Microstructures and corrosion properties of novel Fe46.8-Mo30.6-Cr16.6-C4.3-B1.7 metallic glass coatings manufactured by vacuum plasma spray process

Metallic glass coating layers were fabricated using new Fe-46.8-Mo-30.6-Cr-16.6-C-4.3-B-1.7 metallic glass powders via vacuum plasma spray process (VPS). The microstructure and corrosion properties of the VPS Fe-based metallic glass coating layer were examined and compared with coating layer of same composition prepared through the conventional atmospheric plasma spray process (APS). Broad halo peaks were found in the metallic glass powder feedstock and two coating layers. Splat particles and minor un-melted powders were observed in the two metallic glass coating layers. For APS coating layer deposited under aerobic condition, Fe-Cr based oxides were detected at the particle boundaries and Cr element was found depleted in regions near the oxide. Meanwhile, all the alloying elements in the VPS material were evenly distributed throughout the coating layer. Corrosion tests showed that the corrosion properties of the APS coating layers were E-corr:-0.347 V and I-corr: 1.38 x 10(5)A/cm(2), whereas for the VPS coating layer, E-corr:-0.342 V and I-corr: 3.21 x 10(-6)A/cm(2), signifying superior corrosion resistance in the VPS material to the APS material. The corrosion started from the pores and particle boundaries in both the coating layers and then advanced along the particle boundaries. It was apparent that the Cr depletion area inside the APS coating layer was susceptible to corrosion. Based on the above results, the corrosion mechanisms of the Fe-based metallic glass coating layers fabricated by the VPS and the APS processes were also discussed.