High-strength TaMoNbCrTi x Refractory high-entropy alloy and method of making same

Abstract

The application belongs to the technical field of high-entropy alloys, and discloses a high-strength TaMoNbCrTi x The application discloses a refractory high-entropy alloy and a preparation method thereof. x The refractory high-entropy alloy (0.25<=x<=1) is composed of a BCC matrix phase and two kinds of precipitated phases, has a uniform structure, small grains, a room-temperature compression yield strength of 2410-3229 MPa, a compression strength of 2686-3253 MPa, a strain amount of 11.2%-16.8% at the time of fracture, and a hardness of 662-792 HV. The application further discloses a preparation method of the refractory high-entropy alloy, which combines mechanical alloying and spark plasma sintering, is flexible in composition control, can realize rapid forming of the alloy at a low sintering temperature (<=1200 DEG C), and effectively solves the problems of coarse structure and poor room-temperature mechanical properties of the alloy prepared by traditional arc melting.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of high-entropy alloys, and particularly relates to a high-strength TaMoNbCrTi x A refractory high-entropy alloy and a preparation method thereof. BACKGROUND

[0002] With the rapid development of high-end equipment manufacturing industry such as aerospace, more stringent requirements are put forward for high-temperature structural materials. Due to the limitation of melting point, it is difficult to meet the increasingly harsh high-temperature working conditions by adjusting the composition of traditional materials, so it is necessary to develop high-temperature alloys with higher performance. The emergence of high-entropy alloys provides a new exploration direction for the research and development of new high-temperature materials. Unlike the traditional alloy design idea of taking one element as the main element, high-entropy alloys take multiple elements as the main elements, form a microstructure mainly composed of single-phase solid solutions by means of unique high-entropy effect, and show a series of excellent properties such as high strength, high hardness and high wear resistance. Among them, the refractory high-entropy alloy taking refractory metal elements as the main elements is considered to be a strong candidate material for application in high-temperature extreme environment due to its excellent high-temperature mechanical properties. However, due to the poor room temperature ductility which greatly limits the cold processability of the alloy, combined with the characteristics of most refractory metal elements with large density, the practical engineering application of the refractory high-entropy alloy is hindered. Therefore, it is of great scientific and practical significance to design a refractory high-entropy alloy with good comprehensive mechanical properties and a preparation method thereof.

[0003] Microstructure and composition adjustment are two ways to solve the above problems of refractory high-entropy alloys. So far, due to the high melting point and large difference of melting point of the components, the preparation method of bulk refractory high-entropy alloy is mainly vacuum arc melting. However, in order to ensure the uniformity of the organization, the multiple turnover remelting makes the process cumbersome, the power consumption is large, and the composition segregation, coarse dendrite and other solidification defects often worsen the mechanical properties of the alloy. In recent years, domestic and foreign scholars have begun to use powder metallurgy to prepare refractory high-entropy alloys. Powder metallurgy includes two steps of mechanical alloying and solid phase sintering: mechanical alloying method can avoid the difference of physical properties of each main element, effectively promote the alloying of refractory elements, and obtain uniform alloy powder; and the discharge plasma sintering has the advantages of high heating rate, short holding time, small sintered material grain, and energy saving and environmental protection. Therefore, the preparation process of refractory high-entropy alloy combined with mechanical alloying and discharge plasma sintering can not only realize the free regulation of alloy composition and rapid short-time sintering of alloy, but also has the advantages of uniform composition, fine structure and excellent performance. In addition, adjusting the composition of the elements can effectively improve the room temperature plasticity of the refractory high-entropy alloy. The addition of Ti element not only helps to improve the plasticity of the alloy, but also can reduce the density of the alloy. Therefore, selecting appropriate composition and forming process to improve the microstructure and performance of the alloy is very important for the research and application of refractory high-entropy alloy. SUMMARY

[0004] In order to overcome the defects of the prior art, the present application selects appropriate alloy element types and relative contents, combines mechanical alloying process and discharge plasma sintering technology, and prepares a high-strength TaMoNbCrTi x (0.25≤x≤1) refractory high-entropy alloy, which effectively solves the problems of complex preparation process, coarse grain and poor room temperature mechanical properties of existing refractory high-entropy alloy.

[0005] The object of the present application is achieved by the following scheme:

[0006] A high-strength TaMoNbCrTi x The preparation method of the refractory high-entropy alloy uses Ta, Mo, Nb, Cr and Ti five kinds of metal powder as raw materials, first carries out mechanical alloying by high-energy ball milling to obtain refractory high-entropy alloy powder with single BCC structure, and then uses discharge plasma sintering technology to prepare refractory high-entropy alloy bulk.

[0007] A high-strength TaMoNbCrTi x Refractory high-entropy alloy and preparation method thereof, specifically comprising the following steps and process conditions:

[0008] Step one: preparing TaMoNbCrTi xRefractory high-entropy alloy powder;

[0009] The five metal powders of Ta, Mo, Nb, Cr and Ti are weighed according to the proportion, and then are put into a stainless steel ball mill tank and stainless steel grinding balls, wherein the molar ratio of Ta, Mo, Nb, Cr and Ti is 1:1:1:1:(0.25-1), no process control agent is added, the weight ratio of ball to material is 5:1-15:1, the process of vacuum extraction and argon filling is repeated three times to ensure that the residual air in the tank reaches a low level, the ball milling speed is 250-350 rpm, the ball milling time is 10-70 h, and the machine is stopped for 10 min every 30 min, thereby obtaining alloy powder with single BCC solid solution structure; the alloy powder is placed in a vacuum drying box, vacuum extraction is performed to 0.1 kPa, constant temperature drying is performed at 50-80 DEG C for 10-20 h, and then cooling to room temperature, thereby obtaining dry powder for subsequent sintering.

[0010] Step two: preparing TaMoNbCrTi by using a spark plasma sintering technology x Refractory high-entropy alloy bulk.

[0011] The alloy powder obtained in step one is placed in a graphite mold for sintering under vacuum. The sintering adopts direct current pulse current, the on-off ratio of the pulse current is 12:2, the heating rate is 50-150 DEG C / min, the sintering temperature is 1000-1200 DEG C, the sintering pressure is 20-40 MPa, the holding time is 5-15 min, the pressure is removed after sintering is completed, and the furnace is cooled to room temperature, thereby obtaining a refractory high-entropy alloy bulk.

[0012] A TaMoNbCrTi x The refractory high-entropy alloy is composed of an equiaxed crystal matrix phase and a precipitate phase, the matrix phase is a BCC structure, the average grain size is between 0.32-0.51 mu m, the precipitate phase is a Laves phase rich in Cr, Ta and Nb and an FCC phase rich in Ti, O and N, and the average size is between 0.23-0.75 mu m and 0.21-0.76 mu m, respectively.

[0013] A TaMoNbCrTi x The refractory high-entropy alloy has a compression yield strength of 2410-3229 MPa, a compression strength of 2686-3253 MPa, a strain of 11.2%-16.8% at the time of fracture, and a Vickers hardness of 662-792 HV at room temperature.

[0014] The beneficial effects of the present application are that:

[0015] (1) The present application proposes a new TaMoNbCrTi x(0.25≤x≤1) refractory high-entropy alloy and a preparation method thereof. The alloy is composed of a BCC structure matrix phase, a Cr, Ta and Nb-rich Laves phase and a Ti, O and N-rich FCC phase, and the BCC matrix phase has extremely fine grains (0.32-0.51 μm). Compared with a refractory high-entropy alloy prepared by a traditional arc melting method, the preparation method in combination with the unique microstructure makes the TaMoNbCrTi x The refractory high-entropy alloy has high strength and high hardness at room temperature and certain plasticity.

[0016] (2) The present application adopts a preparation method combining mechanical alloying and spark plasma sintering technology. On the one hand, for metal elements with extremely high melting points, it is not necessary to heat to the melting point temperature (> 1600 ℃), and only one-time short-time solid-phase sintering (sintering temperature ≤ 1200 ℃) can obtain a bulk material with good performance, which is energy-saving and environment-friendly, and the composition can be flexibly and conveniently adjusted.

[0017] 3) The TaMoNbCrTi 0.75 The refractory high-entropy alloy has obvious fine-grain strengthening effect, and has a compression yield strength of 24696 MPa, a compression strength of 3098 MPa, a strain at break of 16.8% and a microhardness of 662 HV at room temperature. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The TaMoNbCrTi x (x = 0.25, 0.5, 0.75, 1) refractory high-entropy alloy X-ray diffraction pattern;

[0019] Figure 2 The TaMoNbCrTi 0.75 SEM diagram of the refractory high-entropy alloy powder;

[0020] Figure 3 The TaMoNbCrTi 0.75 Backscattered electron diagram of the refractory high-entropy alloy. DETAILED DESCRIPTION

[0021] The present application will be further described in detail by the following examples. It should be noted that the following description is an explanation of the present application rather than a limitation.

[0022] Example 1

[0023] The present embodiment is a TaMoNbCrTi 0.25 The preparation method of the refractory high-entropy alloy is carried out according to the following steps:

[0024] Step 1: Preparation of TaMoNbCrTi using mechanical alloying method 0.25 Refractory high-entropy alloy powder;

[0025] Weigh out 41.71g of Ta powder (particle size <48μm, purity >99.9%), 22.12g of Mo powder (particle size <48μm, purity >99.9%), 21.42g of Nb powder (particle size <48μm, purity >99.9%), 11.99g of Cr powder (particle size <75μm, purity >99.95%), and 2.76g of Ti powder (particle size <75μm, purity >99.95%), and mix them thoroughly. Add 100g of the mixed powder and 1000g of stainless steel grinding balls to the grinding jar of a planetary high-energy ball mill for ball milling. Evacuate the grinding jar and fill it with high-purity argon (99.99%) as a protective atmosphere; repeat this process 3-4 times. The alloy powder with a single-phase BCC structure was obtained by ball milling at 350 rpm for 50 hours, with a 10-minute rest period after every 30 minutes of operation. The alloy powder was placed in a vacuum drying oven, evacuated to 0.1 kPa, and dried at a constant temperature of 60°C for 10 hours, followed by cooling to room temperature. The dried powder was then passed through a 200-mesh sieve for subsequent spark plasma sintering.

[0026] Step 2: Prepare TaMoNbCrTi using spark plasma sintering technology 0.25 Refractory high-entropy alloy bulk.

[0027] Weigh 25g of alloy powder and load it into the inner diameter. outer diameter A cylindrical graphite mold, 45 mm high, was used. To facilitate demolding after sintering, a 0.2 mm thick graphite foil was placed between the powder and the inner wall of the mold, as well as between the pressure head and the mold. The powder was loaded into the mold and compacted after filling, ensuring that the lengths of the upper and lower pressure heads protruding from the mold were equal. The mold was wrapped with a 10 mm thick graphite felt to reduce radiative heat loss and maintain a constant mold temperature. The assembled graphite mold was placed in the furnace cavity and evacuated. The temperature was increased to 1200°C at a rate of 100°C, and then a pressure of 40 MPa was applied. The temperature was held at 1200°C for 10 minutes. After sintering, the pressure was released, and the mold was cooled to room temperature in the furnace to obtain the alloy block. Throughout the sintering process, an infrared thermometer was used to focus on the temperature measuring hole of the mold to measure the temperature of the inner wall of the mold.

[0028] like Figure 1 The XRD pattern shows that the TaMoNbCrTi obtained after sintering 0.25The refractory high-entropy alloy bulk material is composed of BCC phase, Laves phase and FCC phase. The BCC phase is a matrix phase, the grain of which is equiaxed, and the average grain size is 0.32 μm; the Laves phase is rich in Cr, Ta and Nb, and the average size is 0.23 μm; the FCC phase is rich in Ti, O and N, and the average size is 0.21 μm. The TaMoNbCrTi 0.25 The microhardness of the refractory high-entropy alloy is 792 HV, and the compression yield strength of the alloy is 3229 MPa, the maximum compression strength is 3253 MPa, and the strain at fracture is 11.8% through the room temperature compression test.

[0029] Example 2

[0030] The TaMoNbCrTi 0.5 The preparation method of the refractory high-entropy alloy is carried out in the following steps:

[0031] Step one: the TaMoNbCrTi 0.5 Refractory high-entropy alloy powder;

[0032] 40.59 g of Ta powder (particle size < 48 μm, purity > 99.9%), 21.52 g of Mo powder (particle size < 48 μm, purity > 99.9%), 20.85 g of Nb powder (particle size < 48 μm, purity > 99.9%), 11.67 g of Cr powder (particle size < 75 μm, purity > 99.95%) and 5.37 g of Ti powder (particle size < 75 μm, purity > 99.95%) are weighed and uniformly mixed. 100 g of mixed powder and 1000 g of stainless steel grinding balls are added to the ball milling tank of the planetary high-energy ball mill for ball milling. The ball milling tank is vacuumed and filled with high-purity argon gas (99.99%) as a protective atmosphere, and this process is repeated 3-4 times. Ball milling is carried out at a speed of 350 rpm for 50 h, with a 10 min rest every 30 min of operation, to obtain alloy powder with single-phase BCC structure. The alloy powder is placed in a vacuum drying box, vacuumed to 0.1 kPa, dried at a constant temperature of 70°C for 10 h, and then cooled to room temperature. The dried powder is sieved through a 200 mesh sieve and used for subsequent spark plasma sintering.

[0033] Step two: the TaMoNbCrTi 0.5 Refractory high-entropy alloy bulk.

[0034] 25 g of alloy powder is weighed and placed in an inner diameter outer diameter A cylindrical graphite mold with a height of 45 mm. To facilitate demolding after sintering, a graphite foil with a thickness of 0.2 mm is placed between the powder and the inner wall of the mold and the pressure head. The powder is loaded into the mold, and after the loading is completed, the powder is compacted, and during this process, the length of the upper and lower pressure heads exposed to the mold is ensured to be equal. The mold is wrapped with a graphite felt with a thickness of 10 mm to reduce radiation heat dissipation and maintain the temperature of the mold constant. The assembled graphite mold is placed in the furnace cavity and vacuumized, and after being heated to 1200℃ at a rate of 100℃, a pressure of 40 MPa is applied, and the temperature is maintained at 1200℃ for 10 min. After sintering is completed, the pressure is removed, and the furnace is cooled to room temperature to obtain an alloy block. During the entire sintering process, an infrared temperature detector is used to measure the temperature of the mold through the temperature measuring hole.

[0035] As shown in the XRD pattern of Figure 1 TaMoNbCrTi 0.5 The refractory high-entropy alloy bulk material is composed of a BCC phase, a Laves phase and an FCC phase. The BCC phase is the matrix phase, the grain is equiaxed, and the average grain size is 0.40 μm; the Laves phase is rich in Cr, Ta and Nb, and the average size is 0.58 μm; the FCC phase is rich in Ti, O and N, and the average size is 0.40 μm. The TaMoNbCrTi 0.5 The microhardness of the refractory high-entropy alloy is 733 HV, and the compression yield strength of the alloy is 2820 MPa, the maximum compression strength is 3020 MPa, and the strain at fracture is 13.3% through room temperature compression test.

[0036] Example 3

[0037] The TaMoNbCrTi 0.75 The preparation method of the refractory high-entropy alloy is as follows:

[0038] Step one: the TaMoNbCrTi 0.75 refractory high-entropy alloy powder is prepared by a mechanical alloying method;

[0039] Take 39.53 g of Ta powder (particle size < 48 μm, purity > 99.9%), 20.96 g of Mo powder (particle size < 48 μm, purity > 99.9%), 20.30 g of Nb powder (particle size < 48 μm, purity > 99.9%), 11.36 g of Cr powder (particle size < 75 μm, purity > 99.95%) and 7.85 g of Ti powder (particle size < 75 μm, purity > 99.95%) and mix uniformly. 100 g of mixed powder and 1000 g of stainless steel grinding balls are added to the ball mill pot of the planetary high-energy ball mill for ball milling. The ball mill pot is evacuated and filled with high-purity argon (99.99%) as a protective atmosphere, which is repeated 3-4 times. Ball mill at a speed of 350 rpm for 50 h, stop every 30 min for 10 min rest, get alloy powder with single-phase BCC structure. As shown in the SEM image of Figure 2 , the powder particle size is uniform and small, the average particle size is 7.6 μm. Due to the size too small, the surface energy is too high, the powder appears a certain degree of agglomeration. The alloy powder is placed in a vacuum drying box, vacuumed to 0.1 kPa, dried at 60 ℃ for 20 h and then cooled to room temperature, the dried powder is sieved through 200 mesh sieve for subsequent spark plasma sintering.

[0040] Step two: TaMoNbCrTi 0.75 refractory high-entropy alloy bulk is prepared by spark plasma sintering technology.

[0041] Take 25 g of alloy powder and put it into a cylindrical graphite mold with an inner diameter of and an outer diameter of high 45 mm. To facilitate demolding after sintering, a graphite foil with a thickness of 0.2 mm is placed between the powder and the inner wall of the mold and the pressure head. Fill the powder into the mold, compact the powder after filling, and ensure that the upper and lower pressure heads are equal in length during the process. Wrap the mold with a graphite felt with a thickness of 10 mm to reduce radiation heat loss and maintain the temperature of the mold constant. Put the assembled graphite mold into the furnace cavity, vacuumize, heat to 1200 ℃ at a rate of 100 ℃, and then apply a pressure of 40 MPa. Keep the temperature at 1200 ℃ for 10 min. After sintering, remove the pressure and cool to room temperature to get the alloy bulk. During the whole sintering process, an infrared thermometer is focused on the temperature measuring hole of the mold to measure the temperature of the inner wall of the mold.

[0042] As shown in the XRD pattern of Figure 1 , the TaMoNbCrTi 0.75 refractory high-entropy alloy bulk obtained after sintering is composed of BCC phase, Laves phase and FCC phase. As shown in the SEM image of Figure 3The backscattered electron image of the sintered alloy shows that three different phases can be clearly distinguished, the light phase corresponds to the BCC matrix phase, the gray phase and the black phase correspond to the Laves phase and the FCC phase, respectively. The BCC phase has equiaxed grains with an average grain size of 0.45 μm; the Laves phase is rich in Cr, Ta and Nb, and has an average size of 0.54 μm; the FCC phase is rich in Ti, O and N, and has an average size of 0.56 μm. The TaMoNbCrTi 0.75 The microhardness of the refractory high-entropy alloy is 693 HV, and the compressive yield strength of the alloy is 2696 MPa, the maximum compressive strength is 3098 MPa, and the strain at fracture is 16.8% as tested by the room temperature compression test.

[0043] Example 4

[0044] The present embodiment is a preparation method of a TaMoNbCrTi refractory high-entropy alloy, which is carried out according to the following steps:

[0045] Step one: preparing a TaMoNbCrTi refractory high-entropy alloy powder by mechanical alloying method;

[0046] Take 38.52 g of Ta powder (particle size < 48 μm, purity > 99.9%), 20.43 g of Mo powder (particle size < 48 μm, purity > 99.9%), 19.78 g of Nb powder (particle size < 48 μm, purity > 99.9%), 11.07 g of Cr powder (particle size < 75 μm, purity > 99.95%) and 10.19 g of Ti powder (particle size < 75 μm, purity > 99.95%) and mix them evenly. Put 100 g of the mixed powder and 1000 g of stainless steel grinding balls into the ball milling tank of a planetary high-energy ball mill for ball milling. The ball milling tank is evacuated and filled with high-purity argon (99.99%) as a protective atmosphere, and this process is repeated 3-4 times. Ball mill at a speed of 350 rpm for 50 h, stop every 30 min and rest for 10 min, to obtain an alloy powder with a single-phase BCC structure. Place the alloy powder in a vacuum drying box, evacuate to 0.1 kPa, dry at a constant temperature of 60°C for 20 h, and then cool to room temperature. Screen the dried powder through a 200-mesh sieve for subsequent spark plasma sintering.

[0047] Step two: preparing a TaMoNbCrTi refractory high-entropy alloy block by spark plasma sintering technology.

[0048] Take 25 g of the alloy powder and put it into a graphite die with an inner diameter of 20 mm and an outer diameter of 25 mm. outer diameter The powder was loaded into the mold, and after the loading was completed, the powder was compacted, and during the process, the length of the upper and lower punches exposed from the mold was ensured to be equal. The mold was wrapped with a graphite felt with a thickness of 10 mm to reduce radiation heat dissipation and maintain the mold temperature constant. The assembled graphite mold was placed in the furnace cavity and vacuumized, and after being heated to 1200 DEG C at a rate of 100 DEG C, a pressure of 40 MPa was applied, and the temperature was maintained at 1200 DEG C for 10 min. After sintering was completed, the pressure was removed, and the furnace was cooled to room temperature to obtain an alloy block. During the entire sintering process, an infrared temperature detector was used to focus on the temperature measuring hole of the mold to measure the temperature of the inner wall of the mold.

[0049] As shown in the XRD pattern of Figure 1 The sintered TaMoNbCrTi refractory high-entropy alloy block material obtained after sintering is composed of a BCC phase, a Laves phase and an FCC phase. The BCC phase is the matrix phase, the grain is equiaxed, and the average grain size is 0.40 μm; the Laves phase is rich in Cr, Ta and Nb, and the average size is 0.58 μm; the FCC phase is rich in Ti, O and N, and the average size is 0.40 μm. The microhardness of the TaMoNbCrTi refractory high-entropy alloy prepared in this embodiment is 662 HV, the compression yield strength of the alloy is 2410 MPa, the maximum compression strength is 2686 MPa, and the strain at fracture is 11.2%.

[0050] The above is only the preferred exemplary embodiment of the present application, but the embodiments of the present application are not limited to the above-described embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. A method for preparing a high-strength TaMoNbCrTi_x refractory high-entropy alloy, characterized in that: In the high-strength TaMoNbCrTi_x refractory high-entropy alloy, 0.25≤x≤1, where x is the relative atomic ratio of Ti; the preparation method includes the following steps: (1) preparing TaMoNbCrTi_x refractory high-entropy alloy powder by mechanical alloying: mixing five elemental powders of Ta, Mo, Nb, Cr and Ti in a molar ratio of Ta, Mo, Nb, Cr and Ti of 1:1:1:1:(0.25~1) and then performing high-energy ball milling without adding any process control agent, using argon as the protective atmosphere, with a ball-to-material weight ratio of 5:1~15:1, a ball milling speed of 250~350rpm, a ball milling time of 10~70h, and stopping for 10 minutes after every 30 minutes of ball milling. (1) Obtain alloy powder with single-phase BCC structure; (2) Prepare TaMoNbCrTi_x refractory high-entropy alloy bulk using spark plasma sintering technology: The alloy powder obtained in step (1) is subjected to spark plasma sintering under vacuum conditions, using DC pulse current with a pulse current on / off ratio of 12:2; heating rate of 50~150 ℃ / min; sintering temperature of 1000~1200 ℃; sintering pressure of 20~40 MPa; holding time is 5~15min; pressure is removed after sintering and the furnace is cooled to room temperature; the TaMoNbCrTi_x refractory high entropy alloy prepared by the method has a microstructure composed of an equiaxed matrix phase and two irregular precipitate phases. The matrix phase has a BCC structure, and the precipitate phases are Laves phase enriched with Cr, Ta, and Nb and FCC phase enriched with Ti, O, and N; the average grain size of the matrix phase is between 0.32~0.51μm, and the average size of the precipitate phases is between 0.23~0.75μm and 0.21~0.76μm, respectively.

2. A refractory high-entropy alloy TaMoNbCrTi_x is prepared by the preparation method described in claim 1.

3. The TaMoNbCrTi_x refractory high-entropy alloy according to claim 2, characterized in that: The TaMoNbCrTi_x refractory high-entropy alloy has a compressive yield strength of 2410~3229 MPa, a compressive strength of 2686~3253 MPa at room temperature, a strain of 11.2%~16.8% at fracture, and a microhardness of 662~792 HV.

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