Materials Science Forum Vols. 490-491

Abstract: In this paper, we report on residual stress analysis in physical vapour deposited (PVD) CrN coatings. Two 9 µm thick coatings were grown on tool steel substrates with bias voltages of - 50 V and -300 V, respectively. High-energy (E=80 keV) synchrotron radiation measurements have been performed to investigate residual stresses in both as-deposited and annealed CrN coatings. To understand the origins of non-linear distribution of lattice strain versus sin2ψ for certain (hkl) planes in both coatings, a stress orientation distribution function (SODF) analysis has been carried out, which yields grain-orientation-dependent residual stresses. The results are compared to previous analyses using Reuss and Vook-Witt models on the as-deposited coatings.

Abstract: The evaluation of stress in sub-micron tracks is critical for the microelectronics industry and there is a need for new methods of measurement. This paper advocates the use of a rotating beam sensor structure which can be fabricated on the wafer along side electronic devices and used to monitor stress generation and relaxation as a function of processing. The rotation can be observed with a reflected light microscope and correlated to the actual stress level. Several samples, assputtered and sintered, were prepared with the aim of having different residual stress states. X-ray diffraction with a low incident angle geometry, was used to evaluate the residual stresses on the aluminum layer. Computer simulations using ANSYS were also performed in order to correlate the sensor rotation with the experimental stress values. It was observed that the extrinsic stress from the mismatch in expansion coefficients between the aluminum layer and the silicon substrate dominates over the compressive stress from the sputter growth. Sintering the layers at temperatures above 150°C reduces this compressive stress due to the action of creep. The calibration of the rotation of the device with the direct measurements of the X-ray diffraction shows that the sensor has a resolution better than 2.8 MPa.

Abstract: The pattern formation during delamination and buckling in sputter-deposited tungsten thin films under large compressive stresses was investigated. The films were analyzed in situ by a cantilever beam technique, and ex situ by atomic force microscopy (AFM) and focused ion beam. Depending on the magnitude of compressive strain in thin films, different types of buckling patterns were observed. For stresses above a critical value, there was a regime of steady growth in which the incipient blister evolves into a regular sinusoidal-like propagation. At higher strains, the sinusoidallike wrinkles were developed with constant widths and wavelengths. Some of the wrinkles bifurcated to form branches. With further increase in stress the complicated buckling patches were formed with many irregular lobes. These types of pattern formation have been supported by elastic energy calculations.

Abstract: The residual stress in epoxy adhesive layer deposited on metal and other substrate at room temperature is studied. With embedded strain gauges in arranged depth of epoxy layer, the strain changes in the adhesive layer induced by the curing procedure and the changes of ambient temperature were measured to evaluate the changes of residual stress in place during a period after the curing procedure finished. The actual strain in epoxy adhesive layer from curing is used to estimate the residual stresses in it. While taking the strain obtained from the surface of the adhesive layer as free strain, the residual stress can be calculated and presented a strongly cyclic variation with a period of 24 h. The inner stress is also analyzed using the finite element method.

Abstract: A scanning X-ray microdiffraction beamline using white or monochromatic beam has been recently made available to the user’s community at the Advanced Light Source, Berkeley, USA. Samples are scanned under an X-ray beam with size ranging from 15 microns down to less than a micron, and 2D diffraction patterns are collected at each step. A specifically written software allows for the full treatments of these patterns to obtain as outputs high spatial resolution grain orientation, strain/stress or mineral species distribution maps. The range of applications of this technique goes from the study of the mechanical properties of thin films to the understanding of trace elements speciation in environmental sciences.

Abstract: The TiN films with the thickness of 0.1, 0.2, 0.5, 1.0, and 4.0 µm were coated on a steel substrate by the ion beam mixing method. The film had a strong fiber texture with <001> axis perpendicular to the film surface. The in-plane stress measurement was applicable to the thickness down to 0.1 µm of TiN films. The stress was a compression of around 2 GPa. The compressive stress was found to increase below the surface layer of 20 to 30 nm. Thinner films had a steeper increase of the compressive stress in the very-near surface region. The strain distribution measured by the SV method was nearly constant over the region of the penetration depth between 0.3 and 0.6 µm from the surface. The two-tilt method combined with the surface removal method showed a nearly constant distribution of compression in the subsurface region and a sharp increase near the interface to the substrate.

Abstract: Under specific manufacturing processes and heat treatments, the gamma titanium Aluminide Ti- 47Al-2Cr-2Nb presents a nearly lamellar microstructure with coarse lamellar grains (with alternating g and a2 lamellae) and dispersed small g grains. The obtained microstructure gives a relatively coarse grain size (approximately 0.4 mm x 3 mm). Residual stresses can then be generated between g and a2 lamellae inside the lamellar grain and also between different grains because of the lattice mismatch between tetragonal structure of g phase and hexagonal structure of a2 phase. A specific single crystalline XRD method is applied on these two non-cubic phases to determine the local residual stresses in two grains on each side of a grain boundary.

Abstract: The main objective of this work is to contribute to the study of the 301LN unstable austenitic stainless steel by determining the distribution of residual stresses after deep drawing, taking into account the phase transformation. In the first part, kinetics of martensitic transformation are determined for uniaxial loading. Tensile tests are performed at different pre-strains at room temperature for two different strain rates. The austenite/martensite content is measured by X-ray diffraction and is coupled with the determination of residual stresses distribution. In addition, to establish a relation between the complex loading path effect and the residual stresses state, deep drawing are done for different drawing ratios for two different temperatures. Macroscopic tangential residual stresses are determined by the separation technique. It appears that the residual stresses increase with increasing drawing ratios and the maximum value is located at middle height of the cup.

Abstract: YBa2Cu3O7-δ(YBCO) films with highly biaxial textures were deposited on SrTiO3 single crystal, textured polycrystalline Ag and NiO/Ni substrates using pulsed laser deposition, metal-organic decomposition and ultrasonic spray pyrolysis method. The microstrains in different specimens with strong textures were measured using x-ray diffractometer and were compared each other.