M. Podeyn, F. Gärtner, T. Klassen, Helmut Schmidt University, Hamburg, Germany; H. Kreye, Helmut Schmidt University Hamburg, Hamburg, Germany
Apart from high hardness, good wear performance and high corrosion resistance, ideal coatings should also show a high toughness, which in turn could influence wear and corrosion. So far, toughness of HVOF-sprayed Cermet coatings were mainly investigated under ‘quasi static’ conditions by using procedures that are related to hardness testing. Other, dynamic test methods, based on superimposed wear, so far demonstrated difficulties to distinguish different influences. Coating toughness under sudden dynamic loads, as obtained in applications, so far misses a comprehensive description.
In the present investigation, key parameters are developed that describe cermet coating toughness by analysing energies for plastic deformation and track morphologies, as obtained in a single pendulum scratch test. Operating in a regime of sudden impact velocities between 2 and 4 m/s, resulting data can give a good estimate for the coating toughness under real applications. The results show that lower HVOF process temperatures are most beneficial for improving the performance of WC - Co or WC - CoCr coatings with metallic binder contents of 17 or 14 wt. %. For HVOF spraying of cermets with higher hard phase content, as WC Co 88 - 12, better toughness is achieved by increased HVOF process temperatures, which can be attributed to the heat capacities of the powder particles. Thus, the present results from dynamic toughness testing supply an additional and simple tool to investigate thermal spray coatings performance with respect to applications.
Summary: The present study describes cermet coating toughness by single pendulum scratch tests. Operating in a regime of sudden impact velocities between 2 and 4 m/s, resulting data can give a good estimate for the coating toughness under real applications. The results show that lower HVOF process temperatures are most beneficial for improving the performance of WC - Co or WC - CoCr coatings with metallic binder contents of 17 or 14 wt. %. For HVOF spraying of cermets with higher hard phase content, as WC Co 88 - 12 better toughness is achieved by increased HVOF process temperatures. Thus, the present results from dynamic toughness testing supply an additional and simple tool to characterize thermal spray coatings.
