Impact fatigue failure of HVOF coatings and modeling of the viscoelastic properties of coating-substrate compound

Abstract

Dynamic impact-wear and coating fatigue at cyclic loading conditions demonstrates a verydemanding failure mode, which occurs in a number of mechanical applications and it becomes very criticalwhen the application concerns aggressive working environments. The coating impact testing is a novelexperimental technique developed to investigate the fatigue behavior of coating-substrate compounds,which was not possible with the common testing methods previously available. The objective of this studyis to investigate the influence of the impact load on the fatigue strength of thermal spray high velocityoxy-fuelHVOFcoatings. Furthermore, the overall aim of the current research is to prove the reliability ofthe impact testing method to assess the coating lifetime against fatigue, to interpret the coating failuremodes, and thereby to explore its capability, whether this nonstandard test can be used in industrial scaleas a reliable technique in the development and optimization of fatigue resistant coatings. Based on theabove method the current research provides experimental results concerning the coating fracture in termsof cohesive and adhesive failure modes. The fatigue strength of the tested coatings is determined in termsof fatigue-like diagrams by means of scanning electron and white light interference microscopy, as well asby electron dispersive x-ray analysisEDXat discrete loads and number of loading cycles. From theconducted experiments, it was shown that the optimum HVOF coating against fatigue is the WC-CoCr.