Solidification characteristics and mechanism of feeding surface metallurgical coating by DC-plasma-jet

The ferroalloy coatings with powder mixtures of different constituent,different size,different density and different shape were prepared on Q235 steel using the feeding surface metallurgical technology by DC-Plasma-Jet.The composition,microstructure of alloying coating and microstructure transformation of heat-affected zone were investigated using optical microscope,scanning electron microscope,electron microprobe analysis and X-ray diffraction.Results indicated that plasma surface metallurgical coating of Fe-Cr-Ni-B-Si had well wettability,and metallurgical bonding was obtained between coating and substrate.The rapid solidifing structure of coating was laminar,from epitaxial planar crystal on the bottom to equiax crystal in the middle to bunchy crystal on the top.The matrix of surface coating was malleable γ-(Fe,Ni) dendritic cyrstal,which was supersaturated solid solution of many Cr and small Ni,B,Si,C elements.And eutectic structure of(Cr,Fe)₇(C,B)₃ and γ-(Fe,Ni) dispersed on interdendrite.Due to heat cycle influenced by plasma beam,the heat-affected zone had two layers,phase transformation zone and recrystallization zone.