Different Introduction Ways Of Submicron MC-type Reinforcement By Laser Alloying

Medium-carbon steel, high-carbon steel and cast iron, which have low price and goodperformance, are widely used in manufacturing of transmission parts, shafts, fasteners andmoulds. These parts require a higher wear resistance of the surface in working.In order to develop a kind of alloy powder composited of base powder andreinforcement phase, which can be applied on the substrate of medium-carbon steel,high-carbon steel and cast iron, TiC reinforced Fe-based composite coatings wereprepared on45steel, T10steel and CrMo cast iron by laser alloying. There were threeintroduction ways of the reinforcement, namely in situ reaction of Ti and C, in situreaction of TiO2and C and native C5Ti4W direct addition. SEM, EDAX, XRD,microhardness tester and the wear test machine were applied to test the microstructure andproperties of alloy layers. Strengthening mechanism was studied.In optimization of the base powder composition, it was found that the compatibilitybetween base powder and substrates was reflected in the C content. To eliminate cracks incoatings, the higher C content in the substrate, the lower C content should be in the basepowder. But CrMo cast iron had a bad formability and cracks in its surface can’t beremoved by reducing C content. When reinforcement content reaches35%, the beststrengthened alloy layer can be prepared.In situ reaction of Ti and C on45steel obtained the best wear resistance. Samephases constituted the alloy layers, namely residual austenite, martensite, and MC typecarbide. Compatibility between carbide added directly into the coating and matrix waspoor, so it was easy for carbide to wear off the matrix and the worst wear resistance wasgot. MC-typed carbides introduced by in situ reaction had a good compatibility with thematrix and cubic granular ones were dispersed in the matrix. Reaction between TiO2and Ccaused the consumption of solid-solution C in Fe-base. It led to right shift of the C curve,improvement of the austenite stability and lower martensite content. So both hardness andwear resistance were lower than the reaction between Ti and C.In situ reaction of Ti and C on T10steel obtained the best wear resistance. Same phases constituted the alloy layers, namely residual austenite and MC type carbide.Residual austenite transformed into martensite during working hardening. It led to a950HV surface hardness. Hardness value tested before wear testing was not correspondingto the wear resistance. Compatibility between carbide added directly into the coating andmatrix was poor, so its wear resistance was the worst one. Composite carbide Cr0.2Ti0.8Cintroduced by reaction between Ti and C had higher strength and better wear resistancethan carbide TiC introduced by reaction between TiO2and C because of solid-solution Crresulting in lattice distortion.When in situ reaction between TiO2and C was applied on different substrates, wearresistance of CrMo cast iron was best, followed by T10steel, and finally the45steel.There were a lot of fine uniform ledeburite in alloyed layer of CrMo cast iron, which hadhigh hardness and strength, so wear resistance was best. T10steel had a high C contentand residual austenite would transform into needle-like martensite in work Hardening.45steel had a medium C content and its martensite was in lath and needle-like morphology.Needle-like martensite contained more twins sub-structure than lath-like one. So T10steelhad a better wear resistance than45steel.