Unravelling thermal-mechanical effects on microstructure evolution under superplastic forming conditions in a near alpha titanium alloy

Abstract

The superplastic formability of titanium alloys has been extensively exploited by various industries, especially for manufacturing of high value aerospace components. Material's microstructural characteristics, such as grain size and dislocations density, determine superplastic formability during manufacturing process and various constitutive relationships have been proposed to take their effects into consideration in modelling and simulation. However, most existing models do not include all these characteristics in their analyses due to the limitations in characterization techniques. This paper reports the results of a systematic study on the effects of thermal (i.e., static) and mechanical (i.e., dynamic) process parameters on the evolution of dislocations and microstructure, both independently and simultaneously, at superplastic forming regime. The evolution of microstructural phase fraction, grain size, crystallographic texture, and geometrically necessary dislocation (GND) density are investaged over a temperature range of 880–920 °C and under strain rates between 0.0005 and 0.01s−1. The results provide valuable insights into the microstructure evolution during superplastic forming on TA15 titanium alloy and form a basis for future physically based constitutive modelling.

Keywords

• Superplastic forming
• Dynamic crystallization
• Microstructure evolution
• Dislocation