Development of oxidation resistant coatings on Mo-30W alloy

In order to improve the high-temperature oxidation resistance of Mo-30W alloy, silicide and Al-Si composite coatings of about 25 and 65 μm thicknesses were formed by halide activated pack cementation technique. Substrate alloy samples embedded in the pack mixture consisting of Si or and Al powders and ammonium halide activators were heat treated at 1000 °C for 16 h. Coated samples were characterized by SEM, XRD, optical microscopy, EPMA and hardness measurements. Mainly two layers of different phases were formed in Al-Si coating of Mo-30W alloy. The inner layer comprises of (Mo, W)Si2 phase and the outer layer was Al-rich phase containing small amount of Si, Mo and W. Only one layer of (Mo, W)Si2 phase was formed in the silicide coated alloy. All the coated layers were adherent and uniform. Coated samples exhibited good resistance to oxidation during heating up to 1100 °C in air for 10-15 h.