Laser assisted nitriding of nickel–chromium-based superalloy surface: Heating and diffusion analysis

Inconel 718 is a nickel–chromium-based superalloy, and it is widely used in power industry because of its resistance to high-temperature environments. Treatment of the alloy becomes essential to prevent niobium segregation at the surface. Laser controlled melting and gas assisted nitriding is one of the methods to minimize changes in the elemental composition of the alloy surface. In general, high pressure nitrogen assisting gas is used coaxially with the laser beam to form a nitride layer and avoiding high-temperature exothermic oxidation reactions in the laser-irradiated region. The present study is carried out to model and simulate sequentially coupled thermal-diffusion process during laser assisted surface nitriding of nickel–chromium-based superalloy in line with experimental conditions. High pressure nitrogen gas jet is considered to impinge onto a workpiece surface coaxially with the laser beam during the treatment process. Finite element model is incorporated to predict the nitrogen concentration and temperature in the laser treated layer. It is found that the predictions of surface temperature and nitriding are found to be in close agreement with the experimental data. The study is extended to include the effect of laser intensity on the nitriding behavior.