Influence of Cr addition on the interface purification of vacuum brazed NiCr-Cr3C2 coatings on single crystal superalloy

In order to improve the high temperature wear- and oxidation resistance of single crystal superalloy, NiCr-Cr3C2 coatings were vacuum brazed on the surface. Different weight ratios of Cr were added into the coatings to control the diffusion of Si and C into the base metal, which would be harmful to the base metal stability. The results show that, when no Cr was added into the coatings, a layer of Ni3Si phase at the interface and MC precipitates in base metal were produced. With the increase of the Cr addition, the coating/base metal interface was gradually purified. The Ni3Si layer and the MC precipitates disappeared when the Cr addition increased to 30 wt% and an interface was clearly presented with the γ′ phases on both sides epitaxially growing on some extent. After 200 thermal fatigue cycles, the total crack lengths were measured, which decreased with increasing Cr addition, indicating that the thermal fatigue resistance was improved.