Sharif Digital Repository

Anodic aluminum oxide (AAO) was used as a template to prepare highly ordered Ni-Fe-Co alloy nanowire arrays. This membrane was fabricated with two-step anodizing method. It is found that there is an optimum barrier thickness to obtain a successful electrodeposition in pores of AAO. The thickness of barrier layer can be modified by additional electrochemical process after completing the anodizing step. Barrier layer thinning can create a rooted structure at the bottom side of the AAO pores and the electrodeposited nanowire arrays. The triple Ni-Fe-Co alloy was deposited in AAO membrane by ac voltage in a simple sulfate bath. The composition of nanowires shows anomalous deposition features... 

In this paper, results of an investigation on strain hardening mechanisms of aged AEREX350 alloy during room temperature compression testing are reported. TEM studies were conducted on commercial samples aged at 850 °C both before and after deformation in a strain range of 0.15-0.27. It was found that only coherent γ′ precipitates with L12 structure formed in these samples prior to deformation. TEM studies also showed twin intersections in the deformed samples. Based on these observations, it is suggested that the high strain hardening rate of the aged material in this strain range is mainly related to the formation of intersecting deformation twins. This is attributed to the decrease in the... 

A mathematical model for cold rolling of two-layer strip is proposed using the upper bound theorem to investigate the plastic deformation behavior of the strip at the roll gap. The effects of total thickness reduction on the rolling power, rolling force, thickness reductions of each layer, and bonding strength of bimetal strip are discussed. Furthermore, experiments on two-layer strip rolling are conducted by employing aluminum-tin alloy and mild steel as the layers of the two-layer strips. It is found that all of theoretical predictions are in good agreement with the experimental measurements. Through the study, it becomes clear that the proposed analytical model is applicable for... 

The structure, age hardening response, precipitate type and hardness of A319 cast aluminum alloy without and with zirconium addition were investigated. The as-solutionized and artificially-aged hardness values were higher for the Zr-containing alloy. This is believed to be a consequence of the precipitation of Al3Zr particles produced during sufficiently long solutionizing treatments. © 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved  

We have applied Rosenbrock's optimization algorithm to obtain the optimized efficiency of a solar cell and its structural parameters. To obtain these parameters, we have developed a computer program for simultaneous optimization and simulation of the solar cell. We have used experimental data on the electrical and optical properties of a-Si1-xCx layers, put them into the written code and obtained the optimized parameters of this solar cell. The maximum efficiency is 6.32% which is close to one experimental result. © 2004 Elsevier B.V. All rights reserved  

The dendritic structure of a cast ZA27 alloy can be transformed into a globular structure, if it is cold worked prior to being held in a semi-solid condition. The globular or the equiaxed particles are surrounded by the lower melting matrix. The dendritic structure was swaged and recrystallised prior to holding in a semi-solid state in this investigation. The semi-solid holding of the alloy at temperatures above and below that of peritectic reaction was carried out for various lengths of time. It was shown that the liquid fraction is decreased to below the peritectic temperature which leads to a reduction of lubrication between the solid globules and an increasing deformation force. Holding... 

Ni-Fe and the Ni-Fe-Cr-Mo alloy films were electrodeposited from a chloride solution containing complexing compounds on ITO/glass substrates. AFM studies revealed a spherical structure for the alloy films with roughnesses from 10 up to 50 nm. The Ni-Fe-Cr-Mo alloy films were found to have a fine-grain structure. The quaternary alloy compounds containing up to 4% Cr and 2% Mo showed higher resistivity and little decrease in magnetoresistance (MR) relative to the Ni80Fe20 alloy compound. The MR of the quaternary alloy compounds was decreased for higher Cr and Mo contents. Moreover, the anisotropy (AMR) was also decreased by the addition of Cr and Mo to Permalloy films. Auger studies indicated... 

Shape Memory Alloys (SMA's) are inherently non-linear devices exhibiting significant hysteresis in their stress-strain-temperature characteristic. We have used the variable sub-layer SMA model of Ikuta [3] to extract the advanced dynamic model of our proposed varying stress SMA actuator. A nonlinear finite element analysis was used to model the proposed bending spring in the actuator and the extended variable sub-layer model of Ikuta was considered to extract stress-displacement relations. Finally, these two models are combined with thermo dynamic model of SMA and a schematic flowchart is proposed to calculate SMA resultant strain under an arbitrary current input. At the end, we applied this... 

In this work, milled Nd12.8Fe79.8B7.4-type powders with three different oxygen contents were processed into sintered anisotropic magnets via a standard powder metallurgy technique. Minimizing the oxygen content within the powder material, resulted in an almost full densification in the sintered magnets even at the lower end of the sintering temperature limit. Under this condition, the amount of hard magnetic Φ phase (Nd2Fe14B) was maximized in the structure of sintered bodies, which resulted in the highest energy density [BHmax] values. In the sintered magnets made from the powder with a higher oxygen content, full densification could only be obtained at the upper end of the sintering... 

In recent years, there have been some endeavors in order to characterize and model Shape Memory Alloy (SMA) behavior both in tension and compression. However, the one-dimensional behavior of SMA has been mostly studied for the case of wire elements subjected to tension. The objective of this paper is to analyze the behavior of Ni-55.7% wt Ti SMA in tension, compression, and at various temperatures. The effects of cycling, annealing, and friction on the mechanical behavior of this material in compression are discussed as well and, where applicable, compared to those of tension. The compressed SMA rings are finally used as clamping-force actuators in loosed bolted joints. In the second part of... 

The mathematical modeling of a bolted joint with a Shape Memory Alloy (SMA) actuator ring is presented. In this way, phase transformation, constitutive and displacement compatibility equations are used. The obtained model is utilized to show how the application of the SMA actuator ring in the bolted joint can help the joint to recover a significant amount of its lost clamping force. The model is run using the experimental data obtained for the Ni-55.7%wt Ti SMA in the companion paper (Part 1). The mechanical properties of SMA are calculated using the mentioned equations and compared to the experimental findings. It is observed that the final clamping force obtained theoretically is close to... 

Commercially pure nickel-titanium powders were mechanically milled in a vertical attritor mill under protective atmosphere for various times from 10 to 24 hr. Products were then compacted and sintered at different temperatures for different times. Amorphization and interatomic phase formation were determined by X-ray diffractometry, scanning electron microscopy, and differential scanning calorimetry. Porosity, virtual density, transition temperatures, and the amount of Ni3Ti first increased and then decreased with the milling time. Presence of oxygen in the milling atmosphere showed partial crystallization of NiTi intermetallic compound accompanied by titanium oxide formation  

The concentration distribution and microstructure of NiTi shape memory alloys produced in vacuum induction furnaces operating at high and medium frequencies are compared with those of materials melted in vacuum resistance furnaces. The production procedure consisted of charging pure metals into a graphite crucible; raising the temperature to 1450°C under vacuum; holding the materials in high and medium frequency induction and resistance furnaces for 3, 5, and 120 min under vacuum; and allowing alloys to solidify in the crucibles under the same vacuum. The procedures in each of the three furnaces were made as similar as possible. Chemical composition, microstructure, and surface hardness of... 

Tearing energy of AA5010 aluminum alloy sheets has been studied by the single tensile testing (STT) and multiple tensile testing (MTT) methods. The total energy required to tear the specimens was assumed to be composed of two components; one associated with uniform plastic deformation, which occurs in the work-hardening range of the material, and the other with post-uniform deformation and tearing which leads to the failure of the specimens. In the STT method, tearing energy was calculated by subtracting the plastic deformation energy, dissipated in the uniform deformation range, from the total energy absorbed by a single specimen during tension. In the MTT method, which uses different... 

In the present paper, employing compression experiments for three grades of low carbon steel, the effects of deformation condition and chemical composition on the occurrence of dynamic strain ageing are studied. Also, based on the achieved results, the flow behavior of steels under warm deformation conditions is predicted for the employed steels. The results show that both chromium and niobium postpone the happening of serrated flow and shifts the serrated flow region to lower temperatures in comparison with low carbon steel, while the activation energy for commencing dynamic strain ageing increases. © 2003 Elsevier Science B.V. All rights reserved  

Cyclic voltammetry and transient time (τ) measurements have been used to characterize the system, while potentiostatic I-t transients have been recorded to obtain the nucleation and growth mechanism. The electrodeposition of nickel, iron and nickel-iron alloys on the platinum was studied by electrochemical techniques in the presence of complexing compounds. The cyclic voltammetry results clearly show that the electrodeposition of nickel, iron and nickel-iron alloys is a diffusion-controlled process with a typical nucleation mechanism. The redox potentials of the Ni and Fe are shifted to more cathodic potentials in the complexing electrolytes. In addition, the current transients reveal that... 

An approach for calculating weld efficiency from the results of a peel test has been developed for 5754-aluminum strips. The method is based on estimating the effective load-bearing area of peel test specimens. A convincing agreement between the results and the theoretical model-earlier developed by Wright et al. (Metals Technol. 5 (1978) 24)-has been found. The influence of surface expansion and rolling pressure on the weld efficiency has been studied by the new approach. © 2002 Elsevier Science B.V. All rights reserved  

This paper describes the influence of a fractional melting process on the reduction of interdendritic phases, which in turn have an impact on the tensile strength of ZA-27 alloys. The procedure consists of compressing a semi-solid specimen through a porous grinding disc, resulting on coarsening of the dendritic phase, reduction of the microporosity and homogenization of the alloy. © 2002 Elsevier Science B.V. All rights reserved