Experimental study on the wear behavior of B4C and TiB2 monolayered PVD coatings under high contact loads

There are several ways to characterize the wear resistance of coatings in the laboratory, almost all of them applying relatively low loads, both punctually and more widely. Pin-on-disc, reciprocal sliding, and micro-abrasion wear tests are quite common configurations for this purpose. Thus, a gap was identified in terms of characterization of hard PVD coatings subject to higher loads. This work aims to study and compare the wear behavior of two different coatings obtained by PVD, both monolayer, B4C (boron carbide) and TiB2 (titanium diboride), focused on identifying the wear mechanisms present in different coatings provided with high hardness. Both coatings were initially characterized in terms of chemical composition, thickness, morphology, structure, hardness, and adhesion to the substrate, being subsequently tested in laboratory equipment for wear tests following the block-on-ring configuration and relatively high loads; with a view to study the failure mechanisms of the coatings and their wear rate, it was found that the main wear mechanism, sustained by the analyzed coatings, was abrasive wear in the contact area. In the craters left by the tests, it was determined that the main wear mechanism was two-body abrasion. The B4C and TiB2 coatings performed well in relation to the load and configuration used, in line with the behavior already observed in other used wear test configurations. However, under the imposed conditions, and comparing the two coatings, TiB2 is the best option when high loads need to be applied to the coated surfaces, as these coatings did not suffer perforation during testing and the amount of removed volume was inferior to that of the B4C coated samples.The authors would like to thanks to Dr. Rui Rocha from CEMUP (Porto, Portugal), due to his active collaboration in getting the best SEM pictures, helping with his critical analysis of some phenomena. Authors also would like to thanks to Prof. Maria José Vaz Marques due to her crucial help in getting and analyzing the XRD spectra, as well as Ing. Ricardo Alexandre due to his extremely important role in proving all the coatings through TEandM company. Prof. Jorge Seabra is also acknowledged due to his support, as well as LAETA/ INEGI/CETRIB due to the financial support provided in this work and in many others.