Study On Preparation And Properties Of TiC/Ni Composite Coatings By Plasma Cladding On 42CrMoA Steel

With the development of China's ship industry in recent years,repairing and remanufacturing of ship components becomes a top research subject.Crankshaft which is one of the most important components in ship turbine easily suffered from failure on material surface such as frictional wear during operation process.Aimed at solving above problem,appropriate material surface technologies are needed to repair damaged crankshaft of ship turbine.Comparing with other material surface technologies,plasma cladding shows great advantages based on its wide scope of application,low preparation cost,high reliability and quality.Hence,repairing and remanufacturing of ship turbine crankshaft by plasma cladding have both theoretical research value and profound application prospects.In this paper,Ni60A mixed-powder series were designed and in-situ TiC/Ni composite coatings were prepared on42CrMoA steel by plasma cladding.The phase composition and microstructure of TiC/Ni composite coatings were characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?and energy-dispersive spectroscopy?EDS?.In addition,the mechanism properties of TiC/Ni composite coatings were tested by micro-hardness tester,nanoindentation and tribometer.Furthermore,electrochemical workstation and simulated marine environment immersion corrosion analysis method were used to study the corrosion behavior of TiC/Ni composite coatings.The results indicate that both[Ti+C]and[Ti+Cr₃C₂]mixed-powder series can successfully prepare TiC/Ni composite coatings which perform a fine metallurgical bond between coating and substrate.Macro-defects such as pores,cracks and inclusions are not detected in TiC/Ni composite coatings.TiC/Ni composite coatings are mainly composed of?Fe,Ni?,TiC,Cr₇C₃ and Cr₂₃C₆ phases.With regard to[Ti+C]prepared TiC/Ni composite coatings,columnar crystal and dendritic-structure columnar crystal distribute gradiently from bonding zone to the upper area of the coating.TiC ceramic phase that shows fine particles disperses uniformly in?Fe,Ni?metal matrix.[Ti+Cr₃C₂]prepared TiC/Ni composite coatings are mainly composed of dendritic-structure columnar crystal and dendrite.When the content of in-situ TiC reaches to 12wt.%in TiC/Ni composite coatings,TiC ceramics aggregate into reunite state along the grain boundaries of?Fe,Ni?metal matrix.The mechanical properties and wear-resistance of TiC/Ni composite coatings are improved obviously comparing to 42CrMoA steel and Ni-based coating.TiC/Ni composite coatings are affected by various reinforcement mechanisms such as solid solution strengthening,grain refinement strengthening and dispersion strengthening.Among them,8wt.%TiC/Ni composite coatings prepared by[Ti+Cr₃C₂]mixed-powder series exhibit the optimum mechanical properties(Micro-hardness=632HV,E=212GPa,K_IC=72.8MPa?m).The more content of TiC ceramics in the TiC/Ni composite coatings,the better wear-resistance is performed.The resistance to plough and adhesive wear of TiC/Ni composite coatings is enhanced evidently.In relation to corrosion resistance,the corrosion tendency of TiC/Ni composite coatings is slightly higher than that of Ni-based coating and the self-corrosion current density of TiC/Ni composite coatings shows positively correlated with the mass fraction of TiC ceramic phase according to the polarization curves.Simulated marine environment immersion corrosion test indicates that the corrosion rate of TiC/Ni composite coatings is lower than that of 42CrMoA steel.The corrosion products of TiC/Ni composite coatings are mainly composed of Ni?OH?₂,Cr₂O₃ and Fe₂O₃ phases.The corrosion morphology is mainly pitting corrosion and the pitting pits are easier formed near the TiC-rich ceramic phase.