High temperature dry sliding wear behaviour of laser powder bed fused Inconel 718

Abstract

This research investigates the microstructure, mechanical, residual stress and tribological properties of as-printed Inconel 718 by laser powder bed fusion. The microstructure exhibits a hierarchical structure composed of melt pool boundaries and directionally solidified columnar thin dendrites. No significant size of defects or undesirable phases such as Laves phases or macrosegregation was found in the microstructure. The Vickers microhardness results did not show any significant differences in hardness value across the tracks and layers of melt pool boundaries. This implies that the anisotropy is insignificant in the as-printed condition. The hot tribological behaviour of the alloy was investigated for the range of temperatures (28 °C, 400 °C, 500 °C and 600 °C) in a high temperature pin (Inconel 718) on disc (EN31 steel) set up. The worn surface and loose wear debris were analysed with the aid of SEM/EDS and XRD analysis. The wear loss and friction coefficient increase with the test temperature. The friction results show the running-in-period and steady-state-period for the high temperature cases. These regions correspond well with the slope change in the wear loss. The abrasion wear is predominant at 28 °C. In contrast, delamination wear and oxidation wear are dominant for high temperature cases. The observation of high friction and wear loss with the test temperature is attributed to the increased intensity of delamination wear and oxidation rate of non-lubricative NiO. The wear debris size increases with the test temperature and the shape has undergone changes from short angular to long angular sheets.