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【Popular Science Series】A new generation of materials in high temperature environment - refractory high-entropy alloy

  • Time: 2023-02-23
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Research Purpose


With the development of aerospace technology, reusable aircraft have become one of the hot spots in the field of aerospace. Severe aerodynamic heating phenomena can have a great impact on the aircraft, such as structural failure, equipment failure, and even flight accidents. The high temperature performance and heat resistance of traditional materials can no longer meet the requirements of hypersonic vehicles, and it is urgent to develop a new generation of high-entropy alloys (HEAs) used in high temperature environments, which is a new type of alloy composed of more than five major elements, and the atomic fraction of each principal element is in the range of 5% ~ 35%, which is considered to be one of the three major breakthroughs in alloying theory in recent decades. High-entropy alloys have a series of excellent properties such as high strength, high room temperature toughness, wear resistance, oxidation resistance, corrosion resistance and thermal stability.


Definition of refractory high-entropy alloys


High-entropy alloys (HEAs) are a new type of alloy composed of more than five major elements, and the atomic fraction of each principal element is in the range of 5%~35%, which is considered to be one of the three breakthroughs in alloying theory in recent decades. High-entropy alloys have a series of excellent properties such as high strength, high room temperature toughness, wear resistance, oxidation resistance, corrosion resistance and thermal stability.


Refractory high entropy alloys (RHEAs) are a new type of high-entropy alloys with refractory metal elements with melting points higher than 1650 °C as the main elements. Refractory high-entropy alloy has a high melting point and excellent high-temperature performance because most of the constituent elements are high melting point elements, while the alloy has the characteristics of high-entropy alloy, becoming one of the very potential superalloys.


As a potential high-temperature load-bearing structure and high-temperature heat-resistant coating material, refractory high-entropy alloy can be widely used in petrochemical, aerospace and other fields, and has great application potential in the future. At present, people's research on refractory high-entropy alloys is still in the initial stage, as an emerging field of material research, refractory high-entropy alloys have high research value and broad application prospects.

Preparation method


Refractory high-entropy alloys are mainly divided into three types: blocks, coatings, and thin films. At present, the methods for preparing refractory high-entropy alloys are mainly vacuum arc melting, powder metallurgy, vacuum magnetron sputtering, laser cladding and other methods. The preparation methods and advantages and disadvantages of different types of refractory high-entropy alloys are shown in Table 1.


High temperature mechanical properties


As a high-performance alloy composed of high melting point elements, refractory high-entropy alloys have outstanding high-temperature mechanical properties (high strength), and are expected to be candidates for high-temperature alloy materials for aerospace engines and turbine blades. As shown in Figure 2, the compressive strength of conventional superalloys Inconel 718 and Haynes 230 decreases significantly above 800 °C compared to refractory high-entropy alloys. When the temperature is higher than 900 °C, the compressive strength of refractory high-entropy alloys is greater than that of traditional superalloys, showing excellent high-temperature mechanical properties.


High temperature mechanical properties


As a high-performance alloy composed of high melting point elements, refractory high-entropy alloys have outstanding high-temperature mechanical properties (high strength), and are expected to be candidates for high-temperature alloy materials for aerospace engines and turbine blades. As shown in Figure 2, the compressive strength of conventional superalloys Inconel 718 and Haynes 230 decreases significantly above 800 °C compared to refractory high-entropy alloys. When the temperature is higher than 900 °C, the compressive strength of refractory high-entropy alloys is greater than that of traditional superalloys, showing excellent high-temperature mechanical properties.


Conclusion


As a potential high-temperature load-bearing structure and high-temperature heat-resistant coating material, refractory high-entropy alloy can be widely used in petrochemical, aerospace and other fields, and has great application potential in the future. At present, people's research on refractory high-entropy alloys is still in the initial stage, as an emerging field of material research, refractory high-entropy alloys have high research value and broad application prospects.