The characterization of the adhesive and cohesive strength of thermally sprayed coatings is often evaluated according to given standardized testing procedures. These tests require the preparation of normally large coupons which have to be fixed together using an appropriate adhesive. Additionally they need time for preparation (e.g. annealing/curing of the adhesive) and require test equipments normally not available at job shops for coating development. One of the largest limitations of these tests is the applicability only for non-porous coatings, and in some cases the limited strength of the adhesive. Within a European CRAFT research project on “standards, measurements and testing”, a new shear test method was developed to characterize the mode and value of failure of thermally sprayed layers in a more reliable and less limited manner. This new shear test does not need any adhesive and yields more intrinsic information on coating quality than conventional tensile tests.

Metallurgical powders can be characterized by different techniques including image analysis, laser particle size analysis, and various forms of sieve analysis. This paper evaluates a new method that uses a high-resolution slide scanner in combination with automated image analysis. The results obtained with this system are comparable to powder analysis via laser scattering and classical sieving techniques, but are more sensitive to changes in powder quality. Paper includes a German-language abstract.

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.

Until now the use of thermal sprayed metallic coatings for wet corrosion protection is limited to applications where the coating (Al-alloys, Zn-alloys and their mixtures) acts as an anode to protect the substrate or special cases, where thick cold sprayed metallic layers give good results. Other atmospheric cold sprayed layers made of corrosion resistant Ni, Co, Cu or Fe base alloys have their limitations due to the process related discontinuities like pores and oxide films. In more aggressive environments thermal sprayed and fused layers made of so called self-fluxing Ni and Co based alloys are commonly applied. Also in some applications the use of specially designed gas shrouds or of spraying techniques running in inert gas atmospheres or vacuum can yield protective coating solutions. However, these techniques have high investment or service costs or the size of the parts to be coated is restricted. Recent developments in HVOF-spraying open new possibilities in applying cold sprayed coatings on site with good corrosion resistance. The aim of this paper is on one hand to give a comparative overview about the wet corrosion behaviour of thermally sprayed metallic coatings using different spraying techniques related to the performance of the corresponding bulk materials and on the other hand to demonstrate the potential of a new generation of coatings to protect or repair structures exposed to aggressive environments. Keywords: corrosion behavior, thermal sprayed metallic coatings, cermet coatings HVOF, HVIF, PTAW.