Characterization of Cold-Sprayed IN625 and NiCr Coatings

Ni-based coatings IN625^® and Ni20%Cr were cold sprayed on a low-alloy steel (AISI 4130) substrate, using Helium as the process gas. Dense coatings up to 3-mm thickness were deposited, having a hardness of 500-550 HV. The coatings showed a hardness maximum, with heat treatment, before dropping to a lower value. The coating microstructure revealed two distinct types of regions, comprising grains with a high dislocation density and elongated shear bands having twins. Heat treatment led to 30-50 nm grains in the IN625 coating, and >1-2 μm grains for NiCr. Both coatings showed a compressive residual stress in the as-sprayed condition, which relaxed to a zero residual stress, at 650 °C. The NiCr coatings showed a much higher compressibility, as compared to IN625. The IN625 coatings induced a much larger deformation on the 4130 steel. Overall, while both types of Ni-based alloy coatings showed similarities in terms of hardness and microstructure, they revealed distinct differences in their deformability, thermal stability, and substrate deformation, indicating a different behavior between a binary solid solution (NiCr) as compared to a multielement solid solution (IN625), as elucidated via a detailed characterization of these coatings.     

Dry Sliding Wear Behavior of Ti–6Al–4V Implant Alloy Subjected to Various Surface Treatments

Titanium alloys are extensively used in various fields of engineering, medicine, aerospace, marine due to their excellent mechanical properties. Their usage is more pronounced today in the field of biomedical implants due to superior biocompatibility, corrosive resistance and high strength. However, titanium alloys have poor wear resistance due to high coefficient of friction. Poor abrasive wear resistance results in the formation of wear debris at the implant area causing toxicity, inflammation and pain. Surface treatment of the implant alloy through heat treatment, application of protective coatings and introduction of compressive residual stresses by shotpeening are some of the methods to mitigate wear of the implant alloy. In this work Ti?C6Al?C4V implant alloy is treated under various conditions of heat treatment and shotpeening operations on a pin on disc wear testing machine. Scanning electron micrograph along with energy dispersive spectrometry analysis is done to authenticate the experimental results obtained during the wear testing procedure.     

Adsorptive removal of direct azo dye from aqueous phase onto coal based sorbents: a kinetic and mechanistic study

This communication presents the results pertaining to the investigation conducted on color removal of trisazo direct dye, C.I.Direct Brown 1:1 by adsorption onto coal based sorbents viz. charfines, lignite coal, bituminous coal and comparing results with activated carbon (Filtrasorb-400). The kinetic sorption data indicated the sorption capacity of the different coal based sorbents. The sorption interaction of direct dye on to coal based sorbents obeys first-order irreversible rate equation and activated carbon fits with the first-order reversible rate equation. Intraparticle diffusion studies revealed the dye sorption interaction was complex and intraparticle diffusion was not only the rate limiting step. Isothermal data fit well with the rearranged Langmuir adsorption model. R(L) factor revealed the favorable nature of the isotherm of the dye-coal system. Neutral solution pH yielded maximum dye color removal. Desorption and interruption studies further indicated that the coal based sorbents facilitated chemisorption in the process of dye sorption while, activated carbon resulted in physisorption interaction.     

A monolithic 5 Gb/s p-i-n/HBT integrated photoreceiver circuit realized from chemical beam epitaxial material

The authors report on a high performance monolithic photoreceiver fabricated from chemical beam epitaxy (CBE) grown InP/InGaAs heterostructures, incorporating a p-i-n photodetector followed by a transimpedance preamplifier circuit configured from heterojunction bipolar transistors (HBTs). The optoelectronic integrated circuit (OEIC) was fabricated on a semi-insulating Fe-doped InP substrate. Microwave on-wafer measurements of the frequency response of the transistors yielded unity current gain cutoff frequencies of 32 GHz and maximum oscillation frequencies of 28 GHz for collector currents between 2 and 5 mA. The photoreceiver was operated up to 5 Gb/s, at which bit rate a sensitivity of -18.8 dBm was measured at a wavelength of 1.5 mu m. The results demonstrate that the CBE growth technique is suitable for high performance HBT-based OEICs.<>     

A Servo-Control System Using a Self-Controlled Synchronous Motor (SCSM) with Sliding Mode Controller

The application of sliding mode control for improving the dynamic response of a self-controlled synchronous motor (SCSM) based position servo system is presented. Sliding mode control gives fast dynamic response with no overshoot and zero steady-state error. It has the important feature of being highly robust, i.e., insensitive to plant parameter variations and external disturbances. A design procedure is outlined for the sliding mode controller for a servo driving using the self-controlled synchronous motor. A novel scheme for fast torque reversal is proposed and implemented. Digital computer simulation of the overall position control system is carried out using a time domain model in the d-q reference frame. The rigorous simulation of the servo system with sliding mode control shows the existence of limit cycles in the position response with certain type of speed encoder. Experimental results are provided for a 3-hp synchronous motor based servo drive. The sliding mode controller is implemented using a single-board microcomputer which controls a GTO thyristor current source inverter to drive the motor.     

Evolution of mixing in a microfluidic reverse-staggered herringbone micromixer

Microfluidic platforms offer a variety of advantages including improved heat transfer, low working volumes, ease of scale-up, and stronger user control on operating parameters. However, flow within microfluidic channels occurs at low Reynolds number (Re), which makes mixing difficult to accomplish. Adding V-shaped ridges to channel walls, a pattern called the staggered herringbone design (SHB), alleviates this problem by introducing transverse flow patterns that enable enhanced mixing. Building on our prior work, we here developed a microfluidic mixer utilizing the SHB geometry and characterized using CFD simulations and complimentary experiments. Specifically, we investigated the performance of this type of mixer for unequal species diffusivities and inlet flows. A channel design with SHB ridges was simulated in COMSOL Multiphysics® software under a variety of operating conditions to evaluate its mixing capabilities. The device was fabricated using soft-lithography techniques to experimentally visualize the mixing process. Mixing within the device was enabled by injecting fluorescent dyes through the device and imaging using a confocal microscope. The device was found to efficiently mix fluids rapidly, based on both simulations and experiments. Varying Re or species diffusion coefficients had a weak effect on the mixing profile, due to the laminar flow regime and insufficient residence time, respectively. Mixing effectiveness increased as the species flow rate ratio increased. Fluid flow patterns visualized in confocal microscope images for selective cases were strikingly similar to CFD results, suggesting that the simulations serve as good predictors of device performance. This SHB mixer design would be a good candidate for further implementation as a microfluidic reactor.