Microstructure And Temperature Field Researches On Laser In Situ Formation Of (TiB_x+TiC)/TiNi Composite Coatings

TC4 alloy has good specific strength and abrasive resistance, but the hardness and wear resistance of TC4 alloy are less than satisfactory, so three kind of mixed powders(10B4C+90TiNi,20B4C+80TiNi,30B4C+70TiNi(wt%)) are pre-pasted and melted to form a kind of gradient and composite coating of which the basement is TiNi that has excellent toughness and plasticity and the strengthen phase is TiC and TiB that is used to increase the hardness of the coating.Firstly, Comsol Multiphysics is used to compute the temperature field and gradient in the process of laser cladding. On the base of simulation, single pass laser cladding experiment was implemented. The result agrees well with the simulation and it shows that optimal parameter of the cladding for the powder (10B4C+90TiNi(wt%)) is P=1900W, V=6.67mm/s,L=310mm.The mixed powders (10B4C+90TiNi,20B4C+80TiNi,30B4C+70TiNi(wt%)) are pre-pasted on TC4 and melt to form the gradient and composite coating by multi-track cladding. Analyses of the coatings’Microstructure and properties are by means of OM, SEM,XRD, micro-hardness test and friction experiment.Results show that many kind of the ceramic reinforcement are in-situ formed in all three kind of the gradient and composite coatings including TiB2, TiB, TiC and TiB, the amount of the reinforced phase increases with the number of coatings. Many rod-shaped TiB and block-shaped (TiB+TiC) eutectic organization exist in the first layer. A lot of acicular TiB appear in the second layer and many block-shaped (TiB2+TiC) eutectic organization grow out around them. More large rod and block-shape TiB2 appear in the third layer and the (TiB2+TiC) eutectic organization grow becides them.The micro-hardness of the single coating, two gradient composite coating and three gradient composite coating is 1368HV,2650HV and 3543HV respectively, which is much higher than the TC4. The results of friction experiment show that the abrasion resistance of all the three kind of gradient composite coatings is much better than the TC4’s and the abrasion of two gradient composite coating is the best of all.