Coherent precipitation of cuboidal nanoparticles in Al1Ti5Zr4Nb3Ta3 lightweight refractory high entropy alloy based on laser metal deposition

Abstract

Usually, the Al-containing lightweight refractory high entropy alloys (RHEAs) prepared by casting require complex heat treatment to obtain BCC/B2 coherent microstructure, thereby achieving excellent room temperature (RT) and high temperature (HT) mechanical properties. In this work, we design a novel lightweight RHEA of Al₁Ti₅Zr₄Nb₃Ta₃ (ρ = 7.46 g·cm⁻³) via the cluster formula approach and utilize high cooling rate and in-situ heat treatment effects of laser metal deposition (LMD) to directly obtain the BCC/B2 coherent microstructure with cuboidal BCC nanoparticles precipitated. The LMD-fabricated alloy exhibits good formability, with equiaxed grains (∼ 38 μm in size) uniformly distributed along the deposition direction. Compared with the RT compressive yield strength of the as-cast alloy (σ_YS = 1070 MPa), the LMD-fabricated alloy exhibits a notable enhancement by 50 % reached to 1600 MPa, which is attributed to the unique BCC/B2 coherent microstructure. Furthermore, this LMD-fabricated alloy possesses prominent elevated temperatures mechanical properties (σ_YS = 1124 MPa at 873 K and σ_YS = 259 MPa at 1273 K) due to the excellent thermal stability of the BCC/B2 coherent microstructure. The exceptional yield strength of the LMD-fabricated alloy is mainly ascribed to the grain boundary strengthening, dislocation strengthening, precipitation strengthening, and solid solution strengthening. The present work provides a new strategy for the design and fabrication of high-strength and high-plasticity RHEAs.