Microstructure And Wear Properties Of Ultrafine TiC Particles Reinforced Fe-based Composite Coatings By Laser Cladding

With the upgrading of modern industrial production and construction level,higher requirements are raised for the service life and comprehensive performance of equipment materials.Metal matrix ceramic composite coating combines the plastic toughness of the metal phases and the wear resistance of ceramic phases,which is a common material system for laser cladding.It is often used for surface strengthening and remanufacturing of mechanical parts in service environment such as friction,corrosion and high temperature.At present,the metalbased coatings are mainly enhanced by the introduction of micron ceramic particles by external addition method.Due to the large difference in thermal property parameters and poor wettability between ceramic phases and alloys matrix,the micron ceramic particles introduced by the additive method are prone to be peeled off and lose the strengthening effect in friction service.In the thesis,using laser cladding technology,ultrafine TiC particles are introduced into the Fe-based alloy coatings by adding nano-TiC,generating in-situ TiC,and using rare earth nano-CeO2 to reduce the agglomeration degree of nanoparticles,so as to realize the preparation of high-performance Fe-based TiC composite coating,which provides reference for remanufacturing of heavy parts of equipment,and the research results and innovations achieved are as follows.To improve the wettability of the external micron-ceramic phase in the alloy melt,a new Fe-based composite powder with micro-nano structure was prepared,and the alleviation effect of nano-TiC on the typical defects of Fe55 coatings was elucidated.The microstructure evolution,wear behaviors of modified cladded coatings were investigated.The results show that the larger surface effect and laser absorption rate of nano-TiC itself contributed to reduce the crack sensitivity of the coating,and prompted transformation of columnar dendrites into petal-like dendrites.With the addition of nano-TiC,the TiC in the coating tends to aggregate,and the morphology gradually changes from spherical shape to petal-like shape with increasing particle size.FT2 cladded coating(Fe55+10 wt.%n-TiC)shows the best wear performance,and the wear volume is 39.7%lower than that of the initial Fe55 coating.In order to further reduce or eliminate nano-TiC agglomeration,different contents of nanoCeO2 were added to the FT2 composition.The synergistic mechanism of the effect of nano-TiC and nano-CeO2 on the wear resistance of Fe-based coatings was revealed.Nano-CeO2 is beneficial to inhibit nano-TiC particles melting decomposition in the melt pool,and affects the wear resistance of Fe-based cladded coatings by regulating the particle size,morphology and dispersion of ultrafine TiC particles.Among them,the addition of 1 wt.%nano-CeO2 contributes to the spheroidization and dispersion of TiC particles in Fe-based TiC composite coating,improves the interfacial bonding strength between TiC particles and cladded coating,which further reduces the friction coefficient and wear volume of the FT2 coating,and respectively decreased by 11.8%and 49%than initial Fe55 coatingThe ultrafine TiC particles reinforced Fe-based composite coatings with compact microstructure,high phase interface strength and good wear resistance were successfully obtained by laser cladding with synchronous powder feeding,which solved the problem of low efficiency and poor surface of the presetting method.The effects of(Ti+C)contents and TiC particle introduction methods on the microstructure evolution and wear behavior were explained.With the increase of(Ti+C)content,the diffraction intensity of TiC phase gradually increases,the ultrafine TiC particles gradually transform from massive to petal-like with larger particle size,accompanied with the wear volume of Fe-based TiC cladded coatings first decreases and then increases.The ultrafine TiC particles in the metal matrix play the role of deflection crack and wear skeleton,where the higher the content of fine bulk TiC particles,the better the wear resistance.Among them,the addition of 10 wt.%(Ti+C)of TS2 coating had the smallest wear volume,which was 77.4%lower than that of Fe55 coating.The coatings prepared by in-situ and additive methods have different dendrite morphologies and TiC contents.The TD2 coating with 10 wt.%n-TiC added was mainly petal-like dendrites(4.59 wt.%),while the TS2 coating was mainly columnar dendrites(8.11 wt.%TiC),and the higher TiC content reduced the wear volume of the TD2 coating by 45.2%.