Microhardness Testing Applications

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 1 to 2000 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 behaviour. Conversions from microhardness values to tensile strength and other hardness scales (e.g. Rockwell) are available for many metals and alloys. 

Most microhardness testing is typically performed on samples that have been metallographically mounted and polished. These samples can be as large as about 100 mm square by 75 mm thick. 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. 

Typical Applications include :-
 
Surface phenomena – surface treatment
  • Case-hardening of steels
  • Surface hardening of titanium
  • Electrodeposited coating - hardness, brittleness, adhesion
  • Effects of various mechanical and thermal treatments on the surface layers
  • Hardness of thin coatings
Study of Alloys and Alloy Constitution
  • ·Quantification of transition areas
  • Decarburization in steels
  • Evaluation of welds
  • Bulk hardness of small samples
  • Evaluation of machinability
Heat Treatment
  • Heat treated steel case depth, non ferrous alloys, precipitation treatments and age-hardening
  • Segregation and coring, rates of diffusion
  • Recrystallisation
Materials science
  • Brittleness: ratio hardness/toughness
  • Elastic/plastic properties
  • Correlation with Young modulus
  • Paint films – hardness of painted surfaces
Tribology Research
  • Work hardening
  • Estimate mild wear losses
  • Correlation hardness number – wear resistance
Metal Powder Particles
  • Mechanical properties
  • Durability and performance of alloy components
Ceramics
  •  Determination of the hardening degree of glaze
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