Effect of Ni-to-Fe ratio on structure and properties of Ni–Fe–B–Si–Nb coatings fabricated by laser processing

Ni–Fe–B–Si–Nb coatings have been deposited on mild steel substrates using high power laser cladding process followed by laser remelting. The influence of Ni-to-Fe concentration ratio in (Ni100−xFex)62B18Si18Nb2 (x = 55, 50, 45 and 40) powders on the phase composition and microstructure is analyzed by X-ray diffraction, scanning- and transmission-electron microscopies. The microhardness and corrosion resistance properties of the coatings are also measured. The results reveal that amorphous matrix layers are obtained for all coatings. The increase of the Ni-to-Fe ratio can promote the formation of γ(Fe–Ni) phase and decrease the formation of Fe2B phase and α-Fe phase. The coating with 1:1 ratio of Ni-to-Fe exhibits the highest microhardness of 1200 HV0.5 and superior corrosion resistance property due to its largest volume fraction of amorphous phase in the coating. Higher or lower than 1:1 ratio of Ni-to-Fe may result in lower amorphous forming ability. However, even that the coating with ratio of 3:2, shows a minimum of microhardness, it shows a better corrosion resistance than other two coatings.