Microstructure And Formation Mechanism Of The Particles Reinforced Intermetallic Matrix Composite Coatings In-situ Synthesized By Laser

In this paper, TiC reinforced intermetallic matrix composite coatings are respectively fabricated on0.2%C carbon steel, electrolytic nickel and Ti-6Al-4V alloy substrates by laser surface alloying with Al\TiC powders blend as the precursor material. Microstructure of the composite coatings are analyzed, dissolution and precipitation behavior of TiC phase is investigated. Temperature distribution and dissolution rates of the alloy pools are simulated. Microhardness and nanohardness of coatings are tested. Microstructure formation mechanisms of the composite coatings are discussed.Results show that for the TiC/Fe3Al coatings fabricated on0.2%C carbon steel substrate, when the temperature is above2300K, TiC dissolve into the Fe-Al alloy melt, then precipitate as in-situ particles. Under laser power of1.25kW and1.50kW, the simulated dissolution rates of the alloy molten pools are62.50%and72.22%, while the test values are64.41%and79.31%. The simulated results have a good response to the actual situation. Microhardness of the coatings are415.74HVo.2and441HVo.2, which are2.7and2.6times higher than that of the substrates respectively. Nanohardness of large size undissolved TiC particle is30.219Gpa, while nanohardness of small size precipitated TiC particle is19.755Gpa. The nanohardness value of the precipitated TiC particle is greatly influenced by matrix.For the TiC/NiaAl coatings fabricated on electrolytic nickel substrate, when the temperature is above2700K, TiC dissolve into the Ni-Al alloy melt, then precipitate as in-situ particles. Under laser power of1.25kW and1.75kW, the simulated dissolution rates of alloy molten pools are61.54%and73.91%, while the test values are66.67%and78.30%. The simulated results have a good response to the actual situation. Microhardness of the coatings are479.9HVo.2and456.6HV0.2, which improve4.72and4.49times compared to the substrates.For the TiC/TiAl coatings fabricated on Ti-6A1-4V alloy substrate, TiC don’t dissolve and precipitate in Ti-Al alloy melt. Under laser power of1.25kW and1.50kW, the simulated dissolution rates of alloy molten pools are46.4%and57.7%, while the test values are43.5%and54.5%. The simulated results have a good response to the actual situation. Because exist of amount of undissolved TiC particles, microhardness distribution of the coatings are uneven.Microstructure formation mechanism of the in-situ particles reinforced composite coatings can be discribed as follows:The Al/TiC powders blend and the shallow layer of the substrate are melted under irradiation of the laser beam. Through metallurgical reaction between Al and substrate metal, the intermetallic are produced which save as the matrix of composite coating, TiC precipitate from the molten pool as the in-situ reinforced particles.