Effect of Nb addition on Fe-Ni-B-Si amorphous and crystalline composite coatings by laser processing

The effect of Nb addition on Fe–Ni–B–Si amorphous and crystalline composite coatings was studied. Firstly, the coatings with different forms of Nb were investigated by X-ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM) tests. It was found that ferroniobium can increase the glass forming ability (GFA) of the coatings and large negative mixing enthalpies of elements are helpful to form an amorphous phase in coatings. A precipitation phase with complex structure in supercooled liquid is helpful to form an amorphous phase. Secondly, the coatings with different amounts of Nb were investigated, too. It was found that one stage crystallization reaction happened in Fe31Ni31Si18B18Nb2 coating with low Nb content and two stage crystallization reactions in Fe30Ni30Si18B18Nb4 and Fe28Ni28Si18B18Nb8 coatings by laser processing. The thickness of amorphous and crystalline composite layer of coatings is about 0.4 mm. The hardness of composite layer is higher than that in the clad layer. Breaking off of hard phases in high Nb content coatings will increase the mass loss in wear tests.