Microstructural evolution in hot compressed TiHy 600 titanium alloy

Abstract

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 and 975oC and alpha
laths transformed from deformed beta grains at 1000oC and 1050oC.