Guang Yang

An Experimental Platform for Controlled Solidification and Heat Treatment and its Application in TiAl Alloys

An experimental platform for controlled solidification and heat treatment and its applications in TiAl alloys are reported. The controlled solidification facility can be used to study the microstructure evolution of metals and alloys during solidification process and the controlled heat treatment device can realize the complex heat treatments and high temperature quenching conveniently. Compared with the traditional experimental equipments, this platform has three advantages. First, it can precisely control heating and cooling speed as well as isothermal holding time during solidification and heat treatment. Second, the high temperature microstructure can be obtained by quenching with high accuracy. Third, these two devices are cheaper and suitable to use in laboratory.

Microstructure evolution of isothermal holding treatment during melt solidification of Ti–6Al–4V alloy

Abstract Effect of isothermal holding treatment in the solidification process on the microstructure of Ti–6Al–4V alloy was studied by temperature controlled induced melting apparatus. The result shows that with isothermal holding treatment above the β transus temperature during solidification, the colony structure consisting of parallel lamellae was obtained. While the isothermal holding treatment was set at 960 °C, a unique bi-modal microstructure consisting of coarse primary α and fine secondary lamellar α was obtained. The primary lamellar α tended to break into several pieces, globularize and present equiaxed morphology. The formation mechanism of the equiaxed α can be explained with the atom immigration, high density dislocations, combined action with the interface tension of formed α phase during the isothermal holding treatment. After the isothermal holding, the retained α matrix transformed into fine lamellar α, thus, bi-modal microstructure was acquired. Compared with the lamellar structure, the grain boundary α presented discontinuously and cannot be distinguished from the primary α lamellae easily. The size of colonies α was greatly decreased. The microstructure tended to be much more homogeneous in the whole section of the samples.