An industrial and cost-effective online quality control method for thermally sprayed coatings will be presented. A new concept in pulse-thermography allows online, during the spraying process, the non-destructive evaluation of coated surfaces. This technique employs a heat source that produces a heat impulse. The impulse is directed toward the examined surface and the from the surface reflected and/or emitted signal is collected by an infrared-camera and subsequently treated in a computer. It will be demonstrated that the spraying process itself can be used as a heat source. In principle, the fading behavior of the signal captured by a high speed infrared camera is observed, or else the progression of the induced heat wave within the coating. Differences in coating thickness, coating and adhesion defects, microstructural changes, an aggregation of pores as well as oxide or metallic inclusions provoke a significant change in the signal intensity and are therefore detected. Pulse-thermography enables the non-destructive assessment of the quality of thermally sprayed coatings. A coated part can be examined to check if the desired coating structure has been successfully attained or if and where there are any areas with critical deviations in respect to coating thickness or coating microstructure. The simple set-up allows the integration of the technique in the production line.

Infrared techniques are well introduced in industry for several types of inspections. For non-destructive testing of thermal sprayed layers they couldn't be applied very successfully due to the limited resolution. Although, new developed and very fast infrared sensors combined with a miniaturised cooling system (like Stirling motors) allowing today the development of a new generation of portable infrared systems for non-destructive and fast testing of sprayed layers on large surfaces. This paper reports on results got with a first prototype of such a new designed infrared camera. It will be demonstrated that it is possible to prove coatings quality on large machine components independent of the material combination. The inspection speed is several times faster than the time used for spraying. Coating thickness measurements as well as defects like cracks or areas of bad bonding can be done with a resolution down several micrometers. Even differences in coatings quality are possible to identify, as for example the level of dilution of carbides of HVOF sprayed WC-Co coatings. Paper text in German.