Materials Science Forum Vols. 524-525

Abstract: The non-destructive analysis by GIXRD allows us to determine the residual stress distribution as a function of XRD penetration depth and film thickness. A new development on the determination of residual stresses distribution is presented here. The procedure, based on the GIXRD geometry (referred to here as the ‘sin2ψ*’), enables non-destructive measurement of stresses gradient with only one diffraction family plan at a chosen depth taking into account the correction of measured direction. The chosen penetration depth is well defined for different combination of ψ and Φ and needs not to be changed during experimentation. This method was applied for measurement of residual stress gradient in Cu thin films. The obtained residual stress levels and their distribution were quite comparable with those determined by another multi-reflection method.

Abstract: Thin hard coatings for wear protection usually do not consist of single layers but of stacks of alternating sublayers which have to meet different demands. With respect to X-ray residual stress analysis (XSA) such multilayer systems pose a series of challenges. In addition to those problems which generally arise in thin film diffraction like small layer thickness or strong texture, neighbouring sublayers with similar chemical composition may superimpose each other, or sublayers of identical structure and composition, which contribute to the same diffraction line, are separated by other sublayers. Starting from a formalism that yields the X-ray penetration depth τ in multilayer systems of arbitrary sublayer sequences, we show how a combination of measurements using ‘conventional’ photon sources available at any X-ray lab and synchrotron radiation allowing for wavelength tuning near the TiKβ absorption edge, can be used to evaluate the residual stress state in the top sublayer stack of a hard coating multilayer system deposited by chemical vapour deposition.

Abstract: PVD-coated cutting tools show a typical kind of failure in use: cohesive damage, which is believed to be a result of the residual stress state of substrate and coating. As the sin2ψ-technique does not give satisfactory information on near surface residual stress trends of coated tools the scattering vector method was applied to determine residual stress depth distributions of coating and substrate. The results are presented and an attempt for an interpretation is given.

Abstract: This paper introduces the recent progress in two-dimensional X-ray diffraction as well as its applications in residual stress analysis in thin films. The stress measurement with twodimensional x-ray diffraction can be done with low incident angle and is not limited to the peaks with high two-theta angles like the conventional method. When residual stresses of thin films are measured, a low incident angle is preferred to maximize the diffraction signals from the thin films surfaces instead of from the substrates and matrix materials. Since one stress measurement at one fixed incident angle is possible, stress gradients in depth can be measured by series of incident angles. Some experimental examples are given to show the stress measurement at low and fixed incident angle.

Abstract: Residual stresses and microstructural changes during phase separation in Ti33Al67N coatings were examined using microfocused high energy x-rays from a synchrotron source. The transmission geometry allowed simultaneous acquisition of x-ray diffraction data over 360° and revealed that the decomposition at elevated temperatures occurred anisotropically, initiating preferentially along the film plane. The as-deposited compressive residual stress in the film plane first relaxed with annealing, before dramatically increasing concurrently with the initial stage of phase separation where metastable, nm-scale c-AlN platelets precipitated along the film direction. These findings were further supported from SAXS analyses.

Abstract: Recently a new welding technique, the so-called ‘Cold Metal Transfer’ (CMT) technique was introduced, which due to integrated wire feeding leads to lower heat input and higher productivity compared to other gas metal arc (GMA) technique. Here microstructure formation and residual stress state in aluminum CMT welds are characterized and compared to those produced by pulsed MIG- and Laser-hybrid techniques. The results show a small heat affected zone (HAZ) in the MIG weld, the HAZ in the CMT and the laser hybrid welds was not visible by optical and scanning electron microscopy. Compared to the MIG welding the CMT process appears to introduce slightly smaller maximum tensile residual stresses into the weld.

Abstract: An anhydrite-dolomite rock was investigated in order to find correlations between intracrystalline strain and texture. The sample represents a composite rock, called Zuckerdolomit, occurring for instance in the central Alps. Zuckerdolomit may occasionally respond to mechanical impulses with a complete break down of its structure. Residual strain was scanned at the strain/stress diffractometer EPSILON-MDS and the crystallographic texture was obtained by neutron time-of-flight diffraction at the texture diffractometer SKAT at the pulsed neutron source IBR-2 in Dubna, Russia. Texture was additionally determined by the U-stage microscopy. The texture of the rock could be derived from the main constituents: anhydrite and dolomite. The anhydrite texture appears to be characterised by an orthorhombic symmetry. One plane of the symmetry trends parallel to the rock’s foliation plane, with basal planes subparallel to and a small circle distribution within the foliation plane. There is a subordinated small circle orientation pattern relating in 45° to the rock’s foliation plane. On the other hand, the subordinated regulation pattern of anhydrite is fixed to the orientation of the foliation plane. The determined residual strain data for anhydrite and dolomite reflect a generally opposed directed state, regarding both, compression and dilatation. Moreover, taking into account the elastic constants for both minerals, which differ approximately by the factor two, the special geomechanical behaviour of the studied Zuckerdolomit appears to be considerably determined by interactions between its residual strain and textural properties. This may be of particular importance for underground activities (mining, tunnelling etc.). The dangerous geomechanical behaviour of the rock seems to be determined by its residual straintexture relations more than so far believed (anhydrite hydration).

Abstract: The martensitic phase transformation in an ultra fine grained (UFG) TRIP (transformation induced plasticity) steel with combination of high strength and high elongation was investigated during room temperature tensile test using in situ neutron diffraction. Two types of specimens, namely coarse grained (grain size of about 50 μm) and ultra-fine-grained (grain size of about 350 nm) specimens were examined. The lattice strain evolution of the austenite and martensite phases was observed and the load partitioning between the phases was identified.

Abstract: The micromagnetic measurement method is a well known technique for a qualitative estimation of residual stresses in ferromagnetic materials. The application due to the advantages of a fast and manageable use is hindered by the high complexity of the calibration procedure for the quantitative residual stress determination when additionally a changing microstructure influences the measured signals. Therefore basic investigations were performed for the residual stress determination of welded joints by the micromagnetic method. A multi-parameter approach by using different micromagnetic techniques was evaluated by a linear regression analysis. For each structural steel a regression polynomial can be calculated for the residual stress determination of differently welded specimens. The accuracy of the prediction depends on the magnetization direction. The experimental results show, that this strategy enables a useful possibility of an easier method for the determination of residual stresses in welded joints.