High specific yield strength and superior ductility of a lightweight refractory high-entropy alloy prepared by laser additive manufacturing

Lightweight refractory high-entropy alloys (LRHEAs) exhibit lower density and better ductility than other refractory high-entropy alloys, which bestows upon them substantial prospects for application across diverse engineering domains. laser directed energy deposition additive manufacturing (LDED) technology emerges as an ideal process for preparing such refractory metals owing to its exceptional attributes, such as rapid cooling rates and design flexibility. In this study, a new LRHEA Al0.3NbTi3VZr1.5 was fabricated by LDED, and a comprehensive investigation was conducted to explore the microstructure evolution and the plastic deformation mechanisms. A graded microstructure with body-centered cubic (BCC) matrix, Laves phases near grain boundaries, and coarsened ω particles in the matrix is detected in as-deposited samples. In solid solution treated (SST) samples, the Laves phase disappears, and the ω particles decrease in size, forming a nanoscale two-phase mixture with the matrix. The as-deposited samples exhibit distinct brittle fractures, with a fracture strength of 902 MPa and 1% fractured strain. While the SST samples exhibit a considerable fracture strain of about 25 ± 2% with 1032 ± 12 MPa yield strength and a specific yield strength of 180 MPa·g−1·cm3. The high strength is mainly attributed to the solid-solution strengthening, while the excellent ductility is achieved by activating the unique deformation mechanism, including the formation of multi-stage microbands and kinking. The refinement of microband spacing accommodates more plastic deformation, and cross-slip further refines the microbands spacing in three dimensions. Microband-induced kinking effectively relieves local stress concentration and slows fracture. This work provides new insights into the design and preparation of LRHEAs using additive manufacturing technology and makes a remarkable contribution to the comprehensive and in-depth understanding of their plastic deformation mechanisms.