High temperature fretting wear prediction of exhaust valve material

IC Engine valve components are generally made from Nickel based (Nimonic-80A) super alloys and these components are exposed to severe operating conditions while the engine is running. Interface fretting combined with impact wear causes major wear related failures to the valve and seat components. There is a need to predict wear of such interfaces so that their life and residual life (i.e. inspection) can be assessed. This paper focusses on a fretting wear of Nimonic-80A material line contact (cylinder-on-flat) at both room temperature and at high temperature conditions. The objective of this study is also to be able to understand the effect of interface fretting displacement, which is the key parameter that controls wear. Tests were performed at three different displacement amplitudes at room temperature (RT) and at high temperature (620°C) for 25,000 cycles. Experimental constants such as wear coefficient (k) and friction coefficient (µ) were derived from the test results. The wear and friction coefficients were then used in the wear-model to predict the wear depth. Further, this model was used to predict wear at 100,000 cycles. Predicted results are compared then with results from tests which have been run beyond 25,000 cycles (i.e. 100,000 cycles).