CHARACTERISTIC BEHAVIORS OF PARTICLE PHASES IN NiCrBSi-TiC COMPOSITE COATING BY LASER CLADDING ASSISTED BY MECHANICAL VIBRATION

The good high temperature wear resistance and corrosion behavior of particle reinforced Ni-based alloy composite coating have attracted extensive attention in material science and engineering. It is necessary to analyze the morphologic characteristics and distribution of particles in composite coating. TiC particle reinforced NiCrBSi composite coating on medium carbon steel surface was fabricated by mechanical vibration assisted laser cladding technique. According to the distribution characteristics of hard phase particles in laser cladding molten pool, the growth morphology of TiC particle and endogenous M23C6 carbide, formation mechanism and its distribution characteristics in gamma-Ni solid solution were analyzed by XRD, SEM and EDS. The results showed that most of TiC particles dissolved into the melted Ni-based alloy, but some supersaturated Ti and C atoms were precipitated in the form of TiC particles eutectic during cooling process. The TiC particles lateral growth with heterogeneous nucleation way depended on M23C6 type carbide substrate. At the same time, some composite carbide core-shell structure with (Ti, Cr, Ni, Fe, Si)C encapsulated TiC were generated in the coating. Under the effect of vibrant force, the bulky branch crystal eutectic structure disappeared in the bottom of laser cladding coating, the TiC particle floatation trend slowed down with the fluid stratosphere which caused by vibratory force and high-pressure gas, and some double and petal shape TiC particle clusters were also formed. The precipitated TiC particle increases with the Cr content in the inter-dendrite reticular (Fe, Ni) solid solution, and the average particle size was increased by more than 25%. The XRD results indicated that the diffraction peak intensity and lattice integrity of the main hard phases were enhanced, the half peak width was broadened and the crystalline grain size become smaller. The mechanical vibration promoted the dispersion of particles in the matrix dendrites and inter-dendrite.