Investigation of temperature and stress fields in laser cladded coatings

Temporal and spatial distributions of temperature and strain-stress have been modelled and investigated experimentally for the laser cladding process. The model corresponded to experimental conditions where the multilayer protective coatings were prepared by direct laser cladding of stellite SF6 powder on X10Cr13 chromium steel by means of a 1.2 kW CO₂ laser. For calculations the effect of base preheating, temperature dependent material properties, and also influence of time-break between cladding of the consecutive layers were taken into account. The calculated temperature fields indicated good bonding of the substrate and coating, which was in agreement with the micro-analytical test results. A decrease of the number of microcracks in the coating with an increase of substrate preheating temperature was concluded from stress calculations and confirmed in the experiment. Moreover, an increase of the cracking susceptibility with an increase of the time delay between cladding of the consecutive layers was evidenced by modelling. The best technological results were obtained for the case of single-layer coatings prepared on a preheated substrate and for higher coating thickness required the processing of consecutive layers with a possibly short time delay is advisable due to effective usage of laser beam energy for preheating and lower temperature gradients.