Investigations into Lattice Strain and Hardness of WC-10Co-4Cr Coating on Laser Surface Textured 420 Stainless Steel
V. Kumar, R. Verma, V.S. Sharma and A.D.V.S. Prasad
Martensitic steel is a hard ferrous alloy familiar for wear resistance requirements such as in hydro-turbines. To improvise the efficiency and reliability of the energy conversion systems, thermally sprayed wear resistant hard coatings have been investigated lately. In this research, WC-10Co-4Cr coating was deposited on textured and non-textured 420 martensitic stainless steel using high velocity oxy-fuel (HVOF) coating process. Laser surface texturing (LST) was performed to improve the deterministic surface hardness and thus mechanical interlocking at the coating-substrate interface. The WC-10Co-4Cr coating’s Vickers hardness showed an increase in microhardness compared to the sand blasting pre-treatment. The modified Williamson Hall (W-H) plot method has been employed to estimate selected lattice parameters using X-ray diffraction (XRD) data of the pristine 420 stainless steel substrate, the laser surface textured 420 stainless steel and the WC-10Co-4Cr coated and laser surface textured surfaces. Results indicate that the lattice strain in the textured surface was found to be highest among other surfaces due to the microstructural modifications primarily due to the surface dislocations resulting from the laser ablation. Whereas, the WC-10Co-4Cr coated surface had less strain ascribed to the regularly ordered roughness of the laser patterning before coating; moreover, LST resulted in an effective increase in the surface hardness of the coated specimens.
Keywords: Fibre laser, 420 martensitic stainless steel, WC-10Co-4Cr, coating, laser surface texturing (LST), high velocity oxy-fuel (HVOF), lattice strain, microhardness