Anti-corrosive and anti-microbial properties of nanocrystalline Ni-Ag coatings

Anti-corrosive and anti-bacterial properties of electrodeposited nanocrystalline Ni-Ag coatings are illustrated. Pure Ni, Ni-7 at.% Ag, & Ni-14 at.% Ag coatings were electrodeposited on Cu substrate. Coating consisted of Ni-rich and Ag-rich solid solution phases. With increase in the Ag content, the corrosion resistance of the Ni-Ag coating initially increased and then decreased. The initial increase was due to the Ni-Ag solid solution. The subsequent decrease was due to the increased galvanic coupling between the Ag-rich and Ni-rich phases. For all Ag contents, the corrosion resistance of the Ni-Ag coating was higher than the pure Ni coating. Exposure to Sulphate Reducing Bacteria (SRB) revealed that the extent of bio-fouling decreased with increase in the Ag content. After 2 month exposure to SRB, the Ni-Ag coatings demonstrated less loss in corrosion resistance (58% for Ni-7 at.% Ag and 20% for Ni-14 at.% Ag) when compared pure Ni coating (115%). (C) 2016 Elsevier B.V. All rights reserved.

Orientation Selection and Microstructural Evolution in Directionally Solidified Tb0.3Dy0.7Fe1.95

Tb0.3Dy0.7Fe1.95 alloy was directionally solidified by using a modified Bridgman technique at a wide range of growth rates of 5 to 100 cm/h. The directionally grown samples exhibited plane front solidification morphology up to a growth rate of 90 cm/h. Typical island banding feature was observed closer to the chilled end, which eventually gave rise to irregular peritectic coupled growth (PCG). The PCG gained prominence with an increase in the growth rate. The texture study revealed formation of strong aOE (c) 311 > texture in a lower growth rate regime, aOE (c) 110 > and ``rotated aOE (c) 110 > aEuroe in an intermediate growth regime, and aOE (c) 112 > in a higher growth rate regime. In-depth analysis of the atomic configuration of a solid-liquid interface revealed that the growth texture is influenced by the kinetics of atomic attachment to the solid-liquid interface, which is intimately related to a planar packing fraction and an atomic stacking sequence of the interfacial plane. The mechanism proposed in this article is novel and will be useful in addressing the orientation selection mechanism of topologically closed packed intermetallic systems. The samples grown at a higher growth rate exhibit larger magnetostriction (lambda) and d lambda/dH owing to the absence of pro-peritectic (Tb,Dy)Fe-3 and formation of aOE (c) 112 > texture, which lies closer to the easy magnetization direction (EMD).

Resputtering Effect on Nanocrystalline Ni-Ti Alloy Films

We report on the effect of resputtering on the properties of nanocrystalline Ni-Ti alloy thin films deposited using co-sputtering of Ni and Ti targets. In order to facilitate the formation of nanocrystalline phases, films were deposited at room temperature and 573 K (300 A degrees C) with substrate bias voltage of -100 V. The influence of substrate material on the composition, surface topography microstructure, and phase formations of nanocrystalline Ni-Ti thin films was also systematically investigated. The preferential resputtering of Ti adatoms was lesser for Ni-Ti films deposited on quartz substrate owing to high surface roughness of 4.87 nm compared to roughness value of 1.27 nm for Si(100) substrate.

Critical investigation of high performance spin-coated high-kappa titania thin films based MOS capacitor

We report the tunable dielectric constant of titania films with low leakage current density. Titanium dioxide (TiO2) films of three different thicknesses (36, 63 and 91 nm) were deposited by the consecutive steps of solution preparation, spin-coating, drying, and firing at different temperatures. The problem of poor adhesion between Si substrate and TiO2 insulating layer was resolved by using the plasma activation process. The surface roughness was found to increase with increasing thickness and annealing temperature. The electrical investigation was carried out using metal-oxide-semiconductor structure. The flat band voltage (V-FB), oxide trapped charge (Q(ot)), dielectric constant (kappa) and equivalent oxide thicknesses are calculated from capacitance-voltage (C-V) curves. The C-V characteristics indicate a thickness dependent dielectric constant. The dielectric constant increases from 31 to 78 as thickness increases from 36 to 91 nm. In addition to that the dielectric constant was found to be annealing temperature and frequency dependent. The films having thickness 91 nm and annealed at 600 A degrees C shows the low leakage current density. Our study provides a broad insight of the processing parameters towards the use of titania as high-kappa insulating layer, which might be useful in Si and polymer based flexible devices.

Thermal mismatch stress in SiC whisker reinforced aluminium composite: new measurement method by X-ray diffraction

A new X-ray diffraction method for characterising thermal mismatch stress (TMS) in SiC_w–Al composite has been developed. The TMS and thermal mismatch strain (TMSN) in SiC whiskers are considered to be axis symmetrical, and can be calculated by measuring the lattice distortion of the whiskers. Not only the average TMS in whiskers and matrix can be obtained, but the TMS components along longitudinal and radial directions in the SiC whiskers can also be deduced. Experimental results indicate that the TMS in SiC whiskers is compressive, and tensile in the aluminium matrix. The TMS and TMSN components along the longitudinal direction in the SiC whiskers are greater than those along the radial direction for a SiC_w–Al composite quenched at 500°C.

Evaluation of termination techniques for 4H-SiC PiN diodes and trench JFETs

An investigation concerning suitable termination techniques for 4H-SiC trench JFETs is presented. Field plates, p+ floating rings and junction termination extension techniques are used to terminate 1.2kV class PiN diodes. The fabricated PiN diodes evaluated here have a similar design to trench JFETs. Therefore, the conclusions for PiN diodes can be applied to JFET structures as well. Numerical simulations are also used to illustrate the effect of the terminations on the diodes' blocking mode behaviour.

Switching performance of epitaxially grown normally-off 4H-SiC JFET

Static and dynamic behavior of the epitaxially grown dual gate trench 4H-SiC junction field effect transistor (JFET) is investigated. Typical on-state resistance Ron was 6-10mΩcm2 at VGS = 2.5V and the breakdown voltage between the range of 1.5-1.8kV was realized at VGS = -5V for normally-off like JFETs. It was found that the turn-on energy delivers the biggest part of the switching losses. The dependence of switching losses from gate resistor is nearly linear, suggesting that changing the gate resistor, a way similar to Si-IGBT technology, can easily control di/dt and dv/dt. Turn-on losses at 200°C are lower compared to those at 25°C, which indicates the influence of the high internal p-type gate layer resistance. Inductive switching numerical analysis suggested the strong influence of channel doping conditions on the turn-on switching performance. The fast switching normally-off JFET devices require heavily doped narrow JFET channel design. © (2009) Trans Tech Publications, Switzerland.

An elasto-plastic constitutive relation of whisker-reinforced metal-matrix composite

A material model for whisker-reinforced metal-matrix composites is constructed that consists of three kinds of essential elements: elastic medium, equivalent slip system, and fiber-bundle. The heterogeneity of material constituents in position is averaged, while the orientation distribution of whiskers and slip systems is considered in the structure of the material model. Crystal and interface sliding criteria are addressed. Based on the stress-strain response of the model material, an elasto-plastic constitutive relation is derived to discuss the initial and deformation induced anisotropy as well as other fundamental features. Predictions of the present theory for unidirectional-fiber-reinforced aluminum matrix composites are favorably compared with FEM results.

Effect of hydrogen dilution on the deposition of carbon-rich a-SiC:H films by the electron cyclotron resonance method

The deposition of hydrogenated amorphous silicon carbide (a-SiC:H) films from a mixture of silane, acetylene and hydrogen gas using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) process is reported. The variation in the deposition and film characteristics such as the deposition rate, optical band gap and IR absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of about 250 Å min-1 at a hydrogen dilution ratio of about 20 (hydrogen flow (sccm)/acetylene + silane flow (sccm)) and decreases in response to a further increase in the hydrogen dilution. There is no strong dependence of the optical band gap on the hydrogen dilution within the dilution range investigated (10-60) and the optical band gap calculated from the E04 method varied marginally from about 2.85 to 3.17 eV. The room temperature photoluminescence (PL) peak energy and intensity showed a prominent shift to a maximum value of about 2.17 eV corresponding to maximum PL intensity at a moderate hydrogen dilution of about 30. The PL intensity showed a strong dependence on the hydrogen dilution variation.

Effect of Work of Adhesion on Nanoindentation

Three adhesion contact models, JKR (Johnson-Kendall-Roberts), DMT (Derjaguin-Muller-Toporov) and MD (Maugis-Dugdale) are compared with the Hertz model in dealing with the nano-contact problems. It has been shown that the dimensionless load parameter, $\bar{P}=P/(\pi\Delta\gamma R)$, and the transition parameter, $\Lambda$, have significant influences on the contact stiffness (contact area) at micro/nano-scale and should not be ignored in shallow nanoindentation.

The temperature dependence of effective thermal conductivity of open-celled steel alloy foams

The effective thermal conductivity of steel alloy FeCrAlY (Fe-20 wt.% Cr-5 wt.% Al-2 wt.% Y-20 wt.%) foams with a range of pore sizes and porosities was measured between 300 and 800 K, under both vacuum and atmospheric conditions. The results show that the effective thermal conductivity increases rapidly as temperature is increased, particularly in the higher temperature range (500-800 K) where the transport of heat is dominated by thermal radiation. The effective conductivity at temperature 800 K can be three times higher than that at room temperature (300 K). Results obtained under vacuum conditions reveal that the effective conductivity increases with increasing pore size or decreasing porosity. The contribution of natural convection to heat conduction was found to be significant, with the effective thermal conductivity at ambient pressure twice the value of vacuum condition. The results also show that natural convection in metal foams is strongly dependent upon porosity. © 2003 Elsevier B.V. All rights reserved.

High temperature direct double side cooled inverter module for hybrid electric vehicle application

In this paper a novel approach to the design and fabrication of a high temperature inverter module for hybrid electrical vehicles is presented. Firstly, SiC power electronic devices are considered in place of the conventional Si devices. Use of SiC raises the maximum practical operating junction temperature to well over 200°C, giving much greater thermal headroom between the chips and the coolant. In the first fabrication, a SiC Schottky barrier diode (SBD) replaces the Si pin diode and is paired with a Si-IGBT. Secondly, double-sided cooling is employed, in which the semiconductor chips are sandwiched between two substrate tiles. The tiles provide electrical connections to the top and the bottom of the chips, thus replacing the conventional wire bonded interconnect. Each tile assembly supports two IGBTs and two SBDs in a half-bridge configuration. Both sides of the assembly are cooled directly using a high-performance liquid impingement system. Specific features of the design ensure that thermo-mechanical stresses are controlled so as to achieve long thermal cycling life. A prototype 10 kW inverter module is described incorporating three half-bridge sandwich assemblies, gate drives, dc-link capacitance and two heat-exchangers. This achieves a volumetric power density of 30W/cm3.