Benchtop Hardness Testers
Since different industries define hardness testing according to the purpose of their testing, we can expect different definitions of hardness testing. To the coatings industry, hardness means the resistance to scratch. The metal industry defines hardness as resistance to permanent deformation. Some understand hardness as wear, flow stress, etc. Accordingly, hardness testing is carried out a scratch test, flow test, static indentation, cutting test, erosion, and ultrasonic tests.
The primary reason for carrying out a hardness test is the evaluation of test material properties and then identifying them for specific industrial applications. With the so-called static indentation test, a cone, ball or pyramid pressed into the test material and the depth of indentation defines the hardness. Methods for testing can be Rockwell, Brinell or Vickers. While Rockwell testing – the most commonly carried out hardness test, is determined by depth, Brinell is determined by the impression left behind by exerting specific indenter into test material under specific force and time/duration. The Vickers hardness test is determined by the size of an impression created under load by a pyramid-shaped diamond indenter.
Microhardness testing, unlike macro-hardness testing, applies loads between the range of L < 2 N and penetrations h > 0.2 µm . Ideal for small samples, foils, and wires. Vickers and Knoop are the main methods of micro-hardness testing where a pyramidal shaped diamond indenter is penetrated to determine test material resistance. Similar to macro hardness indentation tests, the hardness is calculated as the correlation between the depth of indenter, the given load and within a length of time. Micro-Vickers Test employs forces below 1 kgf (~9.8 N). Specifically, the Knoop test uses a rhombic-based pyramidal diamond with an elongated diamond shaped indenter. ASTM E384 is the standard test method for Vickers and Knoop. The values of both micro-hardness can be converted to other hardness scales using ASTM E140. A2LA and ISO accreditation specify the following ranges for Knoop (100, 500HK) and Vickers (100g, 300g, 500g, 1000g, HV).