Powder Metallurgy Preparation of Co-Based Alloys for Biomedical Applications

Co-based alloys represent very important group of materials used for medical applications. Currently, fabrication of these materials is preferentially done by casting or forming. Production by powder metallurgy techniques is less common. However, powder metallurgy fabrication of these alloys brings advantages such as reduced machining, possibility of alloying by high-melting elements, preparation of nanocrystalline materials with enhanced mechanical properties or producing of porous alloys with improved ability to integrate into issues. In this work, our attention was focused on fundamental preparation of an CoCrMo alloy by two methods of powder metallurgy. In the first method, pure metallic powders were mixed, pressed and sintered in vacuum furnace. The second applied technology consisted of mechanical alloying using planetary ball mill and compaction by spark plasma sintering technique. A series of samples was prepared under various conditions by these procedures. Dependence of microstructure, phase composition and mechanical properties of prepared samples on fabrication conditions (milling parameters, sintering temperature etc.) was studied. Obtained results were compared with properties of commercial cast cobalt alloy used for medical applications

Investigation of laminar detachment by means of simultaneous microphone and surface hot wire measurements

An experimental study on the acoustic characterization of the laminar separation bubble on an airfoil is presented. The acoustic near- and far-fields are sampled by means of microphone arrays. Additionally the wall shear stresses are measured on the airfoil suction side by means of 24 MEMS surface hot wires in the region where the separation bubble was expected. Dierent processing strategies both in the frequency and in the time domain were applied for an acoustic characterization of the bubble. A focus of the study presented here is the application of the so called causality correlation method. The wall shear stresses on the airfoil surface together with the pressure fluctuations in the near- and far-field are recorded simultaneously. This enables the calculation of the cross-correlation between the measured quantities. An analysis of the resulting coecient matrix in the space-time domain identies perturbations traveling along the airfoil, showing a linear dependency on the sound generating process. For the case of the correlation between the wall shear stresses on the airfoil and the pressure fluctuations in the far-field the validity of the results were improved signicantly by using the focused pressure signals from the microphone-array

Effcient generation of energetic ions in multi-ion plasmas by radio-frequency heating

We describe a new technique for the effcient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed 'three-ion' scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate effcient acceleration of3He ions to high energies in dedicated hydrogen-deuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast3He ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular,3He-rich solar flares

Overview of the JET results with the ITER-like wall

Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential