Microstructural stability and mechanical properties of the non-equiatomic NbCrTiMoVHf refractory complex concentrated alloy

In this study, the refractory complex concentrated alloy (RCCA) NbCrTiMoVHf was subjected to high-temperature heat-treatment to investigate its microstructural stability and its implications for mechanical properties. Heat-treatment (HT) in the temperature range of 800–1200 °C for 1 h in a vacuum led to the evolution of disordered BCC and C15 Laves (HfV₂) phases. The dendritic regions primarily exhibited a disordered BCC structure, while the interdendritic (ID) regions contained the Laves phase. Elemental distribution was inhomogeneous, with higher concentrations of Hf and Cr in the ID regions, whereas Mo and Nb were more prevalent in the dendritic arms. Microsegregation in the ID regions promoted the formation of HfV₂ and Ti–rich phases in both as-cast and heat-treated samples. The as-cast sample comprised approximately 30% HfV₂ and 70% BCC phases, while HT reduced the HfV₂ fraction to 22–25%. Further evolution of the HfV₂ Laves phase occurred in the dendritic regions when RCCA sample underwent prolonged HT at 1200 °C for 96 h, indicating microstructural instability. The as-cast material exhibited high strength, approximately 1.3 GPa, at an operating temperature of 1000 °C. Notably, the strength remained stable after HT at various temperatures. Indentation hardness measurements revealed a higher modulus of elasticity (E) in the dendritic regions compared to the ID regions across all the RCCA conditions. Overall, the newly developed NbCrTiMoVHf RCCA demonstrated excellent mechanical properties at both room and elevated temperatures, highlighting its potential for high-temperature applications.