ASTM E384 Test for Microindentation Hardness of Materials

Scope:

ASTM E384 is a Microindentation hardness test that determines hardness variations that occur over a small distance. It is used for materials evaluation, quality control, and research and development. Hardness is correlated to tensile strength for many metals and alloys, and it is an indicator of machinability, wear resistance, toughness, and ductility.

Because microindentation hardness tests determine hardness variations, a single test value will not represent the bulk hardness. Bulk Hardness can be calculated by making numerous indents and calculating their average and standard deviation. 

Micro indentation hardness test requires very small physical indentations. Therefore, testers should be able to create indents at very low test forces. They should be able to apply the test forces exactly at the desired location. They should have a high-quality optical system to precisely measure the diagonal of the small indents.

Test Procedure:

A Knoop or Vickers indenter applies a small test force on the surface of the specimen. The size of the indentation is measured by a light microscope.

The Knoop hardness number is calculated by dividing the test force by the projected area of the indentation. The Vickers hardness number is calculated by dividing the test force by the surface area of the indentation.

Specimen size:

Optimally, the test specimen should be flat with a polished surface free of preparation-induced damage. The surface must be free of any problems that could affect the indentation or the subsequent measurement of the diagonals. 

Data:

1. The Knoop hardness number:

P = force, 

A_p = projected area of indentation.

2. The Vickers hardness number:

P = force,

A_s = surface area of the indentation.