Abstract
Metal matrix composite layer formation by means of laser alloying using 6 μm particle size SiC powder (SiCp) preplaced on titanium surfaces in a nitrogen environment produced golden coloured tracks and a complete solution of SiCp in the melt zones under a range of processing conditions. The melt layers consisted of dendrites at the top (titanium nitride based) followed by threadlike particle structures (titanium silicides), and the sizes of dendrites and the threadlike particles werefound to increase with increasing laser power density. The surface layer of the dendrites developed a hardness 4·5–9 times that of the base metal (150 HV), and the deep underlying threadlike structures had a plateau of hardness of aboout 2·8–4 times the base hardness. The metal matrix composite layers were found to be 2–4 times thicker than those produced previously in a helium environment under similar processing conditions. The exothermic reactions due to the formation of titanium nitride, titanium carbide, or titanium carbonitride along with titanium silicide during laser melting of SiCp coated titanium surfaces under a nitrogen environment are considered to be responsible for the greater melt depth and complete dissolution of ceramic particles, by increasing the temperature of the melt.
MST/3208
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