Microstructure evolution of laser deposited Ti60A titanium alloy during cyclic thermal exposure

Cyclic thermal exposure tests of infrared heating to 800 degrees C in 120 s followed by compressed air cooling to 150 degrees C in 60 s were performed for the laser deposited Ti60A (Ti5.54Al3.38Sn3.34Zr0.37Mo0.46Si) alloy. The effects of thermal exposure cycles on length of beta phase, area fraction of alpha phase and microhardness of alloy were examined by OM, SEM and EDS. The results indicate that thermal exposure cycles have significant effects on length of beta phase, area fraction of alpha phase and microhardness of the alloy. The original fine basket-weave beta and 78.5% alpha transform to transient wedge-like beta, finally leaving granular beta and 97.6% coarsened alpha with the increased thermal exposure cycles. The formation mechanism of coarsened alpha and broken-up beta microstructure is discussed. The alloy after 750 thermal exposure cycles has the maximum microhardness, 33.3% higher than that of the as-deposited alloy.