Friction properties of high temperature boride coating under dry air and water vapor ambiences

NiCoCrAlY/ZrB2-B4C composite coatings were prepared by atmospheric plasma spraying using a clad powder and their microstructure, phase composition and mechanical properties were characterized. The friction and wear behavior of the coatings were evaluated from room temperature to 800 degrees C in dry air and water vapor atmospheres using a ball-on-disk tribometer. The results show that the NiCoCrAlY/ZrB2-B4C composite coating exhibited low porosity (6.7 +/- 0.8%), high Rockwell hardness (HR45y82 +/- 5) and high cohesive strength (18 +/- 3 MPa), as well as good friction and excellent anti-wear ability up to 800 degrees C. The friction coefficients and wear rates of the coating under water vapor ambience were lower than that under dry air. The main reason is the synergistic effect of layer structured lubricating H3BO3 and molten B2O3 films, which were produced by the reaction of the boride with O-2 and H2O in the water vapor atmosphere. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.