The influence of flowing temperature on the structure and properties of the self-fluxing coatings

The coatings made of self-fluxing powder of the Ni-Cr-Si-B system (Ni - base; 15.1 wt. % Сr; 2.0 wt. % Si; 2.0 wt. % В; 0.4 wt. % С) are deposited on low carbon steel substrate (0.2 wt. % C) by plasma spraying. The study considers the influence of flowing temperature on structure and properties of the specified materials. The samples with coatings are heated in furnace up to 1030, 1050, 1070 and 1100 ºС for 1 hour with the following air cooling. The structure and phase composition of the coatings is investigated using optical and scanning electron microscopy, and X-ray diffractometry. Moreover, the results of microhardness measuring and wear-resistance testing in conditions of sliding friction are demonstrated. X-ray diffractometry showed that the major phases of the coatings before fluxing and after one are the following: γ-Ni, Ni3B, CrB и Сr7С3. The results obtained using optical and scanning electron microscopy brought out that the coatings fluxed at 1030, 1050 and 1070 ºС consist of dendrites of solid solution of Cr, Si and Fe in γ-Ni, Cr7C3, CrB inclusions and Ni-Ni3B, Ni3B-Ni6Si2B eutectics. The coatings fluxed at 1100 ºС consist of dendrites of solid solution of Cr, Si and Fe in γ-Ni, Cr7C3, CrB2 inclusions and (γ-Ni)-CrB, Ni-Ni3B eutectics. A quantity of hard phases (eutectic, chromium carbides and chromium borides) increases with the rise of temperature. It leads to increase of microhardness and wear-resistance of the coatings. The results of the experiments demonstrate that the coatings fluxed at 1100 ºС have maximum microhardness (953 HV) and wear resistance. Unfortunately, high fluxing temperatures can promote to layer separation.

self-fluxing alloys on the Ni base, Ni-Cr-Si-B system alloys, plasma spraying, fluxing