Effect of scan strategy and heat input on the shear strength of laser cladded Stellite 21 layers on AISI H13 tool steel in as-deposited and heat treated conditions

摘要

Coating of hard-facing, wear and corrosion resistant materials on working surfaces of engineering parts made of relatively lower grade materials plays an important role in their service life as this is dictated by the coating material rather than the substrate material. However, the quality of coating in terms of pores- and crack- free deposition, low dilution and good bond strength is vital for the working life of coatings. In this work, bond strength of laser cladded Stellite 21 layers deposited on AISI H13 tool steel with different scanning strategies and line energy is investigated by subjecting the clad-substrate interface to shear force. As Stellite 21 is deposited to improve surface property of high-temperature dies and also for refurbishing worn out dies, bond strength of cladded specimens subjected to a high thermal cycle was also measured. Three sets of shear test specimens of rectangular clad build-up were made with different deposition strategies. First two sets have same laser line energy, but interfacial layers have overlapped clad tracks deposited in two orthogonal directions to study the effect of track orientation on the bond strength. In the third set line energy was doubled by reducing the scan speed. Bond strength was more for shear force applied along the direction of clad tracks. Higher interfacial bond strength of clad tracks parallel to shear stress direction compared to transverse tracks could be resulting by the similar effect that the orientation of fibers in a composite have on its strength. Deposition with higher line energy also had higher bond strength because of more uniform overlapped clad interface. However, specimens subjected to heating up to 1000 degrees C followed by furnace cooling had much reduced bond strength due to grain coarsening. Results are supported by the micro-structure, micro-hardness, dilution and elemental analyses of cladding and fractured surfaces.