Dependence of sliding wear resistance and microhardness of Al-spray coating layers on substrate conditions using high-velocity oxygen fuel (HVOF)

Thermally sprayed coatings based on hard carbides embedded in a metallic matrix are considered as an important option to replace galvanic chromium deposits on many industrial components. Such components are often sprayed using the high-velocity oxygen-fuel (HVOF) spray systems. This technique is increasingly being used in industrial applications where high wear and corrosion resistance are needed. In this work, coatings of oxide ceramics were deposited on aluminum substrate using the flame spray process (i.e., HVOF). Employing uniform design experiments, the dry wear resistance and microhardness of the coatings were systematically investigated. The dry wear resistance was measured under dry sliding conditions against constant counter weight of 2000gm on a ball-on-disc arrangement, which was specially designed, built, and calibrated to standards before being used in tests. Spraying deposition time was varied in order to get coating layers with different thickness. The substrate surface roughness was varied as well as its initial temperature before coating. The results showed great impact of substrate surface roughness as well as its preheating temperature on the characteristics of the deposited coating layers. The wear resistance appeared to be critically improved by increasing the surface roughness of the aluminum substrate above a certain value (0.52 mu m). However, optimum values of the substrate conditions were obtained.