Fabrication of Ni34.1Fe27.9B18Si18Nb2 amorphous matrix coating on mild steel by laser processing

Ni34.1Fe27.9B18Si18Nb2 coating was deposited on mild steel substrate using high power laser cladding followed by laser remelting process.The laser processing was conducted by the powder feeding method using low purity materials without shielding box.To learn the surface amorphous matrix coating forming mechanism,the coating without remelting process was also studied.The phases and microstructures were analyzed by X-ray diffraction (XRD),scanning-and transmission-electron microscopy(SEM,TEM).The microhardncss and corrosion resistance property of the coating were also measured.The results of SEM,XRD and TEM analysis show that the remelted coating has an amorphous matrix layer embedded with some crystals due to high cooling rate during remelting process.The crystals phases are identified as Fe2B phase,γ(Fe,Ni)phase and α-Fe phase.No oxidation phases are found in the coating surface.Hardness profiles reveal microhardness more than 1100 HV0.5over the full depth of the amorphous matrix layer,while the unrerntled coating and the substrate show relatively lower hardness than the remelted layer.Corrosion resistance tests exhibit that the remelted coating is nobler than the unremelted coating and the substrate material.