Advanced characterization of bulk alloy and in-situ debris nanoparticles formed during wear of Fe–Nb–B ultrafine eutectic laser cladding coatings

Abstract

The microstructure of Fe76·5Nb8·5B15 (at.%) ultrafine eutectic (UE) coatings were processed by laser cladding, then the bulk alloy coating and wear debris were evaluated by advanced electron microscopy techniques in order to understand the ultrafine matrix and nanoscale intermetallic sub-micron and nanoscale phases formed, as a result of rapid solidification. In addition, according to the laser cladding processing parameters used, the coatings presented nanoscale borides that increased mechanical properties, with the coating michohardness values reached being four times higher than those of the AISI mild steel substrate. Combined with the sliding speeds, it played an important role in the definition of different wear mechanisms. The wear performance of the coatings and substrate was evaluated by three-body wear tests using a pin-on-disc device. It can be seen at lowest sliding speed a plastic deformation and for higher slidding speed, an accumulation of debris on the laser clad coating surface. Different wear mechanisms were observed in the coatings samples: abrasive, adhesive, shearing and delamination. The presence of oxide particles, responsible for the formation of a tribofilm, was also observed for some coatings. Debris nanoparticles from 10 to 100 nm, resulting from fracture or breakage of the coatings during wear tests, were also be identified as Fe-based and oxide nanoparticles. Thus, the Fe–Nb–B ultrafine eutectics laser clad coatings showed wear resistance properties comparable to or even superior to commercial alloys and other materials processed by rapid solidification.