Iquebal Ashif S, Sagapuram Dinakar, Bukkapatnam Satish T S
Texas A&M University, Department of Industrial & Systems Engineering, College Station, 77843, Texas, USA.
Sci Rep. 2019 Jul 23;9(1):10617. doi: 10.1038/s41598-019-46997-w.
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 μm) 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.
我们提供了实验证据，证明了在诸如抛光等重复滑动接触过程中光滑表面形成的一种新机制。通过增材制造实现的具有球形粗糙结构的Ti-6Al-4V表面在连续抛光阶段的电子显微镜观察表明，粗糙-磨料接触呈现粘性行为，其中粗糙材料以薄（1-10μm）的流体状层的形式流动。这些层随后在相邻粗糙之间桥接，导致表面逐渐平滑。通过分析粗糙-磨料接触温度模型和微观结构表征，我们表明滑动接触遇到的闪温约为700-900K，这在所考虑材料的动态再结晶温度范围内，从而支持了实验观察结果。除了为长期以来的抛光机制提供新的视角外，我们的观察还提供了一种基于图论的新颖方法来定量表征表面形态的演变。结果表明，图表示法为表征抛光各阶段出现的表面形态提供了一种更有效的方法。这些研究结果和观察结果对于理解材料加工、摩擦学和自然地质过程中普遍存在的滑动接触的塑性流动行为具有广泛的相关性，并且为通过控制粗糙-磨料接触的热机械性能来定制微观结构提供了独特的机会。
