Selecting process parameters of crack-free Ni60A alloy coating prepared by coaxial laser cladding

Ni60A alloy coating prepared by laser cladding is limited by the high cracking susceptibility. In this study, the crack-free Ni60A coating is obtained by selecting suitable process parameters. In order to avoid size effect on heat dissipation and stress evolution, the width and height models of cladding track are established to obtain same size track with different process parameters. These two models divide the three main parameters laser power, powder feed rate and scanning speed into two groups, namely line energy (the ratio of laser power to scanning speed) and powder feed rate, and determine their experimental values. Then the influence of deter-mined line energy and powder feed rate on cracking are tested, which significantly reduces the amount of tests compared with common optimization methods. The results show that large line energy and low powder feed rate are helpful to prevent crack, but lead to low microhardness. In order to obtain crack-free Ni60A coating with higher microhardness, the combination method of preheating to 300 C and adding insulating plate under the substrate is further studied, which can not only reduce thermal damage to the substrate but also improve the microhardness up to 510-553 HV.