Experimental-computational method of calibrating universal beta-type coating thickness gauges

Abstract

Thickness gauges which operate on the principle of recording the back-scattered beta-radiation are suitable for measuring the thickness of various coatings. In view of this universality of these instruments, many sets of reference coating specimens are required for their initial calibration and subsequent periodic checkouts. The preparation and the certification of such reference specimens is a difficult project which has not been quite completed yet. No such reference specimens are produced serially in the USSR at this time, mainly because of the stringent requirements as to substrate surface flatness (+- 0.3 ..mu..m) and finish (nabla 10-nabla 11), further complicated by the necessity of a coating layer with a ''step'' suitable for certification tests by either the pneumatic or the contact method on standard interference apparatus. These factors impede the adaptation of such thickness gauges by industry. The authors report here the results of a study concerning an experimental-computational method of calibrating universal beta-type coating thickness gauges with one set of reference coating specimens and one combination of materials, so as to ensure the feasibility of measuring the coating thickness in many combinations of coating and base materials.