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Residual stress has a significant effect on the performance of thin films, in terms of adhesion, hardness, wear and fatigue resistance. Thus, when assessing innovative coatings or new deposition technologies, it is important to perform residual stress evaluation by means of a suitable and reliable technique. X-ray diffraction (XRD) is one of the commonly used techniques, because it is non-destructive, surface sensitive and phase selective. However, it is subject to certain limitations: X-ray diffraction allows stress evaluation (i.e. its indirect deduction from the measured diffraction profile) only in case of crystalline materials, and the results may be subject to aberrations in the presence of texture or stress gradients often occurring in thin films. Recently, a new class of methods for residual stress evaluation has been proposed, based on incremental focused ion beam (fib) milling, combined with high-resolution in situ scanning electron microscopy (SEM) imaging and full field strain analysis by digital image correlation (DIC). The aim of the present paper is to explore in some detail the significance of the stress values obtained for the same coating by X-ray diffraction and focused ion beam milling, and to demonstrate that the analysis of residual stress depth gradients is possible by using FIB-DIC techniques. Finally, a comparative assessment of the weaknesses and strengths of the two techniques will be carried out. For this purpose, a chromium nitride highly textured thin film sample was chosen. The residual stress state evaluation by the two methods was carried out for the coating deposited by the cathodic arc evaporation (CAE-PVD) technique. Although many significant differences were identified between the X-ray diffraction and focused ion beam milling methods, careful consideration of the gauge volumes and weighting demonstrated that satisfactory agreement was obtained. The analysis highlighted the importance of the issues related to (a) probe-to-sample interaction volume (gauge volume), (b) film texture, and (c) the elastic anisotropy. All these factors must be taken into account in order to enable valid comparisons to be drawn. [ABSTRACT FROM AUTHOR]

Cathodic arc evaporation CrN double layer coatings were deposited onto tool steels in two steps by industrial apparatus. Microblasting was performed on CrN first layer in order to remove metallic droplets and surface defects and to promote the adhesion of the second layer. Surface morphology effects were assessed by a scanning electron microscope coupled with Image analyser software. Nanoindentation and scratch tests were performed to evaluate the changes of coating adhesion and mechanical properties. Structure, microstructure and residual stress were evaluated by X-ray diffraction. In particular, by means of Cu and Cr wavelengths, the residual stresse of both steel substrates and coatings was calculated. The results show that microblasting has no effect on coating hardness and slightly affects the adhesion of the coating to the substrate. On the other hand, microblasting increases coating resistance to cohesive failure and the substrate compressive stress at the coating interface. [ABSTRACT FROM AUTHOR]

Abstract: In this work we have explored the shape memory capabilities of a novel type of covalently cross-linked semi-crystalline polymers, prepared by exploiting the mild sol–gel chemistry, starting from alkoxysilane-terminated poly(ε-caprolactone) (PCL), and using silica-based domains as cross-link points. By adopting PCL precursors with different molecular weights, semi-crystalline networks with well defined cross-link densities and with different crystallization and melting temperatures were obtained. Beside a satisfying one-way shape memory behaviour, the materials have displayed a significant two-way shape memory response, undergoing a reversible elongation-contraction process between two distinguished strain levels when subjected to a constant load and cyclically heated/cooled on a temperature region spanning from below the crystallization temperature to above the melting temperature. The applied load and the cross-link density are revealed as key-parameters to obtain tailored actuations. Concurrent wide-angle X-ray diffraction (WAXD) and DSC analyses allowed to ascribe the effect to a structural evolution process occurring during melting and crystallization. [Copyright &y& Elsevier]