Effects of environment on dry sliding wear of powder metallurgical Ti-47Al-2Cr-2Nb-0.2W

The effects of environment on the dry sliding wear behavior of Ti-47Al-2Cr-2Nb-0.2W (at.%) prepared by hot isostatic pressing (HIP) of powders have been investigated. Room temperature pin-on-disk tribotests were performed against an yttria-stabilized zirconia counterface in four different environments: air, oxygen, 4% hydrogen in nitrogen, and argon. It was found that this alloy is sensitive to the presence of oxygen, i.e. the pins had much lower wear rates in the oxygen-free environments. The presence of water vapor and molecular hydrogen had little effect on the wear rate. The effects of the different sliding speeds were also studied in air and argon and it was found that slower sliding rates led to greater wear of the pins, particularly in air. The tips of the worn pins were examined using both scanning electron microscopy and transmission electron microscopy, the latter using specimens produced by focused ion beam milling. At the higher sliding speed, the abrasive particles largely consisted of the counterface material and the zirconia particles were found to be embedded in a tribolayer on the worn tips of the pins. At the lower sliding speed, the abrasive particles mainly arose from the pins. The results indicate that both two-body and three-body abrasive wear, as well as plastic deformation and delamination, were the main wear mechanisms. Phase transformations in both the pin and the counterface at the contact area probably also played a role in the wear processes. (C) 2014 Elsevier Ltd. All rights reserved.