Carbide evolution and its potential reduction methods in Ti-22Nb based alloys prepared by metal injection moulding

Abstract

Carbide evolution was investigated in order to find methods to reduce the carbide precipitation because it lowers the ductility of metal injection moulded <beta>-Ti alloys. Comparing Ti-22Nb and Ti-22Nb-2/10Zr alloys, the crystal structure of carbides is unchanged, but the lattice parameter of <beta>-Ti increases, then carbide fraction slightly decreases. Dissolution of carbides occurs fast around <beta>-transus temperature via short circuit diffusion but it becomes slow with decreasing temperature because of uniform atomic detachment. Based on these results, a multiple step treatment was proposed which in conjunction with grain refinement by adding Y/Y2O3, can significantly decrease the carbide fraction of Ti-22Nb-10Zr-xY/Y2O3.