Effect of substrate roughness on the fatigue behavior of a SAE 1045 steel coated with a WC–10Co–4Cr cermet, deposited by HVOF thermal spray

▶ Surface roughness of the steel substrate is of utmost importance prior to HVOF deposition. ▶ Although a fine-ground surface does not introduce deep notches and particles, which are stress concentrators for the nucleation of fatigue cracks, it impairs the mechanical bonding of the coating to the substrate. ▶ Early delamination of the coating from the base steel is expected to occur at relatively high maximum alternating stresses. ▶ Grit blasting with alumina particles improves mechanical bonding, but introduces flaws that enhance the initiation of fatigue cracks. ▶ Grit blasting with alumina particles improves mechanical bonding, but introduces flaws that enhance the initiation of fatigue cracks. ▶ HVOF deposition of a WC–10Co–4Cr cermet onto the grit blasted steel substrate, delays significantly fatigue crack initiation at such flaws, allowing a similar behavior of the coated substrate in comparison with the as-polished substrate. ▶ The beneficial effect of the WC–10Co–4Cr cermet coating is due to its compressive residual stress state. ▶ Grit blasting with alumina particles of sizes