Microstructure and properties of Nb-Cr based multi-element alloy

A master alloy ingot of Nb-Cr based multi-element alloy has been prepared by vacuum non-consumable arc-melting, and then vacuum consumable arc-melting and heat treated at 1450°C for 24 h and 1000°C for 24 h, then oxidized at 950°C in air for different times for the heat treated samples. The room temperature fracture toughness is measured by a three-point bending method. It has been found that the Nb based solid solution (Nbss) transforms from dendrites into equiaxed grains, and the Cr₂(Nb, Ti, Hf) Leves phase transforms from blocks into rods with more smooth boundaries after heat treatment. The arc-melted samples rupture in a brittle cleavage mode, but the heat treated samples rupture in a quasi-cleavage mode. The scale is composed of CrNbO₄, HfO₂, TiO₂, CrNb₁₁O₂₉ and Ti₂Nb₁₀O₂₉ phases when the samples are oxidized at 950°C for different times.