Oxidation resistance of a Mo-W-Si-B alloy at 1000–1300 °C: The effect of a multicomponent Mo-Si-B coating
The oxidation behavior and microstructures of a three phase Mo50W20Si15B15 alloy containing (Mo, W) solid solution, (Mo, W)5Si3 and (Mo, W)5SiB2 were investigated over the 1000–1300 °C temperature range. At 1300 °C, the alloy exhibited a large initial mass loss and eventually transitioned to a steady state behavior associated with the development of an amorphous borosilica scale. The oxidation resistance at lower temperature was unsatisfactory due to the pesting of Mo and W. Grazing Incident Angle X-ray Diffraction (GIXRD) measurements during the initial transient stage of oxidation identified the evolution of surface oxide products that were responsible for the large weight loss and pesting behavior. In order to address the large initial weight loss and the low temperature pesting behavior, the alloy was coated with a Mo-Si-B based coating by employing the pack cementation process followed by a conditioning treatment at 1450 °C. The microstructures of the coatings and the interlayer between the base alloy and the coating were studied, and the oxidation resistance of the coated alloys was evaluated over the 800–1300 °C temperature range. The coated alloy showed improved oxidation resistance with nearly zero mass change for extended period of time over the entire range of temperatures studied.