Study On The Process And Tribology Of Chromium Carbide Reinforced Ni-Base Composite Coatings Fabricated By Laser Cladding

In order to research ceramic reinforced Ni-base composite coatings, this work adopts in situ synthesized laser surface cladding (LSC) chromium carbide reinforced Ni base composite coatings on45#steel. The microstructure and properties of coatings have been studied, also the affect of laser scanning speed on the coating has been analysized. In order to introduce new method for the powder of LSC. Mechanical alloying(MA) process at different times for the cladding material powder were adapted before LSC, then characterizations of the MA powder were conducted and some feathers were drawn. Finally, Two different kind of coatings laser clad separately with MA and atomized Ni-Cr-C powder, afterwards the microstructure and properties were of these two coatings were investigated. The effect of MA of powder on the laser clad coating microstructure and properties were also discussed.The result indicates that, the cladding material made by MA method can be mixed more homogeneously, and the grain size of the powder is finer than the atomized powder. In the process of MA, a certain amount of Cr7C3can also be produced. With the increase of time for MA, the grain size of powder become smaller gradually even reaches nanometer level.The microstructure of LSC chromium carbide-Ni-based Composite coatings obviously refined compared with that of substrate, also have more excellent properties. The laser cladding coatings is mainly composed of Cr-Ni-Fe-C solid solution and chromium carbides ceramic, due to difference of scanning speed, the chromium carbides has different content and types, the main forms of the chromium carbides are Cr7C3and Cr3C2. With the grow of scanning speed, the content and type of chromium carbides in LSC coatings also increased. With the increase of scanning speed, the refining level of the laser cladding coatings microstructure also improved, but the level of homogeneity is worsened. Compared with the substrate, the microhardness of the coatings has been improved obviously, the average microhardness can reach2.5-3.5times of that of substrate. With the rise of the scanning speed, the microhardness is alsoenhanced, but the level of homogeneity is decreased. The friction and wear properties of LSC coatings has been obviously improved, with respect to the test result of friction coefficient, wear weight loss and wear morphology. The friction coefficient of coatings can be reduced to3/5of that of substrate, the wear weight loss of cladding layer was about1/4of the substrate. It is clearly found that the corrosion resistance of the LSC coatings is highly greater than the substrate after electrochemical test for the LSC coatings and the substrate. The scanning speed is a key factor to influcnce the phase composition and distribution, microstructure, wear resistance and corrosion resistance.Under the same processing condition of LSC, the microstructure and properties of LSC coating made from MA powder is better than that from atomized powder. In detail, the microstructure is much more refined, and with the increased of time of MA the refinement is more obvious while the precipitates is dispersed more homogeneously; The microhardness of the LSC coatings also increased, meanwhile, the distribution of microharness is more uniformly with wear resistance and corrosion resistance be increased.