Unveiling the complex wear sequence of a directed energy deposited 316L+WC hierarchical composite against alumina

Abstract

In this work, the addition of 20 vol % of tungsten carbide (WC) to 316L powder processed by direct energy deposition (DED) leads to a hierarchical composite. The modified austenitic microstructure is reinforced by partially dissolved WC, and by a network of solidification carbides. Wear tests for DEDed composite sliding against alumina were carried out, highlighting a cyclical wear regime different from the steady state one achieved on the reference DEDed 316L under similar conditions. The wear behaviour of the DEDed composite sliding against alumina was investigated when considering significant variations of both the friction coefficient (CoF) and the penetration depth (PDe). A novel approach based on interrupted wear tests was applied to better understand the role of the complex hierarchical microstructure of the DEDed composite on its wear behaviour. The wear tracks were analysed through scanning electron microscopy and profilometer at the different stages. This approach allows to observe the evolution of the wear rate with the progress of the test and to identify the corresponding mechanisms that involve adhesive, abrasive and oxidative wears. The influence of WC reinforcements, of the composite matrix or of the counterbody considered solely or in association under dry sliding conditions are discussed thus helping to unveil the complex wear sequence of the DEDed composite. The interrupted wear tests approach also helps to highlight the contribution of the short run-in period and that of the subsequent cyclical regime to the wear rate while considering repeated compaction, breakdown and reformation of a protective tribolayer.