Microhardness testing is an indentation method for measuring the hardness of a material on a microscopic scale. A precision diamond indenter is impressed into the material at loads from 15 to 1000 gf. The impression length, measured microscopically, and the test load are used to calculate a hardness value.

The indentations are made using a square-based pyramid indenter (Vickers hardness scale) or an elongated, rhombohedral-shaped indenter (Knoop hardness scale). The hardness impressions can be precisely located with the microscope to perform tests on microscopic features. The hardness values obtained are useful as an indicator of materials properties and expected service behavior. Conversions from microhardness values to tensile strength and other hardness scales (e.g. Rockwell) are available for many metals and alloys.

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Bulk hardness-Randomly-located impressions can be used to obtain a representative bulk hardness value for a relatively homogeneous material.

Localized hardness-Impression can be precisely located at discrete features to determine the hardness of the material comprising that feature. Hardness can be measured for phases and features less than 0.1 mm across.

Hardness profile-Making a series of hardness impressions at various distances from a surface or a specific point to measure the hardness variation within a sample.

Thin coatings-The hardness of coatings as thin as a few microns can be determined by measuring directly on the coated surface of a sample. Coating thickness must be known to assess accuracy of the measurements.

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• Bulk hardness of small samples
• Heat treated steel case depth
• Decarburization in steels
• Evaluation of welds
• Hardness of thin coatings
• Evaluation of machinability

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Model: SHIMADZU TYPE M

Most microhardness testing is typically performed on samples that have been metallographically mounted and polished. These samples can be as large as about 1 in. (25 mm) by 1 in. (25 mm) by 1/2 in. (12 mm) thick. Larger samples can be tested with special fixturing. Thin sheet material can be tested without mounting or preparation if the surface finish is suitable.

The ideal surface finish is a high-quality metallographic polish. Where polishing is not feasible, surface finish must be sufficiently reflective to clearly resolve the microscopic hardness impression. The specific finish requirement will be dependent on the material and test load.

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