Preparation and Properties of a New Cost-effective Amorphous Composite Coating

Abstract

A NiFeBSiNb amorphous/nanocrystalline composite coating was prepared through flame thermal spraying, where a gas atomized alloy powder substituted an amorphous powder. The microstructure and thermal behavior of the laboratory-produced powders and the produced as-sprayed coating were characterized. The results demonstrate that the powder, which is spherical or ellipsoidal, is mainly composed of Nb₂Ni₂₁B₆ and (Ni,Fe)₂₃B₆ crystalline phases, whereas the as-sprayed coating consists of a glassy structure and certain nanocrystalline phases. It is obtained through calculations that the R_c (critical cooling rate) of the powder and the as-sprayed coating for the amorphous phase formations is 6.01×10⁵ and 4.56×10³ K/s, respectively. The explanation for the amorphous structure, as it occurred in the as-sprayed coating, is the rapid quenching from the melt at the cooling rates which exceeds the critical cooling rate R_c. The as-sprayed amorphous coatings displays a low friction coefficient of 0.17 and excellent wear resistance.