CN115747605B - High-entropy refractory alloy resistant to 1300 ℃ high-temperature oxidation and preparation method thereof - Google Patents

Abstract

The invention discloses a refractory high-entropy alloy resistant to 1300 ℃ high-temperature oxidation and a preparation method thereof, and belongs to the technical field of high-temperature metal materials. The refractory high-entropy alloy has a chemical formula of (Al _a Hf _b Nb _c M _d Ti _e Zr _f ) _100‑x Si _x Wherein M is one of Cr and Mo, a b c e f=1:1:1:1:1, x is more than 0 and less than or equal to 5, and the refractory high-entropy alloy material can form continuous and compact HfSiO under the high-temperature environment of 1300 ℃ ₄ Protective composite oxide film, inhibit O ^‑ And continuous diffusion of metal cations, a continuous oxidation weight gain of 20mg/cm or less within 10 hours ² Has excellent oxidation resistance. The refractory high-entropy alloy is obtained by a preparation method of respectively vacuum smelting Hf, nb, zr, M high-density or high-melting-point elements and finally alloying and smelting Al, ti and Si low-density or low-melting-point elements.

Description

A refractory high-entropy alloy resistant to high-temperature oxidation at 1300°C and its preparation method

Technical field

The invention relates to the technical field of high-temperature metal materials, and specifically relates to a refractory high-entropy alloy that is resistant to high-temperature oxidation at 1300°C and a preparation method thereof.

Background technique

The service temperature of the hot-end components of the new generation of advanced military aviation aircraft with high thrust-to-weight ratio has exceeded 1300°C. Traditional high-temperature alloys such as INCONEL718, Haynes230, MAR-M247, etc., due to the limitation of the melting point of the alloy main element, the service temperature does not exceed 1200°C. Unable to meet service requirements, there is an urgent need to develop new high-temperature materials with excellent high-temperature mechanical properties and high-temperature oxidation resistance. Refractory high-entropy alloys have become potential new high-temperature materials due to their high operating temperature range and high-temperature strength and toughness matching characteristics.

The concept of refractory high-entropy alloy was proposed based on the traditional high-entropy alloy concept. It was started in 2010. The main elements are composed of Hf, Nb, Ta, Ti, Zr, V, Cr, Mo, and W. The current main research direction is focused on Preparation method, microstructure, performance matching, strengthening and toughening mechanism. The main advantage of refractory high-entropy alloy is that its operating temperature range exceeds 1200°C, and it can still maintain good strength in high temperature environments above 1200°C. , toughness, meeting the use needs of aero-engine blades and blisks.

However, the biggest problem currently limiting the application of refractory high-entropy alloys is their room temperature brittleness and poor oxidation resistance. Research has found that the oxidation increase of refractory high-entropy alloys at the same high temperature is much higher than that of high-temperature alloys and even higher than that of stainless steel. This is because the constituent elements of refractory high-entropy alloys often contain W, Mo, and V. Such elements are The oxides generated in high-temperature environments are extremely volatile and affect the overall anti-oxidation performance. Secondly, the refractory high-entropy alloy system is composed of multiple elements in nearly equiatomic proportions. Theoretically, within a certain period of time, all elements in the system can be Oxidation, which makes it difficult for refractory high-entropy alloys to form a single protective oxide such as Al ₂ O _3. Instead, it will form a variety of complex complex oxides, such as MBO ₄ , MB ₂ O ₆ , etc. These oxides They are rare in traditional alloys and their properties are not clear, which also makes it difficult to design and improve the oxidation resistance of refractory high-entropy alloys.

Contents of the invention

In view of the problem of poor oxidation resistance of existing refractory high-entropy alloys, the purpose of the present invention is to provide a refractory high-entropy alloy that is resistant to high-temperature oxidation at 1300°C and a preparation method thereof, by adding Si elements and adjusting the types and types of elements in the alloy system. The content enables the alloy to form a typical three-layer oxide film structure in a high temperature environment of 1300°C. The outer oxide layer product is mostly Al ₂ O ₃ and the middle layer is a continuous and dense protective HfSiO ₄ oxide film. This structure can It inhibits the continuous diffusion of O anions and metal cations, so that the continuous oxidation weight gain of this refractory high-entropy alloy is ≤20 mg/cm ² within 10 hours of exposure to a high temperature environment of 1300°C. It has excellent anti-oxidation properties, and the refractory high-entropy alloy has excellent anti-oxidation properties. The preparation process of high-entropy alloys is simple and easy to operate.

In order to achieve the above objects, the technical solutions adopted by the present invention are as follows:

A refractory high-entropy alloy that is resistant to high-temperature oxidation at 1300°C. Its chemical expression is (Al _a Hf _b Nb _c M _d Ti _e Zr _f ) _{100- x} Si _x , a, b, c, d, e, f , x is the atomic percentage; among them, M is one of Cr and Mo, a:b:c:d:e:f=1:1:1:1:1:1, 0<x≤5.

The refractory high-entropy alloy can form a typical three-layer oxide film structure in a high temperature environment of 1300°C. The outer oxide layer product is mostly Al ₂ O ₃ and the middle layer is a continuous and dense protective oxide film.

In a high-temperature environment of 1300°C, the refractory high-entropy alloy can form a continuous and dense HfSiO ₄ protective composite oxide film in the middle layer due to the addition of Si in the alloy system, and the diffusion and filling of Si ions at high temperatures, inhibiting The continuous diffusion of O anions and metal cations, the continuous oxidation weight gain within 10 hours is ≤20 mg/cm ² , and it has excellent antioxidant properties.

The preparation method of the refractory high-entropy alloy that is resistant to high-temperature oxidation at 1300°C adopts vacuum arc melting. First, low-density or low-melting-point elements of Al, Ti, and Si are alloyed and smelted, and then turned over five times, and then Hf, Nb, Zr, M high-density or high-melting point elements are alloyed and smelted, turned over more than 5 times, and finally the two alloy ingots are alloyed and smelted again to obtain the refractory high-entropy alloy.

The advantages and beneficial effects of the present invention are as follows:

1. The refractory high-entropy alloy of the present invention can withstand high-temperature oxidation at 1300°C. Under a high-temperature environment of 1300°C, a typical three-layer oxide film structure can be formed, and the outer oxide layer product is mostly Al ₂ O ₃ .

2. In the refractory high-entropy alloy system of the present invention, the reaction free energy of HfO ₂ generated by the combination of Hf and O is the most negative, so the refractory high-entropy alloy of the present invention must be formed first in the initial oxidation stage. A large amount of HfO2, while a small amount of Si element is added, can diffuse and fill the gaps between Al ₂ O ₃ and HfO ₂ at high temperatures based on the properties of oxide semiconductors, and chemically react to generate new HfSiO ₄ composite oxidation products, forming continuous and dense HfSiO ₄ The protective oxide film inhibits the continuous diffusion of O anions and metal cations. The continuous oxidation weight gain within 10 hours is ≤20 mg/cm ² and has excellent antioxidant properties.

3. The preparation method of the refractory high-entropy alloy according to the present invention can be realized by simple vacuum arc melting, and the operation is simple.

Description of the drawings

Figure 1 is a continuous oxidation curve of the refractory high-entropy alloy of the present invention in a high temperature environment of 1300°C.

Figure 2 is an SEM image of the surface and cross-sectional morphology of the refractory high-entropy alloy of the present invention after high-temperature oxidation at 1300°C; wherein: (a) surface oxidation product; (b) oxide layer cross-section; (c) is (b) enlarge.

Figure 3 is an EDS element distribution chart of the surface oxidation product of the refractory high-entropy alloy of the present invention after high-temperature oxidation at 1300°C.

Figure 4 is an EDS element distribution chart of the cross-sectional oxidation product of the refractory high-entropy alloy of the present invention after high-temperature oxidation at 1300°C.

Figure 5 is an EDS element distribution chart of the cross-sectional oxidation product of the refractory high-entropy alloy of the present invention after high-temperature oxidation at 1300°C.

Figure 6 is an XRD pattern of the oxide film of the middle dense layer of the refractory high-entropy alloy of the present invention after high-temperature oxidation at 1300°C.

Figure 7 is a TEM image of the internal oxidation zone structure of the refractory high-entropy alloy of the present invention after high-temperature oxidation at 1300°C.

Figure 8 is a TEM high-magnification EDS element distribution diagram of the internal oxidation zone structure of the refractory high-entropy alloy of the present invention after high-temperature oxidation at 1300°C.

Detailed ways

The present invention will be described in detail below with reference to the drawings and examples.

The chemical expression of the refractory high-entropy alloy that is resistant to high-temperature oxidation at 1300°C is (A _a Hf _b Nb _c M _d Ti _e Zr _f ) _100-x Si _x , a, b, c, d, e, f, x are atomic percentages; among them, M should be one of Cr and Mo, a:b:c:d:e:f=1:1:1:1:1:1, 0 <x≤5. This refractory high-entropy alloy can withstand high-temperature oxidation at 1300°C. Under a high-temperature environment of 1300°C, it can form a typical three-layer oxide film structure, and the outer oxide layer product is mostly Al ₂ O ₃ . Moreover, in the refractory high-entropy alloy system of the present invention, the reaction free energy of _HfO2 generated by the combination of Hf and O is the most negative, so the refractory high-entropy alloy of the present invention must be formed first in the initial oxidation stage. A large amount of HfO2, and in the refractory high-entropy alloy system of the present invention, a small amount of Si element is added, based on the oxide semiconductor properties at high temperature, it can diffuse and fill the gap between Al ₂ O ₃ and HfO ₂ , and chemically react to generate new HfSiO ₄ complex oxidation products form a continuous and dense HfSiO ₄ protective oxide film, which inhibits the continued diffusion of O anions and metal cations. The continuous oxidation weight gain within 10 hours is ≤20 mg/cm ² and has excellent antioxidant properties.

Example 1:

In this embodiment, the chemical expression of the refractory high-entropy alloy is (A _a Hf _b Nb _c M _d Ti _e Zr _f ) _100-x Si _x , a, b, c, d, e, f, x is the atomic percentage; among them, M is one of Cr and Mo, a:b:c:d:e:f=1:1:1:1:1:1, 0<x≤5. Using the vacuum arc melting method, firstly alloy and smelt low-density or low-melting-point elements of Al, Ti, and Si, and turn them over 5 times. Then, alloy and smelt high-density or high-melting-point elements such as Hf, Nb, Zr, and M, and turn them over 5 times. Above, the two alloy ingots are finally alloyed and smelted again. After 10 hours of continuous oxidation in a high-temperature environment of 1300°C, the mass increase of the produced refractory high-entropy alloy does not exceed 20 mg/cm ² , as shown in Figure 1, curves No. 1, 2, and 3 in Figure 1 It is obtained by testing with Si content 0<x≤5. At the same time, the refractory high-entropy alloy of the present invention can form a typical three-layer oxidation structure, as shown in Figures 2(b) and 2(c). It can be observed that this The intermediate oxide film of refractory high-entropy alloy is continuous and dense. It can be seen from Figure 2(a) and Figure 3 that the surface oxide of this refractory high-entropy alloy is mostly Al ₂ O _3. It can be seen from the EDS element distribution results of the cross-sectional oxide film in Figures 4 and 5 that this refractory high-entropy alloy is refractory. After the molten high-entropy alloy is oxidized at high temperature of 1300°C, a continuous dense middle oxide film enriched in Hf and Si elements is formed, and O elements are mostly enriched in the surface layer. This is because the middle dense oxide film prevents the inward flow of O anions. Continuous diffusion, further analysis of the XRD diffraction pattern in Figure 6 shows that the main phase component of the middle layer oxide film rich in Hf and Si elements formed by this refractory high-entropy alloy is HfSiO ₄ , forming the main component of the composite oxide. The reason is that in the refractory high-entropy alloy system of the present invention, the quantitative addition of Si element can continue to diffuse and fill the gaps between Al ₂ O ₃ and HfO ₂ through semiconductor characteristics, and chemical reactions can occur to generate new HfSiO ₄ composite oxides. The product forms a continuous and dense HfSiO ₄ protective oxide film. It can be seen from the TEM analysis results of the internal oxidation zone in Figure 7 that this refractory high-entropy alloy forms three oxides at 1300°C, showing three colors of black, white and gray. The high-magnification dark field image and transmission electron EDS element distribution of Figure 8 The observation results show that Si element can exist in Hf-O, Al-O and other oxides in the form of filling or reaction, which further proves the effect of quantitative addition of Si element in this refractory high-entropy alloy on improving the oxidation resistance. To sum up, As mentioned above, the refractory high-entropy alloy system proposed in this embodiment and the produced refractory high-entropy alloy material have excellent oxidation resistance in a high temperature environment of 1300°C.

Example 2:

The difference from Example 1 is that the expression of the refractory high-entropy alloy system is (A _a Hf _b Nb _c M _d Ti _e Zr _f ) _{100- x} Si _x , a:b:c:d:e:f =1:1:1:1:1:1, M is one of Cr and Mo, but x=6. At this time, after 10 hours of high-temperature oxidation at 1300°C, the weight of the alloy system exceeds 30 mg/cm ² , the oxidation resistance of the alloy decreases. The specific analysis is shown in curve No. 4 in Figure 1.

Example 3:

The difference from Example 1 is that the expression of the refractory high-entropy alloy system is (A _a Hf _b Nb _c M _d Ti _e Zr _f ) _{100- x} Si _x , a:b:c:d:e:f =1:1:1:1:1:1, 0<x≤5, but M is Ta element. At this time, after 10 hours of high-temperature oxidation at 1300°C, the weight of the alloy system exceeds 50mg/cm ² , and the alloy The antioxidant performance dropped significantly. The specific analysis is shown in curve No. 5 in Figure 1. .

Example 4:

The difference from Example 1 is that the expression of the refractory high-entropy alloy system is (A _a Hf _b Nb _c M _d Ti _e Zr _f ) _{100- x} Si _x , M is one of Cr and Mo, 0< x≤5, but a:b:c:d:e:f≠1:1:1:1:1:1, the oxidation resistance of the refractory high-entropy alloy at this time is still greatly reduced and it is unable to form a continuous dense Intermediate protective oxide film.

It can be seen from the above examples and comparative examples that the refractory high-entropy alloy of the present invention can withstand high-temperature oxidation at 1300°C. Under a high-temperature environment of 1300°C, a typical three-layer oxide film structure can be formed, and the outer oxide layer product Mostly Al ₂ O ₃ . In the refractory high-entropy alloy system of the present invention, the reaction free energy of _HfO2 generated by the combination of Hf and O is the most negative, so the refractory high-entropy alloy of the present invention must first generate a large amount of HfO2 in the initial oxidation stage. , and the small addition of Si element can diffuse and fill the gaps between Al ₂ O ₃ and HfO ₂ at high temperatures based on the properties of oxide semiconductors, and chemically react to generate new HfSiO ₄ composite oxidation products, forming a continuous and dense HfSiO ₄ protective layer. The oxide film inhibits the continuous diffusion of ^O- and metal cations. The continuous oxidation weight gain within 10 hours is ≤20 mg/cm ² and has excellent antioxidant properties. This preparation technology also provides guidance for the design and preparation of materials for high temperature environments above 1200°C.

Claims (4)

1. A refractory high-entropy alloy resistant to oxidation at high temperatures of 1300 ℃, characterized by: the refractory high-entropy alloy has a chemical expression of (Al _a Hf _b Nb _c Cr _d Ti _e Zr _f ) _100-x Si _x Wherein: a. b, c, d, e, f, x is an atomic percent; a, b, c, d, e, f=1:1:1:1:1, x is more than 0 and less than or equal to 5.

2. The refractory high-entropy alloy resistant to high-temperature oxidation at 1300 ℃ according to claim 1, wherein: the alloy forms a typical three-layer oxide film structure under the high-temperature environment of 1300 ℃, and the products of the outer oxide layer are mostly Al ₂ O ₃ The middle layer is a continuous and compact protective oxide film.

3. The refractory high-entropy alloy resistant to high-temperature oxidation at 1300 ℃ according to claim 2, wherein: the alloy forms continuous dense HfSiO in the middle layer under the high temperature environment of 1300 DEG C ₄ Protective composite oxide film for inhibiting continuous diffusion of O anion and metal cation, and continuous oxidation weight gain within 10 hours is less than or equal to 20mg/cm ² Has excellent oxidation resistance.

4. A method for preparing a refractory high entropy alloy resistant to oxidation at high temperatures of 1300 ℃ according to any one of claims 1 to 3, characterized by: the method adopts a vacuum arc melting mode, al, ti and Si are subjected to alloying melting for more than 5 times, then Hf, nb, zr and Cr are subjected to alloying melting for more than 5 times, and finally two alloy ingots are subjected to alloying melting again to obtain the refractory high-entropy alloy.