Carbide-reinforced CoCrNi-based medium-entropy alloy and preparation method thereof

Abstract

The present invention provides a carbide-reinforced CoCrNi-based medium-entropy alloy and a preparation method thereof. The chemical formula of the CoCrNi-based medium-entropy alloy is (CoCrNi) 97 Mo3‑xB4C / TiC; (CoCrNi) 97 The Mo3 portion is expressed in atomic percentage; x is 1 to 9 at.%, and x represents (CoCrNi) 97 The medium-entropy alloy is prepared by mixing the raw materials and then melting them in a vacuum melting furnace. The carbide-reinforced CoCrNi-based medium-entropy alloy provided by the present invention has excellent corrosion resistance and hardness, which is significantly improved compared to CoCrNi medium-entropy alloys.

Description

Technical Field

[0001] The present invention belongs to the field of medium-entropy alloys and relates to a carbide-reinforced CoCrNi-based medium-entropy alloy and a preparation method thereof. Background Art

[0002] As a vital component of modern energy conversion, marine gas turbines demand high material performance and reliability. Medium-entropy alloys, with their excellent mechanical properties, corrosion resistance, and high-temperature resistance, have become a key material choice for gas turbines. Because gas turbines face extremely high temperatures and pressures during operation, traditional materials often struggle to meet the demands of long-term operation. However, through optimized composition, medium-entropy alloys maintain excellent performance in high-temperature environments, significantly improving the overall efficiency and service life of gas turbines.

[0003] Since 2004, medium- and high-entropy alloys (MEAs) have attracted increasing attention due to their exceptional strength, toughness, fatigue resistance, and corrosion resistance. The unique properties of MEAs are generally derived from the synergistic effects of multiple main elements, including four typical core effects: high entropy effect, slow diffusion effect, severe lattice distortion effect, and cocktail effect. Among MEAs, face-centered cubic (FCC) single-phase CoCrNi-based MPEAs (e.g., CoCrNi, CoCrFeNi, and CoCrFeMnNi) are among the most studied MEAs due to their exceptional low-temperature fracture toughness. Furthermore, due to the high content of passivating elements such as Cr and Ni, MEAs based on CoCrNi exhibit excellent corrosion resistance and therefore have great potential as next-generation marine gas turbine components.

[0004] However, the relatively low room-temperature strength of CoCrNi-based medium- and high-entropy alloys (MEAs) due to their single-phase microstructure limits their widespread application. FCC single-phase alloys, with their uniform composition and stable structure, are suitable matrix materials, while carbides offer high hardness and a stable phase structure. Therefore, to enhance the hardness and corrosion resistance of CoCrNi-based MEAs and more effectively meet the stringent requirements of marine gas turbines, it is crucial to develop a CoCrNi-based MEA composite material with carbide as the reinforcement phase. Summary of the Invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide a carbide reinforced CoCrNi based medium entropy alloy, which solves the problems of low hardness and poor corrosion resistance of CoCrNi based medium entropy alloy by adding carbides.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned carbide-reinforced CoCrNi-based medium-entropy alloy.

[0007] The third objective of the present invention is to illustrate the specific application of the above-mentioned carbide-reinforced CoCrNi-based medium-entropy alloy and explore the potential use of this system in the subsequent coating preparation process.

[0008] In order to achieve the above object, the present invention provides a carbide-reinforced CoCrNi-based medium-entropy alloy, the chemical formula of the CoCrNi-based medium-entropy alloy is (CoCrNi) 97 Mo3-xB4C / TiC; among which, (CoCrNi) 97 The Mo3 portion is expressed in atomic percentage; x is 1 to 9 at.%, and x represents (CoCrNi) 97 B4C or TiC in terms of atomic percentage of Mo3.

[0009] The present invention also provides a method for preparing the above-mentioned carbide-reinforced CoCrNi-based medium-entropy alloy, comprising the following steps:

[0010] S1: According to (CoCrNi) 97 The atomic percentage of Mo3 alloy components is prepared and mixed to obtain a primary raw material;

[0011] S2: According to (CoCrNi) 97 Atomic percentage of Mo3-xB4C / TiC alloy components: B4C or TiC is weighed and fully mixed with the primary raw material obtained in S1 to obtain an alloy raw material for vacuum melting.

[0012] S3: The raw materials obtained in S2 were placed in a high vacuum arc melting furnace for melting. The melting current was 400A and the vacuum degree was 6.0×10 -3 Pa, repeatedly smelted 8 to 10 times to obtain (CoCrNi) 97 Mo3-xB4C / TiC alloy.

[0013] As described above, the Co raw material is a granular Co block with a purity of 99.99 wt.%. The Cr raw material is a granular Cr block with a purity of 99.99 wt.%. The Ni raw material is a granular Ni block with a purity of 99.99 wt.%. The Mo raw material is a granular Mo block with a purity of 99.95 wt.%. The BC raw material is a granular BC block with a purity of 99.5 wt.%. The TiC raw material is a granular TiC block with a purity of 99.5 wt.%.

[0014] The present invention also provides potential applications of the above-mentioned ceramic phase reinforced CoCrNi-based medium entropy alloy in the preparation of multi-principal component alloy coatings.

[0015] The present invention adds 3at.% of Mo element to CoCrNi and then 97 On the basis of Mo3, 1-9at.% B4C / TiC is further added. The specific molar percentages are as follows: Co: 32.33at.%; Cr: 32.34at.%; Ni: 32.33at.%; Mo: 3at.%, and 1-9at.% B4C / TiC is added on this basis. The metal elements and carbides are mixed and melted into a cast alloy ingot according to the ratio using a high vacuum arc melting method. The surface structure of the alloy ingot is dense and there are no obvious defects on the surface. The main crystal structure is FCC structure and there is a small amount of carbide precipitation phase. Compared with the CoCrNi medium entropy alloy, (CoCrNi) 97 The hardness and corrosion resistance of Mo3-xB4C / TiC alloy are improved, its preparation process is easy to industrialize, and its application prospects are very broad.

[0016] The present invention makes (CoCrNi) by adding Mo element 97 Mo3 medium entropy alloy has FCC single phase structure to avoid galvanic corrosion. However, FCC single phase structure makes the alloy hardness low, which is difficult to meet the application in marine environment. Therefore, carbides are added to further improve the hardness and corrosion resistance of the alloy. B4C ceramics have high hardness and can be made by B4C and (CoCrNi) 97 The boron carbide with coherent phase boundary generated by the Mo3 reaction improves the hardness and corrosion resistance of the alloy. TiC improves the hardness of the alloy to a certain extent due to the heterogeneous strengthening effect, and the introduction of Ti element produces TiO2 during the corrosion process, which greatly improves the corrosion resistance of the alloy.

[0017] The beneficial effects of the present invention are:

[0018] The present invention provides a carbide-reinforced CoCrNi-based medium-entropy alloy and a preparation method thereof. The carbide-reinforced CoCrNi-based medium-entropy alloy mainly solves the problems of low hardness and poor corrosion resistance of CoCrNi-based medium-entropy alloys by adding carbides. The prepared carbide-reinforced CoCrNi-based medium-entropy alloy has excellent corrosion resistance and hardness, which is greatly improved compared with CoCrNi medium-entropy alloys, and shows broad application prospects in key components such as ship gas turbine devices. In addition, this system can be subsequently expanded to the field of coating technology to further reduce costs, increase efficiency, and save resource loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The X-ray diffraction patterns of Comparative Example 1 and Examples 1-6 are shown.

[0020] Figure 2Scanning electron microscope images of the alloy surfaces of Comparative Example 1 and Examples 1-6.

[0021] Figure 3 The potentiodynamic polarization curves of Comparative Example 1 and Examples 1-6 in 3.5 wt.% NaCl solution.

[0022] Figure 4 This is a comparison chart of the Vickers hardness obtained by comparative example 1 and examples 1-6 under a load of 100 g and holding pressure for 15 seconds. DETAILED DESCRIPTION

[0023] The embodiments of the present invention will be described in detail and comprehensively below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0024] The present invention provides a carbide-reinforced CoCrNi-based medium-entropy alloy, the chemical formula of which is (CoCrNi) 97 Mo3-xB4C / TiC; among which, (CoCrNi) 97 The Mo3 portion is expressed in atomic percentage; x is 1 to 9 at.%, and x represents (CoCrNi) 97 B4C or TiC in terms of atomic percentage of Mo3.

[0025] Material:

[0026] The purity of the granular Co blocks, granular Cr blocks, and granular Ni blocks is 99.99 wt.%, the purity of the granular Mo blocks is 99.95 wt.%, and the purity of the granular B4C blocks and granular TiC blocks is 99.5 wt.%. The above raw materials were purchased from Linyi Yanchuangxin Materials Technology Co., Ltd.

[0027] equipment:

[0028] High vacuum arc melting furnace: Equipment model YC2016-0024 vacuum arc furnace, water-cooled copper crucible.

[0029] Example 1 (TiC=1 at.%)

[0030] The composition of carbide reinforced CoCrNi based medium entropy alloy is (CoCrNi) 97 Mo3-1 at.% B4C, selected high-purity Co (99.99wt.%), Cr (99.99wt.%), Ni (99.99wt.%), Mo (99.95wt.%), TiC (99.5wt.%) small pieces. The cast alloy ingot is prepared according to the following steps:

[0031] S1: Carry out preliminary raw material ratio according to (CoCrNi) 97 The Mo3 alloy components are mixed in an atomic molar ratio to obtain a primary raw material.

[0032] S2: Further raw material ratio, according to (CoCrNi) 97 The atomic molar ratio of the alloy component Mo3-1 at.% TiC is weighed and B4C is fully mixed with the primary raw material obtained from S1 to obtain an alloy raw material for vacuum melting.

[0033] S3: The raw materials obtained in S2 were placed in a high vacuum arc melting furnace for melting. The melting current was 400A and the vacuum degree was 6.0×10 -3 Pa, repeatedly smelted 8 times to obtain (CoCrNi) 97 Mo3-1 at.%TiC alloy.

[0034] Example 2 (TiC=6 at.%)

[0035] The composition of the carbide ceramic phase reinforced CoCrNi based medium entropy alloy is (CoCrNi) 97 Mo3-6 at.% B4C, high-purity Co (99.99wt.%), Cr (99.99wt.%), Ni (99.99wt.%), Mo (99.95wt.%), and TiC (99.5wt.%) small pieces were selected. The cast alloy ingot was prepared according to the following steps:

[0036] S1: Carry out preliminary raw material ratio according to (CoCrNi) 97 The Mo3 alloy components are mixed in an atomic molar ratio to obtain a primary raw material.

[0037] S2: Further raw material ratio, according to (CoCrNi) 97 The atomic molar ratio of the alloy component Mo3-6 at.% TiC is weighed and TiC is fully mixed with the primary raw material obtained in S1 to obtain the alloy raw material for vacuum melting.

[0038] S3: The raw materials obtained in S2 are placed in a high vacuum arc melting furnace for melting. The melting current is 400A and the vacuum degree is 4.0×10 -3 Pa, repeatedly smelted 8 times to obtain (CoCrNi) 97 Mo3-6 at.%TiC alloy.

[0039] Example 3 (TiC=9 at.%)

[0040] The composition of the carbide ceramic phase reinforced CoCrNi based medium entropy alloy is (CoCrNi) 97Mo3-9 at.% TiC, selected high-purity Co (99.99wt.%), Cr (99.99wt.%), Ni (99.99wt.%), Mo (99.95wt.%), TiC (99.5wt.%) small pieces. The cast alloy ingot is prepared according to the following steps:

[0041] S1: Carry out preliminary raw material ratio according to (CoCrNi) 97 The Mo3 alloy components are mixed in an atomic molar ratio to obtain a primary raw material.

[0042] S2: Further raw material ratio, according to (CoCrNi) 97 The atomic molar ratio of the Mo3-9 at.% TiC alloy component is 4C, which is weighed and fully mixed with the primary raw material obtained in S1 to obtain the alloy raw material for vacuum melting. S3: The raw material obtained in S2 is placed in a high vacuum arc melting furnace for melting, with a melting current of 400A and a vacuum degree of 6.0×10 -3 Pa, repeatedly smelted 8 times to obtain (CoCrNi) 97 Mo3-9 at.%TiC alloy.

[0043] Example 4 (B4C=1 at.%)

[0044] The composition of the carbide ceramic phase reinforced CoCrNi based medium entropy alloy is (CoCrNi) 97 Mo3-3 at.% TiC, selected high-purity Co (99.99wt.%), Cr (99.99wt.%), Ni (99.99wt.%), Mo (99.95wt.%), BC (99.5wt.%) small pieces. The cast alloy ingot is prepared according to the following steps:

[0045] S1: Carry out preliminary raw material ratio according to (CoCrNi) 97 The Mo3 alloy components are mixed in an atomic molar ratio to obtain a primary raw material.

[0046] S2: Further raw material ratio, according to (CoCrNi) 97 Mo3-1 at.% B4C Atomic molar percentage of alloy components B4C is weighed and fully mixed with the primary raw material obtained in S1 to obtain an alloy raw material for vacuum melting.

[0047] S3: The raw materials obtained in S2 were placed in a high vacuum arc melting furnace for melting. The melting current was 400A and the vacuum degree was 6.0×10 -3 Pa, repeatedly smelted 8 times to obtain (CoCrNi) 97 Mo3-1 at.%B4C alloy.

[0048] Example 5 (B4C=6 at.%)

[0049] The composition of the carbide ceramic phase reinforced CoCrNi based medium entropy alloy is (CoCrNi) 97 Mo3-6 at.% B4C, selected high-purity Co (99.99wt.%), Cr (99.99wt.%), Ni (99.99wt.%), Mo (99.95wt.%), B4C (99.5wt.%) small pieces. The cast alloy ingot is prepared according to the following steps:

[0050] S1: Carry out preliminary raw material ratio according to (CoCrNi) 97 The Mo3 alloy components are mixed in an atomic molar ratio to obtain a primary raw material.

[0051] S2: Further raw material ratio, according to (CoCrNi) 97 The atomic mole percentage of the Mo3-6 at.% B4C alloy component is weighed. TiC is fully mixed with the primary raw material obtained in S1 to obtain the alloy raw material for vacuum melting.

[0052] S3: The raw materials obtained in S2 were placed in a high vacuum arc melting furnace for melting. The melting current was 400A and the vacuum degree was 6.0×10 -3 Pa, repeatedly smelted 8 times to obtain (CoCrNi) 97 Mo3-6 at.%B4C alloy.

[0053] Example 6 (B4C=9 at.%)

[0054] The composition of the carbide ceramic phase reinforced CoCrNi based medium entropy alloy is (CoCrNi) 97 Mo3-9 at.% B4C, selected high-purity Co (99.99wt.%), Cr (99.99wt.%), Ni (99.99wt.%), Mo (99.95wt.%), B4C (99.5wt.%) small pieces. The cast alloy ingot is prepared according to the following steps:

[0055] S1: Carry out preliminary raw material ratio according to (CoCrNi) 97 The Mo3 alloy components are mixed in an atomic molar ratio to obtain a primary raw material.

[0056] S2: Further raw material ratio, according to (CoCrNi) 97 The atomic molar ratio of the alloy component Mo3-9 at.% B4C is weighed, and TiC is fully mixed with the primary raw material obtained in S1 to obtain the alloy raw material for vacuum melting.

[0057] S3: The raw materials obtained in S2 were placed in a high vacuum arc melting furnace for melting. The melting current was 400A and the vacuum degree was 6.0×10 -3 Pa, repeatedly smelted 8 times to obtain (CoCrNi) 97 Mo3-9 at.%B4C alloy.

[0058] Comparative Example 1 (CoCrNi)

[0059] Select high-purity Co (99.99 wt.%), Cr (99.99 wt.%), and Ni (99.99 wt.%) small pieces. Alloy ingots are prepared according to the following steps:

[0060] S1: Raw materials are proportioned and mixed according to the atomic molar ratio of the CoCrNi alloy components to obtain alloy raw materials for vacuum melting.

[0061] S2: The raw materials obtained in S1 were placed in a high vacuum arc melting furnace for melting. The melting current was 400A and the vacuum degree was 6.0×10 -3 Pa, and the CoCrNi medium-entropy alloy was obtained by repeated smelting 8 times.

[0062] The medium entropy alloys prepared in Examples 1 to 6 and Comparative Example 1 were subjected to XRD diffraction tests, and the XRD diffraction patterns were as follows: Figure 1 shown.

[0063] from Figure 1 It can be seen that the crystal structure of the CoCrNi alloy represented by Comparative Example 1 has only FCC diffraction peaks, indicating that the alloy is an FCC single-phase structure, which results in a lower hardness of the alloy.

[0064] The (CoCrNi) represented by Examples 1-3 97 As the TiC content of Mo3-xTiC alloy increases, its phase structure is FCC face-centered cubic structure and contains a small amount of TiC phase, and no other carbides are formed.

[0065] Different from (CoCrNi) 97 Mo3-xTiC alloy, represented by Example 4 (CoCrNi) 97 In addition to the typical FCC diffraction peaks, the Mo3-1 at.% B4C alloy also has the diffraction peaks of boride (Cr3B3). As the B4C content increases, the (CoCrNi) represented by Example 5 97 The Mo3-6 at.% B4C alloy shows borides such as Co3B and carbides such as Mo2C. 97The Mo3-9 at.% B4C alloy also exhibits typical FCC diffraction peaks. Furthermore, as the B4C content increases, the boride precipitates (Cr3B3, Co3B) and carbide precipitates (Mo2C) in Example 6 significantly increase compared to Examples 4 and 5.

[0066] The surface morphology of Examples 1-6 and Comparative Example 1 was observed using a scanning electron microscope. Figure 2 As shown. Figure 2 It can be seen that the surface of comparative example 1 (i.e. CoCrNi) has no obvious defects and a dense structure. 97 The surface structure of Mo3-1 at.%TiC alloy is dense. Compared with comparative example 1, a small amount of black precipitate phase appears on the surface of the alloy of example 1. Combined with the XRD results, it can be seen that the precipitate phase is TiC. As the TiC content continues to increase, it can be clearly observed that the surface of the alloy of example 2 (i.e. (CoCrNi) 97 Mo3-6 at.% TiC) and Example 3 (i.e. (CoCrNi) 97 The TiC precipitation phase on the surface of Mo3-9 at.% TiC (Mo3-9 at.% TiC) significantly increased, and the formation of dendrites was clearly observed in Example 3, which is beneficial for improving the hardness of the alloy. However, the presence of dendrites can cause element segregation, resulting in a certain degree of decline in the corrosion resistance of the alloy.

[0067] (CoCrNi) shown in Example 4 97 The surface structure of Mo3-1 at.%B4C alloy is dense, compared with CoCrNi alloy, (CoCrNi) 97 A large number of light gray and white precipitates appeared on the surface of the Mo3-1 at.% B4C alloy. Combined with XRD results, these precipitates were confirmed to be Cr3B3 and MoC hard phases. The formation of precipitates can greatly improve the hardness of the alloy through precipitation strengthening. As the B4C content gradually increases, the scanning electron microscopy images ( Figure 2 ) can be clearly observed in Example 5 (i.e. (CoCrNi) 97 The surface microstructure of the Mo3-6 at.%B4C) alloy gradually changes to a dendritic morphology. The presence of dendrites further improves the hardness of the alloy, but also reduces the corrosion resistance of the alloy. 97 In Mo3-9at.%B4C), due to the addition of excessive B4C, some black long strips of precipitation appeared on the alloy surface, which may lead to a further decrease in the corrosion resistance of the alloy.

[0068] The corrosion resistance of the alloys of Comparative Example 1 and Examples 1-6 was evaluated using an electrochemical workstation. Figure 3The potentiodynamic polarization curves of Comparative Example 1 and Examples 1-6 in 3.5 wt.% NaCl solution are shown in FIG. Figure 3 It can be clearly seen that the range of the cathode polarization and anodic polarization curves of Examples 1-6 is wider than that of Comparative Example 1, showing a more obvious passivation zone, which indicates that the addition of carbides (B4C or TiC) can make the alloy form a denser passivation film with better corrosion resistance.

[0069] The self-corrosion current density of comparative example 1 is 0.319 μA / cm 2 , while Examples 1 to 3 ((CoCrNi) 97 The self-corrosion current density of Mo3-xTiC) is 0.1127μA / cm 2 、0.08113μA / cm 2 、0.09585μA / cm 2 , Examples 4 to 6 ((CoCrNi) 97 The self-corrosion current density of Mo3-xB4C) is 0.1414μA / cm 2 , 0.1447μA / cm 2 , 0.273μA / cm 2 Compared with Comparative Example 1, the self-corrosion current density of Examples 1-6 decreased significantly, which shows that Examples 1 to 6 have better corrosion resistance than Comparative Example 1. 97 In the Mo3-x B4C system, Example 4 showed the best corrosion resistance, while the (CoCrNi) 97 In the Mo3-x TiC system, Example 2 exhibits excellent corrosion resistance.

[0070] The Vickers hardness of the alloys prepared in Comparative Example 1 and Examples 1-6 was tested using an FM700 Vickers hardness tester. The Vickers hardness was measured after a standard Vickers diamond quadrangular pyramid indenter was loaded with a load of 300 g and a holding time of 15 s. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that the Vickers hardness of Comparative Example 1 is 158±10HV 0.3 The Vickers hardness of Examples 1-6 is 303±8HV respectively. 0.3 、316.4±6HV 0.3 、316±10HV 0.3 、466±8HV 0.3 、549±6HV 0.3 , 685.9±10HV 0.3The hardness of Examples 1-6 is significantly improved compared to Comparative Example 1, and they have better mechanical properties, indicating that adding carbides (B4C or TiC) can significantly improve the mechanical properties of the alloy. Among them, Example 6 has the highest Vickers hardness.

[0071] It can be seen from the above examples that the carbide-reinforced CoCrNi-based medium-entropy alloy prepared by the present invention can comprehensively improve the corrosion resistance and hardness of the CoCrNi alloy, has a low cost and a simple experimental method, is easy to industrialize, and has broad application prospects.

[0072] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A carbide-reinforced CoCrNi-based medium-entropy alloy, characterized in that: The chemical formula of the CoCrNi-based medium entropy alloy is (CoCrNi) 97 Mo3-xB4C / TiC; among which, (CoCrNi) 97 The Mo3 portion is expressed in atomic percentage; x is 6~9 at.%, and x represents (CoCrNi) 97 B4C or TiC expressed as atomic percentage of Mo3; The preparation method of the carbide-reinforced CoCrNi-based medium-entropy alloy comprises the following steps: S1: According to (CoCrNi) 97 The atomic percentage of Mo3 alloy components is prepared and mixed to obtain a primary raw material; S2: According to (CoCrNi) 97 Atomic percentage of Mo3-xB4C / TiC alloy composition: B4C or TiC is weighed and fully mixed with the primary raw material obtained in S1 to obtain an alloy raw material for vacuum melting; S3: The raw materials obtained in S2 were placed in a high vacuum arc melting furnace for melting. The melting current was 400 A and the vacuum degree was 6.0×10 -3 Pa, repeatedly smelted 8 to 10 times to obtain (CoCrNi) 97 Mo3-xB4C / TiC alloy.

2. The carbide-reinforced CoCrNi-based medium-entropy alloy according to claim 1, wherein: The raw material of Co is granular Co block, and the purity of Co raw material is 99.99 wt.%; the raw material of Cr is granular Cr block, and the purity of Cr raw material is 99.99 wt.%; the raw material of Ni is granular Ni block, and the purity of Ni raw material is 99.99 wt.%; the raw material of Mo is granular Mo block, and the purity of Mo raw material is 99.95 wt.%; the raw material of B4C is granular B4C block, and the purity of B4C raw material is 99.5 wt.%; the raw material of TiC is granular TiC block, and the purity of TiC raw material is 99.5 wt.%.

3. Use of the carbide-reinforced CoCrNi-based medium-entropy alloy as claimed in claim 1 in the preparation of a multi-principal component alloy coating.

Images