Thermal spray coatings of austenitic materials are mainly used under corrosive conditions. The relatively poor wear resistance strongly limits their use. A selective enrichment of the surface layer region with carbon by means of thermochemical heat treatment improves the residual stresses and increases the wear resistance. The interstitial deposition of carbon causes strong compressive residual stresses and a high surface hardness. The low process temperature of the thermochemical heat treatment avoids the precipitation of chromium carbide, whereas the corrosion resistance is not affected. Increases in the service life of existing applications or new material combinations with face-centred cubic friction partners are possible. In the absence of dimensional change, uniform as well as partial carbon enrichment of the thermal spray coating is possible. In comparative studies between carburized and untreated thermal spray coatings, the influence of the carbon enrichment on the coating properties and the microstructure was investigated. Carburized coatings demonstrate a significant improvement in adhesive wear resistance and an extremely high surface hardness. The cross section micrograph of the carburized coating shows the S-phase formation in the surface layer region. The depth profile of the carbon concentration was determined by GDOS analysis.

The FeAl intermetallic compound offers a combination of attractive properties such as thermal barrier, good strength at intermediate temperatures and an excellent corrosion resistance at elevated temperatures under oxidizing, carburizing and sulfidizing atmospheres. So they have attracted considerable attention as potential candidates for structural and coatings applications at elevated temperatures. However, the application of these intermetallics has been limited due to lack of deposition techniques and their low ductility at room temperature. To overcome the drawbacks we apply Low Pressure Cold Spray (LPCS) with following sintering for improving coating ductility and structure. The aim of this paper is to present the first results of FeAl intermetallic compound synthesis with this technique. A CS deposit is built up by the successive impact of individual powder particles that are the ‘‘building blocks’’ of the deposit. Sintering is applied to utilize reactions between the particles and obtain complex intermetallic compound. The microstructures and properties of the coatings were characterized by SEM, EDX and thermal diffusivity tests to define the structure formation mechanisms.

Degradation of components that operate under elevated temperature and carburizing environments involves the diffusion of C and the precipitation of carbides. Industries have been seeking for materials that can withstand these service conditions. The present work aimed to develop coatings to address this challenge through the enrichment of a Ni based alloy with Al. An atomized Ni alloy without Al and different powder mixtures with 15 and 30wt%Al were deposited by PTA on a carbon steel. Coatings were analyzed in the as deposited condition and after temperature exposure in an air furnace and pack cementation tests at 650º and 850ºC. Vickers microhardness profiles under a 500gf load, X-ray diffraction, optical and scanning electronic microscopy were done Results revealed that the presence of Al lead to the development of a complex intermetallic phases which were associated with the enhanced metallurgical stability of the coatings under the tested temperatures. The superior performance of the coatings deposited with the powder mixture containing 30wt%Al after pack cementation was associated with the development of the NiAl intermetallic phase and of the oxide layer Al 2 O 3 that stabilized the microstructure at the tested temperatures and reduced the diffusion of C.

This paper contributes to the broadening of knowledge about process combinations in connection with thermally sprayed coatings. It describes the influence of a later annealing, nitriding, and carburizing on different thermal sprayed coatings. The connection between the processes is determined and optimal process parameters is adjusted for both processes. The paper analyzes the coating characteristics and the alterations of the substrate. The results of the metallographic and X-ray analysis as well as of the wear and corrosion tests are discussed. Prospects for possible further applications are given. Paper includes a German-language abstract.

Duplex processes consist in applying a treatment, like annealing, carburizing, or nitriding for example, to a plasma sprayed coating in order to improve particular physical characteristics of this coating. Trials of vacuum heat treatment or low pressure carburizing have been performed on APS NiCr coatings, previously sprayed on a steel type 16MnCr5. As a result, densification and adherence of the coating on the substrate have been significantly increased. To a lesser extent, the coating hardness has also gone up. The diffusion of chemical elements have been highlighted by X-ray analysis, showing the creation of a physicochemical bonding at the interface zone.