Tribological and high-temperature mechanical characterization of cold sprayed and PTA-deposited stellite coatings

Stellite 6 is a cobalt-base alloy commonly used for coatings useful in wear and corrosion protection of several components over a wide range of temperatures. Stellite coatings can be obtained by many deposition techniques: plasma transferred arc (PTA) is certainly an optimal choice that gives thick, dense coatings, but thermal spray techniques like high velocity oxy-fuel (HVOF) are also widely used to deposit such materials. The present study investigates wear and mechanical properties of Stellite 6 deposited by cold spray in comparison to PTA-deposited Stellite 6, aiming to obtain a very dense coating without the dilution zone typically resulting from PTA weld surfaces. Tribological behavior of cold sprayed Stellite 6 deposited on AISI 304 stainless steel was evaluated by block-on-ring wear test; friction coefficients and mass and volume variations were analyzed, followed by SEM-EDS on wear tracks. Mechanical properties were evaluated by four-point bending test from room temperature up to 750 °C, and by dynamic indentation. Vickers microhardness and porosity were also evaluated.