Microstructure evolution and nitriding mechanism of Ti‐6Al‐4 V alloy in alumina‐based refractories

Abstract

AbstractThe aims of this study were to explore the nitriding mechanism of Ti‐6Al‐4 V alloy in Al2O3‐based refractories. Al2O3‐based composite refractories were fabricated using Ti‐6Al‐4 V and sintered alumina as main materials, followed by nitriding at different temperatures in a nitrogen atmosphere. Phase and microstructure evolution of the products was analyzed by X‐ray diffraction and field‐emission scanning electron microscopy equipped with energy‐dispersive X‐ray spectroscopy. The results reveal a multi‐stage nitridation process of Ti‐6Al‐4 V at different temperatures. At 900°C, nitridation of the Ti‐6Al‐4 V surface results in the formation of a (Ti,V)N solid solution, while Al and V migrate inward, forming intermetallic compounds Ti3Al and a‐Ti (Ti1‐x‐yVxAly) with rich Al and V. At 1100°C, nitridation of Ti3Al produces intermediate products like Ti2AlN or Ti3AlN, with continued inward migration of Al or V to form the intermetallic α2 phase of (Ti1‐xVx)3yAly in the center of the alloy particles. At 1300°C, decomposition of Ti2AlN or Ti3AlN results in the outward migration of Al atoms and the presence of AlN on the outer layer of Ti‐6Al‐4 V particles, thus forming a hollow structure. Finally, at 1500°C, the (Ti,V)N solid solution grains grow as a result of further diffusion and dissolution of nitrogen.