MICROHARDNESS
Background
Vickers Indenter
Originally, the Vickers hardness test was developed for test loads of 1 to 120 kgf. The need for smaller indentations was subsequently recognised and a low-load "microhardness" or more correctly "microindentation" Vickers tester was developed. The shape of the Vickers indentation is geometrically similar at all test loads and therefore, the hardness value is constant over a very wide test load range, provided the test specimen is homogeneous.
Knoop Indenter
The Vickers test uses a square pyramidal indenter which is prone to crack brittle materials. Consequently, the Knoop test using an rhombic-based (diagonal ratio 7.114:1) pyramidal indenter was developed which produces longer but shallower indentations. For the same load, Knoop indentations are about 2.8 times longer than Vickers indentations. Experience with a wide range of ceramics has proven that the Knoop indentations are far less likely to crack than Vickers indentations.
Applications
- Hardness gradients
- Surface hardness
- Case depth
- Coating hardness
- Phase hardness
- Hardness of grains
- Hardness at grain boundaries
- Hardness of powders
- Hardness of fragile materials
Leitz Miniload 2 Microhardness Tester
Specification
| Indenters | Vickers, Knoop |
| Loads | 5 ± 0.05, 10, 15, 25, 50, 100, 200, 300, 500 g |
| Objectives | 10x, 50x |
| Magification | 100x, 500x |
| Stage size | X axis 135mm, Y axis 135mm |
| Stage travel | X axis 25mm, Y axis 25mm |
| Max sample height | 100mm approx |
Standards
| (BS 3900-E12.1:2000), (ISO 6441-1:1999) | Methods of test for paints. Determination of Knoop hardness by measurement of the indentation length using a microscope |
| (BS 3900-E12.2:2000), (ISO 6441-2:1999) | Methods of test for paints. Determination of Knoop hardness by measurement of the indentation depth |
| (BS 5411-6:1981), (ISO 4516-1980) | Methods of test for metallic and related coatings. Vickers and Knoop microhardness tests |
| BS EN 843-4:2005 | Advanced technical ceramics. Monolithic ceramics. Mechanical properties at room temperatures. Vickers, Knoop and Rockwell superficial hardness tests |
| ASTM B578-87(2015) | Standard Test Method for Microhardness of Electroplated Coatings |
| ASTM B931-14(2018) (ASTM B721-91(1999)) | Standard Test Method for Microhardness and Case Depth of Powder Metallurgy (P/M) Parts |
| ASTM C730-98(2013) | Standard Test Method for Knoop Indentation Hardness of Glass |
| ASTM C849-88(2016) | Standard Test Method for Knoop Indentation Hardness of Ceramic Whitewares |
| ASTM C1326-13 (2018) | Standard Test Method for Knoop Indentation Hardness of Advanced Ceramics |
| ASTM C1327-15 | Standard Test Method for Vickers Indentation Hardness of Advanced Ceramics |
| ASTM E384-17 | Standard Test Method for Microindentation Hardness of Materials |