Effect of triple heat treatment on basket-weave structure and tensile properties of TC21 titanium alloy

Abstract:

The effect of heat treatment temperature and cooling rate on the basket-weave structure and tensile properties of TC21 titanium alloy is studied by triple heat treatment experiments. The results indicated that the microstructure of TC21 alloy presents a typical basket-weave structure, which is achieved by high temperature (990℃) solid solution in the β single-phase region, and then through high temperature(870~910℃)aging in the (α + β) phase region and low temperature (590℃) aging. With the increasing of the second heat treatment temperature, the content and length of the flake α phase decrease significantly, and the thickness of the flake α phase increases slightly, the strength of the alloy increases, the ductility decreases. After being treated with different cooling rates, the microstructure of TC21 titanium alloy consists of α phase, β phase and α′martensite in both water cooling and air cooling samples, but only α phase and β phase are identified in furnace cooled sample, Compared with the tensile properties of the three samples, the water cooling and air cooling samples showed better strength and poorer ductility, furnace cooling samples show good ductility and poor strength. The better triple heat treatment process for TC21 alloy is 990℃/1 h AC+870℃/1 h AC+590℃/4 h AC.

Key words:TC21 titanium alloy; triple heat treatment; basket-weave structure; Tensile properties