Influence of High-temperature Heat Treatment on Microstructure and Mechanical Property of AlZrNbMo Core High-entropy Alloy

The new generation of reactors puts forward more stringent requirements for fuel elements and structural materials. Under the action of multiple fields such as higher radiation fluence, higher operating temperature, complex stress and medium corrosion, the design and development of nuclear structural materials needs to balance various services such as radiation resistance, toughness, thermal conductivity, and corrosion resistance. Due to the balance of performance, conventional metal materials face greater challenges when balancing various service performance requirements due to their singleprincipal characteristics. The emergence of multiprincipal highentropy alloys provides ideas for the research and development of a new generation of nuclear structural materials. The radiation resistance and service performance brought by multiprincipal elements can be adjusted to become a new generation of reactor cladding materials. At present, lowneutron crosssection highentropy alloys for nuclear use usually have a BCC structure, and there are various phase structures, and their strength varies greatly with the change of the microstructure. At present, it is still difficult to control the microstructure and optimize the mechanical properties of BCC highentropy alloys. In order to achieve a significant improvement in the mechanical properties of lowneutron crosssection highentropy alloys for nuclear use, four lowneutron crosssections Zr (0.018 MPa), Al (0.02 MPa), Nb (0.11 MPa), and Mo (0.23 MPa) were used in this paper. Based on the elements, AlZrNbMo highentropy alloys with BCC structure were prepared by arc melting. The compressive mechanical properties test shows that the strength of AlZrNbMo highentropy alloys after hightemperature solution treatment at 1 200 ℃ increases by 31% compared with that of the ascast alloy, reaching about 2 210 MPa. Through comparative analysis of the ascast and 1 200 ℃ hightemperature solution of AlZrNbMo highentropy alloy phase composition, element distribution and other microstructures, it is found that there are various phase structures in the as-cast sample, including the main NbMorich BCC highentropy alloy phase, As well as the Al2Zr3 phase with intergranular tetragonal structure, there is a certain difference in Mo content in different intergranular regions, and there is also a small amount of elemental Zr. However, after the hightemperature heat treatment at 1 200 ℃ for 1 h, the phase structure and morphology distribution changes significantly, the NbMorich BCC highentropy alloy phase and intergranular size decrease by about 50%, and granular precipitates appear at the interface, all of which are beneficial to the improvement of strength. And the content of Nb and Mo in the intragranular phase region of the AlZrNbMo highentropy alloy after heat treatment greatly increases, resulting in an increase in the lattice distortion of the matrix phase, which is conducive to a significant increase in strength. At the same time, the intergranular black region in the original as-cast structure is Zrrich elemental particles region, and the strength is relatively low. With the rapid quenching after hightemperature heat treatment, the migration and diffusion of elements lead to the formation of more highhardness AlZr intermetallic phases, which is also conducive to a substantial increase in the strength of the alloy. The relevant results will provide theoretical reference and design basis for the design of new ultrahighstrength nuclear highentropy alloys.