Kinetics of the α grain growth in a binary Ti–44Al alloy and a ternary Ti–44Al-0.15Gd alloy

Grain growth in the single α region was studied both in a binary Ti–44Al alloy and in a ternary Ti–44Al–0.15Gd alloy. Cast ingots were solution treated at 1623 K for various times from 2 min to 20 h and the average grain sizes were measured. The α grain growth was much slower in the Gd-containing alloy. The kinetics of grain growth can be described by the traditional power–law relationship between the grain size (μm) and time (s) with a rate constant of 308 μm/s0.17 and a time exponent of 0.17 for the binary alloy, and 316 μm/s0.045 and 0.045 for the Gd-containing alloy, respectively. Some ingots were solution treated at temperatures from 1543 to 1673 K for 1 h and the logarithmic grain size was plotted against reciprocal temperature. The activation energy obtained was 81 kJ/mol for the binary alloy and 50 kJ/mol for the ternary alloy. The implications of these values were discussed.