Influence of Tool Geometry and Process Parameters on the Properties of Friction Stir Spot Welded Multiple (AA 5754 H111) Aluminium Sheets.

Friction stir spot welding is an emerging spot-welding technology that offers opportunities for joining a wide range of materials with minimum energy consumption. To increase productivity, the present work addresses production challenges and aims to find solutions for the lap-welding of multiple ultrathin sheets with maximum productivity. Two convex tools with different edge radii were used to weld four ultrathin sheets of AA5754-H111 alloy each with 0.3 mm thickness. To understand the influence of tool geometries and process parameters, coefficient of friction (CoF), microstructure and mechanical properties obtained with the Vickers microhardness test and the small punch test were analysed. A scanning acoustic microscope was used to assess weld quality. It was found that the increase of tool radius from 15 to 22.5 mm reduced the dwell time by a factor of three. Samples welded with a specific tool were seen to have no delamination and improved mechanical properties due to longer stirring time. The rotational speed was found to be the most influential parameter in governing the weld shape, CoF, microstructure, microhardness and weld efficiency. Low rotational speeds caused a 14.4% and 12.8% improvement in joint efficiency compared to high rotational speeds for both tools used in this investigation

Bridging the Mid-Infrared-to-Telecom Gap with Silicon Nanophotonic Spectral Translation

Expanding far beyond traditional applications in optical interconnects at telecommunications wavelengths, the silicon nanophotonic integrated circuit platform has recently proven its merits for working with mid-infrared (mid-IR) optical signals in the 2-8 {\mu}m range. Mid-IR integrated optical systems are capable of addressing applications including industrial process and environmental monitoring, threat detection, medical diagnostics, and free-space communication. Rapid progress has led to the demonstration of various silicon components designed for the on-chip processing of mid-IR signals, including waveguides, vertical grating couplers, microcavities, and electrooptic modulators. Even so, a notable obstacle to the continued advancement of chip-scale systems is imposed by the narrow-bandgap semiconductors, such as InSb and HgCdTe, traditionally used to convert mid-IR photons to electrical currents. The cryogenic or multi-stage thermo-electric cooling required to suppress dark current noise, exponentially dependent upon the ratio Eg/kT, can limit the development of small, low-power, and low-cost integrated optical systems for the mid-IR. However, if the mid-IR optical signal could be spectrally translated to shorter wavelengths, for example within the near-infrared telecom band, photodetectors using wider bandgap semiconductors such as InGaAs or Ge could be used to eliminate prohibitive cooling requirements. Moreover, telecom band detectors typically perform with higher detectivity and faster response times when compared with their mid-IR counterparts. Here we address these challenges with a silicon-integrated approach to spectral translation, by employing efficient four-wave mixing (FWM) and large optical parametric gain in silicon nanophotonic wires

Refractive Index Sensor Based on a 1D Photonic Crystal in a Microfluidic Channel

A refractive index sensor has been fabricated in silicon oxynitride by standard UV lithography and dry etching processes. The refractive index sensor consists of a 1D photonic crystal (PhC) embedded in a microfluidic channel addressed by fiber-terminated planar waveguides. Experimental demonstrations performed with several ethanol solutions ranging from a purity of 96.00% (n = 1.36356) to 95.04% (n = 1.36377) yielded a sensitivity (Δλ/Δn) of 836 nm/RIU and a limit of detection (LOD) of 6 × 10−5 RIU, which is, however, still one order of magnitude higher than the theoretical lower limit of the limit of detection 1.3 × 10−6 RIU

An experimental study on lap joining of multiple sheets of aluminium alloy (AA 5754) using friction stir spot welding

Friction stir spot welding (FSSW) process is widely used in the automobile industry for a range of applications such as battery components, standard wire connectors and terminals. This manuscript addresses two grand challenges in the arena of FSSW, hitherto, unaddressed in the extant literature: (i) lap joining of thin sheets (0.3 mm thickness) of AA 5754 alloy and (ii) lap joining of more than two sheets using FSSW. To accomplish this task, a novel pinless convex shaped tool was designed to alter the stress state while gradually advancing the tool which led to achieving stress state necessary for obtaining defect free lap joints. The weld joints were inspected by optical microscopy, SEM imaging and analysed by nanoindentation tests and Vickers microindentation tests for assessment of the quality of the weld interface (WI). Process parameters of FSSW such as torque on the tool and axially applied load were used to analytically obtain the average local measure of peak normal and axial stresses as well as the coefficient of friction in the contact zone. In samples welded at low rotational speeds, strain-hardening mechanism was seen dominating in contrast to samples welded at higher rotational speeds, which showed thermal softening. As a direct consequence of this, the samples welded at low rotational speeds showed much higher hardness at the weld surface than the samples welded at higher speeds. A strong transition of strain hardening to thermal softening was noticeable beyond an applied strain rate of 400 s-1. This is a post-peer-review, pre-copyedit version of an article published in International Journal of Advanced Manufacturing Technology . The final authenticated version is available online at: http://dx.doi.org/10.1007/s00170-020-05214-

Growth of non-regular a-CNx : H cluster arrays on pulse plasma nitrided hot work steel samples

Samples made of hot work steel grade H11 were pulse plasma nitrided in hydrogen nitrogen mixture and post-nitrocarburized in carbon-containing discharge. Microhardness measurements, optical microscopy, SEM, Raman, XRD and infrared spectra analyses revealed the existence of a thin epsilon+ gamma compound zone onto 150 pin thick diffusion layer after plasma nitriding, while a dense 3 gm thick amorphous hydrogenated carbon nitride overcoating was grown during plasma post-processing in carbon-containing atmosphere. On the surface of plasma deposited hydrogenated carbonitride films intended for tribological applications non-regular arrays of different size conductive clusters were found. Similar arrays architecture, when obtained intentionally, could be used for the resonant optical connections in nanooptics and macro optics. Some coupled arrays, like the fiberoptic waveguide in fiber optics interferometers, were also observed. Computer simulation showed that in the case of similar geometry spherical Ag clusters deposited onto dielectric substrate the resonant interaction of light beam with coupled arrays is possible resembling to the light beam coupler on nanoscale. (c) 2005 Elsevier B.V. All rights reserved.32nd International Conference on Metallurgical Coatings and Thin Film, May 02-06, 2005, San Diego, C

Plasma post oxidation of nitrocarburized hot work steel samples

Pulse plasma oxidation of untreated, salt bath nitrocarburized and plasma nitrided/nitrocarburized samples made of hot work steel grade H11 was investigated. A continuous multi-step plasma processing was performed consisting of a half an hour plasma nitriding at 520 degreesC followed by 3.5 h nitrocarburizing at the same temperature and by a subsequent post-oxidation in a low current density H2O glow discharge during 45 min at 450 degreesC. The salt bath nitrocarburizing was carried out at a temperature of 580 degreesC for 210 min and was followed by the oil quench. In order to compare the oxide layer growth on the base material and on the epsilon-Fe-2(N,C)(1-x) layer, the salt bath treated sample. was half cut and plasma post-oxidized in a 80% H2O-20% H-2 glow discharge for 45 min at the temperature of 480 degreesC. In plasma processing pulse power supply was used with 57 mus pulse duration and 3 mus pulse pause. The surface structures were analyzed by optical microscopy, SEM and XRD, while Vickers microhardness test was used for measuring the surface microhardness and microhardness distribution over the sample cross sections. On the nitrocarburized surfaces XRD analyses revealed the existence of a superficial magnetite oxide layer and the presence of a e phase and a small amount of gamma phase, while a hematite Fe2O3 layer was formed on untreated sample surface. (C) 2003 Elsevier B.V. All rights reserved.30th International Conference on Metallurgical Coatings and Thin Films, Apr 28-May 02, 2003, San Diego, C

Pulsed plasma-oxidation of nitrided steel samples

Plasma nitrided/nitrocarburized samples made of steel grade DIN C15 were post oxidized in a mixtures of H-2 and O-2 gases using pulse power supply. Plasma nitrocarburizing post-oxidation were performed at 520 degreesC. The applied process is a combination of plasma nitriding, plasma nitrocarburizing and plasma-oxidation of the compound layer. Pulse plasma was used in all process steps at 5 kHz frequency and pause/pulse ratio 1:19. The XRD examination revealed the existence of the compound zone composed of of the gamma or gamma+ epsilon carbonitride phase with a thin overlayer of magnetite Fe3O4. The architecture of formed surface structure provides the unique mechanical and tribological properties with the diffusion zone responsible for load bearing capacity, wear and fatigue resistance and the double compound layer resistant to wear and corrosion. The results of Vickers microhardness measurements, optical microscopy, XRD and SEM analyses were presented. The obtained surface structures were compared with the samples salt bath nitrided in a conventional industrial unit. (C) 2003 Elsevier Science B.V. All rights reserved.8th International Conference on Plasma Surface Engineering, Sep 09-13, 2002, Garmisch Partenki, German

Characterization of parametric RF channelized receiver through time domain monitoring

We present the characterization of a parametric RF channelized receiver with 1GHz resolution. Instantaneous analysis is demonstrated and operating margins are studied from simultaneous monitoring of five sub-channels using real-time oscilloscope

Effect of surface oxide layers in Solid-State Welding of Aluminium Alloys - Review

This review sheds novel insights on the residual oxide behaviour of solid-state weld joints of aluminium alloys. Understanding the influence of oxides on the aluminium surface before and during welding, its impact on the weld structure and possible solutions for reducing its impact were addressed. The solid-state techniques most relevant to the transportation sector namely, diffusion bonding, friction stir spot welding and ultrasonic welding were surveyed, analysed and reviewed. During this analysis, the implication of the presence of oxides on aluminium substrate affecting the metallurgical characteristics of the weld joints were reviewed. Visible defects such as voids, delamination, kissing bond, and hook defects, and problems associated with these defects were analysed and few suggestions are made to partially overcome these issues