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2063 |
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An Instrument for Nanoindentation Without Frame Stiffness Dependency |
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Metrology: Instrumentation, Design & Testing |
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Hardness is typically measured by indenting a specimen and then correlating the applied force to the projection area, surface area or depth of the indent. Generally, hardness is divided into three regimes: macrohardness, microhardness, and nanohardness. The macro and micro hardness tests are well established but still have a variety of problems. Most notably, there is a large dependency on the frame stiffness of the instrument on the measured hardness values and there is a lack of quantifiable units between different hardness tests. As a result, the hardness value, which is typically given by a dimensionless number, is inconsistent between scales, making it difficult to compare results between instruments.
The measurement of nanohardness is necessary for several fields including thin films for tool coatings and adhesives as well as for micro-electrical mechanical systems and semiconductors. The goal of the nanohardness measurement is to quantify material properties on the nanoscale and compare the values with the bulk properties. However, measuring hardness of materials on the nanoscale is challenging and there is not a well established methodology for assessment of the test procedure and estimating uncertainties based on a specific instrument design.
The goal of this research is to design a new instrument for nanoscale indentations and hardness measurements. The purpose of this instrument is to quantify hardness measurements in accordance with the ISO Standard 14577 by removing the dependency on frame stiffness. This project will redesign and improve an existing nano-indentation instrument, based on the previous work at UNC Charlotte. The major improvements will be to increase the force resolution to near 1 micro-newton, to decrease the electrical noise resulting in a displacement resolution of better than 1 nm, and to measure the frame deflection based on a constant reference force.
Once the instrument is built and tested, UNC Charlotte will participate in an international round robin of nano-indention hardness measurements. Three samples, single crystal aluminum, fused silica, and rolled tungsten, will be tested at numerous institutes around the world and the results compared. These institutes include, but are not limited to NIST, PTB, Oklahoma State University, and the University of California at Berkeley. The goal of this round robin is to determine the variability in different nanohardness measurement instruments and to attempt to reduce these differences.
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