Microstructure and high temperature mechanical properties of refractory Cr-Nb-Ti-Zr alloy prepared by laser directed energy deposition

The microstructure and mechanical properties of Cr-Nb-Ti-Zr complex concentrated alloy (CCA) prepared from the blend of elemental powders by laser directed energy deposition (L-DED) technique were investigated. Variation of the laser power and laser-induced substrate platform preheating were utilized to deposit 3D bulk samples. Deposition at maximum laser power of 500 W followed by long-term homogenization heat treatment at 1200 °C results in the crack free, locally homogeneous material. The final chemical composition of the deposited sample Cr15-Nb28-Ti23-Zr34 differs from the equimolar composition of the blended elemental powders due to Cr evaporation during deposition. The homogenized microstructure is formed by equiaxed grains with the size below 100 μm and fine Cr 2 (Zr, Nb, Ti) Laves phase particles dispersed predominantly at grain boundaries. Mechanical properties were investigated by compression tests at RT, 400 °C and 800 °C. At RT, the homogenized alloy exhibits yield stress of 1558 MPa (ductility is about 8 %). Deformation at 400 °C decreases the yield stress by 20 %, while the ductility remained unchanged. Serrated flow appearing at compression curves at 400 °C can be attributed to the PLC effect. It was shown that L-DED technique can produce refractory CCAs directly from elemental powders by careful optimization of processing parameters. Deposition with a thermally insulating platform effectively suppresses crack formation and reduces the number of unmelted Nb particles. However, the utilization of the homogenization heat treatment after the deposition is required to achieve microstructural homogeneity at the length-scale of powder particles (tens of micrometers). • Directed energy deposition of Cr-Nb-Ti-Zr alloy from blended elemental powders. • The use of a thermally insulated plate reduces the number of unmelted Nb particles. • Cr 2 (Nb, Ti, Zr) Laves phase was formed during the homogenization heat treatment. • The homogenized alloy exhibits yield stress of 1558 MPa and ductility of 8 % at RT. • The Portevin–Le Chatelier effect was observed during deformation at 400 °C.