Study on annealing treatment of NbMoTaTiNi high-entropy alloy with ultra-high strength disordered-ordered transition structure for additive manufacturing

Abstract

In this paper, an ultra-high-strength, fine-grained NbMoTaTiNi high-entropy alloy was formed by SLM(selective laser melting). The compressive yield strength at room temperature can reach 1728Mpa, the ultimate strength is as high as 2753 MPa, the strain is 21.75 %, and the tensile strength is 1205Mpa. The as-cast alloys were annealed at 600 ℃, 800 ℃, 1000 ℃, 1200 ℃, and 1300 ℃ to study their microstructure and mechanical properties. After annealing at 1200 ℃, the compressive plasticity of the alloy is as high as 33.55 %, an increase of 54.3 %. With the increase of annealing temperature, the alloy gradually transforms from dendrites to cellular crystals, and the XB phase, which is the grain boundary phase resists thermal stress crack defects through stacking faults. The calculation of alloy stability parameters shows that the alloy forms a disordered (matrix phase)-transition (XB grain boundary phase)-ordered (B2 grain boundary phase) structure, and with the increase of annealing temperature, the lattice distortion of the matrix phase decreases. The matrix phase tends to be more disordered and stable. The lattice distortion of the B2 phase increases and the B2 phase tends to be more ordered and stable, and the XB phase increases the stability of the disorder-ordered phase boundary of the alloy. In this paper, through the research on the annealing process of NbMoTaTiNi high-entropy alloy, the plasticity of NbMoTaTiNi high-entropy alloy is improved, and the engineering application of NbMoTaTiNi high-entropy alloy in aerospace, nuclear energy and other fields is proposed.