On the role of residual strain in controlling sensitisation of twin-boundary engineered type 304 stainless steel

Sensitisation in twin boundary engineered type 304 austenitic stainless steel (SS) was investigated using electrochemical potentiokinetic reactivation technique. As-received (AR) specimens of type 304 SS were given two solution-annealing treatments at 1000 °C for 0.5 and 2 h. Solution-annealed specimens were given a small strain of 5% using cold-rolling followed by strain–annealing (strain–annealing) at 927 °C for 24, 48, and 72 h. Electron backscatter diffraction analyses have shown increase in fraction of special boundaries $(\Sigma ?29)$ in two solution-annealed specimens. Twin-boundary engineered specimens were given two potential sensitisation treatments at 575 and 675 °C for 1 h. The increase in twin fraction and decrease in grain average misorientation (GAM) always resulted in reducing the extent of sensitisation. An exponential correlation between GAM and twin-fraction was established and increase in GAM always associated with increase in twin-fraction.     

Controlling End-Grain Corrosion of Austenitic Stainless Steels

SS 304L is widely used as a structural material in applications handling nitric acid such as nuclear fuel processing plants and nuclear waste management facilities. Bar, wire, and tubular products of this material are especially susceptible to end-grain corrosion in nitric acid environment. Such an attack takes place on the tubular and forged surfaces that are perpendicular to the hot-working direction and occurs as localized pitting type attack. This study shows that the possible reasons for the directional nature of end-grain attack are the manganese sulfide inclusions aligned along the hot-working direction and/or segregation of chromium along the flow lines during the fabrication stage itself. It has been shown in this study that controlled solution annealing, laser surface remelting, and weld overlay can be used to avoid/minimize end-grain corrosion. Different annealing heat-treatments were carried out on two heats of SS 304L tube and susceptibility to corrosion was measured by ASTM A 262 practice C and electrochemical potentiokinetic reactivation (EPR) test. Solution annealing at 950 °C for 90 min has been shown to increase the resistance to end-grain corrosion. Laser surface remelting using continuous wave CO₂ laser under argon shield and weld deposition (overlay) using SS 308L material were done on the end faces of the tubes. These samples were completely resistant to end-grain corrosion in nitric acid environments.     

RF sputtering: A viable tool for MEMS fabrication

Fabrication of Micro-Electro-Mechanical-Systems (MEMS) requires deposition of films such as SiO₂, Si₃N₄, ZnO, polysilicon, phosphosilicate glass (PSG), Al, Cr-Au, Pt, etc. for use as structural, sacrificial, piezoelectric and conducting material. Deposition of these materials at low temperature is desirable for fabricating sensors/actuators on temperature-sensitive substrates and also for integrating MEMS structures on silicon in post-CMOS processing procedures. Plasma enhanced chemical vapour deposition (PECVD) and sputtering are amongst potential techniques for preparing films for MEMS fabrication at comparatively low temperatures. The sputtering technique has an added advantage that the process is carried out in an inert ambient (argon) and chemically sensitive substrate/sacrificial layers can be used in realization of MEMS. Furthermore, the same system can be used for depositing dielectric, piezoelectric and conducting materials as per requirement in the fabrication sequence. This enables rapid low-cost prototyping of MEMS with minimum fabrication facilities. In the present work, we report preparation, characterization and application of RF sputtered SiO₂, Si₃N₄ and ZnO films for MEMS fabrication. The effect of RF power, sputtering pressure and target-to-substrate spacing was investigated on the structural and other properties of the films. The residual stress in the films was obtained usingwafer curvature measurement technique. The deposition parameters are optimized to obtain low stress films of SiO₂ and Si₃N₄. The self-heating of the substrate during deposition was advantageously exploited to obtain highly c-axis oriented films of ZnO without any external heating. A variety of MEMS structures such as cantilever beams, micro-bridges, diaphragms, etc. are demonstrated using bulk, surface and surface-bulk micromachining techniques.     

Evaluation of catalytic efficiency of a triple-site phase transfer catalyst and the kinetics of dichlorocarbene addition to 5-vinyl-2-norbornene

A new triple-site phase transfer catalyst viz., 1,3,5-tris(ethylmethyleneammonium bromide)-2,4,6-trimethyl benzene (TEMABTB) was prepared by the quaternization of 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene using triethylamine and its catalytic efficiency was ascertained by following the kinetics of dichlorocarbene addition of 5-vinyl-2-norbornene. Comparative catalytic activity of various onium salts (single-, di- and tri-site) have been investigated in detail. Based on the kinetic results obtained, a plausible mechanism has been proposed.     

Characterisation of the oxide layer on carbon steel during hot conditioning of primary heat transport systems in heavy-water reactors

The corrosion layer formation on carbon steel during hot conditioning of primary heat transport systems of pressurised heavy-water reactors has been characterised using ex-situ methods (gravimetry, electron microscopy, X-ray diffractometry). In addition, the electric and electrochemical properties of the corrosion layers have been followed in-situ by voltammetry and electrochemical impedance spectroscopy during exposure to simulated hot conditioning water chemistry. The corrosion layer formed has been found to be a bilayer oxide of the inverse spinel type. The impedance data have been quantitatively interpreted using the Mixed-Conduction Model for oxide films allowing for the estimation of certain kinetic parameters at the compact layer/electrolyte interface. The obtained results point out to the fact that the electric and electrochemical properties of the carbon steel are determined by the processes in a thin n-type semiconductor layer and at its interface with the electrolyte.     

Secure Distance Based Improved Leach Routing to Prevent Puea in Cognitive Radio Network

Wireless Personal Communications - Routing in cognitive radio networks (CRNs) faces numerous limitations in misbehaving activities and secure the routing requests and reply messages. In this...     

Performance Analysis of Robust GRCR Based Spectrum Detector Using Compressed Sensing with Non-reconstruction Model

Wireless Personal Communications - In cognitive radio applications, a robust detector is essentially required for the determination of spectrum sensing. Gerschgorin radii and centers ratio (GRCR)...     

The role of niobium carbide in radiation induced segregation behaviour of type 347 austenitic stainless steel

The effect of niobium carbide precipitates on radiation induced segregation (RIS) behaviour in type 347 stainless steel was investigated. The material in the as-received condition was irradiated using double-loop 4.8 MeV protons at 300 °C for 0.43 dpa (displacement per atom). The RIS in the proton irradiated specimen was characterized using double-loop electrochemical potentiokinetic reactivation (DL-EPR) test followed by atomic force microscopic examination. The nature of variation of DL-EPR values with the depth matched with the variation of the calculated irradiation damage (dpa) with the depth. The attack on grain boundaries during EPR tests was negligible indicating absence of chromium depletion zones. The interface between niobium carbide and the matrix acts as a sink for point defects generated during irradiation and this had reduced point defect flux toward grain boundaries. The attack was noticed at a few large cluster of niobium carbide after the DL-EPR test at the depth of maximum attack for the irradiated specimen. Pit-like features were not observed within the matrix indicating the absence of chromium depletion regions within the matrix.     

Use of HPLC to monitor olefins,dienes, and aromatics in the dehydrogenated products of higher n-paraffins

The linear higher olefins are generated through catalytic dehydrogenation of long-chain linear paraffins. During the catalytic dehydrogenation, a variety of dienes and aromatics are also formed. These side products not only cause coking of the catalyst, but also hamper in the reaction course of olefins with other substrate. A method has been developed based on the High-Performance Liquid Chromatography with Refractive Index detection for simultaneous estimation of olefins, dienes, and aromatics in the catalytic dehydrogenated product of model compound decane. The application of method for monitoring of the dehydrogenated stream from C10-C14 n-paraffins has also been discussed.