Coprocessor design for multilayer surface-mounted PCB routing

The authors present the issues involved in the design of a special-purpose processing array system, called HAM, which accelerates computationally intensive wire routing tasks. It is especially suited for double-sided surface-mounted boards, which require complex three-dimensional search operations over multiple wiring planes. The novel features of the design include a hexagonal interconnection scheme to improve workload distributions during multilayer concurrent search operations and the VLSI custom design of the processors. Particular emphasis has been placed on the demands of maze routing. A cell-address propagation scheme, which is quite different from the traditional grid-coordinate approach, is discussed. It provides rapid lookup of pertinent routing information and can be extended to any distributed memory multiprocessor system. A global pipelining scheme of cell updates and expands is discussed. Experimental results are presented relating the speedup to various criteria for two different modes of parallel wave propagation     

Evidence for the Microwave Effect During the Annealing of Zinc Oxide

A microwave/conventional hybrid furnace has been used to anneal virtually fully dense zinc oxide ceramics under pure conventional and a microwave/conventional hybrid heating regime with a view to obtaining evidence for the "microwave effect" during the resulting grain growth. In each case it was ensured that each sample within a series had an identical thermal history in terms of its temperature/time profile. The results showed that grain growth was enhanced during hybrid heating compared with pure conventional heating; the greatest enhancement, a factor of ∼3 increase in average grain size, was observed in the range 1100°–1150°C. The grain growth exponent decreased from 3 during conventional heating to 1.4 during hybrid heating in this temperature range, suggesting an acceleration of the diffusional processes involved. Temperature gradients within the samples were found to be too small to explain the results. This suggests that clear evidence has been found to support the existence of a genuine "microwave effect."     

Microstructure and Properties of Spark Plasma-Sintered ZrO2–ZrB2 Nanoceramic Composites

In a recent work, ¹ we have reported the optimization of the spark plasma sintering (SPS) parameters to obtain dense nanostructured 3Y-TZP ceramics. Following this, the present work attempts to answer some specific issues: (a) whether ZrO₂-based composites with ZrB₂ reinforcements can be densified under the optimal SPS conditions for TZP matrix densification (b) whether improved hardness can be obtained in the composites, when 30 vol% ZrB₂ is incorporated and (c) whether the toughness can be tailored by varying the ZrO₂–matrix stabilization as well as retaining finer ZrO₂ grains. In the present contribution, the SPS experiments are carried out at 1200°C for 5 min under vacuum at a heating rate of 600 K/min. The SPS processing route enables retaining of the finer t -ZrO₂ grains (100–300 nm) and the ZrO₂–ZrB₂ composite developed exhibits optimum hardness up to 14 GPa. Careful analysis of the indentation data provides a range of toughness values in the composites (up to 11 MPa·m^1/2), based on Y₂O₃ stabilization in the ZrO₂ matrix. The influence of varying yttria content, t -ZrO₂ transformability, and microstructure on the properties obtained is discussed. In addition to active contribution from the transformation-toughening mechanism, crack deflection by hard second phase brings about appreciable increment in the toughness of the nanocomposites.     

Preparation and Kinetic Considerations for the Dissolution of Cr‐substituted Iron Oxides in Reductive‐complexing Formulations

The dissolution rate coefficients of Cr‐substituted (0‐20 at.% Cr) iron oxides viz. hematite and magnetite were determined by using an inverse cubic rate (ICR) law applicable for spherical particles as well as by a general kinetic equation (GKE) applicable for polydispersed particles. An attempt is made to compare both the treatments for different kinds of dissolution profiles obtained by employing oxides with narrow particle size distribution in V(II)‐EDTA and citric acid‐EDTA‐ascorbic acid formulations at 353±5K. The dissolution profiles could be classified into three types based on the nature of oxide and formulations. It is observed that both ICR and GKE treat the dissolution course as a function of decrease in fraction of undissolved mass, m/m₀. The dissolution rate coefficients determined by ICR and GKE have shown the similar trend of decrease with increasing Cr content of the oxides and was ascribed to lattice stabilization.     

Additive manufacturing of barium titanate based ceramic heaters with positive temperature coefficient of resistance (PTCR)

Lanthanum/manganese doped barium titanate (BT) based PTCR functional heater elements/structures were fabricated with desirable electrical properties for the first time using Additive Manufacturing (AM). 3D printed components of varying size and shape and prototype honeycomb lattices with high density were achieved through AM. Aqueous, less organic containing (2.5 wt% additives versus 10–30 wt% added typically), eco-friendly ink formulations were developed with suitable rheological properties for 3D printing. For BT prints, the sintered densities of the 3D ceramic parts were found to be >99% TD, highest reported value so far. The microstructure, electrical properties and heating characteristics of the printed PTCR components were studied in detail and their thermal stability evaluated using infrared imaging and benchmarked against commercial PTCR heating element. The heating behaviour of the solid and porous 3D printed components was demonstrated to be similar, paving the way for light weight (?47% reduction in weight) heaters suitable for automotive/aerospace applications and less materials wastage during device fabrication.     

Determination of mechanical properties of Al–Mg alloys dissimilar friction stir welded interface by indentation methods

A series of friction stir welds was produced between heat treated Al–Mg–Si and strain hardened Mg–Al–Zn alloy sheets. Weld evaluation by transverse tensile testing showed a wide range of strengths and all the failures occurred along the weld interface. The formation of intermetallic compounds in the weld joints was investigated by X-ray diffraction, scanning electron microscopy imaging, and elemental analysis techniques. Micro and nanoindentation characterization methods were used to evaluate the mechanical properties at the interface, including the fracture toughness. The fracture toughness measurements by a Vickers indenter introduced Palmqvist type cracks at all four corners of the indents and cube corner indenter resulted in the intermetallic chipping. The fracture toughness (K _IC) calculation by both the micro and nanoindentation methods showed very low values, which is the primary reason for the brittle failure of the dissimilar weld joints and concomitant low tensile strengths.     

UHTC–carbon fibre composites: Preparation,oxyacetylene torch testing and characterisation

Current generation carbon–carbon (C–C) and carbon–silicon carbide (C–SiC) materials are limited to service temperatures below 1800 °C and materials are sought that can withstand higher temperatures and ablative conditions for aerospace applications. One potential materials solution is carbon fibre-based composites with matrices composed of one or more ultra-high temperature ceramics (UHTCs); the latter are intended to protect the carbon fibres at high temperatures whilst the former provides increased toughness and thermal shock resistance to the system as a whole. Carbon fibre–UHTC powder composites have been prepared via a slurry impregnation and pyrolysis route. Five different UHTC compositions have been used for impregnation, viz. ZrB₂, ZrB₂–20 vol% SiC, ZrB₂–20 vol% SiC–10 vol% LaB₆, HfB₂ and HfC. Their high-temperature oxidation resistance has been studied using a purpose built oxyacetylene torch test facility at temperatures above 2500 °C and the results are compared with that of a C–C benchmark composite.     

The Effect of Trace Elements on the Cooling Curves,Microstructure and Mechanical Properties of Eutectic Aluminium-Silicon Alloy

Abstract

The effect of trace elements, used for modification, on the cooling curves obtained during solidification, microstructure and mechanical properties of eutectic aluminium-silicon alloy was investigated. The results of this study indicate the following: 1 The addition of sodium or sodium plus strontium or antimony modifies the eutectic silicon while the addition of sulphur does not alter the microstructure.

2 Those elements which modify the eutectic-silicon, lower the eutectic solidification temperature, while those elements which do not bring about modification, do not alter the eutectic solidification temperature.

3 The addition of those elements which modify the eutectic aluminium-silicon alloy, viz., sodium or sodium plus strontium or antimony improves the UTS and percentage elongation. The addition of titanium to eutectic aluminium-silicon alloy containing these trace elements improves the UTS and percentage elongation to a further extent. Among the various trace elements added to eutectic aluminium-silicon alloy, the addition of sodium plus titanium improves the UTS and percentage elongation to the maximum extent.