Abstract This paper aims to characterize with innovative methods bond coat and yttria partially stabilized zirconia powder and coating. Bond coat layers realized with different deposition techniques were anlyzed by X-ray Photoelectron Spectroscopy (XPS) in order to compare deposition technologies from the point of view of the oxide presence. X-ray diffraction and Raman microscopy were performed in order to determine the crystallographic composition of Yttria Partially Stabilized Zirconia powders and top coat layers. The surface and interface roughness is expected to affect spallation resistance of the thermally grown aluminum oxide and the life of thermal barrier coating. Raman microscopy allow to map the surface of the examined samples, retrieving the monoclinic zirconia distribution with high spatial resolution. XPS measurements were carried out in order to determine the surface elemental composition. This turns to be useful to measure the amount of oxides which forms during the spraying process and the thermal treatment. Paper includes a German-language abstract.

Abstract This paper compares two methods for determining the composition of Ti/TiN coatings deposited by reactive plasma spraying. The coatings were obtained by spraying titanium powder in a low-pressure N2/Ar atmosphere. The resulting film has a variable nitrogen content in the form of titanium nitrides, depending on gas partial pressure, total pressure, sample-source distance, and other parameters. The composition of the film was determined using X-ray diffraction and X-ray photoelectron spectroscopy. The two techniques provide similar results and either can be used for the compositional characterization of these coatings.

Abstract The isothermal and cyclic oxidation of freestanding Ni-20Cr-10Al-lY thick coatings has been investigated at 1200°C using TGA, SEM, XRD and XPS techniques. Coatings produced by HVOF are dense and remain crack free after thermal treatments. The protective oxide layer formed did not flake off upon cyclic oxidation as confirmed by SEM analysis. In addition, three oxidation regimes were identified after analyzing TGA data: two below 1000 °C and a third one at approximately 1200°C. The regimes below 1000°C correspond to the selective oxidation of elements on the surface and at the subsurface of the coatings whereas the third regime involves element diffusion from the bulk of the coating to the surface. The oxidation regime became asymptotic at 1200 °C as stable oxides formed. The presence of water vapor affects neither the thickness nor the orientation of oxide crystals formed on the surface as confirmed by the X-ray analysis. The XPS and X-ray results show an inter-diffusion between the coating and substrate with a slight increase in chromium concentration at the interface. Element distribution within the oxide layer was found to follow the order: Al-(oxide)Y-(oxide)/Cr-(oxide)/Ni-(oxide)/NiCrAlY from the outermost oxide layer to the bulk of the coating. These results show that HVOF dense Ni-20Cr-10Al-lY sprayed coatings can be used as anti-oxidant barriers in both isothermal and cyclic oxidation at 1200°C.

Abstract The quasi-steady magneto-plasma-dynamic (MPD) arcjet generator is a promising plasma accelerator, which has a coaxial electrode structure similar to those of conventional plasma torches. The MPD arcjet generator utilizes principally electromagnetic acceleration of the interaction between the discharge current of kiloamperes and the azimuthal magnetic field induced by the discharge current, although the working gas is accelerated aerodynamically through a nozzle in a thermal arcjet generator. In this paper, ablation-type MPD arcjet generators are developed for ceramic coatings. Discharge voltages and ablation rates of ceramic materials are examined, and front velocities of ablated atoms of ceramic component are also estimated using a streak camera. The Vickers hardness of coating is measured. Their cross sections are observed with a scanning electron microscope, and their surfaces are analyzed by means of x-ray diffraction and x-ray photoelectron spectroscopy. Paper includes a German-language abstract.

Abstract The decomposition of bioactive plasma sprayed apatite layers and the weakness of their interface with the metallic substrate limit the longevity of orthopaedic prostheses. Analysis of the coating and of the metal-apatite interface using EDS, XPS, and IR techniques indicates alterations of the apatite composition which can be related to several chemical reactions occurring either in the plasma or on the surface of the implant. EDS shows a calcium-rich layer on the apatite side of the interface whereas after dissolution of the apatite, XPS indicates that phosphorus atoms are incorporated in the metal surface. Depending on the rate of decomposition, calcium oxide may possibly form and weaken the apatite-metal interface. Fluorohydroxyapatite coating have proven to decompose less and differently and to be more effective than hydroxyapatite coatings.