Microstructure evolution in the local loading forming of TA15 titanium alloy under non-isothermal condition

In this paper, the microstructure evolution and processing-microstructure relationship in the non-isothermal local loading forming of TA15 titanium alloy were studied through an analog experiment. Some new microstructural mechanisms are found, which are different from those under isothermal local loading forming. In the non-isothermal local loading forming, the tri-modal microstructure consisted of equiaxed primary alpha, lamellar alpha and beta transformed matrix is achieved. The lamellar alpha, not produced under isothermal condition, is generated by beta -> alpha transformation due to the decrease of component temperature. With the same processing parameters, the volume fraction and grain size of primary alpha are both greater than those processed isothermally. The content of lamellar alpha decreases with heating temperature decreasing and little lamellar alpha can be found when the heating temperature drops to 930 degrees C. Under small deformation degree, the lamellar alpha distributes randomly in each feature region. As deformation increases, the lamellar a in transitional region and second-loading region present a preferred orientation perpendicular to the compression direction. The primary alpha content almost decreases linearly with heating temperature, which is different from the regular that under isothermal condition. Non-isothermal local loading forming with a higher heating temperature (near-beta region) offers a cost-efficient way for the manufacture of TA15 titanium alloy large-scale integral components. (C) 2012 Elsevier B.V. All rights reserved.