Microstructure and phase evolution in laser clad chromium carbide-NiCrMoNb

Microstructural development in laser clad layers of Chromium carbide (Cr,Cy)-NiCrMoNb on SA 516 steel has been investigated. Although the starting powder contained both Cr3C2 and Cr7C3, the clad layers showed only the presence of Cr7C3. Microtexture measurements by electron back scattered diffraction (EBSD) revealed primary dendritic Cr7C3 with Ni rich FCC metallic phase being present in the inter-dendritic spaces. Further annealing of the laser clad layers and furnace melting of the starting powder confirmed that Cr7C3 is the primary as well as stable carbide phase in this multi component system. Increase in laser power and scanning speed progressively reduced carbide content in the laser clad layers. Increased scanning speed, which enhances the cooling rate, also led to reduction in the secondary arm spacing (lambda(2)) of the Cr7C3 dendrites. The clad layer hardness increased with carbide content and with decreased dendrite arm spacing. (C) 2015 Elsevier B.V. All rights reserved.