Microstructural evolution of laser-clad 75Cr3C2+25(80Ni20Cr) powder on Inconel 718 superalloy

Nickel-based superalloys such as Inconel 718 are widely used in the aerospace industry. The surface properties of Inconel 718 can be improved by the addition of chromium carbide-nickel chromium powder. In this study, 75Cr(3)C(2)+25(80Ni20Cr) powder was clad on annealed Inconel 718 superalloy by using a pulsed Nd:YAG laser. The aim of this research is to investigate the effect of laser process parameters such as pulse width, laser frequency and scanning speed on the microstructure and microhardness of the clad samples. It is found that the increasing pulse width and laser frequency or decreasing scanning speed can increase the heat input and the resultant dilution ratio. The clad zone of the samples with a high dilution ratio consists of eutectic structure (gamma and Cr7C3). However, the clad zone of specimens with a low dilution ratio is composed of a hypereutectic structure of Cr7C3 + (gamma +Cr7C3 ). This microstructure leads to the significant increase in the hardness value in comparison with the specimens with a high dilution ratio, due to the presence of proeutectic Cr7C3 carbides in the hypereutectic structure. The maximum hardness value of the clad zone is found to increase almost 2.5 times that for the substrate in the annealed condition. However, the austenitic and Laves phases are formed in the partially mixed zone. This zone is rather narrow, approximately 30 mu m. The grain coarsening occurs in the heat-affected zone of all the deposited specimens. The hardness values of the partially mixed and heat-affected zones are lower than that for the clad zone.