Wear and Scratch Resistance of Cobalt Boride Layer Exposed to a Diffusion Annealing Process

Abstract

This study evaluated the wear (under dry conditions) and scratch resistance of a cobalt boride layer exposed to a diffusion annealing process (DAP). Firstly, the powder-pack boriding process (PPBP) was conducted at 1,223 K with 4 h of exposure to develop a CoB-Co2B layer on the surface of the ASTM F1537 alloy, followed by a DAP at 1,273 K with 2 h of exposure in an argon atmosphere. Before the wear and scratch tests, the resulting cobalt boride layers, obtained by the PPBP and PPBP + DAP, were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and depth-sensing Vickers microindentation techniques. The wear sliding tests, on the PPBP and PPBP + DAP, were performed using a ball-on-flat configuration comprising an alumina ball as a counterpart using a constant normal force and different relative wear distances (50, 100, and 150 m). In addition, the scratch tests were carried out over the surface of the PPBP and PPBP + DAP using a Rockwell-C diamond indenter with a continuously increasing normal force from 5 to 150 N. Finally, and according to the entire set of experimental conditions, the results showed that the presence of the CoB-Co2B layer obtained by the PPBP on the surface of the ASTM F1537 alloy increased the wear resistance compared with the values estimated on the PPBP + DAP. In contrast, the effect of the DAP on the cobalt boride layer enhanced the practical adhesion resistance of the layer-substrate system based on the critical loads obtained during the scratch tests.