Large-size ultra-fine grain refractory high-entropy alloy and preparation method thereof

Abstract

The invention discloses a large-size ultra-fine grain refractory high-entropy alloy and a preparation method thereof, and belongs to the field of refractory high-entropy alloy materials.The method comprises the steps that simple substance powder of refractory elements and strong segregation elements is mixed, compression molding is conducted, a blank is heated to the first temperature and subjected to heat preservation for the first time, and the blank is cooled to the second temperature and subjected to heat preservation for the second time; raising the temperature to a third temperature, keeping the temperature for a third time, and finally quenching to obtain the large-size ultra-fine grain refractory high-entropy alloy. The refractory elements are selected from at least four of zirconium, niobium, molybdenum, hafnium, tantalum and tungsten, and the strong segregation elements are selected from at least one of boron, nickel and titanium; the second time is longer than the first time and the third time. According to the method, the ultra-fine grain refractory high-entropy alloy with the amorphous grain boundary is prepared, so that the room-temperature strong plasticity of the refractory high-entropy alloy is achieved, the stability of the refractory high-entropy alloy at the high temperature can be improved, and compared with vacuum arc melting and discharge plasma sintering, the shape and the size of a blank are less limited.

Description

Technical Field

[0001] The invention relates to a large-size ultrafine-grained refractory high-entropy alloy and a preparation method thereof, and belongs to the field of refractory high-entropy alloy materials. Background Art

[0002] With the rapid development of aerospace technology, the service temperature of some components has further increased. For example, the temperature at the front end of a supersonic aircraft can reach over 2000°C, and the operating temperature of turbine blades of aircraft engines with a high thrust-to-weight ratio is close to 1900°C. The existing nickel-based high-temperature alloys can no longer meet the service requirements.

[0003] Refractory high entropy alloys, which are a mixture of multiple refractory elements, have a high melting point and exhibit high strength in the high temperature range. They are expected to meet the service requirements in extreme environments and have attracted widespread attention. However, most refractory high entropy alloys are severely brittle at room temperature, which limits their processing performance and practical applications. In addition, the current preparation methods of refractory high entropy alloys are mainly vacuum arc melting and discharge plasma sintering, which makes it difficult to prepare large-sized refractory high entropy alloy parts, which has a great limitation on the application and promotion of refractory high entropy alloys. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a method for preparing a large-sized ultrafine-grained refractory high-entropy alloy, and provides a large-sized ultrafine-grained refractory high-entropy alloy prepared by the method, which can be used to prepare large-sized refractory high-entropy alloys with good room temperature and high temperature mechanical properties.

[0005] The technical solution adopted by the present invention to solve the technical problem is: In a first aspect, the present application provides a method for preparing a large-sized ultrafine-grained refractory high-entropy alloy, comprising the following steps: Mixing a single substance powder of a refractory element and a single substance powder of a strongly segregated element to obtain a mixed powder; Pressing the mixed powder into a shape to obtain a blank; The blank is heated to a first temperature and kept for a first time, then cooled to a second temperature and kept for a second time, then heated to a third temperature and kept for a third time, and finally quenched to obtain the large-sized ultrafine-grained refractory high-entropy alloy; The refractory elements are selected from at least four of zirconium, niobium, molybdenum, hafnium, tantalum and tungsten, and the strong segregation elements are selected from at least one of boron, nickel and titanium; the second time is longer than the first time; the second time is longer than the third time.

[0006] The method for preparing a large-sized ultrafine-grained refractory high-entropy alloy provided in the present application can prepare a large-sized refractory high-entropy alloy with an ultrafine-grained structure by multi-step sintering, and the obtained ultrafine-grained refractory high-entropy alloy has strong plasticity at room temperature. Strong segregation elements are added and the sintering in the first two stages is used to make the material have a higher density and avoid excessive grain size. Then, amorphous grain boundaries are formed in the material through short-term high-temperature sintering and rapid cooling in the third stage, which inhibits grain growth and improves the high-temperature stability of the ultrafine-grained structure, thereby obtaining a large-sized ultrafine-grained refractory high-entropy alloy with excellent room temperature and high-temperature mechanical properties.

[0007] Furthermore, the first temperature is 1000°C to 1700°C, the second temperature is 800°C to 1400°C, and the third temperature is 1000°C to 1800°C.

[0008] Short-time treatment at the first temperature initially forms the matrix structure of the billet and improves the density of the billet; long-term insulation at the lower second temperature avoids grain growth and further improves the densification effect; rapid sintering combined with quenching at the higher third temperature forms amorphous grain boundaries, which will significantly improve high-temperature stability and mechanical properties.

[0009] Furthermore, the first time is 0h~4h, the second time is 4h~40h, and the third time is 0h~2h.

[0010] The first stage is a short-term treatment to reduce the grain growth caused by sintering and quickly make the billet have a higher density; the second stage is a long-term treatment to ensure sufficient densification; the third stage is a short-term high-temperature sintering combined with rapid cooling to inhibit grain growth, while forming amorphous grain boundaries and improving the stability of the ultrafine grain structure.

[0011] Furthermore, in terms of the amount of substance, the single substance powder of the strong segregation element accounts for 1% to 25% of the mixed powder.

[0012] The content of this strong segregation element helps to inhibit grain growth; a reasonable ratio ensures that the alloy has stable performance when serving at high temperatures after sintering.

[0013] Furthermore, in the single substance powders of the multiple refractory elements, the atomic ratio between the heterogeneous elements is 1:1, which is conducive to the formation of refractory high entropy alloys and helps to improve the overall mechanical properties of the material.

[0014] Furthermore, the pressing method is cold isostatic pressing, hot isostatic pressing or molding. The process is flexible and suitable for parts of various sizes and shapes.

[0015] Furthermore, the pressing pressure in the pressing forming is 100MPa-500MPa. The appropriate pressure range ensures that the blank has a good initial density, reduces the possibility of pores or defects in the subsequent sintering process, and lays a foundation for the optimization of the alloy microstructure.

[0016] Furthermore, the mixed powder is subjected to high-energy ball milling. High-energy ball milling allows the powder to be uniformly mixed and pre-alloyed, and can increase the surface activity of the powder, enhance the densification effect of the subsequent sintering process, and improve the overall performance of the alloy.

[0017] Furthermore, in the high-energy ball milling, the ball milling speed is 300 rpm to 600 rpm, the ball-to-material ratio is 2:1 to 32:1, and the ball milling time is 5 h to 50 h. The ball milling parameters can effectively control the particle size and uniformity of the powder, promote pre-alloying, provide an ideal powder state for the subsequent preparation of ultrafine-grained alloys, and enhance the uniformity of the pressed blank.

[0018] In a second aspect, the present application provides a large-sized ultrafine-grained refractory high-entropy alloy, which is prepared by the large-sized ultrafine-grained refractory high-entropy alloy preparation method described in the first aspect. The alloy has both high-temperature stability and excellent room-temperature and high-temperature mechanical properties, meeting the service requirements under extreme conditions.

[0019] The beneficial effects of the present invention are as follows: the present invention utilizes a multi-step sintering and heat treatment process in combination with strong segregation elements to prepare a large-sized ultrafine-grained refractory high-entropy alloy with amorphous grain boundaries, thereby achieving room temperature strong shaping of the refractory high-entropy alloy and improving the stability of the refractory high-entropy alloy at high temperatures. Compared with vacuum arc melting and discharge plasma sintering, the present invention has fewer restrictions on the shape and volume of the blank, and is convenient for preparing a large-sized refractory high-entropy alloy.

[0020] Other features and advantages of the present application will be described in the following description, and partly become apparent from the description, or understood by practicing the present application. The purpose and other advantages of the present application can be realized and obtained by the structures particularly pointed out in the written description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a temperature and time relationship diagram during sintering in a method for preparing a large-size ultrafine-grained refractory high-entropy alloy provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure is clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] It should be understood that, under the premise of no conflict, any and all embodiments of the present invention can be combined with the technical features in any other embodiment or multiple other embodiments to obtain another embodiment. The present invention includes such a combination to obtain another embodiment.

[0024] Unless otherwise specified, all technical and scientific terms used herein have the standard meaning in the field to which the claimed subject matter belongs. If there are multiple definitions for a term, the definition herein shall prevail.

[0025] The present application is used to solve the problem that the commonly used preparation methods can only prepare small-volume samples, and the refractory high-entropy alloy has poor room temperature plasticity and high-temperature softening. The present invention innovates in the process route and control mechanism, and uses multi-step sintering at different temperatures and the method of introducing amorphous grain boundaries to prepare large-sized ultrafine-grained refractory high-entropy alloys with excellent mechanical properties. The specific large-sized ultrafine-grained refractory high-entropy alloy preparation method provided includes the following steps: S1: Mixing single substance powder of refractory elements and single substance powder of strongly segregated elements to obtain mixed powder.

[0026] S2: Pressing the mixed powder into a shape to obtain a blank.

[0027] S3: heating the blank to a first temperature and keeping it for a first time, then cooling it to a second temperature and keeping it for a second time, then heating it to a third temperature and keeping it for a third time, and finally quenching it to obtain a large-sized ultrafine-grained refractory high-entropy alloy.

[0028] Among them, the refractory elements are selected from at least four of Zr, Nb, Mo, Hf, Ta, and W, and the strong segregation elements are selected from at least one of B, Ni, and Ti.

[0029] The temperature variation curve in step S3 is as follows: Figure 1 As shown, the third temperature T3>the second temperature T2, the first temperature T1>the second temperature T2, the second time>the first time, and the second time>the third time.

[0030] This method first performs short-term heating at a relatively high temperature T1, even without insulation, to obtain a density of 60% to 90%; then, a long-term insulation treatment is performed at a relatively low temperature T2 to further densify the blank while preventing grain growth; finally, a short-term high-temperature (T3) sintering is performed followed by rapid cooling to form amorphous grain boundaries while preventing grain growth, thereby reducing grain boundary energy, thereby limiting grain growth and improving the high-temperature stability of the material.

[0031] The first temperature is 1000°C to 1700°C, the second temperature is 800°C to 1400°C, and the third temperature is 1000°C to 1800°C. The embodiment of the present application can effectively control the density change and crystal growth behavior change of the material at different stages by specifically setting the range of the first temperature, the second temperature, and the third temperature, thereby ensuring that the final product has an ultrafine grain microstructure with amorphous grain boundaries, and the final product has excellent physical properties. Accurately controlling the temperature parameters can effectively improve the overall performance of the alloy, especially the stability and strength in high temperature environments.

[0032] On the basis of the above temperature control, the first time is 0h~4h, the second time is 4h~40h, and the third time is 0h~2h. The main purpose of the first stage is to make the billet quickly obtain a higher density; in the second stage, the billet is gradually made denser under the condition of preventing grain growth; in the third stage, rapid sintering and rapid cooling are used to ensure the grain refinement and amorphous grain boundary formation of the alloy. Specifically, the rapid heating and heat preservation in the first stage help to quickly remove gas and impurities in the billet and increase density. Rapid sintering and cooling in the later stage can effectively control the grain size and form fine grains and uniform amorphous grain boundary structure.

[0033] Combining the above temperature control and time control is conducive to ensuring that the alloy has excellent mechanical properties and high temperature stability. The optimization of temperature and holding time of multi-step sintering can effectively achieve the densification of the billet, inhibit grain growth and form amorphous grain boundaries. This sintering process combined with the introduction of strong segregation elements significantly improves the high temperature stability of the material and the mechanical properties of the ultrafine grain structure.

[0034] In the single-substance powders of multiple refractory elements, the atomic ratio between dissimilar elements is 1:1, ensuring the formation of high-entropy alloys. The application of this ratio can stabilize the performance of refractory high-entropy alloys and thus meet the service requirements of high-temperature alloy materials in extreme environments.

[0035] Boron, nickel, and titanium have a segregation effect during sintering, and the specific sintering process of this application helps to form small and evenly distributed grains, thereby improving the overall performance of the alloy. Preferably, in terms of the amount of substance, the single substance powder of the strong segregation element accounts for 1% to 25% of the mixed powder, which can effectively improve the strength of the refractory high entropy alloy in the high temperature range and reduce the brittleness problem at room temperature, thereby improving the comprehensive performance and practical application value of the refractory high entropy alloy.

[0036] Specifically, in step S1, the mixed powder is subjected to high-energy ball milling and then pressed into shape. High-energy ball milling allows the powder particles to be fully mixed under mechanical action, so that the mixed powder is pre-alloyed, which is conducive to subsequent pressing and sintering to obtain high-performance large-size ultrafine-grained refractory high-entropy alloys.

[0037] High-energy ball milling subjects the powder to strong mechanical forces during the ball milling process, causing the powder particles to continuously break and recombine, thereby achieving sufficient mixing, thereby pre-alloying the mixed powder, so that the subsequent pressing and sintering processes can obtain large-sized ultrafine-grained refractory high-entropy alloys with excellent performance, thereby improving the performance and quality of the final prepared high-entropy alloy.

[0038] Preferably, the ball milling speed is 300 rpm to 600 rpm, the ball-to-material ratio is 2:1 to 32:1, and the ball milling time is 5 h to 50 h, which can effectively improve the mixing uniformity and refinement effect of the powder, thereby facilitating the pre-alloying of the powder. Reasonable ball milling parameters can ensure the refinement of the mixed powder and make the pressed blank relatively uniform.

[0039] In step S2, the pressing method can be cold isostatic pressing, hot isostatic pressing or molding. High-energy ball milling can significantly improve the mixing uniformity and pre-alloying effect of the powder, so that the blank has better density and molding quality during the molding process. Combined with the pressing molding process, the microstructure of the blank can be further optimized, providing ideal initial conditions for subsequent sintering, and ultimately significantly improving the mechanical properties of the material.

[0040] Preferably, the pressing pressure in the pressing molding is 100MPa~500MPa. The optimized ball milling parameters ensure the refinement and uniformity of the powder, while the reasonable pressing pressure provides sufficient billet density. The above preferred ball milling parameters and preferred pressing parameters are used to promote densification in the subsequent sintering, so that the crystals achieve the expected changes and improve the room temperature plasticity and high temperature stability of the material.

[0041] Example 1 Niobium (Nb), molybdenum (Mo), tantalum (Ta), tungsten (W), titanium (Ti), and nickel (Ni) were mixed in an atomic ratio of 18.8:18.8:18.8:18.8:18.8:6, and were weighed and mixed and pre-alloyed using a high-energy ball mill. To avoid the introduction of impurities, the ball mill and the grinding balls were made of tungsten carbide. The ball mill speed was 500rpm, the ball-to-material ratio was 16:1, and the ball milling time was 30h. The mixed powder after ball milling was cold isostatically pressed under a pressure of 400MPa to form a blank. The blank was then placed in a vacuum sintering furnace for multi-step sintering. The first stage sintering temperature was 1300℃, and the holding time was 1h; the second stage sintering temperature was 1100℃, and the holding time was 10h; the third stage sintering temperature was 1500℃, and the holding time was 0.5h, and then it was taken out and placed in water for rapid cooling. The average grain size of the prepared refractory high entropy alloy sample is 65 nm, the room temperature yield strength is 2534 MPa, and the yield strength at 1200℃ is 764 MPa.

[0042] Example 2 Niobium (Nb), molybdenum (Mo), tantalum (Ta), tungsten (W), titanium (Ti), and nickel (Ni) were mixed in an atomic ratio of 22:22:22:22:6:6, and were weighed and mixed and pre-alloyed using a high-energy ball mill. To avoid the introduction of impurities, the ball mill and the grinding balls were made of tungsten carbide. The ball mill speed was 500rpm, the ball-to-material ratio was 16:1, and the ball milling time was 30h. The mixed powder after ball milling was cold isostatically pressed under a pressure of 400MPa to form a blank. The blank was then placed in a vacuum sintering furnace for multi-step sintering. The first stage sintering temperature was 1300℃, and the holding time was 1h; the second stage sintering temperature was 1100℃, and the holding time was 10h; the third stage sintering temperature was 1500℃, and the holding time was 0.5h, and then it was taken out and placed in water for rapid cooling. The average grain size of the prepared refractory high-entropy alloy sample is 53 nm, the room temperature yield strength is 2673 MPa, and the yield strength at 1200℃ is 851 MPa.

[0043] Example 3 Niobium (Nb), molybdenum (Mo), tantalum (Ta), tungsten (W), titanium (Ti), and boron (B) were mixed in an atomic ratio of 23:23:23:23:7.8:0.2, and were weighed and mixed and pre-alloyed using a high-energy ball mill. To avoid the introduction of impurities, the ball mill and the grinding balls were made of tungsten carbide. The ball mill speed was 500rpm, the ball-to-material ratio was 16:1, and the ball milling time was 30h. The pre-alloyed powder after ball milling was cold isostatically pressed under a pressure of 400MPa to form a blank. The blank was then placed in a vacuum sintering furnace for multi-step sintering. The first stage sintering temperature was 1300℃, and the holding time was 1h; the second stage sintering temperature was 1100℃, and the holding time was 10h; the third stage sintering temperature was 1500℃, and the holding time was 0.5h, and then it was taken out and placed in water for rapid cooling. The average grain size of the prepared refractory high-entropy alloy sample is 42 nm, the room temperature yield strength is 2810 MPa, and the yield strength at 1200℃ is 982 MPa.

[0044] Comparative Example 1 Niobium (Nb), molybdenum (Mo), tantalum (Ta), tungsten (W), titanium (Ti), and nickel (Ni) were mixed in an atomic ratio of 22:22:22:22:6:6, and the samples were prepared in a vacuum arc melting furnace after being weighed separately. The melting was repeated 5 times to ensure the uniform composition of the ingot. The average grain size of the prepared refractory high entropy alloy sample was 127 μm, the yield strength at room temperature was 1573 MPa, and the yield strength at 1200°C was 579 MPa.

[0045] Comparative Example 2 Niobium (Nb), molybdenum (Mo), tantalum (Ta), tungsten (W), titanium (Ti), and boron (B) were mixed in an atomic ratio of 23:23:23:23:7.8:0.2, and were weighed separately and mixed and pre-alloyed using a high-energy ball mill. To avoid the introduction of impurities, the ball mill and the grinding balls were made of tungsten carbide. The ball milling speed was 500rpm, the ball-to-material ratio was 16:1, and the ball milling time was 30h. The pre-alloyed powder after ball milling was cold isostatically pressed under a pressure of 400MPa to form a billet. The billet was then placed in a vacuum sintering furnace for multi-step sintering. The first stage sintering temperature was 1300℃, and the holding time was 1h; the second stage sintering temperature was 1100℃, and the holding time was 10h; finally, it was naturally cooled to room temperature. The average grain size of the prepared refractory high-entropy alloy sample was 38 nm, the room temperature yield strength was 2833 MPa, and the yield strength at 1200℃ was 711 MPa.

[0046] Comparison between Comparative Example 2 and Example 3 shows that Comparative Example 2 has low high temperature yield strength due to the lack of formation of amorphous grain boundaries.

[0047] Comparative Example 3 Niobium (Nb), molybdenum (Mo), tantalum (Ta), tungsten (W), titanium (Ti), and boron (B) were mixed in an atomic ratio of 23:23:23:23:7.8:0.2, and were weighed and mixed and pre-alloyed using a high-energy ball mill. To avoid the introduction of impurities, the ball mill and the grinding balls were made of tungsten carbide. The ball mill speed was 500rpm, the ball-to-material ratio was 16:1, and the ball milling time was 30h. The pre-alloyed powder after ball milling was cold isostatically pressed under a pressure of 400MPa to form a blank. The blank was then placed in a vacuum sintering furnace for multi-step sintering. The first stage sintering temperature was 1300℃, and the holding time was 1h; the second stage sintering temperature was 1100℃, and the holding time was 10h; the third stage sintering temperature was 1000℃, and the holding time was 0.5h, and then it was taken out and placed in water for rapid cooling. The average grain size of the prepared refractory high-entropy alloy is 40 nm, the room temperature yield strength is 2817 MPa, and the yield strength at 1200°C is 705 MPa.

[0048] Comparison between Comparative Example 3 and Example 3 shows that no amorphous grain boundaries are formed in Comparative Example 3 either, resulting in low high temperature yield strength.

[0049] The embodiments of the present application utilize multi-step sintering at different temperatures to prepare a refractory high entropy alloy with an ultrafine grain structure, which has good room temperature plasticity and strength. At the same time, amorphous grain boundaries are introduced by doping strong grain boundary segregation elements combined with the regulation of preparation process parameters to ensure the high temperature stability of the ultrafine grain structure, thereby achieving the preparation of large-size ultrafine-grained refractory high entropy alloys with excellent room temperature and high temperature mechanical properties.

[0050] In the description of this specification, the description with reference to the terms "one embodiment", "certain embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0051] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a large-size ultrafine-grained refractory high-entropy alloy, characterized in that: The following steps are involved: Mixing a single substance powder of a refractory element and a single substance powder of a strongly segregated element to obtain a mixed powder; Pressing the mixed powder into a shape to obtain a blank; The blank is heated to a first temperature and kept for a first time, then cooled to a second temperature and kept for a second time, then heated to a third temperature and kept for a third time, and finally quenched to obtain the large-sized ultrafine-grained refractory high-entropy alloy; The refractory elements are selected from at least four of zirconium, niobium, molybdenum, hafnium, tantalum and tungsten, and the strong segregation elements are selected from at least one of boron, nickel and titanium; the second time is longer than the first time, and the second time is longer than the third time.

2. The method for preparing a large-size ultrafine-grained refractory high-entropy alloy according to claim 1, characterized in that: The first temperature is 1000°C to 1700°C, the second temperature is 800°C to 1400°C, and the third temperature is 1000°C to 1800°C.

3. The method for preparing a large-size ultrafine-grained refractory high-entropy alloy according to claim 2, characterized in that: The first time is 0h~4h, the second time is 4h~40h, and the third time is 0h~2h.

4. The method for preparing a large-size ultrafine-grained refractory high-entropy alloy according to claim 1, characterized in that: Calculated by the amount of substance, the single substance powder of the strong segregation element accounts for 1% to 25% of the mixed powder.

5. The method for preparing a large-size ultrafine-grained refractory high-entropy alloy according to claim 1, characterized in that: In the single substance powder of multiple refractory elements, the atomic ratio between different elements is 1:

1.

6. The method for preparing a large-size ultrafine-grained refractory high-entropy alloy according to claim 1, characterized in that: The compression molding method is cold isostatic pressing, hot isostatic pressing or molding.

7. The method for preparing a large-size ultrafine-grained refractory high-entropy alloy according to claim 1, characterized in that: The pressing pressure in the pressing molding is 100 MPa to 500 MPa.

8. The method for preparing a large-size ultrafine-grained refractory high-entropy alloy according to claim 1, characterized in that: The mixed powder is subjected to high-energy ball milling.

9. The method for preparing a large-size ultrafine-grained refractory high-entropy alloy according to claim 8, characterized in that: In the high-energy ball milling, the ball milling speed is 300 rpm to 600 rpm, the ball-to-material ratio is 2:1 to 32:1, and the ball milling time is 5 h to 50 h.

10. A large-sized ultrafine-grained refractory high-entropy alloy, characterized in that: The large-sized ultrafine-grained refractory high-entropy alloy is prepared by the method for preparing the large-sized ultrafine-grained refractory high-entropy alloy according to any one of claims 1 to 9.

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