Coatings deposited by the high-velocity flame spraying method

The properties (porosity, hardness, wear resistance) of coatings obtained by high-velocity flame spraying were studied. It was shown that high-velocity spraying produces highly dense coatings (porosity below 3%) which have good abrasion resistance under extreme conditions: resistance to abrasive-erosion was 10-12 times better than that of uncoated steel. Abrasive wear resistance at low attack angles was obtained in coatings of maximum hardness, i.e., hardness above that of the abrasive. At high attack angles an optimum ratio of hardness to ductility is desired. The optimal structure for WC - Co coatings is the so-called twice cemented hard alloy structure, in which granules or particles of WC - Co are included within the cobalt binder. At large attack angles the concentration of carbide phase should exceed 50%, and at normal angles is optimally 20-30%.