Deposition and oxidation behavior of Mo(Si,Al)2/MoB layered coatings on TZM alloy

A two-step pack cementation process including first boronizing and then co-depositing of Si-Al-Y with different Al contents (0, 5 and 10 wt%) in the packs was used to deposit oxidation-resistant coatings on TZM alloy. The as-formed coatings are MoSi2/MoB, Mo(Si,Al)2/MoB, and Mo(Si,Al)2/Mo-Al-B/MoB layered coatings respectively. Compared with the MoSi2/MoB coating, the improved oxidation-resistant performance is presented in the Mo(Si,Al)2/MoB and Mo(Si,Al)2/Mo-Al-B/MoB coatings upon oxidation at 1250 °C, which should be attributed to the sluggish inward diffusion of Si into substrate and forming dense scales composed of SiO2 and Al2O3. The microstructure change and oxidation behavior of these coatings are investigated.