Mechanical Engineering

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Friction stir processing (FSP) was carried out for AE42 Mg alloy resulting in significant grain refinement and uniform dispersion of fine in situ precipitates. The average grain size was 20°μm for the as-cast AE42 alloy, which was refined to 1.5°μm after FSP. Tensile testing revealed significantly higher modulus and yield strength for the friction stir processed (FSPed) specimen with some improvement in ductility. The fractured surface of the as-cast alloy showed ridges, grooves and cracks indicating brittle failure. In contrast, the fractured surface of FSPed specimen showed fine dimples, characteristic of ductile failure. Nano-indentation was used to analyze the variation of hardness and modulus across the nugget zone of the FSPed specimen. FSPed specimen demonstrated greater strain-hardening tendency compared to the as-cast alloy. Enhancing the mechanical properties of Mg alloys can result in substantial cost savings across a number of industries and have wide economic impact. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

World University root node

(SoE) School of Engineering

Advanced Engineering Materials

Enhancing the mechanical properties of AE42 magnesium alloy through friction stir processing

We demonstrate the refinement and uniform distribution of the crystalline dendritic phase by friction stir processing (FSP) of titanium based in situ ductile-phase reinforced metallic glass composite. The average size of the dendrites was reduced by almost a factor of five (from 24 μm to 5 μm) for the highest tool rotational speed of 900 rpm. The large inter-connected dendrites become more fragmented with increased circularity after processing. The changes in thermal characteristics were measured by differential scanning calorimetry. The reduction in crystallization enthalpy after processing suggests partial devitrification due to the high strain plastic deformation. FSP resulted in increased hardness and modulus for both the amorphous matrix and the crystalline phase. This is explained by interaction of shear bands in amorphous matrix with the strain-hardened dendritic phase. Our approach offers a new strategy for microstructural design in metallic glass composites. © 2014 National Institute for Materials Science.

Fulltext

Science and Technology of Advanced Materials

Controlling the length scale and distribution of the ductile phase in metallic glass composites through friction stir processing

The mass production of printed electronics can be achieved by roll-to-roll (R2R) printing system, so highly accurate web tension is required that can minimize the register error and keep the thickness and roughness of printed devices in limits. The web tension of a R2R system is regulated by the use of integrated load cells and active dancer system for printed electronics applications using decentralized multi-input-single-output (MISO) regularized variable learning rate backpropagation artificial neural networks. The active dancer system is used before printing system to reduce disturbances in the web tension of process span. The classical PID control result in tension spikes with the change in roll diameter of winder and unwinder rolls. The presence of dancer in R2R system shows that improved web tension control in printing span and the web tension can be enhanced from 3.75 N to 4.75 N. The overshoot of system is less than ±2.5 N and steady state error is within ±1 N where load cells have a signal noise of ±0.7 N. The integration of load cells and active dancer with self-adapting neural network control provide a solution to the web tension control of multispan roll-to-roll system. © Chinese Mechanical Engineering Society and Springer-Verlag Berlin Heidelberg 2014.

Chinese Journal of Mechanical Engineering (English Edition)

Web tension regulation of multispan roll-to-roll system using integrated active dancer and load cells for printed electronics applications

In this paper, slurry erosion performance of high velocity flame-sprayed Ni-Al2O3 based coatings was evaluated. The coatings were deposited on a hydroturbine steel (CA6NM) by varying the content of Al 2O3 in Ni. Using jet-type test rig, erosion behavior of coatings and bare steel was evaluated at different impingement angles. Detailed investigation of the surface morphology of the eroded specimens was undertaken using SEM/EDS to identify potential erosion mechanism. A parameter named "erosion mechanism identifier" (ξ) was used to predict the mode of erosion. It was observed that the coating prepared using 40 wt.% of Al 2O3 showed a highest resistance to erosion. This coating enhanced the erosion resistance of the steel by 2 to 4 times. Spalling in the form of splats and chunks of material (formed by interlinking of cracks) along with fracture of Al2O3 splats were identified as primary mechanisms responsible for the loss of coating material. The erosion mechanism of coatings and bare steel predicted by ξ was in good agreement with that observed experimentally. Among different parameters, a function of fracture toughness (K IC) and hardness (H) showed excellent correlation with erosion resistance of coatings at both the impingement angles. © 2013 ASM International.

Journal of Thermal Spray Technology

Slurry erosion performance of Ni-Al2O3 based thermal-sprayed coatings: Effect of angle of impingement

This paper is focused on printed techniques for the fabrication of hybrid structure of silver (Ag) grid/poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) (PEDOT:PSS) on polyethylene terepthalate (PET) as a flexible substrate. Ag grid has been printed on PET substrate by using gravure offset printing process, followed by PEDOT:PSS thin film deposition on Ag grid through electrohydrodynamic atomization (EHDA) technique. The important parameters for achieving uniform hybrid structure of Ag grid/PEDOT:PSS through printed techniques have been clearly discussed. Field emission scanning electron microscope studies revealed the uniformity of printed Ag grid with homogeneous deposition of PEDOT:PSS on Ag grid. The optical properties of Ag grid/PEDOT:PSS were measured by UV-visible spectroscopy, which showed nearly 80~82% of transparency in the visible region and it was nearly same as PEDOT:PSS thin film on PET substrate. Current-voltage (I-V ) analysis of fabricated hybrid device by using printed Ag grid/PEDOT:PSS as a bottom electrode showed good rectifying behavior with possible interfacial mechanisms. Capacitance-voltage (C-V ) analysis was carried over different frequencies. These results suggest that fabrication of hybrid structure through printed techniques will play a significant role in mass production of printed electronic devices for commercial application by using flexible substrate. Copyright © 2013 American Scientific Publishers All rights reserved.

Journal of Nanoscience and Nanotechnology

Structural and electrical properties of Ag grid/poly(3,4- ethylenedioxythiophene):Poly(styrene sulfonate) coatings for diode application through advanced printing technology

Slurry erosion is a major problem in hydroturbines and other fluid machineries wherein erodent particles entrained in carrier fluid impinge upon the target surface to cause its degradation. Several possible alternative solutions are available to control slurry erosion; however, surface coatings developed using thermal spraying are mostly used owing to their versatile nature. In this work, Ni based thermal spray coatings were deposited on a commonly used hydroturbine steel (CA6NM), with Al2O3 mixed in different proportions. Coatings were developed using high velocity flame spray process (HVFS). Slurry erosion performance of prepared coated and bare steel was investigated using a specially designed jet type test rig with sand as erodent particles. To investigate the effect of concentration on erosion behavior, sand was mixed in water at two different levels, 0.1 wt % and 0.5 wt. %. It was observed that all the coatings helped in improving the erosion resistance of the steel with one containing 40 wt % Al2O3 showing the maximum improvement. This was related to the microstructure, which controlled the micro hardness and fracture toughness of the coatings. Shielding effect of the rebounding particles was found to have profound effect as erosion rates did not show similar augmentation with concentration. Fracturing of alumina phase along with removal of coating in form of splats was observed to be prominent erosion mechanism. © 2013 The Authors. Published by Elsevier.

Procedia Engineering

Slurry erosion of thermal spray coatings: Effect of sand concentration

In the current work, Ni-Al2O3 based composite coatings were fabricated using High Velocity Flame Spray (HVFS) system. The effect of alumina content on the microstructure and various mechanical properties viz. microhardness, fracture toughness, density, residual stress and scratch resistance was studied. Microstructure of the coating was characterized with the help of Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS), Optical Microscope (OM) and X-ray Diffraction (XRD). It was observed that microstructural properties such as splat size, porosity, un-melted particles and surface roughness are highly affected by the alumina content in the coatings. Microhardness improved with the rise in alumina fraction and a maximum of 1151HV could be achieved with 60wt.% alumina blending. Cracking and spallation were found to be the mechanisms responsible for damage of coatings during scratch testing. A model has been proposed to explain the variation in surface roughness and porosity of the Ni-Al2O3 coatings based on coating build-up mechanism. © 2012 Elsevier B.V.

Surface and Coatings Technology

Microstructural and mechanical characterization of thermal sprayed nickel-alumina composite coatings

A microstructure-based internal state variable (ISV) plasticity-damage model was used to model the mechanical behavior of a porous FC-0205 steel alloy that was procured via a powder metal (PM) process. Because the porosity was very high and the nearest neighbor distance (NND) for the pores was close, a new pore coalescence ISV equation was introduced that allows for enhanced pore growth from the concentrated pores. This coalescence equation effectively includes the local stress interaction within the interpore ligament distance between pores and is physically motivated with these highly porous powder metals. Monotonic tension, compression, and torsion tests were performed at various porosity levels and temperatures to obtain the set of plasticity and damage constants required for model calibration. Once the model calibration was achieved, then tension tests on two different notch radii Bridgman specimens were undertaken to study the damage-triaxiality dependence for model validation. Fracture surface analysis was performed using scanning electron microscopy (SEM) to quantify the pore sizes of the different specimens. The validated model was then used to predict the component performance of an automotive PM bearing cap. Although the microstructure-sensitive ISV model has been employed for this particular FC-0205 steel, the model is general enough to be applied to other metal alloys as well. © 2013 by ASME.

Journal of Engineering Materials and Technology, Transactions of the ASME

Plasticity and fracture modeling/experimental study of a porous metal under various strain rates, temperatures, and stress states

Performance of Ni-Al2O3 based composite coatings was evaluated under slurry erosion condition. Erosion resistance was correlated with different properties of the coatings. It was observed that fracture toughness is an important parameter that controls the erosion resistance of coatings. Content of alumina was found to have significant influence on the erosion performance and material removal mechanism of the coatings. Erosion rates were predicted using fracture-contact model. The results were observed to lie in close proximity to the experimental results. Cracking and spalling of coating, fracture of reinforcing phase and removal of splats were observed to be the primary erosion mechanisms. © 2013 Elsevier Ltd.

Tribology International

Slurry erosion performance of Ni-Al2O3 based composite coatings

A finite element based numerical method is employed to analyze the wave radiation by multiple or a group of cylinders in the time domain. The nonlinear free surface and body surface boundary conditions are satisfied based on the perturbation method up to the second order. The first- and second-order velocity potential problems at each time step are solved through a Finite Element Method (FEM). The matrix equation of the FEM is solved through iteration and the initial solution is obtained from the result at the previous time step. The three-dimensional (3-D) mesh required is generated based on a two-dimensional (2-D) hybrid mesh on a horizontal plane and its extension in the vertical direction. The hybrid mesh is generated by combining an unstructured grid away from cylinders and two structured grids near the cylinder and the artificial boundary. The fluid velocity on the free surface and the cylinder surface are calculated by using a differential method. Results for various configurations including the cases of two cylinders and four cylinders and a group of eighteen cylinders are obtained to show the joint influences of cylinders on the first- and second-order waves and forces, including the effects of spacing ratios and wave frequency on the second order waves and the mean force, in particular. © 2013 Publishing House for Journal of Hydrodynamics.