Microhardness Testing

Vickers Hardness, Knoop Hardness Test & More

Microhardness testMicrohardness Testing is a method of determining a material’s hardness or resistance to penetration when test samples are very small or thin, or when small regions in a composite sample or plating are to be measured. It can provide precise and detailed information about surface features of materials that have a fine microstructure, are multi-phase, non-homogeneous or prone to cracking.

The microhardness test can measure surface to core hardness on carburized or case-hardened parts (case depths), as well as surface conditions such as grinding burns, carburization or decarburization.

Microhardness Testing Offered at LTI

Micro hardness testing services are routinely performed at Laboratory Testing Inc. near Philadelphia, PA (USA) to help determine mechanical properties of small parts, evaluate cold work and determine weld quality. We also certify conformance to hardness requirements for carburizing, nitriding, plasma nitriding, induction, flame and many other surface hardening processes.

LTI offers two micro hardness test processes with load weights up to 1000 grams. The Knoop Hardness Test and the Vickers Hardness Test, which is also available for macrohardness with applied loads up to 50 kilograms.

Micro analysis examinations, such as surface contamination, carburization and decarburization, case depth and profiles, provide valuable information about the hardness of small samples and small areas of evaluation. The services can measure the effective case depth in case hardening heat treatments and surface or core hardness of carburized parts, as well as surface conditions such as grinding burns or decarburization.

Microhardness testing from LTI is PRI Nadcap and A2LA accredited and completed according to industry standards. All details about the test and results are documented in certified test reports.

Test Methods/Specifications

  • AMS 4081
  • AMS 4083
  • ASME Sect. IX
  • ASTM B578
  • ASTM E1077
  • ASTM E384
  • MIL Specifications

Hardness Conversion Charts comparing microhardness test values to tensile strength and other hardness scales (e.g. Rockwell) are available.

LTI Capabilities

  • Vickers Hardness Test – micro and macro hardness with load weights up to 50 kilograms
  • Knoop Hardness Test – load weights up to 1000 grams
  • Surface Contamination
  • Carburization & Decarburization
  • Case Depth
  • Profiles

The Microhardness Test Processes

During microhardness testing, a Vickers (DPH) or Knoop (KHN) diamond indenter is pressed into the material’s surface with a penetrator and a light load of up to 1000 grams. The result of applying the load with a penetrator is an indent or permanent deformation of the material surface caused by the shape of the indenter.

Both the Knoop and Vickers hardness test methods use specific measurements from the indent, in conjunction with formulas, to calculate material hardness. Accurate measurement of the resulting indentation requires the use of a special microhardness testing microscope because the indents are so small.

Knoop – The Knoop hardness test is performed by applying controlled force of 1000 grams or less for a specific amount of time to an indenter in a rhombus-shape (elongated four-sided pyramid). The hardness of the material is determined by the depth to which the Knoop indenter penetrates. The impression is measured microscopically and, when combined with the amount of the test load, can be used to calculate the hardness value on the Knoop scale. Knoop hardness numbers are often cited in conjunction with specific load values.

Vickers – The Vickers hardness test can be performed on both the micro and macro scales with a maximum test load of up to 50 kilograms. Like Knoop microhardness testing, these tests are also performed by applying controlled pressure for a standard length of time, but with a square-based diamond pyramid indenter. The diagonal of the resulting indention is measured under a microscope, then this measurement and the test load are used in a specific formula to calculate the Vickers hardness value.

Watch the Microhardness Test process in the Video below.

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