Diffusion barrier effect of Al2O3 layer at the interface between Mo-Si-B coating and Nb-Si based alloy
Yanqiang Qiao, Tao Chen, Xiping Guo
Abstract
An oxidation-resistant composite coating, including Mo-Si-B layer and Al 2 O 3 diffusion barrier, was prepared on Nb-Si-based alloy by a two-step method. The Al 2 O 3 film was fabricated by firstly deposition of Al on the alloy through pack cementation, and then by in situ oxidation of the aluminide coating. Mo-Si-B coating was then prepared on the Al 2 O 3 film by spark plasma sintering. The Mo-Si-B coating is mainly composed of MoSi 2 and a small amount of MoB and SiO 2 particles. After long-term exposure at 1250 °C, the growth of the interdiffusion zone (IDZ) was suppressed effectively at the interface with the Al 2 O 3 diffusion barrier. The results indicate that the diffusion barrier can significantly inhibit the outward diffusion of Nb, Ti and Cr alloying elements as well as the sluggish inward consumption of Si element. The Mo-Si-B coating with Al 2 O 3 diffusion barrier exhibited a good oxidation resistance with a mass gain of about 0.97 mg/cm 2 after 500 h of oxidation.