Near Threshold Fatigue Crack Growth Behavior at Elevated Temperatures in Ti-6Al-4V Alloy and TiAl Intermetallic

Abstract

Near threshold fatigue crack growth (FCG) behavior under cyclic loading in TiAl intermetallic and Ti-6Al-4V alloy was investigated at elevated temperature. Crack opening displacement (COD) was measured by using the Laser speckle strain/displacement gage (SSDG) during the fatigue tests. It was found that the FCG rate in TiAl intermetallic at 800℃ was controlled by the effective stress intensity factor range ΔK_<eff>, while the FCG rate in Ti-6Al-4V alloy above 500℃ was controlled by the maximum stress intensity factor K_<max> as well as ΔK_<eff>. It was also found that the fatigue threshold ΔK_<eff, th> in TiAl intermetallic at 800C was higher than that in Ti-6Al-4V alloy above 500℃.