Annealing study of palladium–silver dental alloys: Vickers hardness measurements and SEM microstructural observations

Three Pd–Ag dental alloys for metal-ceramic restorations, W-1 (Ivoclar Vivadent), Rx 91 (Pentron) and Super Star (Heraeus Kulzer), were subjected to isothermal annealing for 0.5 hr periods in a nitrogen atmosphere at temperatures from approximately 400 ^∘ to 950 ^∘ C. The annealing behavior was investigated by Vickers hardness measurements (1 kg load) and SEM microstructural observations. The highest Vickers hardness occurred at approximately 700 ^∘ C for W-1 and 650 ^∘ C for Rx 91. For Super Star, there were two peaks in hardness at approximately 500 ^∘ and 650 ^∘ C. Additional use of light indenting loads (25 g for W-1; 10 g for Rx 91 and Super Star) revealed that hardness variations during annealing for W-1 and Rx 91 were related to the palladium solid solution matrix phase. For Super Star, the lower-temperature peak was controlled by multi-phase regions and the higher-temperature peak by the matrix phase. While microstructural changes due to annealing were evident with the SEM for Rx 91 and Super Star, no correlation was possible for W-1 because of its finer-scale microstructure. Although commercial Pd–Ag alloys have a relatively narrow composition range, their microstructures and annealing behavior can vary because of differences in proportions of secondary elements utilized for porcelain adherence and grain refinement elements, as well as other proprietary strategies employed by the manufacturers.     

Modelling the orthogonal machining process using coated carbide cutting tools

In this paper finite element methods were used to determine the influence of various coated and uncoated tungsten carbide cutting tools on the machining of a nickel-based super alloy Inconel 718. Disposable coated and uncoated carbide inserts were used both experimentally and as FEA models to study how the stress distribution within different coatings and carbide grades compared to each other, under a range of cutting conditions. Simulation of an orthogonal metal cutting process was performed using FORGE2, an elasto-visco plastic FEA code. All FE models were assumed to be plane strain. The results include the stress and temperature distributions through the primary shear zone, the chip/tool contact region and the coating/substrate boundaries. The tool wear and stress results from the FE modelling agree favourably with those obtained from experimental work.     

An Experimental Investigation of the Effect of Strip Thickness,Metallostatic Head and Tip Setback on the Productivity of a Twin-roll Caster

Summary

An experimental study has been made of the factors affecting productivity during the twin-roll casting of AA 5182. Strip has been cast over a much wider range of thicknesses and tip setbacks than previously reported. An empirical expression is obtained which relates productivity to strip thickness, metallostatic head and tip setback. It is shown that productivities can be considerably increased over the usual commercial practice by casting thin sheet with large tip setbacks.     

Phonological typicality influences sentence processing in predictive contexts: Reply to Staub, Grant, Clifton, and Rayner (2009).

In 2 separate self-paced reading experiments, Farmer, Christiansen, and Monaghan (2006) found that the degree to which a word's phonology is typical of other words in its lexical category influences online processing of nouns and verbs in predictive contexts. Staub, Grant, Clifton, and Rayner (2009) failed to find an effect of phonological typicality when they combined stimuli from the separate experiments into a single experiment. We replicated Staub et al.'s experiment and found that the combination of stimulus sets affects the predictiveness of the syntactic context; this reduces the phonological typicality effect as the experiment proceeds, although the phonological typicality effect was still evident early in the experiment. Although an ambiguous context may diminish sensitivity to the probabilistic relationship between the sound of a word and its lexical category, phonological typicality does influence online sentence processing during normal reading when the syntactic context is predictive of the lexical category of upcoming words. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application

Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching.PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea.     

Non-conventional machining of particle reinforced metal matrix composite

Particle Reinforced Metal Matrix Composites (PRMMC's) have proved to be extremely difficult to machine using conventional manufacturing processes due to heavy tool wear caused by the presence of the hard reinforcement. This paper presents details and results of an investigation into the machinability of SiC particle reinforced aluminium matrix composites using non-conventional machining processes such as Electro Discharge Machining (EDM), laser cutting and Abrasive Water Jet (AWJ). The surface integrity of the composite material for these different machining processes are examined and compared. The influence of the ceramic particle reinforcement on the machining process was analysed by tests performed on samples of the non-reinforced matrix material.     

A Deeper Insight into the Influence of the Electric Field Strength When Melt-Electrowriting on Non-Planar Surfaces

Defined structures for tissue engineering can be achieved by a variety of techniques, one of which includes melt-electrowriting (MEW), a technology that deposits spatially defined microfibers of a molten polymer across an electric field. In this study, the authors investigate how to microfabricate biomaterial-meshes using MEW to non-planar surfaces that will have more applicability to anatomical structures. By modeling the electric field strength associated with MEW, it is found that incorporation of a non-conductive 3D printed mould on the conductive collector plate offers the ability to accurately print patterns on non-planar surfaces successfully. Importantly, if the applied voltage at the nozzle or collector plate is kept constant in the MEW process, the electrostatic behavior of the deposited polymer, and the electric field strength between the collector and nozzle (which is greatest at the nozzle) has the greatest impact on the accuracy of fiber patterning and stacking. Consequently, controlled fiber deposition is exhibited, provided that a constant voltage and a constant vertical distance between the nozzle and the mould are maintained. Overall, this study establishes the groundwork to support further developments in MEW technologies, from flat to anatomically relevant 3D structures in the fields of regenerative medicine and biofabrication.     

COMBINE: The HVAC-design prototype

Integrated intelligent building design systems (IIBDSs) are computer-based design environments which will in the future be used by engineers and architects to assist them in the design of buildings. This paper deals with the class of IIBDSs whose aim it is to improve the energy efficiency and overall performance of buildings. Development of these IIBDSs is a substantial task and may take some time to be realized. The EC COMBINE project and the U.S. AEDOT project have been initiated to take the first step towards developing these future IIBDSs. This paper focuses on the COMBINE project.

COMBINE's first step towards developing IIBDSs is to implement a building product model based on the ‘product modelling’ approach promoted by the computer-integrated manufacturing (CIM) community. This building product model allows information about a building to be passed between different design professionals (e.g. architects, heating, ventilating, and air-conditioning (HVAC) system designers etc.). Data exchange through the product model is tested using various design prototypes one of which is called the HVAC-Design prototype. The HVAC-Design prototype helps a HVAC system designer to select a preliminary HVAC system for a building.

This paper reviews: (a) ongoing research into the development of IIBDSs and (b) various software tools which may be incorporated into future IIBDSs. The main emphasis of the paper is on the COMBINE project and the functionality of the HVAC-Design prototype in COMBINE. There is also a discussion on how HVAC-Design may develop in the future.     

Degradation of MgO refractory in CaO-SiO2-MgO-FeO x and CaO-SiO2-Al2O3-MgO-FeO x slags under forced convection

Experiments based on exposure of MgO to slags under forced convection flow conditions allowed the identification of different degradation mechanisms and the assessment of the role of Al₂O₃ in the degradation process. Slag with no alumina present resulted in direct dissolution. Samples immersed in alumina containing slag underwent indirect dissolution, with a spinel forming at the MgO-slag interface. At 1530 °C, the spinel was not effective in reducing the corrosion rate, as the scattered spinel grains were easily removed from the MgO surface. At 1500 °C, the loss of MgO was reduced due to the formation of a more cohesive spinel layer. Mechanical erosion then appears to play a greater role. Strength of the bond between the spinel and underlying MgO needs to be considered in strategies to reduce degradation of MgO refractories.