This is a new standard for the twist compression test (TCT). The TCT is a variation of the existing galling standards Test Methods G98 and G196 with wider applicability. In addition to material couples, it also incorporates the testing of surface treatments, coatings, and lubricants using a larger contact area, than the existing tests. It is similar in concept to the thrust washer test (for example, Test Method D3702) but with significant differences in test conditions. The TCT has been in use for over 50 years but has recently gained popularity in North America and Europe. More than a dozen North American companies own TCT apparatus and many more use it as a rapid and flexible method of comparing galling resistance of lubricated and nonlubricated contacts. Contacting solid surfaces subjected to this type of testing conditions can develop significant damage in the form of material transfer, delamination, debris generation, extensive plastic deformation, and so forth. Frequently, the damage caused by TCT creates fluctuations or abrupt changes in coefficient of friction. This test method is intended to assess a tribocouple’s relative susceptibility to galling (nonlubricated conditions) or scuffing (lubricated conditions) under conformal unidirectional flat-on-flat conditions. Laboratories that currently use this test find it helpful as a screening test for defining or ranking the range of effectiveness of material couples, surface treatments, and lubricant formulations thus reducing the number of candidates for field-process trials or simulation tests.
The TCT results from different laboratories have been compared without regard or knowledge of individual laboratories’ test parameters. In the absence of a standard, confusion created by comparing test results from different laboratories using their own methodologies is harmful to industry in search of more energy efficient and environmentally friendly materials, surface treatments, coatings, and lubricants. Rapid, flexible test methods such as TCT are needed for the industry to respond to rapid changes in materials and processes that occur in manufacturing.
The title and scope are in draft form and are under development within this ASTM Committee.