Calotest

The Calotest, or calotte test, is a laboratory procedure used in surface engineering to assess the wear resistance and thickness of thin coatings on substrates. It is commonly applied to ceramic, carbide, and metal coatings in order to compare coating performance or to determine coating thickness with a small sample.

Principle and method: A small hemispherical cap (the calotte) or a corresponding abrasive tool is pressed against a coated specimen mounted in a holder. The assembly is rotated in a slurry containing abrasive particles. The coating wears away at a controlled rate until the substrate becomes exposed. By measuring the amount of material removed or the time needed to reach substrate exposure, and knowing the calotte geometry and material densities, the coating thickness can be inferred. In some implementations, the coating thickness is determined directly from post-test measurements such as profilometry or microscopy.

Equipment and procedure: The test uses a Calotest apparatus with a calibrated calotte, a sample stage, and an abrasive slurry. Typical procedure involves mounting the specimen, applying the slurry, rotating for a defined period, and then cleaning and measuring the result. Data are used to compute wear rate or remaining coating thickness, enabling comparisons across coatings and processes.

Applications: The Calotest is employed to evaluate protective coatings on metals and ceramics, thin film coatings produced by PVD/CVD, and multilayer systems. It provides a relatively rapid, small-sample means of assessing coating performance and uniformity under abrasive conditions.

Advantages and limitations: The method is compact, inexpensive, and suitable for small samples and rapid screening. Limitations include dependence on slurry composition, calotte geometry, and coating-substrate adhesion; results assume uniform wear and can be influenced by testing parameters.