A double-stage aging heat treatment method of FCC / B2 dual-phase high-entropy alloy

Abstract

The application discloses a double-stage aging heat treatment method of an FCC / B2 dual-phase high-entropy alloy and belongs to the technical field of high-entropy alloys. The double-stage aging process combining high-temperature aging and low-temperature aging is developed to simultaneously optimize the precipitation phase characteristics in the FCC / B2 two-phase matrix, effectively improve the microstructure of the FCC / B2 dual-phase high-entropy alloy, realize effective regulation of the FCC / B2 dual-phase high-entropy alloy organization form, and significantly improve the room-temperature and high-temperature strength and plasticity of the alloy. The mechanical properties of the alloy in a wide temperature range are obviously improved, and good matching between the high strength and the high plasticity of the alloy is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-entropy alloys, and particularly relates to a two-stage aging heat treatment method of an FCC / B2 dual-phase high-entropy alloy. BACKGROUND

[0002] Since the concept of high-entropy alloys was proposed, the composition of high-entropy alloys composed of multiple main elements is located in the broad unknown region of the center of the multi-component phase diagram, which opens up a broad composition design space for metal structural materials and also broadens the diversity of alloy microstructures. Among them, the dual-phase high-entropy alloy containing face-centered cubic (FCC) and body-centered cubic (BCC) structures combines the advantages of strong work hardening ability of FCC structure and high yield strength of BCC structure, and has become one of the research hotspots in the field of high-entropy alloys. Recent studies have shown that the FCC / B2 (i.e., ordered BCC) dual-phase high-entropy alloy of the Ni-Co-Cr-Fe-Al system has considerable low-temperature and high-temperature mechanical properties, oxidation resistance and casting performance, and a higher Al content also endows it with the advantage of low density, and it is expected to become a new generation of structural material serving in a wide temperature range of extreme environment.

[0003] The good room temperature performance of the FCC / B2 dual-phase high-entropy alloy benefits from its in-situ composite structure composed of soft and hard phases, that is, the high strength is derived from the strengthening effect of the hard B2 phase, and the excellent deformation ability of the relatively soft FCC phase guarantees high plasticity. However, existing research results have shown that the softening rate of the B2 phase at high temperature is relatively fast, which makes the high-temperature strength of the FCC / B2 dual-phase high-entropy alloy relatively low. The microstructure often determines the final service performance of the alloy, and in view of the actual industrial application of the FCC / B2 dual-phase high-entropy alloy, researchers have begun to try to optimize the microstructure of the alloy in order to further improve its wide-temperature-range mechanical properties. Aging heat treatment is a necessary process for promoting the formation of precipitates in the FCC / B2 dual-phase high-entropy alloy, but the traditional single-stage aging only forms a single temperature corresponding to the characteristics of the precipitates in the structure, and its strengthening effect is usually limited and greatly loses the plasticity of the alloy; the type, size and morphology of the precipitates contained in the structure are not optimized, which limits the possibility of simultaneous improvement of the microstructure optimization and strength-plasticity of the alloy. SUMMARY

[0004] The application provides a two-stage aging heat treatment process for an FCC / B2 dual-phase high-entropy alloy, which can significantly improve the yield strength and fracture elongation of the FCC / B2 dual-phase high-entropy alloy at room temperature and high temperature.

[0005] To achieve the above-mentioned purpose, the following technical solutions are adopted in the application:

[0006] The application provides a two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy, which comprises the following steps:

[0007] Step 1, the FCC / B2 dual-phase high-entropy alloy material is placed in 1050-1250℃ for 1h-4h, and process material one is obtained after cooling;

[0008] Step 2, process material one is placed in 750-950℃ for 1h-4h, and process material two is obtained after cooling;

[0009] Step 3, process material two is placed in 550-750℃ for 2h-30h, and the FCC / B2 dual-phase high-entropy alloy is obtained after cooling.

[0010] The further improvement of the present application is that:

[0011] Preferably, in step 1, the holding temperature is 1200℃.

[0012] Preferably, in step 1, the holding time is 2h.

[0013] Preferably, in step 2, the holding temperature of process material one is 800℃.

[0014] Preferably, in step 2, the holding time of process material one is 2h.

[0015] Preferably, in step 3, the holding temperature of process material two is 650℃.

[0016] Preferably, in step 3, the holding time of process material two is 16h.

[0017] Preferably, the cooling mode in step 1, step 2 and step 3 is air cooling or water cooling.

[0018] Preferably, the yield strength of the FCC / B2 dual-phase high-entropy alloy at room temperature can reach 1178MPa, and the high-temperature yield strength at 650℃ can reach 1044MPa.

[0019] Preferably, the elongation of the FCC / B2 dual-phase high-entropy alloy at room temperature can reach 17.2%, and the high-temperature elongation at 650℃ can reach 28.2%.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The present application discloses a two-stage aging heat treatment method of FCC / B2 dual-phase high-entropy alloy, which realizes effective control of the FCC / B2 dual-phase high-entropy alloy organization form by developing a new heat treatment process, and significantly improves the room temperature and high-temperature strength and plasticity of the alloy. For such alloys, the traditional aging process is a single-stage aging process consisting of single temperature holding. The present application simultaneously optimizes the precipitation phase characteristics in the FCC / B2 two-phase matrix through the two-stage aging process combining high-temperature aging and low-temperature aging. For example, compared with Figure 1The precipitates of the dual-stage aging alloy are different from the precipitates of the single-stage aging alloy Figure 6 As can be seen from the characteristics of the precipitates of the single-stage aging alloy, the FCC phase in the dual-stage aging alloy has more coarse precipitates, and the precipitates in the B2 phase are coarse lath-shaped L12 phase; but the FCC phase in the traditional single-stage aging alloy has more fine and uniform precipitates, and the precipitates in the B2 phase are fine needle-shaped FCC phase. Therefore, compared with the traditional single-stage aging process, the types, sizes and morphology characteristics of the precipitates of the alloy obtained by the dual-stage process proposed by the application have obvious differences. Compared with the traditional single-stage aging process, the dual-stage aging process of the application can obtain precipitates formed at different temperature stages under multi-temperature stage holding, introduce high-density precipitates into the microstructure, be beneficial to enrich the phase composition of the FCC / B2 dual-phase high-entropy alloy, and the aging sequence of high temperature first and then low temperature is beneficial to the control of the characteristics of the precipitates, i.e. the optimization of the size and distribution characteristics of the phases in the microstructure, so that the room temperature and high temperature mechanical properties of the alloy can be significantly improved.

[0022] In terms of micro-deformation mechanism, due to the coarse but ductile precipitates in the B2 phase under the dual-stage aging process, the high strain accumulated on the B2 phase during the deformation of the alloy can be released, thereby delaying the cracking of the B2 phase and the failure of the alloy. Finally, the microstructure of the FCC / B2 dual-phase high-entropy alloy can be effectively improved, and the room temperature and high temperature mechanical properties of the alloy can be significantly improved, the mechanical properties in a wide temperature range are obviously improved, and a good match between high strength and high plasticity of the alloy is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a transmission electron microscope photo of the precipitates in the FCC and B2 phases under dual-stage aging, i.e. the microstructure of the FCC / B2 dual-phase high-entropy alloy of Example 1.

[0024] Figure 2 is the room temperature mechanical response of the alloy under dual-stage aging, i.e. the room temperature tensile stress-strain curve of the FCC / B2 dual-phase high-entropy alloy of Example 1.

[0025] Figure 3 is the 650℃ high temperature mechanical response of the alloy under dual-stage aging, i.e. the 650℃ high temperature tensile stress-strain curve of the FCC / B2 dual-phase high-entropy alloy of Example 1.

[0026] Figure 4 is the room temperature mechanical response of the alloy under dual-stage aging, i.e. the room temperature tensile stress-strain curve of the FCC / B2 dual-phase high-entropy alloy of Example 2.

[0027] Figure 5 is the 650℃ high temperature mechanical response of the alloy under dual-stage aging, i.e. the 650℃ high temperature tensile stress-strain curve of the FCC / B2 dual-phase high-entropy alloy of Example 2.

[0028] Figure 6 is a transmission electron microscope photo of precipitated phase in FCC and B2 two phases under single aging, that is, the microstructure of the comparative example 1 FCC / B2 dual-phase high-entropy alloy.

[0029] Figure 7 is the room temperature mechanical response of the alloy under single aging, that is, the room temperature tensile stress-strain curve of the comparative example 1 FCC / B2 dual-phase high-entropy alloy.

[0030] Figure 8 is the high temperature mechanical response of the alloy at 650 DEG C under single aging, that is, the high temperature tensile stress-strain curve of the comparative example 1 FCC / B2 dual-phase high-entropy alloy at 650 DEG C.

[0031] Figure 9 is the room temperature mechanical response of the alloy, that is, the room temperature tensile stress-strain curve of the comparative example 2 FCC / B2 dual-phase high-entropy alloy.

[0032] Figure 10 is the high temperature mechanical response of the alloy at 650 DEG C under single aging, that is, the high temperature tensile stress-strain curve of the comparative example 2 FCC / B2 dual-phase high-entropy alloy at 650 DEG C.

[0033] Figure 11 is a microstructure photo in B2 phase of the alloy deformed at 650 DEG C under two-stage aging.

[0034] Figure 12 is a microstructure photo in B2 phase of the alloy deformed at 650 DEG C under single-stage aging.

[0035] Figure 13 is the change trend of KAM value and LAM value in B2 phase of the alloy during the deformation of the alloy at 650 DEG C under single-stage aging and two-stage aging; wherein, (a) is the KAM value; (b) is the LAM value. DETAILED DESCRIPTION

[0036] The application will be further described in detail below with reference to the drawings:

[0037] The precipitated phase characteristics in the microstructure obtained by the traditional solid solution plus single-stage aging process are relatively single, so that the final comprehensive mechanical properties are often poor. In order to optimize the precipitated phase characteristics of the FCC / B2 dual-phase high-entropy alloy and obtain a microstructure with excellent strengthening and toughening effect, the application designs a two-stage aging process after solid solution for the FCC / B2 dual-phase high-entropy alloy, which specifically includes the following steps:

[0038] Step 1, place the FCC / B2 dual-phase high-entropy alloy plate in 1050 DEG C to 1250 DEG C for 1h to 4h, and then perform air cooling or water cooling to obtain the process material one; in this step, the elements in the alloy can be uniformly distributed at high temperature;

[0039] Step 2, the alloy obtained in step 1 is kept at high temperature 750-950℃ for 1-4h, and then air-cooled or water-cooled to obtain process material two, the purpose of this step is mainly to form the coarse L12 precipitates in FCC and the coarse lath-shaped L12 phase and spherical σ phase in B2 phase as shown in Figure 1

[0040] Step 3, the alloy obtained in step 2 is kept at 550-750℃ for 2-30h, and then air-cooled or water-cooled to avoid further growth and coarsening of the precipitates in the alloy structure.

[0041] Based on the above technical scheme, each step can also specifically adopt the following preferred mode or parameter.

[0042] As preferred, the alloy keeping time in step 1 is 1200℃.

[0043] As preferred, the alloy keeping time in step 1 is 2h.

[0044] As preferred, the alloy keeping temperature in step 2 is 800℃.

[0045] As preferred, the alloy keeping time in step 2 is 2h.

[0046] As preferred, the alloy keeping temperature in step 3 is 650℃.

[0047] As preferred, the alloy keeping time in step 3 is 16h.

[0048] The second aspect of the present application discloses an FCC / B2 dual-phase high-entropy alloy prepared by the above-mentioned two-stage aging heat treatment method, and the microstructure of the alloy is composed of FCC / B2 two phases.

[0049] The following will be further analyzed in combination with specific examples:

[0050] Example 1

[0051] The FCC / B2 dual-phase high-entropy alloy of this example is composed of Ni 44 Co 19 Cr 10 Fe 10 Al 15 Ti2(at.%), and the heat treatment steps are as follows:

[0052] (1) The FCC / B2 dual-phase high-entropy alloy plate is kept at 1200℃ for 2h, and then air-cooled;

[0053] (2) The alloy obtained in step (1) is kept at high temperature 800℃ for 2h, and then air-cooled;

[0054] ​(3) The alloy obtained in step (2) is kept at a low temperature of 650 °C for 16 h and air-cooled. The microstructure of the obtained alloy is shown in FIG. 3. A large number of L12 phases with a size of about 50 nm are formed in the FCC matrix, and a large number of σ phases are produced in the B2 matrix in addition to the lath-shaped L12 phases with a larger size. Figure 1 The yield strengths of the obtained alloys at room temperature and at 650 °C are shown in FIG. 2 and FIG. 3, respectively. The yield strengths are as high as 964 MPa and 862 MPa, respectively, while the elongations are maintained at 17.2% and 28.2%, respectively. As shown in FIG. 4, the coarse L12 phases in the microstructure can deform in a mode of shear through stacking faults under a high stress and a high strain state, which is beneficial to promote the continuous dislocation motion in the B2 phase, thereby relieving the stress concentration at the FCC / B2 phase boundary, finally delaying the fracture of the alloy and improving the high-temperature tensile plasticity of the alloy.

[0055] The yield strengths of the obtained alloys at room temperature and at 650 °C are shown in FIG. 2 and FIG. 3, respectively. The yield strengths are as high as 964 MPa and 862 MPa, respectively, while the elongations are maintained at 17.2% and 28.2%, respectively. As shown in FIG. 4, the coarse L12 phases in the microstructure can deform in a mode of shear through stacking faults under a high stress and a high strain state, which is beneficial to promote the continuous dislocation motion in the B2 phase, thereby relieving the stress concentration at the FCC / B2 phase boundary, finally delaying the fracture of the alloy and improving the high-temperature tensile plasticity of the alloy. Figure 2 Figure 3 The yield strengths of the obtained alloys at room temperature and at 650 °C are shown in FIG. 2 and FIG. 3, respectively. The yield strengths are as high as 964 MPa and 862 MPa, respectively, while the elongations are maintained at 17.2% and 28.2%, respectively. As shown in FIG. 4, the coarse L12 phases in the microstructure can deform in a mode of shear through stacking faults under a high stress and a high strain state, which is beneficial to promote the continuous dislocation motion in the B2 phase, thereby relieving the stress concentration at the FCC / B2 phase boundary, finally delaying the fracture of the alloy and improving the high-temperature tensile plasticity of the alloy. Figure 11 The yield strengths of the obtained alloys at room temperature and at 650 °C are shown in FIG. 2 and FIG. 3, respectively. The yield strengths are as high as 964 MPa and 862 MPa, respectively, while the elongations are maintained at 17.2% and 28.2%, respectively. As shown in FIG. 4, the coarse L12 phases in the microstructure can deform in a mode of shear through stacking faults under a high stress and a high strain state, which is beneficial to promote the continuous dislocation motion in the B2 phase, thereby relieving the stress concentration at the FCC / B2 phase boundary, finally delaying the fracture of the alloy and improving the high-temperature tensile plasticity of the alloy.

[0056] Example 2

[0057] The FCC / B2 dual-phase high-entropy alloy of the present example has a composition of Ni 44 Co 19 Cr 10 Fe 10 Al 15 Ta2 (at. %), and the heat treatment steps are as follows:

[0058] (1) The FCC / B2 dual-phase high-entropy alloy plate is kept at 1250 °C for 2 h and air-cooled;

[0059] (2) The alloy obtained in step (1) is kept at a high temperature of 850 °C for 2 h and air-cooled;

[0060] (3) The alloy obtained in step (2) is kept at a low temperature of 600 °C for 24 h and air-cooled. The yield strengths of the obtained alloy at room temperature and at 650 °C are shown in FIG. 2 and FIG. 3, respectively. The yield strengths are as high as 1178 MPa and 1044 MPa, respectively, while the elongations are maintained at 15.6% and 15.5%, respectively. Figure 4 Figure 5 The yield strengths of the obtained alloys at room temperature and at 650 °C are shown in FIG. 2 and FIG. 3, respectively. The yield strengths are as high as 964 MPa and 862 MPa, respectively, while the elongations are maintained at 17.2% and 28.2%, respectively. As shown in FIG. 4, the coarse L12 phases in the microstructure can deform in a mode of shear through stacking faults under a high stress and a high strain state, which is beneficial to promote the continuous dislocation motion in the B2 phase, thereby relieving the stress concentration at the FCC / B2 phase boundary, finally delaying the fracture of the alloy and improving the high-temperature tensile plasticity of the alloy.

[0061] Example 3

[0062] The FCC / B2 dual-phase high-entropy alloy of the present example has a composition of Ni 44 Co 19 Cr 10 Fe 10 Al 15 Ta2 (at. %), and the heat treatment steps are as follows:

[0063] ​​(1) The FCC / B2 dual-phase high-entropy alloy plate was placed at 1150 °C for 1 h, and air-cooled;

[0064] (2) The alloy obtained in step (1) was kept at high temperature 900 °C for 3 h, and air-cooled;

[0065] (3) The alloy obtained in step (2) was kept at low temperature 550 °C for 30 h, and air-cooled.

[0066] Example 4

[0067] The FCC / B2 dual-phase high-entropy alloy of this example has the composition of Ni 44 Co 19 Cr 10 Fe 10 Al 15 Ta2 (at. %), and the heat treatment steps thereof are as follows:

[0068] (1) The FCC / B2 dual-phase high-entropy alloy plate was placed at 1100 °C for 3 h, and air-cooled;

[0069] (2) The alloy obtained in step (1) was kept at high temperature 750 °C for 4 h, and air-cooled;

[0070] (3) The alloy obtained in step (2) was kept at low temperature 700 °C for 20 h, and air-cooled.

[0071] Example 5

[0072] The FCC / B2 dual-phase high-entropy alloy of this example has the composition of Ni 44 Co 19 Cr 10 Fe 10 Al 15 Ta2 (at. %), and the heat treatment steps thereof are as follows:

[0073] (1) The FCC / B2 dual-phase high-entropy alloy plate was placed at 1050 °C for 4 h, and air-cooled;

[0074] (2) The alloy obtained in step (1) was kept at high temperature 950 °C for 1 h, and air-cooled;

[0075] (3) The alloy obtained in step (2) was kept at low temperature 750 °C for 2 h, and air-cooled.

[0076] Comparative Example 1

[0077] The FCC / B2 dual-phase high-entropy alloy of this example has the same composition as Example 1, which is Ni 44 Co 19 Cr 10 Fe 10 Al 15Ti 2 (at. %), but its heat treatment steps are as follows:

[0078] (1) The FCC / B2 dual-phase high-entropy alloy plate is placed at 1200°C for 2h;

[0079] (2) The alloy obtained in step (1) is kept at a high temperature of 650°C for 16h and air-cooled; the obtained microstructure is as shown in Figure 6 The L12 phase with uniform size distribution and an average size of about 25nm is formed in the FCC matrix, which is relatively small in size compared with Example 1; at the same time, the needle-like FCC phase with relatively small size and high density is precipitated in the B2 matrix, accompanied by a large amount of globular σ phase. The room temperature and high temperature mechanical properties of the obtained alloy are as shown in Figure 7 and Figure 8 respectively, and the yield strength of the alloy under the traditional single-stage aging process is slightly reduced, and the fracture elongation is significantly decreased. It is shown that the dual-stage aging process proposed in the application can significantly optimize the precipitated phase characteristics of the FCC / B2 dual-phase high-entropy alloy, improve the room temperature and high temperature mechanical properties of the alloy, and obtain the FCC / B2 dual-phase high-entropy alloy with excellent strength and plasticity.

[0080] Comparative Example 2

[0081] The FCC / B2 dual-phase high-entropy alloy of the present comparative example has the same composition as Example 2, which is Ni 44 Co 19 Cr 10 Fe 10 Al 15 Ta 2 (at. %), but its heat treatment steps are as follows:

[0082] (1) The FCC / B2 dual-phase high-entropy alloy plate is placed at 1250°C for 2h and air-cooled;

[0083] (2) The alloy obtained in step (1) is kept at a high temperature of 600°C for 24h and air-cooled; the room temperature and high temperature mechanical properties of the obtained alloy compared with the dual-stage aging heat treatment process proposed in Example 2 are as shown in Figure 9 and Figure 10 respectively, and the yield strength and fracture elongation of the alloy under the traditional single-stage aging process are significantly decreased, as shown in Figure 12 In the high-temperature deformation process, the high-density needle-like FCC structure precipitated phase in the B2 phase undergoes phase transition from ductile FCC phase to hard and brittle 18R through a large amount of dislocation motion, which increases the resistance to dislocation motion of the B2 phase, and further weakens the deformation ability of the B2 phase, thereby leading to premature aging of the alloy. Compared with Example 1, as shown in Figure 13As shown, the KAM value in the alloy B2 phase under two-stage aging is obviously higher than that of the single-stage aging alloy, that is, it has stronger ability to accommodate dislocations, and the LAM value at the phase boundary is lower, that is, the stress concentration at the phase boundary is relatively smaller. It can be seen that the different precipitation phase characteristics obtained under the two aging processes determine the high-temperature mechanical properties of the alloy through completely different deformation mechanisms.

[0084] Therefore, under different FCC / B2 dual-phase high-entropy alloy systems, the two-stage aging heat treatment process proposed in the present application can significantly and effectively improve the comprehensive mechanical properties of the alloy at room temperature and high temperature.

[0085] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy, characterized in that, Includes the following steps: Step 1: Place the FCC / B2 dual-phase high-entropy alloy material at 1050~1250℃ for 1h~4h, and then cool it to obtain process material one; Step 2: Place process material one in a 750~950℃ environment for 1h~4h, and after cooling, obtain process material two; Step 3: Place the second process material at 550~750℃ for 2h~30h and cool it to obtain FCC / B2 dual-phase high-entropy alloy; The FCC / B2 dual-phase high-entropy alloy material is Ni. 44 Co 19 Cr 10 Fe 10 Al 15 Ti2 or Ni 44 Co 19 Cr 10 Fe 10 Al 15 Ta2.

2. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, In step 1, the insulation temperature is 1200℃.

3. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, In step 1, the heat preservation time is 2 hours.

4. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, In step 2, the insulation temperature of process material one is 800℃.

5. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, In step 2, the heat preservation time for process material one is 2 hours.

6. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, In step 3, the insulation temperature of process material 2 is 650℃.

7. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, In step 3, the heat preservation time for process material 2 is 16 hours.

8. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, The cooling methods in steps 1, 2 and 3 are air cooling or water cooling.

9. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, The FCC / B2 dual-phase high-entropy alloy has a yield strength of 1178 MPa at room temperature and a high-temperature yield strength of 1044 MPa at 650 °C.

10. The two-stage aging heat treatment method for an FCC / B2 dual-phase high-entropy alloy according to claim 1, characterized in that, The FCC / B2 dual-phase high-entropy alloy exhibits a room temperature elongation of 17.2% and a high temperature elongation of 28.2% at 650℃.

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