Structure gradient in wear-resistant coatings on steel

As shown by scanning electron microscopy, electric-arc surfacing of steel produces a multilayer structure, including the surface coating itself, a transition layer, and a thermal-influence zone. Solidification of the coating is accompanied by the formation of a columnar structure, with alternating layers (thickness 8–10 μm) of two types. The first type is characterized by plate structure, oriented perpendicular to the substrate surface; the thickness of the plates and the interlayers between them is 50–100 nm. The second type has plate and globular structure. On moving away from the surface, the plate structure of the first type breaks down; none remains at the boundary with the transition layer. The globules measure 1.5–3.0 μm; they are fragmented. The structure gradient is also apparent in the transition layer and in the thermal-influence zone. The boundary between the coating and the steel is in an elastic stress state on account of the superhigh heating and cooling rates, as indicated by the presence of microcracks, micropores (in rows), and extended secondaryphase layers.