Variations in strain affect friction and microstructure evolution in copper under a reciprocating tribological load

The microstructure of the materials constituting a metallic frictional contact strongly influences tribological performance. Being able to tailor friction and wear is challenging due to the complex microstructure evolution associated with tribological loading. Here, we investigate the effect of the strain distribution on these processes. High-purity copper plates were morphologically surface textured with two parallel rectangles—referred to as membranes—over the entire sample length by micro-milling. By keeping the width of these membranes constant and only varying their height, reciprocating tribological loading against sapphire discs resulted in different elastic and plastic strains. Finite element simulations were carried out to evaluate the strain distribution in the membranes. It was found that the maximum elastic strain increases with decreasing membrane stiffness. The coefficient of friction decreases with increasing membrane aspect ratio. By analyzing the microstructure and local crystallographic orientation, we found that both show less change with decreasing membrane stiffness

Wear behaviour of DMD-generated high-strength steels using multi-factor experiment design on a pin-on-disc apparatus

Direct metal deposition (DMD) is a laser-based powder-fed-type additive manufacturing technology to create solid and porous structures from high-strength metallic alloys that can be used as coatings, foams and sandwiched structures, and as highly stressed components. This investigation evaluates the quality and capability of DMD-generated high-strength steel alloy parts to withstand severe sliding wear against mild steel counter face involving multi-factor experimental design. The specimens are produced by DMD as cylindrical pins and annular paddings coated on mild steel substrate. Experiments were conducted on a pin-on-disc wear tester under six different experimental regimes designed to take into account different material conditions of H13 tool steel and 316-L stainless steel. The wear characteristics were evaluated following ASTM standard G99 under dry and severe conditions involving direct metal to metal contact. The wear scars and tracks reveal oxidative flaking, plastic deformation and micro-ploughing of the surfaces depending on specific test condition. This study focuses on the evolution of co-efficient of friction and its variation while changing the material and operating conditions. The study also investigates the relationship of primary and secondary wear factors in terms of wear loss from the DMD specimen and the energy dissipation during sliding wear. The results show a strong and consistent behaviour of laser-generated specimen and exhibit very little signs of material degradation and flaking under high loading conditions