the Seebeck coefficient is greatly improved, which promotes the improvement of the power factor of the material.

[0087] The thermal diffusion coefficient D of the Hf-free semi-Heusler alloy composite thermoelectric materials of Examples 1 to 3 and the thermoelectric materials of Comparative Examples 1 to 4 was tested by laser flash method (LFA-457 laser thermal conductivity meter). The material density ρ was measured by the Archimedean drainage method, and the formula C was used to calculate the thermal diffusion coefficient D. p =C ph,H +C D Calculated heat capacity C p , C ph,H is the simple harmonic phonon specific heat, C D is the contribution of the thermal expansion term to the specific heat. Then the total thermal conductivity κ is calculated according to the following formula tot :κ tot =C p The results of Dρ, total thermal conductivity are as follows Figure 4 As shown. Figure 4 It can be seen that the copper-induced grain boundary phase promotes the decrease of thermal conductivity compared with the matrix.

[0088] Using the formula zT=S 2 σT / κ tot , where S, σ, κ tot The thermoelectric figures of merit of the composite Hf-free semi-Heusler alloy thermoelectric materials of Examples 1 to 3 and the thermoelectric materials of Comparative Examples 1 to 4 were calculated. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that by adjusting the content of nano-Cu and the degree of Zr segregation, the thermoelectric performance of the semi-Heusler alloy thermoelectric material with micron-level Zr segregation is greatly improved.

[0089] Figure 6 This is an element distribution map taken with the help of an electron probe. It can be found that the addition of nano-copper powder during the ball milling process will increase the size of Zr segregation. Since the element valence state of ZrCoSb is similar to the Zintl phase combination, the large-size Zr segregation can regulate electron transmission and optimize the electrical conductivity of the material.

[0090] Figure 7This is the element distribution diagram at the grain boundary observed with the help of transmission electron microscopy. It can be seen that the addition of Cu will induce the elements other than Zr to segregate at the grain boundary to form a grain boundary phase. The existence of the grain boundary phase can enhance the scattering of phonons and reduce thermal conductivity.

[0091] It can be seen from the above examples that the composite Hf-free semi-Heusler alloy thermoelectric material provided by the present invention has a high Seebeck coefficient and low thermal conductivity, and has excellent thermoelectric performance.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite Hf-free semi-Heusler alloy thermoelectric material, characterized in that: Chemical composition is xwt% Cu-ZrCoSb 0.8 Sn 0.2 ; Wherein, 0<x≤2.0, x is the mass fraction.

2. A method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 1, characterized in that: The following steps are involved: (1) weighing Zr particles, Co particles, Sb particles, and Sn particles according to the chemical composition of the composite Hf-free semi-Heusler alloy thermoelectric material, and smelting them in a protective atmosphere to obtain an alloy ingot; (2) The alloy ingot is crushed and mixed with Cu powder, and then ground and sintered to obtain the composite Hf-free semi-Heusler alloy thermoelectric material.

3. The method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 2, characterized in that: The molar ratio of the Zr particles, Co particles, Sb particles and Sn particles in step (1) is 1.0:1.0:0.8:0.

2.

4. The method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 2, characterized in that: The smelting in step (1) is magnetic suspension smelting.

5. The method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 2, characterized in that: The smelting in step (1) includes a heating and melting stage and a heat preservation stage; the heating rate in the heating and melting stage is 30-35°C / s, and the time is based on the melting of all the raw materials; the temperature in the heat preservation stage is 1900-2000°C, and the heat preservation time is 20-40s.

6. The method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 2, characterized in that: The Cu powder in step (2) is Cu nanopowder, and the mass ratio of the Cu nanopowder to the crushed alloy ingot is 0.005-0.02:

1.

7. The method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 2, characterized in that: The grinding speed in step (2) is 300-700 rpm, and the grinding time is 10-16 h; the target particle size of the grinding in step (2) is 300-700 nm.

8. The method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 2, characterized in that: The sintering in step (2) is hot pressing sintering, the temperature of the hot pressing sintering is 900-1200° C., the pressure is 20-60 MPa, and the holding time is 40-70 min.

9. The method for preparing the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 2, characterized in that: After grinding in step (2) and before sintering, the mixture needs to be heated; The sintering temperature is 900-1200°C, and the heating is as follows: heating to 280-330°C at a rate of 15-20°C / min, then heating to 900-1000°C at a rate of 12-16°C / min; and then heating to 1000-1200°C at a rate of 5-7°C / min.

10. Application of the composite Hf-free semi-Heusler alloy thermoelectric material according to claim 1 in the field of deep space exploration.

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