Optimization of microstructure and properties in high-strength coherent BCC/B2 multi-principal element alloys via laser directed energy deposition

Abstract

Body-centered-cubic (BCC)-based multi-principal element alloys (MPEAs) are considered promising materials due to their excellent mechanical properties, particularly at elevated temperatures. However, their limited processability and high melting points impose significant challenges for the fabrication of load-bearing components by conventional casting. This work demonstrates the successful development of a novel BCC-based MPEA of Al₂Ti₄Zr₄Nb₃Ta₃ through laser directed energy deposition (LDED). The additive manufactured cylindrical components exhibit excellent formability without cracks and distortion. The LDED processing promotes the in-situ microstructural optimization of the alloy, forming a homogeneous coherent BCC/B2 microstructure with cuboidal BCC nanoparticles precipitated in the B2 matrix, and achieving ultra-high yield strength of 2013 MPa at room temperature. The excellent strength is primarily attributed to the precipitation strengthening of cuboidal BCC nanoparticles and solid solution strengthening of alloying elements. Moreover, the LDED alloy exhibits a yield strength of 1380 MPa at 873 K and retains a yield strength of 290 MPa even at 1273 K. This work provides feasible avenue for additive manufacturing of BCC-based MPEAs, thereby facilitating their industrial applications.