SYNTHESIS OF COMPOSITE POWDERS «TIC – NICRBSI ALLOY BINDER» FOR CLADDING AND DEPOSITION OF WEAR-RESISTANT COATINGS

Abstract

TiC + NiCrBSi binder metal matrix composites were obtained by self-propagating high-temperature synthesis (SHS) in the reaction powder mixtures of titanium, carbon (carbon black) and NiCrBSi alloy. It has been found that steady combustion in a stationary mode occurs when the content of the thermally inert metal binder in reactive mixtures does not exceed 50 vol.%. Porous SHS cakes were crashed and resulting granules were separated to fractions by screening to get the composite powder fraction necessary for coating application. Synthesis products were studied by optical and scanning electron microscopy, X-ray diffraction and electron microprobe analysis. It has been found that the average size of carbide inclusions depends on the content of thermally inert alloy powder in the reaction mixtures and can be purposefully regulated in a wide range. The microhardness of composite powder granules obtained by crushing the SHS conglomerates decreases monotonically with an increasing content of the metal binder having hardness less than that of titanium carbide. According to X-ray diffraction data, the titanium carbide lattice parameter turns out to be considerably less than values known for equiatomic titanium carbide. It has been found by electron microprobe analysis of carbide inclusions in the composite structure that the ratio of carbon and titanium mass contents is 0,21 as compared with 0,25 in equiatomic titanium carbide. Iron and silicon contents in the carbide are negligible, oxygen and nickel contents are below 1 wt.%, and chromium content is 2,5 wt.%. The analysis of known data on the effect of all the above-listed dopants on the titanium carbide lattice allows for a conclusion that the carbon deficit is a main reason of the lattice parameter reduction.