The effects of boro-tempering heat treatment on microstructural properties of ductile iron

In this study, the effects of boro-tempering heat treatment on microstructural properties of ductile iron were investigated. Test samples with dimensions of 10 × 10 × 55 mm were boronized at 900 °C for 1, 3 and 5 h and then tempered at four different temperatures (250, 300, 350 and 450 °C) for 1 h. Both optical microscopy and scanning electron microscopy were used to reveal the microstructural details of coating and matrix of boro-tempered ductile iron. X-ray diffraction was used to determine the constituents of the coating layer. The boride layer formed on the surface of boro-tempered ductile cast iron is tooth shape form and consisted of FeB and Fe₂B phases. The thickness of boride layer increases as the boronizing time increases and tempering temperature decreases. Tempering temperature is more effective than boronizing time on the matrix structure. Boro-tempering heat treatment reduces the formation of lower and upper ausferritic matrix temperature according to classical austempering. This causes formation of upper ausferritic matrix in the sample when tempered at 300 °C. This is in contrast to general case which is the formation of lower ausferritic matrix via austempering at this temperature.     

Nanostructured carbon beads--properties and biomedical applications

In this study, amorphous carbonaceous nanoparticles were prepared by a simple hydrothermal process using glucose as precursor. The nearly perfect spherical particles (beads) with the dimensions in the range of 10-500 nm were obtained depending on the main process parameters (precursor concentration, temperature, and time). The particles size, surface morphology, structure, and composition have been examined by TEM, SEM, X-ray diffraction, XPS, FTIR and Raman spectroscopy. These amorphous carbonaceous nanobeads (a-CNBs) have been found nontoxic in vitro with a variety of cultured cell lines. The size-dependent effect of a-CNBs addition on cell function has been observed. For example, a-CNBs can, in some cases, substantially increase interleukin-12 (IL-12) production by bone marrow dendritic cells. It has been further demonstrated that a-CNBs can be modified with fluorescent dye molecules or loaded with anti-cancer drugs for bioimaging or therapeutic purposes, respectively. The results of these tests and the strategies for the particle preparation and functionalization for biomedical applications have been discussed.     

A subthreshold current‐sensing ΣΔ modulator for low‐voltage and low‐power sensor interfaces

A continuous‐time (CT) ΣΔ modulator for sensing and direct analog‐to‐digital conversion of nA‐range (subthreshold) currents is presented in this work. The presented modulator uses a subthreshold technique based on subthreshold source‐coupled logic cells to efficiently convert subthreshold current to digital code without performing current‐to‐voltage conversion. As a benefit of this technique, the current‐sensing CT ΣΔ modulator operates at low voltage and consumes very low power, which makes it convenient for low‐power and low‐voltage current‐mode sensor interfaces. The prototype design is implemented in a 0.18 µm standard complementary metal‐oxide semiconductor technology. The modulator operates with a supply voltage of 0.8 V and consumes 5.43 μW of power at the maximum bandwidth of 20 kHz. The obtainable current‐sensing resolution ranges from effective number of bits (ENOB) = 7.1 bits at a 5 kHz bandwidth to ENOB = 6.5 bits at a 20 kHz bandwidth (ENOB). The obtained power efficiency (peak FoM = 1.5 pJ/conv) outperforms existing current‐mode analog‐to‐digital converter designs and is comparable with the voltage‐mode CT ΣΔ modulators. The modulator generates very low levels of switching noise thanks to CT operation and subthreshold current‐mode circuits that draw a constant subthreshold current from the voltage supply. The presented modulator is used as a readout interface for sensors with current‐mode output in ultra low‐power conditions and is also suitable to perform on‐chip current measurements in power management circuits. Copyright © 2014 John Wiley & Sons, Ltd.     

Fatigue life estimation of FBGA memory device under vibration

This paper predicts the fatigue life of fine-pitch ball grid array (FBGA) solder joints in memory devices due to harmonic excitation through experiments and finite element analysis. Finite element models of the memory device with simplified solder joints and with detailed solder joints were developed as a global model and a local model, respectively. A global-local modeling technique was used in the finite element simulation to calculate the stress magnitude of solder joints in the memory device under vibration. Stress versus life (S-N) curve was generated for the memory devices under various vibration levels to derive the fatigue constants of solder material. The fatigue life of the memory device was then determined by using the Basquin equation and Miner’s rule. It was experimentally verified that the predicted fatigue life of the memory device under cumulative damage conditions matches the experimental results within reasonable accuracy.     

Effect of 2D WS<Subscript>2</Subscript> Addition on Cold-Sprayed Aluminum Coating

Tungsten disulfide (WS₂) has excellent solid lubrication properties due to its 2D layered structure. This study focuses on depositing Al-2 wt.% WS₂ composite coating by cold spray technique. The effect of WS₂ addition on the microstructure, mechanical and tribological properties of the composite coatings is examined in the as-deposited and heat-treated conditions. After heat treatment, the coating density increased to 99% with improved intersplat bonding. The microhardness of the heat-treated Al-2 wt.% WS₂ coating increased by 56% as compared to the as-sprayed coating. The wear resistance of heat-treated Al-2 wt.% WS₂ coating improved by 75% with a synergistic reduction in the coefficient of friction (COF) by 51%. Transmission electron microscopy investigation reveals the presence of layered WS₂ within aluminum splats with a strong interface. This study shows that cold spraying can be effectively used to integrate 2D layered WS₂ as a solid lubricant in the metallic coatings.     

Investigation of kinetics of borided ductile and lamellar graphite cast iron

In this study, kinetics of borided ductile iron and lameller graphite grey cast iron were investigated by processing boronizing treatment (was carried out in Ekobor-II powders). The process temperatures and durations respectively 1123, 1173, 1223 K for 2, 4 and 6 hours, with pack boronizing method and under atmospheric pressure in electrical resistance furnace. Changing of borided layer properties was investigated by using optical and scanning electron microscopy, X-ray diffraction and micro-Vickers hardness testers. The growth kinetics of the boride layers forming and thickness of boride layer were computed for both cast iron. The main phases for two processes Fe₂B and FeB were defined on the surface.     

Exp-function method for solving nonlinear evolution equations with higher order nonlinearity

In this paper, the Exp-function method is used to obtain generalized solitary solutions of the generalized Drinfel’d–Sokolov–Wilson (DSW) system and the generalized (2+1)-dimensional Burgers-type equation. Then, some of the solitary solutions are converted to periodic solutions or hyperbolic function solutions by a simple transformation. The results show that the Exp-function method is a powerful and convenient mathematical tool for solving nonlinear evolution equations with higher order nonlinearity.