Surface plastic flow in polishing of rough surfaces

Abstract

We present experimental evidence for a new mechanism for how smooth surfaces emerge during repetitive sliding contacts, as in polishing. Electron microscopy observations of Ti-6Al-4V surface with a spherical asperity structure—realized via additive manufacturing—during successive polishing stages suggest that asperity-abrasive contacts exhibit viscous behavior, where the asperity material flows in the form of thin (1–10 μ m) fluid-like layers. Subsequent bridging of these layers among neighboring asperities results in progressive surface smoothening. Using analytical asperity-abrasive contact temperature modeling and microstructural characterization, we show that the sliding contacts encounter flash temperatures of the order of 700–900 K which is in the range of the dynamic recrystallization temperature of the material considered, thus supporting the experimental observations. Besides providing a new perspective on the long-held mechanism of polishing, our observations provide a novel approach based on graph theory to quantitatively characterize the evolution of surface morphology. Results suggest that the graph representation offers a more efficient measure to characterize the surface morphology emerging at various stages of polishing. The research findings and observations are of broad relevance to the understanding of plastic flow behavior of sliding contacts ubiquitous in materials processing, tribology, and natural geological processes as well as present unique opportunities to tailor the microstructures by controlling the thermomechanics of the asperity-abrasive contacts.

Tribology of Ti-6Al-4V Alloy Manufactured by Additive Manufacturing

“…Smoothed surface by UNSM at 25°C is beneficial to improving main structural properties such as tribology, corrosion and fatigue. Commonly, a surface quality of AM fabricated materials is very rough upon completion of AM [29]. This means that surface is required to be machined or finished.…”

A Gaussian Process Model-Guided Surface Polishing Process in Additive Manufacturing

“…In this research, we focus on the polishing process of a metal AM product and, specifically, the 3D-printed Ti-6Al-4V alloy samples. The printing process to obtain these samples involves depositing a 50 μm layer of Ti-6Al-4V powder that consists of Ti-6Al-4V particles of average diameter of 72 μm using a focused beam of 3 mA and a scanning speed of 10 m/s [17]. Each of the Ti-6Al-4V alloy samples is polished from a raw stage ( Fig.…”

Tribological Performance of Additively Manufactured AISI H13 Steel in Different Surface Conditions

“…Again, samples were polished after 3D-printing and subjected to an oxidation treatment to improve their wear resistance [ 12 ]. Interestingly, the surface roughness inherent to additive manufacturing in this case was used as a means to study the polishing processes of rough surfaces [ 20 ]. Grinding and polishing was also necessary when a CoCrFeMnNi high-entropy alloy was processed via an additive manufacturing route, and tribologically tested [ 21 ].…”