Surface Modification of Gamma-Titanium Aluminides with L1₂-Type Tri-Aluminides by Pack Cementation

Abstract

The surface of an L1₀-type TiAl base alloy has been modified by coating it with an L1₂-phase (AlMn)₃Ti(V) using a pack-cementation method in a temperature range of 1273–1473 K and with a treatment time of 18–72 ks. The structural morphology and composition distribution in the coat and substrate were analyzed by EPMA and XRD to examine the factors that control the thickness of the coat. Two-phase equilibrium was confirmed between the L1₀-phase substrate and the L1₂-phase coat at each temperature tested. Aluminum particulates, 1–2 μm in diameter, were observed inside the coat and were confirmed to be related to the experimental condition and to the increase in coat thickness. The coat is 35 μm thick at temperature range of 1373–1473 K, while at the temperature range of 1273–1323 K the thickness is 11–12 μm. The temperature dependence of coating layer is different from that was reported previously. The results are then discussed from facts basically revealed in this experiment and/or based on information about the phase equilibrium between L1₀ and L1₂.