Residual Stresses VII, ICRS7

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Authors: Li-Jian Meng, Rui A. Silva, Hai Ning Cui, Vasco Teixeira, M.P. dos Santos
Abstract: The RuO2 thin films have been deposited onto glass substrates by rf reactive magnetron sputtering at different deposition conditions, such as different substrate temperatures, different sputtering pressures and different reactive gas pressures, using a metallic target. The deposited films have been characterized by the X-ray diffraction and Raman scattering. By analysis of data of the X-ray diffraction, it has been found that all the films are subject to a compressive stress. The residual stress in these films can be released by increasing the substrate temperature. In addition, the films, which have been prepared at the oxygen partial pressure higher than 1 x 10-3 mbar and at the total pressure lower than 6 x 10-3 mbar, show a quite high residual stress because the films peeled off automatically from the substrates when they were moved out from the vacuum chamber. Three Raman models (Eg, A1g and B2g) have been observed in all the Raman spectra. These Raman spectra have shown a strong relation with the residual stress in the films. As the residual stress increases, the Raman peaks move toward to the low wavenumber comparing to the standard value. In addition, the residual stress also results in the disappearance of the A1g Raman mode. In this work, these phenomena will be discussed.
583
Authors: Yao Gen Shen
Abstract: Thin films of molybdenum nitride (MoNx with 0≤x≤0.35) were deposited on Si(100) at room temperature using reactive DC magnetron sputtering. The residual stress of films was measured as a function of sputtering pressure, nitrogen incorporation, and annealing temperature by wafer curvature-based technique. It was found that the stress of the films was strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. The film stresses without nitrogen addition strongly depended on the argon pressure and changed from highly compressive to highly tensile in a relatively narrow pressure range of 0.8-1.6 Pa. For pressures exceeding ~5.3 Pa, the stress in the film was nearly zero. Cross-sectional transmission electron microscopy indicated that the compressively stressed films contained a dense microstructure without any columns, while the films having tensile stress had a very columnar microstructure. High sputtering-gas pressure conditions yielded dendritic-like film growth, resulting in complete relaxation of the residual tensile stresses. It was also found that the asdeposited film was poorly ordered in structure. When the film was heated at ~775 K, crystallization occurred and the stress of the film drastically changed from –0.75 to 1.65 GPa. The stress development mechanism may be due to volumetric shrinkage of the film during crystallization.
589
Authors: M. Qin, Vincent Ji, Y.N. Wu, S.Y. Ma, J.B. Li
Abstract: A new method is applied to investigate the relationship between the yield strength and annealing temperature for a Cu film. By Ion Beam Assisted Magnetron Sputtering (IAMS), Cu film with 2.4 µm thickness was deposited on a strip of super high strength steel 37SiMnCrNiMoV, and the specimens were treated by vacuum-annealing at different temperature. The X-ray tensile test was used to measure the longitudinal and transverse stresses and applied strain for Cu film. Based on the experimental results, the equivalent stress s and the equivalent uniaxial strain t e can be obtained. According to the s- t e relation, the calculated proof stress is acquired. The results indicate that the proof stress of the film decreases with the increasing of annealing temperature. When annealing temperature rises from 150ı to 300ı, the decreasing amplitude of proof stress is the largest. The phenomenon can be explained by the recrystallization and microstructure evolution in Cu film during the annealing treatment.
595
Authors: Hajime Hirose, Shinya Suzuki, Masahide Gotoh, Toshihiko Sasaki
Abstract: In depositing the TiN thin films to the substrate by Physical Vapor Deposition (PVD), it influences the substrate interface. Change of the residual stress and the full-width at half maximum (FWHM) in each process of the TiN deposition of thin film was measured by the X-ray stress measurement. As a result of the X-ray stress measurement, there are no changes in the residual stress and the FWHM. It is thought that there is a difference in the penetration depth to the substrate of X-rays and Ti ion.
601
Authors: L. Li, A. Vaidya, T. Streibl, S. Sampath, A. Gouldstone, Vladimir Luzin, Henry Prask
Abstract: Thermal spray is a well-established, versatile method of producing protective and functional coatings. As with most thin- or thick-film structures, residual stresses developed during processing play an important role in determining the performance and life of sprayed coatings. Diffraction methods (X-ray or neutron) and in situ curvature measurement have been widely used to measure stresses nondestructively, yet results in coating stress measurements seen in the literatures are sometimes ambiguous or conflicting. This is due not only to the experimental error associated with the measurement and simplifying assumptions, but also the complexity and heterogeneity of the coating structure. During deposition, molten, semi-molten or solid particles successively impinge onto a substrate surface, thus forming a layered structure comprised of ‘splats,’ separated by interfaces, cracks and pores. In this study, X-ray micro-diffraction with a 2-D detector has been used to determine the stress magnitude of both splats and coatings on substrates. Neutron diffraction stress measurements have been made through the entire coating thickness. The process of depositing and cooling has been monitored by in situ curvature measurement. Micro- and macro stresses have been examined. The relation between process and splat and coating residual stresses has been evaluated and interpreted by recourse to microstructural and morphological observations under SEM. This study bridges the behaviors of microscopic single splats and macroscopic coatings, hence helps to fundamentally understand the stress generation during thermal spray process.
607
Authors: Kazuya Kusaka, Hanabusa Takao, Kikuo Tominaga, Noriyoshi Yamauchi
Abstract: The crystal orientation and residual stress in gallium nitride (GaN) films deposited on a single-crystal (0001) sapphire substrate using a new sputtering system are examined through x-ray diffraction measurements as part of a study of low-temperature sputtering techniques for GaN. The new rf sputtering system has an isolated deposition chamber to prevent contamination with impurities, and is expected to produce high-purity nitride films. GaN films are deposited at various substrate temperatures and constant gas pressure and input power. This new system is found to produce GaN films with good crystal orientation, with the c-axes of GaN crystals oriented normal to the substrate surface. The crystal size of films deposited at high temperature is larger than that deposited at low Ts. All films except that deposited at 700oC exhibit compressive residual stress, and this residual stress is found to decrease with increasing temperature. Finally, the film deposited at 700 oC was tinged with white, and the surface contained numerous micro-cracks.
613
Authors: Takayuki Murotani, Zhou Wang, Akira Ikenaga, Yukio Hirose
Abstract: The Ni3Al intermetallic compound is of great interest because of its oxidation, corrosion-resistance, and high melting point. The low-temperature hot press + thermal diffusion process method is a technique that uses the thermal reactive diffusions between the elements that compose the intermetallic compound. In this method the powder mixture is heated and be able to generate the diffusions of the powder elements by keeping the heating temperature comparatively lower temperature with other technique. The authors evaluated the preparation conditions and joining quality in Ni3Al coating layer of particular interest is the residual stress due to the different mechanical properties of the coating and the substrate and its effect on the interface joining quality. It is known that residual stresses were generated by the difference in the coefficient of thermal expansion (CTE) of coating and substrate during cooling process. Such a residual stress caused by the differences of mechanical properties has strong influence on composite material strength. X-ray stress measurement techniques has been developed for experimental determination of residual stresses. In this paper, the Ni3Al intermetallic compound was coated on spheroidal graphite cast iron and austenite stainless steel using the reactive sintering method. Wear characteristics and residual stress on these intermetallic compound layers were investigated to evaluate the effect of substrate materials on coating layer properties.
619
Authors: T. Roland, Delphine Retraint, K. Lu, Jian Lu
Abstract: Improved mechanical behavior of surface nanostructured metallic materials produced by means of a surface mechanical attrition treatment (S.M.A.T) is investigated experimentally. Based on microscopic observations and residual stress measurements, factors leading to the high strength and yielding are discussed. The effects due to treatment, as compressive residual stresses, are in that way studied for a better understanding of their influence on the global mechanical response of the nanostructured material. In regards of this, a simple way to increase the ductility of such a nanostructured material is also presented.
625
Authors: Kenji Suzuki, Keisuke Tanaka
Abstract: The spallation of thermal barrier coatings (TBCs) is promoted by thermally grown oxide (TGO). To improve TBCs, it is very important to understand the influence of TGO on the spalling stress. In this study ,the TBCs were oxidized at 1373 K for four diferent periods: 0, 500,1000 and 2000 h. The distribution of the in-plane stress in oxidized TBCs, s1, was obtained by repeating the X-ray stress measurement with low energy X-rays after successive removal of the surface layer. The distribution of the out-of-plane stress, s1− s3, was measured with hard synchrotron X-rays, because high energry X-rays have a large penetration depth. From the results by the low and high energy Xrays, the spalling stress in the oxidized TBCs, s3, was evaluated. The evaluated value of the spalling stress for the oxidized TBC was a small tension beneath the surface, but steeply increased near the interface between the top and bond coating. This large tensile stress near the interface is responsible for the spalling of the top coating.
631
Authors: Dong Ying Ju, T. Ueda, Tetsuo Hatakeyama, T. Arizono, Kazuya Kusaka, Hanabusa Takao
Abstract: In this study, evaluation of residual stress in nano-TiO2 film on ITO glass is carried out. The films with thickness less than 30 nm are prepared by the dual-arcs magnetron sputtering with gas pressure 10 and 20 Pa. The surface microstructure and grain morphology of the nano-TiO2 films are observed by the atomic force microscopy (AFM). In order to accurately evaluate the residual stress in the film, the Young’s modulus of the film is determined by the nanoindentation with three point bending method at first, then the internal residual stress in the film is measured by high energy X-ray diffraction with the synchrotron radiation facility Spring-8. The measured residual stresses of nano-TiO2 films prepared with gas pressure 10 and 20 Pa are -11.6 and -9.1 GPa, respectively. It is shown that the residual stress of TiO2 films decrease with the increasing of gas pressure.
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