Compacted Oxide Layer Formation Under Conditions of Limited Debris Retention at the Wear Interface During High Temperature Sliding Wear of Superalloys

ABSTRACT For many applications, including power generation, aerospace and the automobile industry, high temperature wear provides serious difficulties where two or more surfaces are able to move relative to one another. It is increasingly the case that with for example, aerospace applications, demands for ever more powerful and efficient engines that thus operate at higher temperatures, conventional lubrication is no longer sufficient to prevent direct contact between metallic surfaces and consequent accelerated wear. One phenomenon that has been observed to reduce metallic contact and thus high temperature wear and friction is the formation of what are termed ‘glazes’, essentially layers of compacted oxide wear debris that becomes sintered together to form a low friction wear resistant oxide surface. This thesis studies the nature of the wear encountered with four different combinations of Superalloys, slid together using a ‘block-on-cylinder’ configuration developed for accelerated simulation testing of car engine ‘valve-on-valve-seat’ wear. Predominantly, Nimonic 80A and Incoloy MA956 were used as sample materials and Stellite 6 and Incoloy 800HT were used as counterface materials. The initial part of this study concentrates on sliding speed – during the current experimental programme, testing was conducted at 0.314 m.s 1 and 0.905 m.s 1, between room temperature and 750°C – this supplemented previous testing conducted at 0.654 m.s 1. When Nimonic 80A was slid against Stellite 6, lowering sliding speed to 0.314 m.s 1 between 510°C and 750°C lead to the formation of wear protective glaze layers consisting of cobalt and chromium oxides from the Stellite 6, whereas at 0.905 m.s 1 and during previous testing at 0.654 m.s 1, only high wear was encountered with debris consisting of nickel and chromium oxides from the Nimonic 80A. When Incoloy MA956 was slid against Stellite 6 at the same sliding speeds and over the same temperature range, a wear protective layer readily formed regardless of sliding speed. However, the sliding speed was observed to affect the relative contributions to the glaze layer from sample and counterface – a shift was observed from largely cobalt and chromium oxides from the Stellite 6 at 0.314 m.s 1 to largely iron and chromium oxides from the Incoloy MA956 at 0.905 m.s 1. Also, the use of a higher sliding speed was noted to promote glaze formation at lower temperature, with glaze appearing at 450°C for 0.905 m.s 1, whereas only severe

שנה

2006

שפה

English

הוצאה

Dissertation.com

מהדורות

1

עמודים

372

ISBN

9781581123210

מקור הנתונים: Wikidata