In-situ twin-wire additive manufacturing: Integrated fabrication of refractory medium entropy alloy, correlation between orientation and slip systems activation

An innovative approach, i.e., twin-wire ‘co-pointed’ synergistic additive manufacturing implemented to create crack-free refractory medium entropy alloys eliminating costly powders, has been realized in this work. A self-designed twin-wire co-pointed strategy is suitable for near and high melting point elements. While the electron beam freeform fabrication (EBF³) process exhibits low porosity and defects and significant compositional homogeneity under a stabilized liquid bridge transfer mode, the mechanical properties and their dependence on orientation were studied in detail. Microstructural results of fabricated target non-equiatomic TiZrNbHf reveals a single-phase body centered cubic structure and typical columnar features with a <100>//building direction (BD) fiber texture. Tensile specimens taken from horizontal (<100>⊥tensile direction) and vertical (<100>//tensile direction) directions exhibit a comparable yield strength of 615.39 ± 7.88 MPa and 592.84 ± 5.95 MPa, with the failure elongations of 20.56 ± 1.00 % and 21.45 ± 0.72 %, respectively. In-situ EBSD characterization during tension reveals dislocation slip with {112} as the dominant plane as the only deformation mode. However the grain orientation affects the activation of slip systems, revealing non-Schmid factor behavior exists and determined by the grain boundary misorientation angle rather than the geometric compatibility factor. Horizontal grains enhanced the strength through a hard-oriented heterogeneous structure, while the vertical ones are prone to slip transfer on the same plane and wavy cross-slip to promote uniform deformation.