Executive Summary : | 9-12% Cr steels are commonly used for high temperature applications due to their good mechanical properties and oxidation resistance. However, their high temperature wear resistance is inadequate, necessitating wear-resistant coatings. Co-based superalloys like Stellite-6 can be suitable as hard-facing alloys. Current deposition techniques involve melting the substrate and coating materials, leading to increased Fe content at the interfacial region. This results in the formation of several phases, including Fe/Co-rich α-bcc, Cr-rich ordered bcc α'-phase, σ-phase, and Laves phase. These phases cause cracks at the interface and delamination of the coating. Residual stresses due to differences in thermal expansion coefficients of Stellite-6 and Grade-9 steels are damaging. Some power plants use Stellite-21 as a buffer layer between Grade-9 steels and Stellite-6 coating. However, Stellite 21 also faces similar problems due to the formation of Cr-rich ordered bcc a'-phase and σ-phase at the interfacial region. There is a need for new buffer layers and evaluation of their performance. The Electric Power Research Institute (EPRI) has found that Ni-based alloys can prevent the formation of detrimental σ-phase, allowing for use as a buffer layer. Developing compositionally graded Stellite-6 coating on Grade 9 steels with Ni-based alloy as a buffer layer using laser assisted processing could enhance wear and oxidation resistance without affecting the interface. |