ASTM E384 test method, covers the determination of the microindentation hardness of materials. Micro indentation hardness testing is generally performed to quantify variations in hardness that occur over small distances.
Material Microindentation Hardness ASTM E384 is a method for assessing a material’s hardness on a microscopic level. Microindentation tests are used to measure the hardness of specific phases or gradients that are too tiny for microindentation tests to evaluate. Microindentation hardness is a measure of machinability, wear resistance, toughness, and ductility in metals.
For ASTM E384, a Knoop or Vickers indenter made from diamond is impressed into the test specimen at loads from a few grams to 1 kilogram. The impression length is measured microscopically, and the test load is used to calculate a hardness value. The hardness values obtained are useful indicators of a material’s properties and expected service behavior. The tester then applies the selected test load using dead weights. The length of the hardness impressions is precisely measured with a light microscope using either a filar eyepiece or a video image and computer software. A hardness number is then calculated using the test load, the impression length, and a shape factor for the indenter type used for the test.
The ASTM E384 test should be performed on a flat test specimen with a polished or suitably prepared surface for optimum accuracy of measurement.
For making an accurate measurement of the size of the indentation the test specimen surface should not be etched.
Knoop hardness (HK) is calculated as :
HK = 14.229 (F/D2 ) where, F = the applied load (measured in kilograms-force) D2 = the area of the indentation (measured in square millimeters)
Vickers hardness (HV) is calculated as :
HV = 1.854 (F/D2 ) where, F = the applied load (measured in kilograms-force) D2 = the area of the indentation (measured in square millimeters)