This paper investigates the adhesion of thermally sprayed ceramic particles on metal substrates. Two aluminum oxide powders are applied to nickel-oxide coated steel substrates by detonation and vacuum plasma spraying. SEM and XRD fracture analysis is used to examine the ceramic-metal interface and the morphology of fracture surfaces. In all test samples, failure occurs in the alumina, not at the interlayer boundary, indicating a high level of adhesion between the ceramic and nickel oxide layers. Paper includes a German-language abstract.

Electroplated nickel can be used to fabricate miniature components such as gears, linkages, and other two-dimensional mechanical structures. This process produces excellent parts, but it is slow and somewhat expensive. Because cold spray produces low oxide-content, high-density deposits at a high rate, cold spray processing might be a viable alternative to electroplated nickel components. In addition, cold gas-dynamic spray can process materials, such as stainless steel and aluminum, which can not be electroplated. The purpose of this study was to evaluate the mechanical properties of cold spray nickel in the as-sprayed and heat treated conditions, then compare them to those of bulk nickel and electroplated nickel. Characterization of freestanding structures is subjective since the final product of any thermal spray process produces a material unlike any other material formed by conventional techniques. Specifically, this investigation determines the mechanical characteristics of nickel, through metallographic imaging and tension testing. Metallographic imaging showed that as-sprayed nickel has slightly more voids than the heat-treated structures. Tension tests of the as-sprayed nickel showed little plastic behavior, while a heat treatment gives much more ductility without compromising ultimate strength.

Fiber-reinforced polymer composites are an important class of structural materials, offering high strength-to-weight ratios and high rigidities. For many applications, however, their wear resistance is less than desirable. Wear-resistant thermal spray coatings have the potential to improve the surface properties of fiber-reinforced polymer composites, although some require the application of a bond coat to achieve sufficient adhesion. The present study was conducted to find acceptable bond coat materials and compare their performance. Materials such as polyamides, polyimides, polyether-ether-ketone, or simply aluminum or nickel were found to be suitable bond coats for many composite substrates.

The preheating of metallic substrates before powder deposition in air plasma spraying improves the adhesion of oxide coatings, provided heating is performed with an optimal procedure to avoid a too high oxidation state of the surface. It means that the temperature level and heating time have to be monitored carefully. In these conditions a thin layer (<100 nm) of oxides is formed on the substrate surface, the resulting contact of the molten droplets impinging the hot substrate is excellent (R th <10 -7 m 2 .K/W) and the adhesion properties of coatings are enhanced. This paper is devoted to the study of the metallic surface. The substrate heating and thus oxidation are obtained with a d.c. Ar-H 2 plasma jet flowing in air of which the stand off distance is maintained at 100 mm. The parameters investigated are macroscopic surface temperature and heating time. The characterization of the oxide layers is achieved by Mossbauer spectroscopy, near grazing X-ray diffraction, near UV-Visible-near IR spectroscopy and specular reflection infrared spectroscopy. At the end of this paper an attempt will be made to correlate these characterizations to the splats microstructure and coatings adhesion.