The contact fatigue behavior of a fine-grained hardmetal coated with two distinct ceramic films, either a TiN monolayer or a WC/C multilayer, is studied by means of indentation testing techniques. Spherical indentation tests indicate that the investigated coated systems exhibit different susceptibility to fatigue degradation in terms of emergence of circular cracks at the coating surface. Furthermore, these cracks are found to induce well-defined substrate cracking without any intermediate decohesion. Accordingly, the intrinsic mechanical degradation under cyclic loading of the ceramic films is pointed out as key feature for rationalizing the experimental findings. This is finally sustained by the higher mechanical degradation exhibited by the WC/C film, as compared to the TiN one, on the basis of imprint size and contact stiffness changes with increasing number of cycles under repetitive nanoindentation.Postprint (published version
This work focuses on the possibility of processing stainless steel 316LN powder into lightweight structures using electron beam melting and investigates mechanical and microstructural properties in the material of processed components. Lattice structures conforming to ISO13314:2011 were manufactured using varying process parameters. Microstructure was examined using a scanning electron microscope. Compression testing was used to understand the effect of process parameters on the lattice mechanical properties, and nanoindentation was used to determine the material hardness. Lattices manufactured from 316L using EBM show smooth compression characteristics without collapsing layers and shear planes. The material has uniform hardness in strut shear planes, a microstructure resembling that of solid 316LN material but with significantly finer grain size, although slightly coarser sub-grain size. Grains appear to be growing along the lattice struts (e.g., along the heat transfer direction) and not in the build direction. Energydispersive x-ray spectroscopy analysis reveals boundary precipitates with increased levels of chromium, molybdenum and silicon. Studies clearly show that the 316LN grains in the material microstructure are elongated along the dominating heat transfer paths, which may or may not coincide with the build direction. Lattices made from a relatively ductile material, like 316LN, are much less susceptible to catastrophic collapse and show an extended range of elastic and plastic deformation. Tests indicate that EBM process for 316LN is stable allowing for both solid and lightweight (lattice) structures.
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