Study On In-situ Synthesis TiC/FeAl Coating By Laser Cladding

The traditional steel parts often cause great economic loss in commercial application dueto surface abrasion.The method of preparing high hardness and wear resistant coatings on thesurfaee of parts is an important way to prolong the parts’ life and repair the failure partsofmachinery. In the presents tudy, TiC ceramics particles enhanced FeAl matrix cladding layerwas prepared by laser cladding in-situ synthesized in the form of coaxial powder feeding onthe surface of Q235steel. By means of differential scanning calorimeters(DSC) and X-rayDiffractometer(XRD), the thermodynamics and kinetics of the synthetical reactions inFe-Al-Ti-C system were analyzed; the reaction thermodynamics of the cladding powdersystem were researched, and the kinetic model for the in situ TiC/FeAl composite coatingmade through the laser cladding technique was formulated.Macro morphology, microstructureand worn surface mropologies of coatings were analyzed and characterized by opticalmicroscope and scanning electron microscopy, phase composition was analyzed by energydispersive spectrometer and X-ray diffraction.The hardness and wear resistance were testrespectively by microhardness tester and wear testing machine.The reinforced mechanism andwear mechanism were studied and acquired the best technological parameters.The thermodynamic analysis indicates that the formation gibbs free energy of TiC is theminimum. But in low-temperature stages, the iron aluminium intermetallic compounds ofsystem form mainly by diffusion reaction; then in high-temperature stages, TiC can besynthesis in situ by controlling temperature and other technological, and avoidable ofexistence of Al3Ti and Al4C3phases.The kinetic mechanism of iron aluminium intermetalliccompounds is diffusion, reaction and cooling stages; the kinetic mechanism of TiC in-situ ismelting, diffusion, reaction and cooling stages. The main chemical reactions in the Fe-Al-Ti-Csystem consist of formation Iron aluminium intermetallic compounds by diffusion below themelting point of aluminum, Al3Ti generates after Al melting, the decomposition of Al3Ti andTiC particles which the graphite reacts with its rich Ti layer.The kinetic model of in-situTiC/FeAl composite coating by laser cladding is formulated, based on theoretical analysis andcalculation of kinetic equations. The kinetic analysis reveales that rich Ti layer thickness,carbon particle size and aluminum content decreasing, and the system temperature increasingall resuit in improving the speed and the extent of reaction.The experimental results that a smooth appearance cladding layer with a goodmetallurgical bonding of the the substrate can be obtained under argon shield,2.2kW lasercladding power,5mm/s laser scanning speed,6mm laser spot diameter and with the weight ratio of Al, Fe, Ti, C was42wt%,28wt%,24wt%,6wt%. The black spherical, massive phasesdispersively distribute in cladding layer are in-situ synthesized TiC particles; the gray rod,block phase is FeAl; the bulky columnar crystal in the fusion zone is the α-Fe matrixorganization which is the molten base metal preferential growth to the cladding layer in themolten pool. TiC particles distribute from more to less, particle size increases gradually fromthe cladding layer surface to the substrate, but almost nonexistent in the area of the columnarcrystal.Under the optimum technological parameters and the ratio of powder, the cladding layerhas highest hardness HV2028and average hardness about HV1896, which is6times that ofthe Q235, the hardness has been gradually decline from the top of the cladding layer to matrix.The wear resistance of the cladding layer has a best value, which is about48.5times that ofthe Q235; the wear mechanism of the cladding layer is mainly abrasive wear. The wear rate ofcoating first decreases then increases with the increase of Al content, laser power and laserscanning speed. The weightlessness of overlapping clad track with the lap rate40%significantly is lower than single clad track under the same wear experimental conditions,which shows excellent wear resistance. The overlapping clad track reduced the dilution effectof the base metal bath to the cladding layer powders, weakened the cladding powder diffusingto the pool of base material, in situ synthesis of TiC increased, reducing the distance betweenthe TiC phases, all of above is more conducive to absorbing load and abrasiving wear.