Comparative tribological and adhesion studies of some titanium-based ceramic coatings

In this work different evaluation methods for thin hard coatings were studied in three laboratories. Different coatings and test equipment were used. An agreement on the procedure for testing and data appraisal was made.
The results obtained in the different laboratories varied depending on the test procedure used.
Two test methods, ball crater and scratch test, yielded smaller variations in the results, whereas the hardness measurements and pin-on-disc tests had larger variations, although in the former case these were within the standard deviations of the readings.

It is clear from this work that tests performed in different laboratories cannot be used for comparison purposes, unless strict agreement is reached on the exact test procedure and on the basis of interpretation of the results.
Even tests carried out under nominally identical conditions in one laboratory can in some cases give a spread in performance, since many variables, such as friction coefficient, wear rate and hardness, are not intrinsic materials properties and can statistically vary.
It is thus important to devise standardized test methods, and in all cases to quote the standard deviations on data.