Thermal stability and precipitation strengthening of fully lamellar Ti-45Al-5Nb-0.2B-0.75C alloy

Abstract

The alloy with a composition Ti-45A1-5Nb-0.2B-0.75C (at.%) was prepared by induction melting and centrifugal casting. The fully lamellar microstructure of the alloy without carbides was produced by heat treatment consisting of hot isostatic pressing (HIP) and solution annealing followed by cooling to room temperature. The stability of the fully lamellar gamma(TiAl) + alpha 2(Ti3Al) microstructure was studied at temperatures of 750, 850 and 950 degrees C up to an ageing time of 3400 h. The microstructure analysis shows that the most dominant change in the microstructure was the a2 lamellae thinning, which was more pronounced at a higher ageing temperature and longer time. The formation of recrystallized gamma grains and Ti2AlC carbides was observed during ageing at the temperatures of 850 and 950 degrees C. The microstructural changes affected the microhardness at room temperature (RT) and compression yield strength at temperatures ranging from RT to 950 degrees C.