Effects of Process Parameters on Microstructure and Hardness of Layers by Laser Cladding

Abstract

A series of laser cladding layers of Ni35 on a medium carbon steel substrate by varying powder feeding rate and laser scanning speed were obtained. An investigation of the effects of the laser scanning speed and the powder feeding rate on microstructure and hardness was presented in this paper. The phase constitution, microstructure and hardness were investigated by X-ray diffractometer, energy dispersion spectroscopy, scanning electron microscope and Vickers hardness tester. The results show that as the scanning speed increases, the ratio of the temperature gradient G to the solidification rate R decreases which results in the finer microstructure of the cladding layer, as the powder feeding rate increases, the microstructure becomes finer due to the decrease of the temperature of the substrate and specific energy per unit mass of the powder. Furthermore, as the scanning speed and the powder feeding rate increase, the hardness of the cladding layer increases. This is because that the finer microstructure of the cladding layer results in the increase of grain boundary area, which results in the increase in the ability of deformation resistance. An intuitive and facilitative method which combining the line that joining the turning points of the hardness profile to show the effect rules of the laser scanning and the powder feeding rate on the range of dilution and the region of heat affect zone (HAZ) is adopted. This method is helpful to the study of the bonding interface, the control of the dilution range, the microstructure and properties of the cladding layer.