Sliding wear rate can be determined by the pin-on-disc method (ASTM G99). In this test a pin with a radiused tip, is positioned perpendicular to a flat circular disk onto which the coating has been applied. A rigidly held ball is often used as the pin specimen. The pin or ball is usually a hardened steel or ceramic material. The test procedure involves rotating the disk centre with the pin exerting a specified load on the disk. The wear path is a circle formed on the surface of the disk with the wear rate is expressed as volume loss per km, for the pin and disk separately.

Abrasive wear rate can be determined using the dry sand rubber wheel method (ASTM G65). This technique involves abrading a coated specimen with grit of controlled size and composition. The coated specimen is pressed against the rotating wheel at a specific force by means of a lever arm, while a controlled flow of grit abrades the test surface. The rotation of the wheel is such that its contact face moves in the direction of the grit flow. The wear rate is expressed as volume loss per km.

The ball-cratering test can also be used to determine the abrasion resistance of coatings. In this technique, a ball is rotated and pressed against the sample until a spherical depression is produced. By making a series of these craters and measuring the size of the scar dimensions, the wear rate of both the coating and the substrate can be calculated.

Erosion can be measured in accordance with the standard ASTM G76. This test is based on a repeated impact erosion approach involving a small nozzle delivering a stream of gas containing abrasive particles, which impacts the surface of a specimen. The erosion rate is expressed as volume loss of material per unit mass of abrasive.

Source: TWI