Microstructural evolution in hot compressed TiHy 600 titanium alloy

Abstract

TiHy 600 alloy is a near alpha titanium alloy, widely used for gas turbine engine applications such as disc and blades for high pressure compressors. One drawback of this alloy is that it is susceptible to cold dwell fatigue, which is due to the presence of micro-textured zones. Thus, appropriate processing parameters (i.e. temperature, strain and strain rate) are required to reduce the size of the micro-textured region. In order to find out the optimized processing parameters, hot compression tests were performed up to 50% engineering strain at temperatures range of 900oC-1050oC and strain rate range of 10-3 to 101 s-1 using thermo-mechanical simulator (Gleeble 3800®). Flow behavior characteristics were studied from the data obtained during hot compression and processing map was developed at true strain of 0.6 using Dynamic Materials Modeling (DMM) approach. Microstructural examination of deformed TiHy 600 titanium alloy were carried out at a particular strain rate of 10-3 s-1 and temperatures of 900oC, 950oC, 975oC, 1000oC and 1050oC. Microstructural examination consists of orientation image mapping along compression direction using electron backscatter diffraction. Hot compression mostly resulted into new dynamic recrystallized (DRX) alpha grains at 900oC, mixture of deformed large alpha grains containing subgrain boundaries and transformed beta phase consisting of secondary alpha laths at 950oC and 975oC and alpha laths transformed from deformed beta grains at 1000oC and 1050oC.