Microstructure, grain growth, and hardness during annealing of nanocrystalline Cu powders synthesized via high energy mechanical milling

Akbarpour, M.R.,Kim, H.S. Scientific and Technical Press ; Elsevier Science 2015 Materials & Design Vol.83 No.-

In this paper, the microstructure and hardness evolutions of commercially pure Cu subjected to high energy mechanical milling and subsequent annealing treatments in the temperature range of 400-700<SUP>o</SUP>C are investigated. The results demonstrated the simultaneous occurrence of recovery, recrystallization, and grain growth during annealing of the nanocrystalline Cu. The volume fraction of the recrystallized grains estimated using the grain orientation spread exhibits lower values as a result of its dynamic recovery at higher temperatures. The normal grain growth in the range of 400-600<SUP>o</SUP>C and significant abnormal grain growth at higher temperatures are observed during annealing. As a result of the abnormal grain growth, the microhardness value rapidly decreases for the sample annealed at 700<SUP>o</SUP>C. An analysis of the grain growth kinetics using the parabolic equation in the temperature range of 400-600<SUP>o</SUP>C reveals a time exponent of n~2.7 and an activation energy of 72.93kJ/mol. The calculated activation energy for the grain growth in the nanocrystalline Cu is slightly less than the activation energy required for the lattice diffusion. This low activation energy results from the high microstrain as well as the Zener-pinning mechanism that arises from the finely dispersed impurities drag effect.

Effect of nanoparticle content on the microstructural and mechanical properties of nano-SiC dispersed bulk ultrafine-grained Cu matrix composites

Akbarpour, M.R.,Salahi, E.,Alikhani Hesari, F.,Kim, H.S.,Simchi, A. Scientific and Technical Press ; Elsevier Science 2013 Materials & design Vol.52 No.-

In this study, the microstructural and mechanical features of monolithic pure Cu and Cu matrix nanocomposites reinforced with three different fractions (2, 4, and 6vol%) of SiC nanoparticles (n-SiC) fabricated via a combination of high energy mechanical milling and hot pressing techniques were investigated. The fabricated composites exhibited homogeneous distribution of the n-SiC with few porosities. It was found that the grain refinement, the planar features within the grains, and the lattice strains increase with increase in the n-SiC content. The yield and compressive strengths of the nanocomposites were significantly improved with increases in the n-SiC content up to 4vol%; then they decreased due to the weak interface strength at higher amounts of n-SiC content. This improvement was attributed to the grain refinement strengthening and homogeneous distribution of the n-SiC. Furthermore, studies on different strengthening mechanisms showed that Hall-Petch strengthening mechanism is the most important factor. The yield strength was calculated theoretically using common analytical models. Clyne approach showed good agreement with experimental data and were more accurate than the other methods developed for predicting the strength of metal matrix nanocomposites.

Microstructural development and mechanical properties of nanostructured copper reinforced with SiC nanoparticles

Akbarpour, M.R.,Salahi, E.,Hesari, F.A.,Yoon, E.Y.,Kim, H.S.,Simchi, A. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.568 No.-

Nanostructured Cu and Cu-2vol% SiC nanocomposite were produced by high energy mechanical milling and hot pressing technique. Microstructure development during fabrication process was investigated by X-ray diffraction, scanning electron microscope, scanning transmission electron microscope, and electron backscatter diffraction techniques. The results showed that the microstructure of copper and copper-based nanocomposite composed of a mixture of equiaxed nanograins with bimodal and non-random misorientation distribution. The presence of SiC nanoparticles refined the grain structure of the copper matrix while the fraction of low angle grain boundaries was increased. Evaluation of mechanical properties by compression test showed enhanced yield strength from 505+/-17MPa for the nanostructured copper to 630+/-12MPa for the reinforced metal with 2vol% SiC. We correlated the strength of the nanostructured materials to their microstructural features based on the strengthening mechanisms. The contribution of different mechanisms including Orowan strengthening, high angle grain boundaries, and density of dislocations were analyzed. It is shown that the high angle grain boundaries in nanostructured materials play a significant role in the strengthening mechanism. The effect of nanoparticles is presented and discussed.

Fabrication, characterization and mechanical properties of hybrid composites of copper using the nanoparticulates of SiC and carbon nanotubes

Akbarpour, M.R.,Salahi, E.,Alikhani Hesari, F.,Simchi, A.,Kim, H.S. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.572 No.-

Copper based hybrid composites containing nano-sized silicon carbide and carbon nanotubes reinforcements with minimal porosity were fabricated via mechanical milling followed by hot pressing technique. Microstructures of the powders and consolidated materials were studied using scanning electron microscope, X-ray diffraction, Raman spectroscopy, and scanning transmission electron microscope. Microstructural characterization of the materials revealed that the addition of nanosized silicon carbide reinforcement lowered the grain growth rate and enhanced the homogenization during mechanical milling. Microhardness measurements and compression test showed considerable improvements in mechanical properties of the composites due to the addition of nanoparticulates and the grain refinement. The strength of the composite materials was discussed using theoretical models of the Hall-Petch, Orowan, and thermal mismatch mechanisms to determine the contribution of each mechanism in total strength.

Effect of high-pressure torsion on the microstructure and strengthening mechanisms of hot-consolidated Cu-CNT nanocomposite

Akbarpour, M.R.,Farvizi, M.,Lee, D.J.,Rezaei, H.,Kim, H.S. Elsevier Sequoia 2015 Materials science & engineering. properties, micro Vol.638 No.-

The effect of high-pressure torsion (HPT) on the microstructure and hardness of Cu-carbon nanotube (CNT) nanocomposite and unreinforced Cu, processed by mechanical ball-milling and hot pressing, were investigated. High-resolution transmission electron microscopy observation revealed arrays of equiaxial grains with average grain sizes of 128nm and 140nm for the nanocomposite and Cu, respectively, and strong interfaces between Cu and CNTs after HPT. The addition of CNTs to Cu resulted in further increase in microstrain and decrease in the mean grain size of the nanocomposite. Our findings indicate misorientation between Cu and CNTs at their interface, (i.e., a gradual transition from the lattice planes of face-centered cubic Cu to those of the CNT). Hardness evaluation of the Cu-4vol% CNT nanocomposite indicates high microhardness (2.01GPa), 16.8% higher than that of the nanostructured Cu. The high microhardness of the nanocomposite is due to the nanostructured Cu matrix, uniform distribution of the CNTs, and modified Cu-CNT interface that resulted from the combined processing. Strengthening mechanisms, relative to the microstructural features of the nanocomposite, are discussed.

Microstructural and kinetic investigation on the suppression of grain growth in nanocrystalline copper by the dispersion of silicon carbide nanoparticles

Akbarpour, M.R.,Farvizi, M.,Kim, H.S. Elsevier Ltd 2017 Materials & Design Vol.119 No.-

<P>In this paper, the thermal stability and grain growth kinetics of nanocrystalline Cu, reinforced with SiC nanoparticles and obtained using a mechanical milling process, were investigated during isothermal annealing. The presence of the nanoparticles in the nanocrystalline copper matrix resulted in a significant decrease in grain growth, the formation of partially textured microstructure and twin boundaries at higher temperatures, and an increase in the volume fraction of recrystallized grains, as estimated by grain orientation spread, in comparison to unreinforced Cu during annealing. The lower volume fraction of recrystallized grains at higher temperatures was attributed to dynamic recovery. Normal grain growth was observed in the annealing range of 400-600 degrees C, and significant abnormal grain growth was observed at higher temperatures. An analysis of the grain growth kinetics in the temperature range of 400-600 degrees C revealed a time exponent of n approximate to 3.6 and activation energy of approximate to 34 kJ mol(-1), based on the parabolic equation. The calculated activation energy for grain growth in the SiC dispersion strengthened Cu was found to be less than that of nanocrystalline Cu. The low activation energy and high thermal stability were attributed to high lattice strain and the retarding effect of nanoparticles by the Zener mechanism. (C) 2017 Elsevier Ltd. All rights reserved.</P>

The Effects of Steel Fiber and Nano-SiO2 on the Cyclic Flexural Behavior of Reinforced LWAC Beams

Soodeh Akbarpour,Hooshang Dabbagh,Hamidreza Tavakoli 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.10

The dead load and consequently the burden imposed on the structures due to earthquake can be reduced using Lightweight Aggregate Concrete (LWAC). In this study the cyclic flexural performance of LWAC beams is experimentally investigated to assess the influence of nano-SiO2 and steel fibers on the reversal flexural behavior. Tests were carried out on the reinforced LWAC beams with dimensions of 150 × 200 × 1200 mm under alternative cycles of variable displacement amplitudes. The cyclic behavior of these members including hysteresis response, load bearing capacity, envelope curve, stiffness, energy dissipation capacity and crack pattern are discussed and compared. The results showed that the addition of steel fiber significantly enhanced maximum flexural strength, cumulative dissipated energy, post-cracking stiffness and damage tolerance ability of LWAC beam. Adding nano-silica alone had slight effect on improving the reversal cyclic flexural behavior of LWAC. Furthermore the use of nano-silica increased the effectiveness of steel fiber on enhancement the cyclic flexural performance, especially at higher levels of displacement.

The Approach of the Host Community to the Expansion of Tourism in the Rural Areas -Case Study: Kandovan Village, Oskoo City, Iran-

( Mohammad Akbarpour Saraskanroud ) 한국문화관광학회 2012 문화관광연구 Vol.14 No.1

The goal of this research is to analyze the effective factors on the amount of support of tourism expansion by the residents in the historical village of Kandevan among the villages in the city of Oskoo. This research is done by a walking method based on using questionnaires. The statistical pool has been divided in 3 groups of ordinary residents, actives in the service division and the authority in the public division and the relative class sampling with the sample volume of 100 people. In order to analyze the variables in this study, SPSS software and statistical correlation methods, Regression and non-parametric statistical tests were utilized.

Effect of Thermomechanical Treatment on the Micro-hardness and Crystallization Behavior of an Amorphous Zr65.5Ni16Cu8.5Al10 Alloy

Ali Akbarpour,M. S. Parkhomenko,A. M. Khalil,V. V. Cheverikin,N. Yu. Tabachkova,E. N. Zanaeva,A. I. Bazlov 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.9

This work studied the influence of thermomechanical treatment on the mechanical properties, structure, and crystallizationof the Zr65.5Ni16Cu8.5Al10metallic glass alloy. It established that thermomechanical treatment significantly affects themechanical properties of the alloy while maintaining its amorphous structure due to the formation of regions of chemicalinhomogeneity in the amorphous matrix. In addition, shear deformation affects the initial crystallization of the alloy. As aresult, there is a transition from one-stage crystallization to two-stage crystallization with a strain increase.

The Approach of the Host Community to the Expansion of Tourism in the Rural Areas : Case Study: Kandovan village, Oskoo City, Iran

Mohammad Akbarpour saraskanroud,Mohsen Rahimi 세계문화관광학회 2011 Conference Proceedings Vol.12 No.-

The planning and the expansion of tourism as an important factor in the process of economization of social and cultural matters and an instrumental functional productive natural and cultural approach will make different visions towards tourism necessary. The goal of this research is to analyze the effective factors on the amount of support of tourism expansion by the residents in the historical village of Kandevan among the villages in the city of Oskoo. This research is done by a walking method based on using questionnaires. The statistical pool has been divided in 3 groups of ordinary residents actives in the service division and the authority in the public division and the relative class sampling with the sample volume of 100 people. In order to analyze the variables in this study SPSS software and statistical correlation methods Regression and non-parametric statistical tests were utilized. Also by using SWOT model we attained the situation of this village in the social economic service and cultural fields as such that in this research the expansion of tourism as an independent variable and its positive and negative effects in economic social and environmental dimensions and the amount of support by the community as a dependent variable of the research was explained. The findings of the research show that in general the rural residents of the village of Kandovan with an agreement rate of 82.7% have a positive attitude toward the expansion of tourism in the mentioned area. Also based on the results of the research the nature of the residents' attitude in the area under study compared to tourism has a significant difference and the amount of the support by the residents is effected by the level of the expansion in tourism as such that as the amount of negative effects are increased compared to the profits or advantages gradually the amount of support by the host diminishes.