Effects and Interplays of Spray Angle and Stand-off Distance on the Sliding Wear Behavior of HVOF WC-17Co Coatings

The state of particle impact (velocity and temperature) significantly affects the coating's microstructural, mechanical properties and wear performance. The spray stand-off distance and spray angle dictate particle velocity components and temperature at impact. This work aims in advancing the understanding of their effect and interplay in regard to the sliding wear performance as well as the mechanisms of wear themselves of HVOF-sprayed WC-17Co coatings. Dry sliding wear resistance was evaluated by a pin-on-disk test, and significant interplay between the spray parameters was observed. A large number of experiments in a full-factorial manner provided insights into the progressive tribofilm build-up and wear damage modes and allowed for proposing mechanisms regarding their occurrence. Small deviations from the normal spray angle at long stand-off distances proved to be beneficial for the wear performance of the coatings. The highest friction coefficient and most aggressive wear damage were observed in coatings with a rich coverage of the wear track with a tribofilm. The phase composition of the coatings proved to be the principal contributor in the wear performance.