Structural characterisation of oxygen diffusion hardened alpha-tantalum PVD-coatings on titanium.

Titanium substrates were coated with tantalum layers of 5 µm thickness using physical vapour deposition (PVD). The tantalum layers showed a (110)-preferred orientation. The coated samples were hardened by oxygen diffusion. Using X-ray diffraction the crystallographic structure of the tantalum coatings was characterised, comparing untreated and diffusion hardened specimen conditions. Oxygen depth profiles were determined by glow discharge spectrometry. The hardening effect of the heat treatment was examined by Vickers microhardness testing. The increase of surface hardness caused by oxygen diffusion was at least 50%.

Preparation of metallic samples for electron backscatter diffraction and its influence on measured misorientation.

Preparation of specimens for electron backscatter diffraction has to be done with great care to ensure a high indexing fraction from high-quality patterns. Despite the amount of published and recommended preparation methods for different materials, detailed information about the preparation parameters are either missing, or different preparation methods are recommended for one material. The aim of this contribution is to compare the application of several preparation techniques on different metallic samples to determine a suitable preparation method for high-quality electron backscatter diffraction measurements for a variety of alloys. From the results obtained, polishing with an oxide polishing suspension is the most appropriate preparation method for the materials and preparation methods investigated. Furthermore, the influence of mechanical polishing as well as of oxide polishing suspension polishing on misorientation is found to be negligible for misorientation angles greater than 1°. In the course of this study the absolute indexing reproducibility of the EBSD-system employed was determined to be 1.18° with respect to the misorientation angle θ.