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Incorporation of 3 μm SiCp into Titanium surfaces using a 2.8 kW laser beam of 186 and 373 MJ m-2 energy densities in a nitrogen environment

Mridha, S. and Baker, T.N. (2007) Incorporation of 3 μm SiCp into Titanium surfaces using a 2.8 kW laser beam of 186 and 373 MJ m-2 energy densities in a nitrogen environment. Journal of Materials Processing Technology, 185 (1-3). pp. 38-45. ISSN 0924-0136

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Abstract

The formation of composite layers using a 2.8 kW laser beam of 186 and 373 MJ m−2 energy densities, on commercial purity titanium surfaces preplaced with 3 μm size, 1-4 vol.% SiCp powder in a 100% nitrogen environment, produced gold colour tracks. The tracks gave reflective surfaces after glazing at an energy density of 373 MJ m−2 and dull or a mixture of dull and shiny surfaces at 186 MJ m−2 energy density. Surface cracks were visible in tracks containing 1 and 2 vol.% SiCp, but none were observed in the 4 vol.% SiCp tracks glazed at both energy densities. In the track cross sections, vertical cracks were seen in the 373 MJ m−2 tracks but it was absent in 186 MJm−2 tracks. The SiCp particles completely dissolved in all the tracks processed in this investigation producing a complex and inhomogeneous microstructure of dendrites and needle particles. At the half way of the melt depth from the surface, the dendrites were larger and densely populated, especially after glazing at 373 MJ m−2. The hardness measurement of the MMC layer recorded a wide range of hardness values which gave loops in the hardness profiles. Hardness values ranging from 700 to 1000 Hv were observed up to a melt depth of 1 mm in many tracks and the maximum surface hardness of 2250 Hv was measured in the track containing 1 vol.% SiCp and glazed at 373 MJ m−2. The surface hardness developed 5.6-15 times the base hardness (150 Hv) depending on the dendrite population. The 3 μm size SiCp produced MMC layers 1.5-2 times greater than those previously observed with 6 μm SiCp. The large surface area for an equivalent volume fraction of the three micron carbide particles is considered to have a high laser coupling action and hence absorbed more heat energy to produce deeper melt depth compared to those produced using the 6 μm SiCp.