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

Abstract

Cyclic thermal exposure tests of infrared heating to 800 °C in 120 s followed by compressed air cooling to 150 °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 β phase, area fraction of α 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 β phase, area fraction of α phase and microhardness of the alloy. The original fine basket-weave β and 78.5% α transform to transient wedge-like β, finally leaving granular β and 97.6% coarsened α with the increased thermal exposure cycles. The formation mechanism of coarsened α and broken-up β microstructure is discussed. The alloy after 750 thermal exposure cycles has the maximum microhardness, 33.3% higher than that of the as-deposited alloy.