Tip-Induced Calcite Single Crystal Nanowear
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1049-AA05-15
Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky Department of Mechanical Engineering, University of South Florida, 4202 E. Fowler Ave. ENB118, Tampa, FL, 33620 ABSTRACT Wear behavior of freshly cleaved single crystal calcite (CaCO3) was investigated by continuous scanning using the Hysitron Triboindenter in ambient environment as a function of scanning frequency (1 Hz – 3 Hz) and contact load (2 µN – 8 µN). At lower loads below 4 µN, initiation of the ripples takes place at the bottom of the surface slope, which continue to propagate up the slope as scanning progresses. The orientation of these ripple structures is perpendicular to the long scan direction. As the number of scans increases, ripples become fully developed, and their height and periodicity increase with the number of scans. At 6 µN normal load, tip-induced wear occurs as the tip begins removing the ripple structures with increased number of scan cycles. As the contact load increased further, ripples did not initiate and only tipinduced wear occurred on the surface, and saturated after 20 scans. At 1 Hz frequency wear takes place as material slides towards the scan edges when the tip moves back and forth. Material removal rate increased with contact load and it is observed that the number of scans required to create a new surface is inversely proportional to the contact load. Possible mechanisms responsible for the formation of ripples at higher frequencies are attributed to the slope of the surface, piezo hysteresis, system dynamics, or a combination of effects. The wear regime is due to abrasive wear. Single crystal calcite hardness of 2.8±0.3 GPa and elastic modulus of 75±4.9 GPa were measured using nanoindentation and used to determine the wear mode. INTRODUCTION The development of the nano-mechanics field over the past few decades produced a significant amount of methods for determination of mechanical and tribological properties of materials at micro and nano scales. Among others, nanoindentation and micro/nanotribology methods have been considerably developed, including depth sensing nanoindentation and Atomic Force Microscopy (AFM)/Scanning Tunneling Microscopy (STM). These are powerful and versatile tools for surface topography characterization and local mechanical properties measurements at small scales. In addition, it is possible to utilize the scanning nanoindenter capable of modifying the materials structure. As the use of coatings constantly increases in the field of nanotechnology, it is important to know the behavior of materials at small scales. In recent years the formation and characterization of nanometer-sized structures have attracted a great deal of interest. One of the nanotechnology research motivations is the construction of nanosized surface patterns. In a typical wear experiment a hard material is scanned over the tested material surface, resulting in a wear rate measurement in terms of the removed material depth or volume as a function of normal applied load and the number o
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