HIGH-TEMPERATURE SULFIDATION AND OXIDATION BEHAVIOR OF SPUTTER-DEPOSITED AL-REFRACTORY METAL-ALLOYS

The sulfidation and oxidation behavior of sputter-deposited Al-Mo, Al- Nb, Al-Ta and Al-W binary alloys has been investigated under isotherma l-isobarometric conditions at the temperature ranging from 1073 to 127 3 K. High temperature sulfidation was carried out in He-S-2 atmosphere with sulfur vapor pressure kept constant at 1 kPa, and high temperatu re oxidation was carried out in Ar-O-2 atmosphere with oxygen pressure fixed to 20 kPa. In sulfidation tests, these alloys showed superior h igh temperature sulfidation resistance to the known metallic materials , and the sulfidation rates of these alloys were comparable to those o f refractory metals. The sulfide scales of these alloys were composed of bilayer, and it was revealed that the formation of the inner protec tive sulfide scale of refractory metal was responsible for the lower s ulfidation rate of these alloys. The oxidation rates of these alloys w ere much lower than that of corresponding refractory metals, but highe r than those of typical alumina-forming alloys because of the formatio n of refractory metal oxides or their double oxides with aluminum.