Materials Science Forum Vol. 879

Abstract: A bioreactor is a device simulating physiological environments for different biotechnological applications. In highly promising research fields like tissue engineering micro-sized bioreactors were utilized successfully promoting mammalian cells to grow and build 3D cell structures similar to in vivo environments. For any practical application and even for improved R&D it is necessary to generate and maintain a physiological environment over the whole cultivation period (hours, days or weeks, in case of artificial organs even up to months). Depending on the field of application physiological environments can comprise different parameters. In case of mammalian cell lines these parameters require a complex supply and monitoring system. Thus, we developed a semi-automated bioreactor-system for long-term cultivation of different mammalian cell types imitating physiological conditions. The system included detection and control of the following parameters: temperature, pH-value, gas concentration and the continuous supply with nutrients. A micro fluidic network was established enabling a high through-put cultivating system as bioreactor-system. The bioreactor-system consists of several micro-sized chambers in a microliter scale (the related article discussing the micro-sized chambers “Miniaturized Flow-Through Bioreactor for Processing and Testing in Pharmacology” by Boehme et al is published within this issue). The chambers were placed in a polymeric slide each with an individual medium supply and disposal. Every single chamber thus was connected to an individual syringe-based micro-pump setup and supplied by nutrients solution with a velocity of 100μl/h. The pH-value was observed optically and controlled via CO₂ supply. All gas interchanges into every single chamber were realized via semi permeable membranes. The required temperature was adjusted via an appropriate custom-fit heating system utilizing MOSFETs allocated on an aluminum board along the slides. Two slides each were housed in a PMMA case. This bioreactor-system is a first prototype for larger systems aiming for the parallel operation of up to 100 micro-sized reaction chambers.

Abstract: This study provides a summary of the effect of heat and hot isostatic pressing treatments on the microstructure and mechanical properties of IN625 alloy processed by selective laser melting. IN625 metallographic and tensile testing specimens were additively manufactured in four different orientations and then subjected to stress relief, low solution annealing and hot isostatic pressing treatments. The as-built alloy exhibited the highest tensile strength, the lowest ductility and the highest anisotropy of mechanical properties among all the tested specimens. Heat and hot isostatic pressing treatments provided an improvement in ductility and homogeneity, but at the expense of lower strength characteristics. The results of this study provide some indications for improving the mechanical properties of additively manufactured IN625 alloy components.

Abstract: The yield strength of an A6061 Aluminium alloy for different artificial ageing times, strain rates and temperatures is modelled taking into account precipitation, solid solution and dislocation forest strengthening. Precipitation kinetics during artificial aging and the individual strength contributions are simulated with the thermokinetic software package MatCalc. In the present contribution, we introduce the model for the temperature and strain rate dependence of the yield-strength based on thermal activation theory. The experimental work presented here is performed on a Gleeble 1500 thermo-mechanical simulator, where the solution annealed and quenched samples are heat treated to produce materials in various microstructural conditions. We demonstrate that yield strength simulation is a powerful tool to reduce experimental effort and to cut down costs in the process of alloy engineering. This approach consistently represents the yielding behaviour of alloys in a variety of microstructural conditions with respect to the production history of the alloy and the testing conditions, i.e. temperature and strain rate.

Abstract: The aim of this study was presentation the results of new tomographic techniques application to characterize structural elements in nickel-based superalloys for disc and blades using in aircraft engines and gas turbines in energy systems. Visualization of phases presented in as-service high chromium creep resistant steel for modern power plant applications was also performed using STEM-EDX and FIB-SEM electron tomography. Electron tomography (STEM-EDX) and FIB-SEM tomography were used for 3D imaging and metrology of the precipitates. Transmission electron microscopy and TEM-EDX spectroscopy were used to reveal details of the superalloys and steel microstructures and phases’ chemical compositions. The study showed that electron tomography techniques permit to obtain complementary information about microstructural features (precipitates size, shape and their 3D distribution) in the reconstructed volume with comparison to conventional particle analysis methods, e.g. quantitative TEM and SEM metallography.

Abstract: Based on the data of X-ray texture and structure analysis of the material of main gas pipelines it was shown that the layerwise inhomogeneity of tubes is formed during their manufacturing. The layerwise texture inhomogeneity of steel tubes, obtained by hot rolling at the air, differs depending on variation of technological parameters of their processing in inner and outer layers, i.e. the temperature and deformation gradients, penetration of interstitial impurities into the surface layer from surrounding atmosphere etc. The thickness of the surface layer with modified texture parameters depends on the temperature of rolling and its regime. Under exploitation when stress-corrosion cracks grows and reach the layer with a modified texture, their opening is slowing down or stops because of the high mutual misorientation of grains of different layers and the necessity of changing the plane of moving cracks, what requires additional tensile stresses. Layered textures of different gas tubes were compared. It was shown that character and degree of arising inhomogeneity correlates with the tubes resistance to stress-corrosion cracking.

Abstract: The effect of the prior austenite grain size on the yielding behavior of as-quenched low-C martensitic stainless steel was investigated. Martensite (Fe-16%Cr-7%Ni-1.2%Mo-1.8%Cu-0.01%C alloy) samples with different prior austenite grain sizes were prepared by heat treatment for various times at 1273K. The microstructures of the martensite were observed by optical microscopy, scanning electron microscopy, electron backscatter diffraction, and X-ray diffractometry. Tensile tests were undertaken at various test speeds. Also, a relaxation test was performed before the tensile tests to determine the behavior of mobile dislocations. A lower elastic limit was observed at lower test speeds and a larger prior austenite grain size. Moreover, a lower tensile strength was observed at a larger prior austenite grain size.

Abstract: High strength AW-7xxx sheet alloys are promising candidates to manufacture crash relevant parts, but their limited formability at room temperature presents a major challenge. Formability is controlled through heating rate, heat treatment temperature and time, quenching rate, forming temperature and strain rate. In the literature retrogression forming, W-temper forming, warm forming and hot stamping processes have been proposed to improve the formability of AW-7xxx alloys. Of these the greatest improvement in formability comes from W-temper forming and hot stamping. Considering the similarity to the conventional forming processes of cold stamping for aluminium and hot stamping for steel, the W-temper forming and hot stamping of aluminium are promising for AW-7xxx alloys.

Abstract: Ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) may show both enhanced ductility and strength and hence resolve the so-called strength-ductility paradox. To gain mechanistic insights into such resolution, the effect of high-pressure torsion (HPT) on the microstructure and mechanical behavior was studied using a cast Al-7 wt. % Si alloy. As expected, the grain size decreased while the fraction of high-angle grain boundaries and microhardness increased due to HPT processing. However, tensile testing at room temperature revealed a simultaneous increase in strength and ductility compared to the as-cast sample. The samples showing simultaneous increase in strength and ductility also showed an increased contribution from grain boundary sliding (GBS), even at room temperature, which is attributed to the existence of a high fraction of high-angle and high-energy grain boundaries. It is proposed that the occurrence of moderate GBS, providing ductility, in very small size grains provides Hall-Petch strengthening and this suggests a potential combination for simultaneously achieving high strength and high ductility in SPD-processed UFG materials.

Abstract: Protein adsorption is considered to have a strong influence on the biological reactions of bone-substituting materials. However, the osteoconductivity of protein adsorbed Ti surface is not completely clear. In this study, we produced the protein adsorbed Ti implants using hydro-processing. The hydrothermal treatment in the distilled water gave the super-hydrophilic Ti surface and they had much protein adsorbability. Fibronectin or albumin was picked up as a protein, which was cell adhesive protein and not cell adhesive, respectively. And also, the content of the adsorbed protein was evaluated by FT-IR (ATR) analysis. The water contact angle influenced the amount of the adsorption of the protein and the osteoconductivity of the samples were evaluated by in vivo testing.

Abstract: In previous study, it was investigated damping capacity on various deformation and heat treatment conditions in order to study damping capacity that was influenced by grain size and dislocation motion in detail. Magnesium alloy AZ31 was rolled at 673K with different rolling reduction, respectively. Specimens were machined out parallel to the rolled direction and annealed on various temperature and time. Then, damping capacity, microstructure and hardness was measured at room temperature. Factors affected on damping capacity are grain size, crystal orientation, dislocation motion, and so on. It was found that damping capacity has been affected by grain size and crystal orientation. Grain size and hardness is not examined obvious difference after annealing. In large prior strain, however, low damping capacity is appeared and damping capacity increases with increasing of heat treatment temperature. The reason is that resolved shear stress factor is influenced by damping capacity.