Oxidation behavior of multiphase Mo-Si-B alloys

The oxidation behavior of multiphase Mo, Mo3Si, and Mo5SiB2 (T2) alloys was examined at 800 and 1300 degreesC. The alloys were cast and heat treated at 1600 degreesC before the cyclic oxidation tests were performed. The compositions of the alloys with SUB ratios of 0.5, 0.71, and 1.0 were chosen near the L = (Mo) + T2 eutectic trough to produce a fine dispersion of the different phases. The multiphase alloys showed poor oxidation resistance at 800 degreesC while a protective glass scale formed at 1300 degreesC. At 800 degreesC the oxidation resistance improved as the volume fraction of the T2 phase increased. Conversely, at 1300 degreesC, the glass scaled that formed on the alloys with a SUB ratio of 0.5 was not protective. However, a protective glass scale did form on the alloys with a higher SUB ratio. The near eutectic alloy with a SUB = 1 was found to have the best oxidation resistance at 1300 degreesC. The results indicate the Mo3Si phase provides a source of silicon for controlling the composition of the glass scale at 1300 degreesC. (C) 2004 Elsevier Ltd. All rights reserved.