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Original Date: 11/03/1996
Revision Date: 01/18/2007
Information : Mechanical Properties Microprobe
Hardness represents an important attribute of materials. Traditionally, a material’s hardness is determined by indentation testing using optical microscopy to measure the contact area. When characterizing hardness in thin film, multiphase materials (e.g. superconductors, ion implanted surfaces), hardness needs to be measured on a small scale. Optical methods, however, do not have sufficient resolution to measure indents generated at very low loads (< 20 mN) or at shallow depths (< 250 nm). Since August 1995, Oak Ridge National Laboratory’s (ORNL’s) High Temperature Materials Laboratory (HTML) has been using a mechanical properties microprobe (MPM).
An MPM directly measures the indenter depth during the indentation testing. As a special microhardness tester, an MPM can operate at very low loads from 0.02 to 12 grams. Researchers use a three-sided Berkovich diamond pyramid to make an indentation in the sample. Generated electromagnetically, the indenter load can be controlled by varying the current in the coil surrounding the indenter shaft. A capacitive sensor measures the indenter shaft displacement and relates the information to the contact area by using the appropriate geometrical relationship for the indenter. Consequently, the load and displacement can be continuously measured during the indentation process. Unique to its tester, the HTML’s MPM can be operated with specialized indenter configurations such as spherical and flat punches in addition to the standard Berkovich diamond tip.
The resulting data from MPMs can be used to calculate the hardness (from the loading curve) and elastic modulus (from the unloading curve). The MPM has been successfully used to measure mechanical properties of thin and thick films, surface modified layers, and multiphase materials; deflection of microbeams as related to electronic devices; interfacial properties in composites for debond energy, residual stress, and sliding shear stress; diverse materials such as martensitic and austenitic phases in steel; thermal barrier coatings; and fiber push-in tests on small fibers.
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