The Superplasticity of Near Beta Titanium Alloy Ti-10V-2Fe-3Al

摘要

In this paper the superplasticity of Ti-10V-2Fe-3Al has been investigated. 130mm diameter hot-rolled bars (beta- transus temperature is 798℃)used in these experiments were possessed of finer alpha+beta dual'-phase microstructure and better superplasticity (El is 532%).Thermomechanical treatment process(860℃,>60% deformation, water cooling +780℃, >60% deformation, water cooling+780℃,>60% deformation, air cooling+750℃,1 hour annealing, air cooling) was used for above-mentioned rolled bars. Homogeneous and fine equiaxed crystal microstructure was obtained and the size of globular primary alpha phases is smaller than 2.5μm. Therefore the alloy appears excellent superplasticity, the average elongation is 845% and the elongation of 1087% is reached in individual specimen. The process is an effective way to refine the microstructure of Ti-10V-2Fe-3Al. In this process the heavy reduction is first carry out in beta field so that fine beta recrystallization grains form, followed by water quenching from beta field so that the fine metastable beta, alpha double prime and omega phases are obtained. Afterwards the heavy reduction is carried out in alpha+beta field and grain boundary alpha films and fine acicular alpha phases within beta grains resolved during forging heating are broken and refined and spheroidized through recrystallization ,finally followed by spheroidizing annealing . The tensile specimens treated with this processing appear superplasticity (El=197%～845%), in the range of temperature from 700℃ to 820℃ and the strain rate from 1.1x10~(-2)s~(-1) to 1.1 x 10~(-4)s~(-1). The optimal superplastic deformation condition is 750℃ and 3.3 x 10~(-4)s~(-1), at which the average elongation is 845% and the flow stress is 27.9MPa. Near beta titanium alloy Ti-10V-2Fe-3Al is a favorable superplastic alloy and suitable for isothermal superplastic deformation.