Versatility of the sputtering technique in the processing of WC–Fe–Ni–Cr composites

Abstract

The versatility of the sputtering technique when innovatively applied to the coating of powders was investigated by using three different preparation methodologies to coat WC particles with Fe–Ni–Cr binder: single coating deposition of stainless steel and Ni on WC particles (CP1); sequential sputter deposition of a first Ni coating layer, followed by a second one of stainless steel (CP2) and, finally, a mixed process of Ni deposition on WC particles, followed by stainless steel addition by conventional powder mixing (CP3). The average chemical composition of the three powders was equivalent, having ~10wt.% of Fe–Ni–Cr binder, but their particle surfaces were modified in different ways by the specific sputter-coating conditions, affecting the powder processing and the final composite characteristics, as follows. The composite obtained with only one sputtering step (CP1) attained almost full densification during conventional vacuum sintering, while CP2 and CP3 needed an additional hot isostatic pressing cycle to attain high enough densification. Mixed carbides, (M,W)6C and/or (M,W)4C, with MFe, Ni, Cr, were detected in the composites, whatever has been the processing used in powder preparation, but in different amounts. The best compromise between hardness and toughness was observed for the CP1 composite, although the phase composition shows the highest amount of fragile carbides, ~14 wt.% of carbides (M,W)4C and (M,W)6C. All the composites prepared by the different methods showed Ni homogenization within the metallic binder. Regarding these results, the most effective method for the composite powder preparation was the simplest one with only one deposition step (CP1), since higher densifications and enhanced mechanical properties were obtained, comparatively with the other composites (CP2 and CP3). Additionally, one can conclude that sputtering is, in fact, a versatile process which can be used to modify the powder surfaces' characteristics in different ways, affecting the powder processing and the final material properties.