Features of frictional treatment of the composite NiCrBSi-Cr3C2 laser clad coating

Abstract

The authors conducted a comparative analysis of the effectiveness of frictional treatment with a sliding indenter of a NiCrBSi coating and a composite coating formed by laser cladding of a powder mixture of 85 wt.% NiCrBSi and 15 wt.% Cr 3 C 2. The criteria were intensive strain hardening, favorable compressive stresses, and low surface roughness. Frictional treatment with an indenter made of cubic boron nitride at a load of 350 N provides less intense deformational hardening of the NiCrBSi-Cr 3 C 2 coating (microhardness growth from 900 to 940 HV 0.025) than the NiCrBSi coating (from 570 to 850 HV 0.025). This is due to the significantly higher initial hardness of the composite coating, because its structure, in addition to the phases characteristic of the NiCrBSi coating, contains large primary Cr 3 C 2 carbides, which did not dissolve during cladding, as well as elongated Cr 23 C 6 carbides, precipitated during cooling from a solid solution supersaturated with chromium as a result of the partial dissolution of Cr 3 C 2 carbides during cladding. Frictional treatment also results in a lower level of compressive residual stresses (−250 MPa) on the composite coating surface than on the NiCrBSi coating surface (−390 MPa). In contrast to frictional treatment of the NiCrBSi coating, when a smoothed surface with a nano-roughness is formed (R a = 60 nm), frictional treatment of the composite coating forms a surface with a higher roughness (R a = 310 nm) due to the creation on the surface of supporting "island frame" of large Cr 3 C 2 chromium carbides protruding 2-5 μm.