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Scratch hardness test or scratch test refers to any of a number of methods of measuring scratch hardness. Resistance to abrasion is less affected by surface variations than indentation methods. Scratch hardness is measured with a sclerometer. [1] Attempting to scratch a surface to test a material is a very old technique. [2]
The Turner-Sclerometer test consists of measuring the amount of load required to make a scratch. [1] [2] In test a weighted diamond point is drawn, once forward and once backward, over the smooth surface of the material to be tested. The hardness number is the weight in grams required to produce a standard scratch.
Diamond (Mohs 10) is 1500 (off scale). Diamond was the hardest known naturally occurring mineral when the scale was designed, and defines the top of the scale, arbitrarily set at 10. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can ...
Scratch tests at low loads, such as the Bierbaum microcharacter test, performed with either 3 gf or 9 gf loads, preceded the development of microhardness testers using traditional indenters. In 1925, Smith and Sandland of the UK developed an indentation test that employed a square-based pyramidal indenter made from diamond. [ 11 ]
The principle is that an object made of a harder material will scratch an object made of a softer material. When testing coatings, scratch hardness refers to the force necessary to cut through the film to the substrate. The most common test is Mohs scale, which is used in mineralogy. One tool to make this measurement is the sclerometer.
ASTM G105 Standard Test Method for Conducting Wet Sand/Rubber Wheel Abrasion Tests [21] ASTM G132 Standard Test Method for Pin Abrasion Testing [22] ASTM G171 Standard Test Method for Scratch Hardness of Materials Using a Diamond Stylus [23] ASTM G174 Standard Test Method for Measuring Abrasion Resistance of Materials by Abrasive Loop Contact [24]
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The short B-N (1.57 Å) bond is close to the diamond C-C bond length (1.54 Å), that results in strong covalent bonding between atoms in the same fashion as in diamond. The slight decrease in covalency for B-N bonds compared to C-C bonds reduces the hardness from ~100 GPa for diamond down to 48 GPa in c-BN.