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High efficiency, increasing power densities, lower weight and pollution reduction require new materials for combustion engine components in order to withstand the higher thermo-mechanical loads. Cast Al-Si alloys are used for cylinder heads where they combine light weight, good castability and suitable mechanical properties. Despite casting difficulties and their vulnerability to hot tearing these Al-Cu alloys can be used as candidates to achieve even better mechanical properties at elevated temperatures. These alloys are formed by a ductile precipitation hardening α-Al matrix and brittle intermetallics, mostly Al2Cu. Tensile deformation of AlCu4 as cast and AlCu7 solutionized and aged conditions is investigated by combined application of non-destructive testing and imaging methods (using electron, neutron and synchrotron radiation) to study the stress distribution between the Al2Cu structures and the surrounding Al matrix. The external loads are transferred into the microstructure by strain control due to percolating eutectic structures in AlCu4 and AlCu7 as cast. Homogenization by solution treatment and age hardening significantly increases the strength, although stress controlled behavior becomes dominant. (Some damage tolerance is observed in the as cast as well as in the heat treated condition, as load is transferred from particles which were broken first to the remaining ones maintaining some deformation strengthening.) The stress-strain behavior of the samples is compared, conclusions on deformation mechanisms and internal architectures are drawn.

Diamond reinforced metals are being developed for use as highly sophisticated heat spreading material in power electronics or satellite laser optics. These particle reinforced composites combine the excellent thermal properties of diamond with a metal matrix, which enables shaping and joining onto the components. The mismatch in thermal expansion and Young's moduli of matrix metal and diamond reinforcement is responsible for high micro stresses under operational conditions of thermal cycling. These stresses may lead to interface delamination and/or matrix damage degrading the initially good thermal properties. Therefore, the interface bonding strength and the deformability of the matrix determine the quality of such metal matrix composites. Aluminum is favored as matrix metal due to its high ductility and carbide forming ability on diamond surfaces, which significantly improves the interface bonding strength. Silver offers high thermal conductivity and alloying with silicon produces reactivity with diamond, giving strong bonding strength. The tensile behavior of both composites was investigated by non-destructive in-situ neutron diffraction and acoustic emission (AE) measurements. Post mortem scanning electron microscopy reveal the bonding quality of the composites correlated to the reinforcement architecture and the plasticity of the matrices. Conclusions on the elasto-plastic deformation behavior of the investigated composites for thermal management application are drawn.

Particle reinforced metals are developed as heat sink materials for advanced thermal management applications. Metal matrix composites combine the high thermal conductivity of a metal with a low coefficient of thermal expansion of ceramic reinforcements. SiC and carbon diamond particle reinforced aluminum offer suitable thermal properties for heat sink applications. These composites are produced by liquid metal infiltration of a densely packed particle preform. Wettability, interface bonding strength and thermal mismatch are critical for void formation which leads to thermal fatigue damage under operation. The evolution of voids in AlSiC and AlCD has been studied by in-situ high resolution synchrotron tomography during matrix solidification. Large irregularly shaped matrix voids form during eutectic solidification. These voids help alleviate thermal expansion mismatch stresses by visco-plastic matrix deformation during cooling to RT after solidification, if sufficient interface bonding strength is assumed.

The need for efficient and clean solutions, due to the increasing current environmental regulations puts extra pressure on new combustion engine development, to compete in a market with alternative driving concepts. Downsizing and weight reduction can reduce the engine emission and efficiency, but require light alloys with superior thermo-mechanical properties for high temperature exposure to maintain the same engine performance. Cast Al-Cu could be alternative to standard Al-Si alloys for new engine generations due to their higher temperature strength, creep-resistance and long term stability of engine components. In Al-Si and Al-Cu cast alloys with heterogeneous microstructures a composite-like deformation behavior is responsible for superior high temperature properties. Stiff Si or Al2Cu particles, respectively reinforce a ductile α-Al matrix to a composite with improved thermo-mechanical strength. However, different Young’s moduli and coefficients of thermal expansion are responsible for micro stress gradients and unpredictable micro crack formation under operation. These micro-mechanical deformation mechanisms in Al-Si and Al-Cu systems, responsible for crack initiation and growth, have been scarcely investigated so far. This manuscript describes an example of elasto-plastic deformation mechanisms in an AlCu7 alloy. Tensile testing shows anomalous macroscopic deformation behavior indicating unknown internal micro-mechanical processes. External loading until yield strength and beyond are applied under laboratory conditions and during in-situ neutron diffraction. The results of macroscopic deformation and micro strain evolution are compared and correlated with the heterogeneous micro structure. High resolution synchrotron computed tomography reveals conclusions on the micro-mechanic deformation mechanisms and their effects on the macroscopic damage initiation and material’s service performance.

At the German neutron source Heinz Maier-Leibnitz (FRM II) the diffractometer STRESS-SPEC is the dedicated instrument to tackle problems in the field of engineering and applied materials science. M...

Al alloys with additions of Sc and/or Zr exhibit a reasonably stable grain structure due to a uniform distribution of coherent Al3(Sc,Zr) precipitates that forms at temperatures >300 °C. These precipitates are stable up to the solution treatment temperature and are able to pin subgrain and grain boundaries, inhibiting grain coarsening. The crystallographic structure of these precipitates presents a L12 superstructure coherent with the face-centred cubic Al matrix. Changes in the orientation relation between precipitates and the matrix are described in deformed, recovered and partially recrystallized samples of extrusions of AW7010 (AlZn6Mg2Cu2). The coherency of the intracrystalline Al3(Sc,Zr) precipitates present in the extrusions is lost by severe deformation performed by an equal channel angular pressing process, which produced a fine-grained microstructure. The deformed sample recovers, forming a subgrain structure with restored coherency of the Al3(Sc,Zr) precipitates. Rapid heating to 470 °C causes partial secondary recrystallization, which transforms the precipitates within the recrystallized grains into incoherent groups of particles that maintain their original orientation with each other.

Monofilament reinforced metals (MFRM) are developed as high temperature heat sink materials for fusion reactor applications. These composites combine the high thermal conductivity (TC) of a Cu matrix with low thermal expansion (CTE) of SiC or W filaments. The CTE mismatch between matrix and reinforcement lead to high micro stresses under operation conditions. Stress induced thermal fatigue damage such as interface delamination and fiber/matrix damage degrades the thermal properties of these composites. Different interface designs are developed for SiC as well as W filaments to improve bonding strength and increase the long term stability. Conventional as well as synchrotron tomography was applied on different MFRMs to characterize thermal fatigue damage and its propagation before, during and after thermal cycling.

The creep behavior of a squeeze-cast, short fiber reinforced Al metal matrix composite (MMC), consisting of an Al–11 wt.% Zn–0.2 wt.% Mg alloy reinforced with 15 vol.% Al2O3 Saffil® short fibers is investigated using miniature creep specimens. The small dimensions of the miniature creep specimens permit them to be machined from regions of an MMC block with different microstructures, thus allowing the effect of grain size and fiber texture on creep to be investigated on a more local level than is possible using conventional specimen geometries. The miniature creep specimens are subjected to uniaxial tensile stresses ranging from 3 to 40 MPa at temperatures between 573 and 623 K. It is shown that tests performed using the miniature creep specimen geometry are in good agreement with results previously obtained with standard creep specimens. Through interrupted creep experiments, it is observed that the creep back flow that occurs after unloading increases with increasing accumulated plastic strain. In the as-cast MMC, synchrotron microtomography reveals a fine distribution of pores whose spatial density increases with the spatial density of the fibers. The presence of fractured fibers in the crept MMC is also revealed. Some of the regions between fractured fiber fragments appear to be filled with matrix material, while others are voided.

New materials have to be developed for fusion reactor systems to withstand the high thermal load and heavy irradiation under service conditions. The divertor element collects the residuals of the nuclear reaction and withdraws heat from the reaction chamber into a heat sink. A thermal flux of ≈20 W mK−1 can be expected in such components. A plasma facing W plate is attached to a CuCrZr heat sink suffering CTE mismatch stresses at the interface due to pulsed operation required for the Tokamak reactor design. Fiber reinforced metal matrix composites are applied as an interlayer to reduce macroscopic interfacial stresses in these components. W-wire reinforced copper is a promising material for this application due to a good fiber-matrix bonding strength which is further increased by surface etching or graded interface designs. Thermal stresses in between the matrix and the wires are responsible for thermal fatigue damage within the constituents and at their interface. Neutron and synchrotron diffraction was performed in situ during thermal cycling to determine the micro stress amplitudes and their changes under simulated service conditions.

In fusion reactor systems extreme conditions require materials with high temperature and radiation resistance. The divertor component consists of a plasma facing W plate attached to a Cu heat sink to extract the heat from the nuclear reaction chamber coolant. The Coefficient of Thermal Expansion (CTE) mismatch between the W plate and the Cu heat sink causes interface delamination reducing the long term stability of the divertor. To avert this problem, composites are developed as interlayer materials with a high thermal conducting Cu matrix reinforced with up to 50 vol.% SiC or W monofilaments to increase the mechanical strength and to reduce the CTE mismatch. Thermal stresses are transferred from the macroscopic interface between the components into the bulk of the composite. Oscillating micro stresses may lead to fiber delamination and matrix damage during thermal cycling. Different matrix alloys, fiber materials and interface designs are investigated. In situ neutron diffraction performed during thermal cycling show the effect of bonding strength on the stress amplitudes expected under service conditions. The long term stability is tested by measurements after further ex situ cycling. Thermal fatigue damage and its propagation are visualized by in situ as well as ex situ high resolution synchrotron tomography. The combination of both methods helps to understand the strain induced damage mechanisms. Weak bonding leads to delamination of the fiber–matrix interfaces. Strong bonding causes severe matrix deformation and damage. Fiber cracks originating from sample production cause accumulating thermal fatigue damage during thermal cycling.

Aluminum reinforced by 60 vol.% diamond particles has been investigated as a potential heat sink material for high power electronics. Diamond (CD) is used as reinforcement contributing its high thermal conductivity (TC ≈ 1000 W mK −1 ) and low coefficient thermal expansion (CTE ≈ 1 ppm K −1 ). An Al matrix enables shaping and joining of the composite components. Interface bonding is improved by limited carbide formation induced by heat treatment and even more by SiC coating of diamond particles. An AlSi7 matrix forms an interpenetrating composite three-dimensional (3D) network of diamond particles linked by Si bridges percolated by a ductile α-Al matrix. Internal stresses are generated during temperature changes due to the CTE mismatch of the constituents. The stress evolution was determined in situ by neutron diffraction during thermal cycling between room temperature and 350 °C (soldering temperature). Tensile stresses build up in the Al/CD composites: during cooling

Particle reinforced metal matrix composites are developed for heat sink applications. For power electronic devices like IGBT modules (Insulated Gate Bipolar Transistor) a baseplate material with high thermal conductivity combined with a low coefficient of thermal expansion is needed. Commonly AlSiC MMC are used with a high volume content of SiC particles (~ 70 vol.%). To improve the performance of these electronic modules particle reinforced materials with a higher thermal conductivity are developed for an advanced thermal management. For this purpose highly conducting diamond particles (TC ~ 1000 W/mK) are embedded in an Al matrix. These new diamond reinforced MMC were investigated concerning their thermal fatigue mechanisms compared to the common AlSiC MMC. Differences in reinforcement architecture and their effects on thermal fatigue damage were studied by in situ synchrotron tomography during thermal cycling.

AlSi7Mg/SiC/70p (AlSiC) is used for heat sinks because of its good thermal conductivity combined with a low coefficient of thermal expansion (CTE). These properties are important for power electronic devices where heat sinks have to provide efficient heat transfer to a cooling device. A low CTE is essential for a good surface bonding of the heat sink material to the insulating ceramics. Otherwise mismatch in thermal expansion would lead to damage of the bonding degrading the thermal contact within the electronic package. Therefore AlSiC replaces increasingly copper heat sinks. The CTE mismatch between insulation and a conventional metallic heat sink is transferred into the MMC heat sink. The stability of the interface bonding within a MMC is critical for its thermal properties. In situ thermal cycling measurements of an AlSi7Mg/SiC/70p MMC are reported yielding the void volume fraction and internal stresses between the matrix and the reinforcements in function of temperature. The changes in void volume fractions are determined simultaneously by synchrotron tomography and residual stresses by synchrotron diffraction at ESRF-ID-15. The measurements show a relationship between thermal expansion, residual stresses and void formation in the MMC. The results obtained from the in situ measurements reveal a thermoelastic range up to 200 °C followed by plastic matrix deformation reducing the volume of voids during heating. A reverse process takes place during cooling. Thus the CTE becomes smaller than according to thermoelastic calculations. Damage could be observed after multiple heating cycles, which increase the volume fraction and the size of the voids. The consequence is local debonding of the matrix from the reinforcement particles, which leads to an irreversible reduction of the thermal conductivity after multiple heating cycles.

AlSi7Mg/SiC/70p (AlSiC) eignet sich als Kuhlkorper wegen seiner guten Leitfahigkeit bei gleichzeitig niedrigem thermischen Ausdehnungskoeffizienten (CTE) fur Applikationen in der Hochleistungselektronik. Ein niedriger CTE ermoglicht dauerhaft einen guten thermischen Kontakt zwischen der Kuhlplatte und dem Elektronikbauteil. Materialien mit hohem Ausdehnungskoeffizienten wurden durch thermische induzierte makroskopische Spannungen in der Grenzflache zu Delaminationen in der Kontaktflache fuhren. Aus diesem Grund ersetzt AlSiC Kupfer als Kuhlkorpermaterial in der Leistungselektronik. Das Problem der unterschiedlichen Ausdehnungskoeffizienten ist in den Verbundwerkstoff transferiert und wirkt sich durch innere Mikrospannungen zwischen der Aluminiummatrix und den SiC-Partikeln aus. Insitu Messungen wahrend thermischer Aufheizzyklen bis 400 °C an AlSi7Mg/SiC/70p Proben wurden vorgenommen, um den Porenanteil und die inneren Spannungen zu bestimmen. Der Porenanteil wird aus Synchrotron Tomografie und die inneren Spannungen mittels Synchrotron Diffraktion (ESFR/ID15A) gemessen. Messungen wahrend des Heizens, Kuhlens und nach mehrfachem Zyklieren zeigen einen Zusammenhang zwischen den inneren Spannungen und dem Porenvolumenanteil und der Temperatur. AlSiC verhalt sich von Raumtemperatur bis etwa 200 °C thermo-elastisch, wobei sich die dominanten Zugspannungen in der Matrix in Druckspannungen umkehren. Mit zunehmender Temperatur verformt sich die Matrix plastisch und vermindert dabei den Porenvolumenanteil. Beim Kuhlen von 500 °C wird nach einer elastischen Spannungsumkehr in die Zugrichtung wieder eine Erhohung des Porenvolumenanteils beobachtet. Unter 200 °C verhalt sich AlSiC bis Raumtemperatur wieder thermo-elastisch. Nach mehreren, extremen Temperaturzyklen von –100 °C bis 400 °C wird die Haftung der SiC-Partikel an die Al-Matrix des MMCs lokal gelost und Porenwachstum beobachtet.

The increasing demand for light weight and efficiency of modern combustion engines requires sophisticated light alloys with improved high-temperature strength and creep resistance. Nowadays AlSi alloys are used for structural parts as these materials offer increased wear resistance and long-term stability under operating conditions. The heterogeneous microstructure of AlSi combines the thermal properties of stiff Si particles with ductile α-Al into a composite with sophisticated thermomechanical strength. However, the different Young’s moduli and coefficients of thermal expansion cause large microstress gradients and microcrack formation in service. The micromechanical deformation mechanisms in AlSi systems, responsible for crack initiation and growth, are unknown so far. The current work describes an experimental approach that combines non-destructive diffraction and imaging techniques to investigate the elastoplastic deformation behavior of two engineering alloys, i.e. the hypoeutectic AlSi7MgCu standard alloy for castings and the hypereutectic AlSi17Cu4 piston alloy for improved surface wear resistance. Neutron diffraction is applied for microstress measurements under external load and during thermal cycling. Complementary synchrotron tomography is performed for imaging of microcrack formation and damage within the microstructure. Stress-induced micromechanical deformation mechanisms could be revealed and correlated to damage mechanisms critical for engine components under operating conditions.

The Head and Neck Cancer Tumor Board is a multispeciality comprehensive conference that brings together experts with different backgrounds to make group decisions about the appropriate treatment. Due to the complexity of the patient cases and the collaboration of different medical disciplines most of these decisions have to be made under uncertainty, i. e., with-out knowing all relevant factors and without being quite sure about the outcome.To develop effective team decision making under uncertainty, it is necessary to understand how medical experts perceive and handle uncertainties. The aim of this field study was to develop a knowledge base by exploring additionally the factors that influence group decision making processes. A structured nonparticipant observational study was employed to address the research goal. Video data were analyzed by 2 independent observers using an observation checklist. A total of 20 videotaped case discussions were studied. Observations were complemented by a questionnaire gathering subjective evaluations of board members about the process and quality of their decisions (N=15).The results show that uncertainty is recognized by board members. Reasons for uncertainty may stem from the complexity of the cases (e. g. therapy options) or the assessment from different disciplines coming together at the board.With respect to handling uncertainty and guaranteeing an optimal decision making process potential for improvement could be defined. This pertains to the handling of different levels of competence, the promotion of a positive discussion culture as well as structuring of the decision making process.

Internal stresses are those stresses found in a body when this is stationary and in equilibrium with its surroundings (Withers & Badeshia, 2001). These stresses can arise at different length scales within a microstructure ranging from the size of the analysed body down to the atomic scale. Multiphase materials are prone to develop internal stresses due to the different mechanical and physical properties usually found between the phases that form these materials. This is essential for composites because the distribution and magnitude of the internal stresses may determine their mechanical/physical behaviour. Neutron diffraction has become an essential tool to determine internal stresses nondestructively in metal-based composite materials. The present chapter gives a thorough description of the state of the art of the technique and its use to determine internal stresses developed in lightweight metal matrix composites under mechanical, thermal and thermomechanical loading.

International audience; Metal matrix composites (MMC) are being developed for power electronic IGBT modules, where the heat generated by the high power densities has to be dissipated from the chips into a heat sink. As a means of increasing long term stability a base plate material is needed with a good thermal conductivity (TC) combined with a low coefficient of thermal expansion (CTE) matching the ceramic insulator. SiC particle reinforced aluminum (AlSiC) offers the high TC of a metal with the low CTE of a ceramic. Internal stresses are generated at the matrix-particle interfaces due to the CTE mismatch between the constituents of the MMC during changing temperatures. Neutron and synchrotron diffraction was performed to evaluate the micro stresses during thermal cycling. The changes in void volume fraction, caused by plastic matrix deformation, are visualized by synchrotron tomography. The silicon content in the matrix connecting the particles to a network of hybrid reinforcement contributes essentially to the long term stability by an interpenetrating composite architecture.

In the steel industry, steel slabs are produced by continuous casting to allow fast processing. A complex stress state leads to crack formation in such steel slabs. The stress components relevant for failure were identified by neutron diffraction under simulated casting conditions.

This paper aims to review psychological research results and methods which might be relevant to the issue of team interaction in the medical domain. The complex research on team performance is coherently organized into a proposed framework focussing in detail on task and social orientations of interacting team members.

This paper aims to review psychological research results and methods which might be relevant to the issue of team interaction in the medical domain. The complex research on team performance is coherently organized into a proposed framework focussing in detail on task and social orientations of interacting team members.