レーザー溶融反応によるチタンのアルミナイジングとその耐酸化性

抄録

In order to produce aluminide coatings with an excellent oxidation resistance, aluminizing of titanium substrate was conducted utilizing a high power infrared laser fusion reaction. Titanium substrate painted with aluminum powder was laser fused in argon gas atmosphere. Three types of titanium aluminide coatings of 150μm thickness, i.e., single phase of Ti₃Al, TiAl and composite phase of TiAl₃+Al, could easily be produced with a high reproducibility. The chemical composition of these coatings could be controlled by choosing both the laser irradiation conditions and the amount of painted aluminum powder. Corrosion resistance of these coatings was evaluated at 1073, 1173 and 1273K in the stagnant air. Changes of the composition and the stracture of the laser produced coatings during oxidation were carefully examined by SEM-EPMA and micro-area X-ray diffraction every 6 hours. The Ti₃Al coating was slightly oxidized already at 1073K according to a parabolic law. The TiAl coating was highly resistant to oxidation at 1073K, however, was oxidized at temperatures above 1173K. On the contrary, the composite coating of TiAl₃+Al showed an excellent performance against high temperature oxidation even at 1273K. Aluminum in this composite coating was oxidized during early short exposure and produced alumina of 160μm thickness which contributed as a diffusion barrier of oxygen. The high oxidation resistance of this coating was due to the formation of alumina by the oxidation of Al and also to the thermal diffusion of Al into the titanium substrate, resulting in a protective thick TiAl₃ layer.