Key Engineering Materials Vols. 592-593

Abstract: This work describes an experimental procedure to measure the progressive strain localization and crystal lattice rotation within metallurgical grains. A digital image correlation software was implemented and associated with mechanical tests carried out inside a scanning electron microscope on specimens exhibiting nanometric grainy patterns. Cross-correlation analyzes between electron backscattering diffraction maps were also developed to quantify the corresponding local crystal rotation relative to the original structure. The microscale strain and rotation fields on the surface of a tensile-loaded specimen made of austenitic stainless steel 316L are presented as an illustration. Their direct spatial correlation between strain heterogeneities and the progressive activation of slip systems is put into evidence and discussed.

Abstract: In this study an advanced method for investigation of the microstructure such as electron backscattering diffraction (EBSD) together with in-situ tensile test in a scanning electron microscope (SEM) has been used at room temperature and 300°C. EBSD analyses provide information about crystallographic orientation in the microstructure and dislocation structures caused by deformation. The in-situ tensile tests enabled the same area at different strain levels to be investigated. For the same macroscopic strain values lower mean misorientation angles of individual grains at the elevated temperature indicated that less residual strains at grain levels are gained compared with room temperature. The influence of grain size on plastic deformation on microscopic level, where larger grains tend to accumulate more strains, is discussed.

Abstract: The present paper illustrates a comparison of infrared thermography during ultrasonic fatigue testing of cast steel 42CrMo4 and cast aluminium alloy AlSi7Mg. Against the background of different material properties (e.g. mechanical properties as well as thermal properties) the benefit of this non-destructive material testing method in terms of determining the crack initiation point and time during fatigue testing as well as crack propagation is evaluated and discussed. Moreover, correlations between fractography and infrared thermography are performed for both materials.

Abstract: We used corrosion casts and micro-CT for quantitative description of microvascular network in porcine liver. Using stereological methods, manual tracing of microvessels and analysis of orientation in 3D, we quantified the volume fraction, the surface density, the numerical density, the length density and the tortuosity of microvessels in series of images with 1.875 μm pixel resolution. Biodur E 20 resin was more suitable for preparing and quantifying microvascular tree corrosion casts when compared to Mercox II resin. Quantified data could be applicable for correlating 3D models with 2D liver histopathology, for enhancing the interpretation of routine medical CT and for providing data for computer models of tissue perfusion and angiogenesis.

Abstract: This work is devoted to theoretical and experimental study of energy dissipation and storage processes in titanium alloys under quasistatic loading. The specimen surface temperature was measured by infrared camera FLIR SC 5000 (a spectral range of 3-5 micron). Extending previous results of the research group in Perm, we coupled the experimental investigation of temperature evolution with a statistical description of the mesodefect ensemble. It allowed us to propose a thermodynamic internal variable model of heat dissipation in metals.

Abstract: The paper deals with the mechanism of eutectic formation in a nickel coated aluminium system after heat treatment. The initial coating was produced from a nickel powder by means of high velocity oxyfuel (HVOF) spraying onto an aluminium sheet substrate. Specimens for investigations were manufactured immediately after the spraying. The specimens were heat-treated using a differential thermal analysis (DTA) apparatus up to the temperature of 700 or 900 °C and then cooled down to room temperature in argon atmosphere with a constant heating and cooling rate of 5 °C / min, under which Al-Al₃Ni + Al₃Ni hypereutectic alloys were formed within the initial substrate. Two different alloy microstructures consisting of intermetallic layers and coarse eutectic or an ultrafine well-dispersed eutectic were formed. Formation processes and resulting microstructures were studied by means of DTA, metallography, scanning electron microscopy, focused ion beam, energy dispersive microanalysis and image analysis techniques.

Abstract: The U-phase in the Al₇₂Pd_12.8Co_15.2 alloy was studied under non-equilibrium (casting, differential thermal analysis) and near-equilibrium (long-term annealing) conditions to consider its compositional homogeneity. In the investigation, scanning electron microscopy including energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy, and differential thermal analysis were used. Contrary to the finding reported for the Al_69.8Pd_13.8Co_16.4 alloy, the results obtained for the investigated Al₇₂Pd_12.8Co_15.2 alloy did not confirm the compositional heterogeneity of the near-equilibrium U-phase after annealing at 700°C for 2000 h and at 850°C for 500 h.

Abstract: In order to predict the mechanical behavior of a material during its service life, it is important to evaluate its mechanical response under different types of external stresses by studying the initiation and development of cracks and the effects induced by damage and degradation. The non-destructive technique of analysis of acoustic emission, especially with source location and full wave-form analysis, provides excellent results on detecting and identifying initiations sites, cracking propagation and fracture mechanisms of polymer matrix composite, ceramic materials and rocks. For this study, loading tests in two different configurations were provided on specimens of same material and geometry. The significant AE features were monitored during each test and also locations of each AE event were estimated. Results of AE analysis are compared with a finite element analysis of the stress distribution and crack propagation within the specimens.

Abstract: This paper presents the current research on heat transfer at a sprinkled tube bundle consisting of smooth tubes and located in a chamber inside of which a low pressure is created by a liquid vacuum pump. It also monitors the changes of the heat transfer coefficient in relation to the speed of sprinkled and sprinkling liquid flow, thermal gradient.

Abstract: This paper deals with excess noise sources in dielectric materials. We focus especially on the concrete samples that are frequently tested to ensure information about the reliability and level of degradation. Nevertheless, the testing methods are limited mainly by the proper contact creation, signal detection and noise defined sensitivity. Our efforts are directed to the noise properties assessment. It turns out that the Johnson-Nyquist noise and the 1/f (flicker) noise are generated in the different regions with the different response to the internal or external electric field. In addition the noise analysis is affected by the internal polarization phenomena and the material residual humidity. This issue in connection with the sample geometrical properties and the dielectric noise measurement methodology take part in this paper.