Stainless steel coatings sputter-deposited on tungsten carbide powder particles

Abstract

The aim of this work was to study the feasibility of a sputtering technique to coat WC powder particles, regarding it as an alternative to the conventional mixture of powders. For such purpose, a stainless steel 304 (AISI) coating was sputter deposited on WC powder particles using a magnetron sputtering equipment specially developed to coat powder particles. The morphology of the coated powder was characterized by scanning electron microscopy observations, Brunauer–Emmett–Teller and laser diffraction measurements. The crystallographic structure was determined by X-ray diffraction. Inductively coupled plasma–atomic emission spectrometer and electron microprobe analysis were used to characterize the amount, chemical composition and distribution of the sputtered coating. The characterization results indicated that all WC particles were coated and that all the steel constituent elements were deposited in the same original proportion. The coating had a ferrite b.c.c. structure and presented a columnar growth with some porosity. The compaction behavior of the coated powders was characterized by unidirectional pressing using pressures between 60 and 250 MPa. The maximum of relative density was attained for P≥190 MPa, with values of 57–58% of relative density, comparable to that of non-coated powders, and without the need of any pressing binder to obtain green compacts resistant to handling. High sintered densities, of approximately 95%, were obtained at a relatively low temperature of 1325 °C with only ∼6 wt.% of binder phase in the coated powders.