The Role of Oxide Tribofilms on Friction and Wear of Different Thermally Sprayed WC-CoCr

Abstract

The tribolgical response of five different thermal sprayed WC-CoCr coatings sprayed with HVOF (JP-5000), HVAF (UniqueCoat M3) and Warm Spray (NIMS, Japan) has been evaluated during dry sliding in air and in nitrogen gas. Tests were conducted at room temperature and at 200 °C where both friction and wear were evaluated. Test results indicate that the HVAF and Warm Spray coatings were most dense, while HVOF coatings showed higher degree of porosity and discontinuities in the cross sections. Results show that the sliding atmosphere affects both friction and wear: Sliding in nitrogen reduced predominantly specific wear rate as well as friction coefficient. Higher friction was linked to the formation of tribofilms on the surfaces, aided by higher oxygen content in the sliding atmosphere and temperature.