A. Karimi et al., MICROSTRUCTURE AND HYDROABRASIVE WEAR BEHAVIOR OF HIGH-VELOCITY OXY-FUEL THERMALLY SPRAYED WC-CO(CR) COATINGS, Surface & coatings technology, 57(1), 1993, pp. 81-89
Sand erosion tests were performed on WC-Co and WC-CoCr coatings deposi
ted by the high velocity oxy-fuel spraying method. Several analytical
techniques, including X-ray diffraction, Auger electron spectroscopy a
nd energy-dispersive spectroscopy in a transmission electron microscop
e were used to characterize the microstructures formed during powder p
rocessing and spraying. It was found that a substantial fraction of WC
decomposed into W2C or reacted with the cobalt matrix to form ternary
carbides such as Co3W3C and other mixed compounds. In both cases the
binder phase had a nanocrystalline structure of size 4-8 nm containing
tungsten, cobalt, carbon and chromium elements. The addition of chrom
ium inhibits to a large extent the decomposition of WC and avoids the
formation of metallic tungsten. In addition, chromium improved the ero
sion resistance by several times compared with the WC-Co coating. Scan
ning electron microscopy showed that the CoCr matrix binds carbides be
tter than the cobalt matrix, thereby inhibiting carbide loss at the sp
ray particle boundaries. The hydroabrasive wear behaviour of coatings
and the mechanisms for material removal are discussed with respect to
the microstructures formed during spraying.