An experimentally based thermo-kinetic hardening model for high power direct diode laser cladding

High power direct diode laser (HPDDL) based cladding is found to be an economical process for repairing or building valued components and tools that are used in the automotive, aerospace, nuclear and defense industries. In this study, a 2-kW HPDDL of 808 nm in wavelength, rectangular-shaped laser spot of 12 mm x 1 mm with uniform distribution (top-hat) of laser power is used to carry out the experiments. An off-axis powder injection system is used to deposit tool steel H13 on the AISI 4140 steel substrate. A number of experiments are carried out by changing the laser power and scanning speeds while keeping a constant powder feed rate to produce different sizes of clad. An experimentally based finite element (FE) thermal model is developed to predict the cross-sectional temperature history of the cladding process. The temperature-dependent material properties and phase change kinetics are taken into account in this model. As-used experimental boundary conditions are adopted in this model. The acquired temperature history from the FE model is used to predict the temperature gradient, rates of heating and cooling cycles, and the solidification of the clad to the substrate. The FE thermal model results are coupled with thermokinetic (TK) equations to predict the hardness of the clad to the substrate. Metallurgical characterization and hardness measurements are performed to quantify the effect of processing parameters on the variation of clad geometry, microstructure, and the change of hardness of the clad to the substrate. The results show that a good metallurgically bonded clad of hardness uniformity is achieved. (C) 2011 Elsevier B.V. All rights reserved.