Advanced Materials Research Vols. 89-91

Abstract: A physical model based on three types of dislocations and three nucleation sites for recrystallized grain is applied to hot rolling simulation. This model was implemented into a commercial Finite Element (FE) analysis package FORGE 2008 to calculate both the structure evolution during and the recrystallized volume fraction after hot working of aluminium alloy 5083. It is shown that the main nucleation mechanisms in the aluminium alloy are the particle stimulated nucleation (PSN) and nucleation at grain boundaries. Hence the precipitation kinetics during homogenisation was investigated by use of the thermodynamic calculation software MatCalc. To validate the simulation results hot rolling experiments were performed by means of a laboratory mill. The grain structure evolution was analysed by electron backscatter diffraction (EBSD).

Abstract: Residual stresses near the grain boundary of a bicrystal were measured by synchrotron radiation of SPring-8 at Japan Synchrotron Radiation Research Institute. A copper bicrystal specimen with a 90-degree tilt boundary was deformed 30% in tension. After the plastic extension, kink bands developed in a deformed matrix along the grain boundary. In this study, we focused on the residual stresses in the deformed matrix and the kink band. Residual stresses were evaluated by the X-ray single crystal measurement method. Stereographic projections were used to determine crystal orientations of deformed regions. Our observation showed that crystal orientations were different between the deformed matrix and the kink band. Residual stresses in the direction along the grain boundary in the deformed matrix and kink band were compressive. Residual stresses in the direction vertical to the grain boundary were seen opposite between the deformed matrix and the kink band.

Abstract: In present investigation the influence of second phase particles on microstructure evolution during confined channel-die pressing (CCDP) and mechanical behaviour after CCDP were studied using two-phase Al alloys of Al-1.5Mn and Al-5Zn-1.6Mg. The investigation results revealed different grain refinement kinetics during CCDP and distinct mechanical behaviours after CCDP for both alloys. The results are discussed based on the influence of the second phase particles on dynamic recovery and the interaction with mobile dislocations during plastic deformation.

Abstract: In this paper, a methodology for determining the optimum machining parameters for a face mill operation is presented. Taguchi design of experiments was used in company with orthogonal arrays in order to study the effects and interactions that selected parameters had on the cutting behaviour. The parameters that were included in the study were cutting speed, feed rate, depth of cut and the effects of cutting fluid. Using the orthogonal array experimental runs were set up and carried out on specimens of metal plate on a CNC milling centre. The studied material was 13% Austenitic Manganese Steel. The response factors for the experimental runs were surface finish, spindle load, material removal rate, cutting forces and surface hardness. From the results and using the orthogonal arrays a set of empirical models were derived for each response factor which could be used to predict the optimal controllable factor settings for a given production criteria.

Abstract: In the present study, nucleation at Cube bands during annealing of a cold rolled commercial aluminium alloy AA8079 was investigated. The main goal of this work was to provide experimental data for subsequent modelling. By studying the deformed material the geometrical parameters of Cube bands were determined. The Cube band spacing in the deformed state was measured experimentally and accordingly calculated with a simple geometric model, taking the initial Cube fraction in the pre-deformed state and the deformation degree into account. The nucleation frequency during subsequent annealing of the cold deformed material was estimated from the geometry and size of deformed Cube bands prior to deformation. From investigations of the orientation relationship between the Cube oriented nuclei and the adjacent deformed matrix with S orientation, the fraction of 40°<111> grain boundaries having optimum growth conditions, was established.

Abstract: The deformation process of sputtered tungsten films were investigated according to the morphological characteristics and residual stress analysis. Results show that there are four characteristics depending on the substrates and stress state. For thin films on polyimide, the localized plastic deformation is mediated by the alignment of grain boundaries in the case of tension or line bulges in the case of compression. It results from both in-plane and out-of-plane grain rotation. For thin films on silicon substrate, wedge cracks in the case of tension or regular hillocks in the case of compression become the typical morphology. From this point of view, the deformation behaviors of films depended on the substrate constraint and residual stress states.

Abstract: X-ray stress measurement is useful for determining, in a non-destructive manner, the surface stresses of engineered parts.　However, the railway wheels cannot measure because this it is very large. So it should be measured using a scaled-down model. The problem is, however, how the stress release should be considered. In this analysis, the finite element method (FEM) was applied to estimate the initial stress state using stresses released after cutting a sample obtained by the X-ray method. Railway wheels were studied in this experiment. In the early 1990s, several railroads in the northeast of the U.S.A. experienced extensive cracking in the wheels of the commuter trains. Residual stresses in the hoop direction play an important role in mechanism fatigue damage. This paper will discuss about residual stress in the hoop direction in manufactured wheels. The results of FEM analysis and the X-ray diffraction method confirms that these methods can be used to evaluate the residual stress of the hoop direction. There is very good quantitative agreement between the simulated and measured stress distributions. It can be suggested that guessing guess stress release and the redistribution by the FEM analysis is possible. The residual hoop stress of the unused wheel presumed by this research has the residual stress of high compression in the wheel at the center of the rim up to 40mm depth.　It is very safe because the residual stress state is compressive even when a crack occurs, and obstructs the crack’s progress. If a crack occurs by any chance, the stress state can obstruct the crack’s progress.

Abstract: Biomaterials based tissue engineering requires optimization of several parameters. The most important parameters can be attributed to biocompatibility, degradational behaviour, mechanical stability and structural design. In previous studies we have established a porous gelatine based scaffold material, with parallel oriented pore channels. Although, tomographic data has been derived on dried scaffold samples, it remains unclear how the pore channel network interacts under load in a wet environment. We developed an experimental setup to compress biomaterials in a wet environment during exposure to synchrotron generated X-rays using a micrometer screw with a force sensor. Achieving good X-ray absorption contrast in polymeric biomaterials immersed in water is rather difficult, as water absorption prevents detailed imaging. Phase contrast imaging on the other hand allows for improved imaging results due to the attenuation of phase boundaries in the imaged data, neglecting effects of X-ray absorption in the watery phase nearly completely. Best results were obtained for X-ray energies of 30 keV with a scintillator to sample distance of 1090 mm with the established experimental setup. Due to over attenuation of phase boundaries at higher beam energies, this energy was finally chosen. As a result, we could evaluate the collapsing pore network upon loading with the possibility to enhance the structural design for future studies.

Abstract: Cold spraying is a novel coating method, by which many composites have been successfully sprayed. The objective of this study was to thoroughly characterize the microstructure of copper as well as copper/alumina composite coatings obtained using this technique. Composite coatings which differed to the percentage of Al2O3 in the initial powder blend as well as the Al2O3 particle size were studied. Coatings presented Ra of the order of 6-8 μm, with the copper coating having the highest value. Using optical microscopy the deformation of the copper particles of the cross sections was evident. Thickness ranged from 170 to 450 μm for the different coatings. The surfaces and the cross sections of the coatings were studied by means of scanning electron microscopy. Craters and Al2O3 particles that were embedded in the copper particles were observed. The XRD analysis of the powders and the respective coatings presented no differences.

Abstract: Based on the thermodynamic calculation, two phase separated Zr-based BMGs (Zr63.8Ni16.2Cu15Al5 and Zr66Cu15.3Ni8.7Al10) which developed by the authors previous study were selected for investigating their crystallization behavior and thermal stabilities by means of differential scanning calorimetry (DSC), and X-ray diffractometry. The results show that the Zr66Cu15.3Ni8.7Al10 amorphous alloy exhibits higher GFA than the Zr63.8Ni16.2Cu15Al5 amorphous alloy. But the Zr63.8Ni16.2Cu15Al5 amorphous alloy presents higher activation energy of crystallization (227 kJ/mole and 188 kJ/mole for Zr63.8Ni16.2Cu15Al5 and Zr66Cu15.3Ni8.7Al10 BMGs, respectively). However, Zr66Cu15.3Ni8.7Al10 amorphous alloy contains less atomic percentage of Cu and Ni elements (with positive heat of mixing) may result in forming less volume phase separation as well less interface area between these separated amorphous phase. Overall, the Zr66Cu15.3Ni8.7Al10 amorphous alloy exhibits longer incubation time at higher annealing temperature in comparison with the Zr63.8Ni16.2Cu15Al5 amorphous alloy, suggesting that the amorphous alloy which contains fewer amounts of Cu and Ni elements would have better thermal stability.