A CrCoNi-based medium-entropy alloy with a non-uniform grain heterostructure and a preparation method thereof

Abstract

The present invention discloses a CrCoNi-based medium-entropy alloy with a heterogeneous grain structure and a preparation method thereof. The medium-entropy alloy is composed of Cr, Co, Ni, and V, with the molar ratio of each element being V:Cr:Co:Ni = (0.25-0.35):(0.95-1.05):(0.95-1.05):(0.95-1.05), wherein the molar ratios of Cr, Co, and Ni are equal. By adding the alloying element V and regulating the heat treatment process, the alloy forms a heterogeneous structure with heterogeneous grains and a large number of nanoscale sigma precipitates in the small grain regions. The alloy has a yield strength and tensile strength of 904 MPa and 1210 MPa, respectively, and an elongation at break of 29%. Comparison of the yield strength and elongation with other sigma precipitation-strengthened medium / high-entropy alloys reveals that the alloy has an optimal strength-ductility match, enhancing its application value as an engineering structural component.

Description

Technical Field

[0001] The present invention belongs to the technical field of medium-entropy alloys and relates to a CrCoNi-based medium-entropy alloy with a non-uniform grain heterostructure and a preparation method thereof. Background Art

[0002] High-entropy alloys (HEAs) are now considered important advanced materials, and CrMnFeCoNi (Cantor) alloy is the most successful HEA due to its excellent mechanical properties and microstructure. In this context, variants of Cantor alloys, known as intermediate-entropy alloys (ITA), have attracted significant interest due to their demonstrated industrial potential compared to HEAs and conventional alloys. Among these variants, CrCoNi IATs exhibit the best mechanical properties and excellent strength, ductility, and fracture toughness at low temperatures. However, their room-temperature yield strength is relatively low, at approximately 440 MPa, limiting their use as structural components.

[0003] To improve its room-temperature yield strength, researchers have developed a variety of strengthening strategies, such as grain refinement, solid solution strengthening, deformation strengthening, and precipitation strengthening, with precipitation strengthening being particularly effective. Current precipitation strengthening efforts primarily focus on precipitates that form a coherent or semi-coherent relationship with the matrix, such as the γ′ phase and the B2 phase. Sigma phases, which are incoherent with the matrix, have been less studied. Although this intermetallic phase is brittle, its hardness, as high as 15 GPa, can produce significant precipitation strengthening. It is generally believed that the large lattice mismatch between incoherent precipitates and the matrix can lead to stress concentration during deformation, promote microcrack formation, and severely degrade the material's plasticity. Therefore, the formation of these incoherent, hard, and brittle intermetallic compounds is avoided in traditional alloys. However, compared with traditional alloys, face-centered cubic medium-entropy alloys (FCMEAs) offer lower stacking fault energies, better plasticity, and higher strain hardening rates, allowing them to achieve both strength and plasticity even with the introduction of incoherent precipitates. Studies have shown that when the Cr content in the alloy is high, the addition of V promotes the precipitation of sigma phase and stabilizes the sigma phase. Therefore, the present invention adds a trace amount of V to the CrCoNi medium-entropy alloy to induce the formation of sigma phase precipitation and combines it with a non-uniform grain structure to achieve a good match between the room temperature strength and plasticity of the CrCoNi medium-entropy alloy, thereby enhancing its engineering application value. Summary of the Invention

[0004] The purpose of the present invention is to provide a CrCoNi-based medium-entropy alloy with a non-uniform grain heterostructure to achieve a good match between the strength and plasticity of the CrCoNi medium-entropy alloy at room temperature.

[0005] The technical solution adopted by the present invention is: a CrCoNi-based medium entropy alloy with a non-uniform grain heterogeneous structure is composed of Cr, Co, Ni and V elements, and the amount ratio of each element is V:Cr:Co:Ni=(0.25-0.35):(0.95-1.05):(0.95-1.05):(0.95-1.05), wherein the amount of Cr, Co and Ni is equal. Preferably, the medium entropy alloy is V 0.3 CrCoNi, which has non-uniform grains and contains more nanoscale sigma precipitates in the small grain regions, has a yield strength and tensile strength of 904 MPa and 1210 MPa, respectively, and an elongation at break of 29%;

[0006] Another object of the present invention is to provide a method for preparing a CrCoNi-based medium entropy alloy having a non-uniform grain heterostructure.

[0007] Another technical solution adopted by the present invention is: a method for preparing a CrCoNi-based medium-entropy alloy with a non-uniform grain heterostructure, comprising the following steps:

[0008] 1) According to the composition of the target alloy, Cr, Co, Ni and V metal particles with a purity of ≥99.9% were weighed and proportioned, and the alloy ingot was obtained by vacuum arc melting. The vacuum degree during the melting process was 5×10 -3 Pa below, the melting current is 250 ~ 350A, the melting time is 4 ~ 5min, during which argon with a purity of ≥ 99.999% is filled for protection, and the melting is repeated 6 to 7 times to fully mix the elements in the ingot;

[0009] 2) subjecting the above-mentioned medium-entropy alloy ingot to a homogenization annealing treatment at 1100-1300° C. in a muffle furnace at a heating rate of 10° C. / min and a holding time of 1.5-2.5 h, and then quenching with water to room temperature to obtain a CrCoNi-based medium-entropy alloy with uniform composition and containing sigma phase;

[0010] 3) the ingot is then longitudinally cold rolled at room temperature for 30 to 40 times with a feed rate of no more than 0.1 mm, so that the total thickness is reduced by 75% to 85% to a final thickness of 0.5 to 0.7 mm, thereby obtaining a CrCoNi-based medium-entropy alloy with a fine sigma phase;

[0011] 4) The cold-rolled alloy sample was recrystallized and annealed at 750-850°C in a muffle furnace at a heating rate of 10°C / min for 20-40 min, and then water-quenched to room temperature to obtain a CrCoNi-based medium-entropy alloy with a heterogeneous grain structure.

[0012] The present invention has the following advantages:

[0013] The non-uniform grain heterostructure CrCoNi-based medium entropy alloy has non-uniform grains and the small grain area contains more nano-scale sigma precipitates, which is beneficial to the improvement of strength, while the large grains are conducive to the alloy retaining a certain plasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is an EBSD microstructure diagram of an embodiment of the present invention.

[0015] Figure 2 This is the EBSD microstructure diagram of the comparative example of the present invention.

[0016] Figure 3 The engineering stress-strain curves of the embodiments of the present invention and the comparative example are shown in FIG.

[0017] Figure 4 The figure is a comparison chart of the yield strength and elongation of the embodiments and comparative examples of the present invention and other sigma precipitation strengthened medium / high entropy alloys. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to the accompanying drawings and specific examples.

[0019] Reference Figure 1 As shown, for V 0.3 The microstructure of the CrCoNi medium-entropy alloy was observed, and it was found that more sigma phases were distributed around the areas with smaller grain size, and relatively fewer sigma phases were distributed around the areas with coarse grains, forming a heterogeneous grain structure. Ultrafine grains with a size of 0.5 to 1 μm accounted for 31%, and the average grain size of the alloy was 1.81±1.32 μm.

[0020] Reference Figure 2 As shown in Figure 3, the microstructure of the CrCoNi medium entropy alloy is equiaxed grains with uniform size and an average grain size of 2.96±2.05μm.

[0021] Reference Figure 3 As shown, at room temperature, 10 -3 s -1 The alloy sample was stretched at a rate of , and the yield strength and tensile strength of the CrCoNi medium entropy alloy were 538MPa and 945MPa respectively, and the elongation at break was 53%. 0.3 The yield strength and tensile strength of the CrCoNi medium-entropy alloy sample were 904 MPa and 1210 MPa, respectively, with an elongation at break of 29%. Compared with CrCoNi alloy, its yield strength and tensile strength increased by 68% (333 MPa) and 28% (265 MPa), respectively.

[0022] Reference Figure 4As shown in the figure, compared with the yield strength and elongation of other sigma precipitation strengthened medium / high entropy alloys, V 0.3 CrCoNi medium entropy alloy has the best strength-ductility match.

[0023] Example

[0024] 1) Prepared into V 0.3 The alloy of CrCoNi, wherein the molar ratio of each element is V:Cr:Co:Ni=0.3:1:1:1, is obtained by vacuum arc melting method, and the vacuum degree during the melting process is 5×10 -3 Pa, the melting current is 300A, the melting time is 5min, during which argon gas with a purity of ≥99.999% is filled for protection, and the melting is repeated 6 times to fully mix the elements in the ingot;

[0025] 2) homogenizing the medium-entropy alloy ingot in a muffle furnace at 1200° C. with a heating rate of 10° C. / min and a holding time of 2 h, and then quenching the ingot with water to room temperature to obtain a CrCoNi-based medium-entropy alloy with uniform composition and containing a sigma phase;

[0026] 3) The ingot is then longitudinally cold rolled at room temperature for 30 to 40 times with a feed rate of no more than 0.1 mm, so that the total thickness is reduced by 80% to a final thickness of 0.6 mm, thereby obtaining a CrCoNi-based medium-entropy alloy with a fine sigma phase;

[0027] 4) The cold-rolled alloy sample was recrystallized and annealed at 800°C in a muffle furnace with a heating rate of 10°C / min and a holding time of 30 min, and then water quenched to room temperature to obtain a CrCoNi-based medium-entropy alloy with a non-uniform grain heterostructure.

[0028] Comparative Example

[0029] 1) Prepare an alloy of CrCoNi, wherein the molar ratio of each element is Cr:Co:Ni=1:1:1, and use vacuum arc melting method to obtain alloy ingots. The vacuum degree during the melting process is 5×10 -3 Pa, the melting current is 300A, the melting time is 5min, during which argon gas with a purity of ≥99.999% is filled for protection, and the melting is repeated 6 times to fully mix the elements in the ingot;

[0030] 2) homogenizing the medium-entropy alloy ingot in a muffle furnace at 1200° C. with a heating rate of 10° C. / min and a holding time of 2 h, and then quenching with water to room temperature;

[0031] 3) The ingot is then longitudinally cold rolled at room temperature for 30 to 40 passes with a feed rate of no more than 0.1 mm, reducing the total thickness by 80% to a final thickness of 0.6 mm;

[0032] 4) The cold-rolled alloy sample was subjected to recrystallization annealing treatment at 800°C in a muffle furnace with a heating rate of 10°C / min and a holding time of 30 min, and then water quenched to room temperature to obtain a CrCoNi medium-entropy alloy.

Claims

1. A CrCoNi-based medium-entropy alloy having a non-uniform grain heterostructure, characterized in that: The medium-entropy alloy is composed of Cr, Co, Ni and V elements, with the molar ratio of each element being V:Cr:Co:Ni=0.3:1:1:

1. The medium-entropy alloy is V0.3CrCoNi. The medium-entropy alloy has non-uniform grains, and the small grain regions contain more nanoscale sigma precipitates. The yield strength and tensile strength of the medium-entropy alloy are 904 MPa and 1210 MPa, respectively, and the elongation at break is 29%.

2. The method for preparing a CrCoNi-based medium-entropy alloy having a non-uniform grain heterostructure according to claim 1, wherein: The specific preparation method comprises the following steps: 1) According to the composition of the target alloy, Cr, Co, Ni and V metal particles with a purity of ≥ 99.9% are weighed and proportioned, and the alloy ingot is obtained by vacuum arc melting; 2) homogenizing the alloy ingot in a muffle furnace at 1100-1300°C for 1.5-2.5 hours, and then quenching the ingot in water to room temperature to obtain a CrCoNi-based medium-entropy alloy with uniform composition and containing a sigma phase; 3) The ingot is then longitudinally cold rolled at room temperature for 30 to 40 times with a feed rate of no more than 0.1 mm each time, so that the total thickness is reduced by 75% to 85% to obtain a CrCoNi-based medium entropy alloy with fine sigma phase; 4) The cold-rolled alloy sample was recrystallized and annealed at 750-850 °C in a muffle furnace for 20-40 min, and then water-quenched to room temperature to obtain a CrCoNi-based medium-entropy alloy with a heterogeneous grain structure.

3. The preparation method according to claim 2, wherein Step 1) The vacuum degree during the melting process is 5×10 -3 Pa, the melting current is 250~350 A, the melting time is 4~5 min, during which argon with a purity of ≥99.999% is filled for protection, and the melting is repeated 6~7 times to fully mix the elements in the ingot.

4. The preparation method according to claim 2, wherein In step 2), the heating rate is 10°C / min.

5. The preparation method according to claim 2, wherein The final rolling thickness in step 3) is 0.5~0.7mm.

6. The preparation method according to claim 2, wherein In step 4), the heating rate is 10°C / min.

Images