| In this paper, an attempt had been made to obtain a high hardnessand wear/corrosion resistance of amorphous coating with laser claddingFe-Co-B-Si-Nb alloy on CCS-A steel surface using a high power diodelaser, in order to improve the surface property of CCS-A steel.Microstructure and properties of the coating were analyzed by opticalmicroscope, X-ray diffraction, scanning electron microscope,transmission electron microscope, digital display vickers hardness tester,electrochemical workstation, differential scanning calorimetry as well asfriction and wear tester. Effects of laser power, cladding speed andfeeding rate on the coating forming, dilution, microstructure andmicrohardness were studied, and the microstructure, microhardness,wear/corrosion resistance and thermal stability also were analyzed.The result showed that with the increase of laser power, coatingdilutions increased, the amorphous phase reduced gradually andeventually disappeared, and the microhardness of coating decreased withthe increase of laser power. With the increase of cladding speed, coating dilutions reduced, crystals decreased, and amorphous phase in the coatingincreased, making the microhardness of coating to increase. With theincrease of feeding rate, coating dilutions reduced, and the microhardnessof coating increased due to grain refinement in the coating.Amorphous coating, which was cladded using optimizing process,not only had good forming and metallurgical bonding with substrate, butalso had low crystallinity. The volume content of amorphous phase wasmore than90percent in the middle of amorphous coating.The microstructure of amorphous coating was not uniform. Glassforming ability (GFA) of coating at the centre is higher than that of aplace close to the coating surface and bottom. This was due to thedifferent cooling condition and composition distribution in different placeof coating. There were some crystalline phases in amorphous coating,such as NbC, and a little FexCo(1-x)in the place near the surface andbottom of coating. The microstructure of cross section of amorphouscoating were composed of small dendritic area near the coating surface, alarge amorphous+NbC area near the coating central, and dendritic areanear the coating-substrate interface, which exhibitted observableextensive growth characteristics.The microhardness of amorphous coating reached1200~1300HV,which was about five times as much as substrate. In three kinds ofcorrosion medium,1mol/L H2SO4,10%NaOH and3.5%NaCl solution, the amorphous coating showed better corrosion resistance than substrate.The DSC showed that glass-transition temperature (Tg) of amorphouscoating was568.2, and the crystallization temperature (Tx) was588.9, which implied that the amorphous coating couldn t changecrystalline state in the condition of less than588.9, exhibitting highthermal stability. The friction coefficient of amorphous coating was lowerthan the substrate, and the wear loss of amorphous coating also less thansubstrate greatly under200N,250N and300N load, the amorphouscoating had good wear resistance.In general, Fe-Co-B-Si-Nb amorphous coating was cladded usinghigh power diode laser had high volume content of amorphous phase,exhibitting high hardness and good corrosion/wear resistance. |
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