Volume 5, Issue 6 (June 2008)
Impact Fatigue Failure Investigation of HVOF Coatings
Dynamic impact-wear and coating fatigue at cyclic loading conditions demonstrates a very demanding failure mode, which occurs in a number of mechanical applications and it becomes very critical when the application concerns aggressive working environments. The coating impact testing is a novel experimental 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 study is to investigate the influence of the impact load on the fatigue strength of thermal spray high velocity oxy-fuel (HVOF) coatings. Furthermore, the overall aim of the current research is to prove the reliability of the impact testing method to assess the coating lifetime against fatigue, to interpret the coating failure modes, and thereby to explore its capability, whether this nonstandard test can be used in industrial scale as a reliable technique in the development and optimization of fatigue resistant coatings. Based on the above method the current research provides experimental results concerning the coating fracture in terms of cohesive and adhesive failure modes. The fatigue strength of the tested coatings is determined in terms of fatigue-like diagrams by means of scanning electron and white light interference microscopy, as well as by electron dispersive x-ray analysis (EDX) at discrete loads and number of loading cycles. From the conducted experiments, it was shown that the optimum HVOF coating against fatigue is the WC-CoCr.