An approach to calculate fatigue properties of laser cladded components

Abstract

Regarding the fatigue strength of laser cladded components only very few investigations exist today. This situation induced an investigation whose most important technical results are presented in this paper. The final goal of this work is to predict the optimal process and material parameters for the laser cladding process regarding the fatigue strength and locations of crack initiation. With the intent of calculating the residual stresses in the coating and the adjacent substrate, a FEM-based weld simulation model was developed. On the basis of the calculated residual stresses, the mechanical load situation during cyclic bending is simulated. In order to verify the FE models, round specimens have been laser cladded and analysed regarding clad quality, dilution and hardness as well as fatigue strength during a four-point bending test. The results from simulations and experiments are used as input for calculating the fatigue strength and locations of crack initiation. The Cobalt-based alloy Stellite 21 has been cladded on two substrate materials: the austenitic steel X5CrNi18-10 and the hardened and tempered steel 42CrMo4. Experimental analyses showed that the fatigue limits of the specimens strongly depend on the core materials. The fatigue strength of the steel 42CrMo4 has been figured out to be lower compared to that of the austenitic steel. It is assumed that these results are associated with different residual stresses. A model to simulate residual stresses induced by the cladding process has successfully been set up. Possibilities of fatigue-limit calculation using two approved models for hardened steels have been investigated.