Evaluation of Microstructure and Mechanical Properties at the Interface Region of Laser-Clad Stellite 6 on Steel Using Nanoindentation

The interface area in laser cladding, microstructures and mechanical properties of which determine the structural integrity of the laser-deposited coating, consists of two distinctive zones: the dilution and heat-affected zones (HAZs). The dilution region is the region where melted substrate forms a mixture with coating material and possesses microstructure similar to the coating. The HAZ is the region that lies in the substrate but possesses different microstructures compared with original substrate due to heat transfer from melt pool during processing. There are limited data available on mechanical properties of the dilution and HAZ and, in this study, the mechanical properties of the two regions have been evaluated using nanoindentation. This testing technique has the ability to resolve the mechanical properties at fine spacings, unlike microhardness testing and conventional mechanical testing. Stellite 6 powder was deposited onto a round bar AISI 4130 steel using a continuous wave Nd:YAG laser. The effect of laser cladding process on the microstructure, hardness, and elastic modulus of the coating, at the interface has been examined by nanoindentation testing. The elastic modulus of the substrate measured was found to be 198.76 ± 24.96 GPa, which is in a good agreement with the standard elastic modulus of AISI 4130 reported in literature. For the laser clad specimen, dilution area showed elastic modulus of 192.62 ± 7.67 GPa, slightly higher than the average elastic modulus of the HAZ, 189.94 ± 14.75. This is due to the dilution area containing a mixture mainly of Fe, Cr and Co. The increased level of Fe in this dilution area leads the tendency of this region to behave as substrate.