Influence of Gradient Heat Treatment on Microstructure and Microhardness in Weld Seam of Ti3Al/TC11 Dual Alloys

The changes of the microstructure and the microhardness at the weld interface of near isothermally forged Ti3Al/TC11 dual alloys before and after gradient heat treatment were investigated. The results indicate that the stability of α2 phase and distribution in the grain boundary results in slight changes of microstructures at heat-affected zone on Ti3Al side, but the changes of the microstructure in the weld zone are relatively obvious due to the diffusions of elements such as Ti, Al, Nb and so on. Because growing-up of the α and α2 phase is restricted each other, the continual α or α2 phase grain boundary can not be formed. After gradient heat treatment, the matrix microstructure of the TC11 alloy changes from basketweave structure to equiaxed structure. Because of the diffusions of Ti, Al and Nb, the sizes of α and α2 phases become small and their distribution become dispersive, resulting in the increase in microhardness.