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microhardness
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, M.Sc. Thesis Sharif University of Technology ; Varahram, Naser (Supervisor) ; Davami, Parviz (Supervisor)
Abstract
Al-20Si-5Fe-3Cu-1Mg–xCr (X=0, X=1.5) ribbons were produced by melt-spinning technique at the rotating speed of 20 and 40 ms-1. The thickness of ribbons were 40 to 80 and 15 to 35 μm, respectively. The properties of as-melt spun and as-cast specimen were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-Ray diffractometry (XRD) and the microhardness method. It was found that at the air side of ribbons the microstructure was dendritic while at the wheel side it was featureless. The microstructure of ribbons at two rotating speed showed a homogenous distribution of Si particles embedded in an α-Al matrix. XRD investigations exhibited the absence of any intermetallic...
Age-hardening behavior and phase identification in solution-treated AEREX 350 superalloy
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 37, Issue 7 , 2006 , Pages 2051-2057 ; 10735623 (ISSN) ; Sharif University of Technology
2006
Abstract
This article presents results of an investigation on age-hardening behavior of superalloy AEREX 350. Microhardness testing was employed to evaluate the age-hardening response of the alloy while optical, scanning, and transmission electron microscopy techniques were used to characterize the major phases formed during the aging process. No significant hardening was found in solution-treated samples aged at temperatures up to about 680 °C. Aging at 700 °C up to 950 °C, however, caused a characteristic hardening response. This hardening was concurrent with the formation of γ', an ordered phase with L12 structure, as fine precipitate distributed throughout the fcc matrix. In the temperature range...
The prediction of macroscopic shear bands in flat rolled wire using the finite and slab element method
, Article Materials Letters ; Volume 60, Issue 27 , 2006 , Pages 3265-3268 ; 0167577X (ISSN) ; Karimi Taheri, A ; Sharif University of Technology
2006
Abstract
In this paper, in order to investigate the creation of macroscopic shear bands, due to material flow tracks in the cross section of a wire after flat rolling, the combined Finite and Slab Element Method (FSEM) is used. The effective strain field is predicted for different reductions in height. The validity of the method is assessed by performing the Vickers microhardness measurements on the cross section of the flattened wire. It is found that the FSEM and microhardness results show the minimum and the maximum effective strains at the round edge and the center of the flattened wire, respectively. Also, the results indicate two bands of maximum effective strain in the cross section of the...
The effect of SiC nanoparticles on the friction stir processing of severely deformed aluminum
, Article Materials Science and Engineering A ; Vol. 602, issue , April , 2014 , p. 110-118 ; ISSN: 09215093 ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
Abstract
The 1050 aluminum sheets are severely deformed by two passes of the constrained groove pressing (CGP) process to obtain the strain of 2.32. Friction stir processing (FSP) is then performed on these specimens at two conditions of with and without SiC nanoparticles. Microhardness measurements indicate that in the state of FSP without any particle, the microhardness of stir zone is decreased due to the recrystallization and grain growth occurrence because of high stored strain energy in the CGPed specimens. In order to enhance the mechanical properties of the stir zone, SiC nanoparticles are used during FSP. Also, the effect of FSP pass number on the distribution of nanoparticles is...
Determination of strain field and heterogeneity in radial forging of tube using finite element method and microhardness test
, Article Materials and Design ; Volume 38 , June , 2012 , Pages 147-153 ; 02641275 (ISSN) ; Saidi, P ; Karimi Taheri, A ; Hossein Zadeh, M ; Sharif University of Technology
2012
Abstract
Utilizing the Finite Element Method (FEM), the strain field in the radial forging process of tube is calculated at different process conditions and compared with the experimental results achieved using the microhardness test. The effect of various process parameters such as friction, axial feed, back push and front pull forces and die angles on the strain field are investigated. Using the results of the analysis, it is shown that the deformation inhomogeneity, introduced by an Inhomogeneity Factor (IF), is maximum in the inner zone of tube, while the minimum and the maximum effective strains are appeared at the inner zone of tube and about the core of the tube thickness, respectively. Also,...
Thermal stability investigation of expanded martensite
, Article Surface and Coatings Technology ; Volume 300 , 2016 , Pages 87-94 ; 02578972 (ISSN) ; Bahmannezhad, B ; Nikpoor, N ; Asgari, S ; Sharif University of Technology
Elsevier
2016
Abstract
The aim of this work is to investigate thermal stability of expanded martensite. For this purpose, two martensitic stainless steels, PH 17-4 and 13-8Mo, were low temperature gas carburized. After heat treatment, it was found out that thermal stability of expanded layer of PH 17-4 is higher than that of PH 13-8Mo. Auger Electron Spectroscopy and microhardness machines were used to investigate carbon concentration and hardness of samples, respectively. X-ray diffraction was done to study crystal structures of samples before and after heat treatment
Diffusion brazing of Ti–6Al–4V and AISI 304: an EBSD study and mechanical properties
, Article Journal of Materials Science ; Volume 52, Issue 20 , 2017 , Pages 12467-12475 ; 00222461 (ISSN) ; Shamanian, M ; Atapour, M ; Khosravi, B ; Sharif University of Technology
Abstract
Ti–6Al–4V and AISI 304 stainless steel were joined by diffusion brazing with a Cu interlayer at 900 °C for different bonding times. The influence of the bonding time on the joint width, microstructure, microhardness and shear strength was studied. Interfacial characterizations and the identification of phases were done by scanning electron microscopy and electron backscatter diffraction (EBSD). The results revealed that by increasing the bonding time, the thickness of the joint was first increased and then decreased. Microstructure examinations also showed that the joints consisted of several intermetallics such as TiCu, Ti2Cu, TiCu4, TiCu2, FeTi and Fe2Ti. On the other hand, EBSD results...
Applicability of the FSEM for analyzing wire flat rolling process
, Article Engineering Computations (Swansea, Wales) ; Volume 23, Issue 5 , 2006 , Pages 515-524 ; 02644401 (ISSN) ; Taheri, A. K ; Sharif University of Technology
2006
Abstract
Purpose - The purpose of this paper is to present an assessment of the ability of combined finite and slab element method (FSEM) for analyzing the wire flat rolling process. Design/methodology/approach - Using the FSEM, the effective strain field of flat rolled wire is predicted for different reductions in height and frictional conditions. The validity of the method is assessed by performing the Vickers microhardness measurements on the flattened wire cross section. Also, the creation of macroscopic shear bands in cross section of the flat rolled wire is investigated and confirmed by microhardness and metallographic examinations. Moreover, the lateral spread and width of contact area are...
Investigation of Manganese Addition on Microstructure and Mechanical properties of Al-20Si-5Fe-3Cu-1Mg Ribbons Prepared by Melt Spinning Method
, M.Sc. Thesis Sharif University of Technology ; Davami, Parviz (Supervisor) ; Varahram, Nasser (Supervisor)
Abstract
In this research, Al-20Si-5Fe-1Mg-xMn(x= 0,3,6) ribbons were produced by Melt spinning method. Microstructure and growth morphology of ribbons were studied by optical microscope (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The results were compared with as cast samples. In OM results, two different zones were observed. Featureless zone (with planar growth morphology) and dendrites zone. Microstructure of ribbons were completely different from the as cast samples. It consisted of just Aluminium and silicon. XRD results approved that matter. In fact, high solidification rate of ribbons increased the solubility of silicon and other alloys in aluminium and consequently...
Effects of cold work prior to aging on microstructure of AEREX™350 superalloy
, Article Materials Science and Engineering A ; Volume 480, Issue 1-2 , 2008 , Pages 434-438 ; 09215093 (ISSN) ; Asgari, S ; Sharif University of Technology
2008
Abstract
The influence of different amounts of cold work on the evolution of microstructure during subsequent aging of AEREX™350 superalloy was investigated. Simple compression testing was used to impose desired plastic strain while microhardness testing, XRD, SEM and TEM techniques were used to characterize the response of the alloy following aging treatment. It was found that high levels of cold work followed by aging resulted in a drastic increase in the formation of Widmanstättan η phase and incidence of shear bands in the microstructure. Based on microstructural data, the effect of plastic strain on η phase formation and the physical origin of the localized shear bands are discussed. © 2007...
On the natural aging behavior of Aluminum 6061 alloy after severe plastic deformation
, Article Materials Science and Engineering A ; Volume 580 , 2013 , Pages 202-208 ; 09215093 (ISSN) ; Kazeminezhad, M ; Miyamoto, H ; Sharif University of Technology
2013
Abstract
Natural aging behavior of the aluminum 6061 alloy after a novel Severe Plastic Deformation process called Tube Channel Pressing (TCP) was studied. For this purpose, Vickers microhardness test was used to investigate the changes of mechanical properties while TEM and XRD observations were utilized in order to characterize microstructural evolution during natural aging. Results show that Si-enriched precipitates appear and coarsen rapidly in the first few days of natural aging of TCPed aluminum 6061 alloy which causes consecutive increase and decrease of Vickers microhardness, respectively. Similarly, other alloying elements such as Cu and Fe lead to formation of coarse precipitates during...
Evaluation of crystalline changes and resistance to demineralization of the surface of human dental enamel treated with Er:YAG laser and fluoride using x-ray diffraction analysis and vickers microhardness
, Article Laser Physics ; Volume 28, Issue 6 , 2018 ; 1054660X (ISSN) ; Shahabi, S ; Ghavami lahiji, M ; Sadeghian, S ; Faal Nazari, N. S ; Sharif University of Technology
Institute of Physics Publishing
2018
Abstract
This study aimed to investigate the changes in crystalline structure and resistance to demineralization of human dental surface enamel treated with erbium-doped yttrium aluminium garnet laser (Er:YAG) laser and fluoride. The enamel surfaces were divided into four groups according to the treatment process including, (L): irradiated with Er:YAG; (F): treated with acidulated phosphate fluoride gel (LF): Pre-irradiated surfaces with Er:YAG subjected to acidulated phosphate fluoride gel and (FL): laser irradiation was performed on the fluoridated enamel surface. Before and after the treatment procedure, the samples were evaluated using X-ray diffraction, scanning electron microscope (SEM) and the...
Upset Resistance Welding of Duplex Stainless Steel to Martensitic Stainless Steel
, M.Sc. Thesis Sharif University of Technology ; Movahedi, Mojtaba (Supervisor)
Abstract
Upset Resistance Welding (URW) is a solid-state joining process which can be used to join a variety of parts and profiles including railways, wheel rims and pipes used in oil and petrochemical industries. This process has three primary parameters, welding current, current passage time and mechanical pressure. Martensitic Stainless Steels (MSSs) due to high strength and wear resistance, good atmospheric corrosion resistance and relatively low price and Duplex Stainless Steels (DSSs) because of higher strength and better corrosion resistance in chlorine environments, are widely used in different industries. Dissimilar MSS/DSS joints are of great importance for piping, specially in oil and...
Influence of pulse parameters on electrocodeposition of Cr-Al2O3 nanocomposite coatings from trivalent chromium bath
, Article International Heat Treatment and Surface Engineering ; Volume 6, Issue 4 , December , 2012 , Pages 178-184 ; 17495148 (ISSN) ; Sadrnezhaad, S. K ; Salehi Doolabi, D ; Asadirad, M ; Sharif University of Technology
2012
Abstract
Cr and Cr-Al2O3 coatings were electrodeposited from Cr(III) bath with both pulsating and direct current onto copper substrates. Pulsating current resulted in homogeneous films of higher Al2O3 content and lower particle agglomeration than the direct current. Differences were more tangible at shorter duty cycles and pulse frequencies. Pulsating current improved both microhardness and corrosion resistance. The presence of alumina nanoparticles resulted in greater current efficiency, higher film microhardness and better corrosion resistance. Maximum current efficiency, highest microhardness and densest electrodeposited coatings were achieved at current density of 20 A dm-2, duty cycle of 40% and...
Effect of joint clearance and post-braze heat treatment on the microstructure of joints with BNi-4 filler metal and 4130 steel
, Article IBSC 2012 - Proceedings of the 5th International Brazing and Soldering Conference ; 2012 , Pages 410-413 ; 9781615039753 (ISBN) ; Kokabi, A. H ; Behjati, P ; Madaah Hosseini, H. R ; Sharif University of Technology
2012
Abstract
In this work, the influence of the clearance and post-braze heat treatment on the microstructure of 4130 steel joint brazed by BNi-4 filler metal was investigated. Samples with different clearances were heated to 1100°C and hold for 9 min. Then, some were reheated to 800°C(2hr) and 800°C(2hr)+1000°C(2hr), cycle 1 and cycle 2, respectively. Microscopy techniques and micro-hardness test were used to evaluate the microstructures. Results suggested that in this case 25μm clearance can be considered as the optimum value. Also, it was found that high temperature post-braze heat treatment can be applied as a useful technique for decreasing the fraction of the brittle phases at the joint main body
Effect of iron particle size on the diffusion bonding of Fe-5%Cu powder compact to wrought carbon steels
, Article Materials and Design ; Volume 29, Issue 2 , 2008 , Pages 411-417 ; 02613069 (ISSN) ; Simchi, A ; Kokabi, A. H ; Sharif University of Technology
Elsevier Ltd
2008
Abstract
In the present work, diffusion bonding of Fe-5%Cu powder compact to wrought carbon steels was studied. Effects of iron particle size and carbon content of the solid component on the bond strength, which is the maximum shear stress required to obtain separation at the interface, were investigated. Atomized iron powders with the mean particle size of 36, 56, 90, 106, and 148 μm and wrought steels with 0.22, 0.33, and 0.47 wt% carbon content were used. To evaluate the bonding zone, "ring shear" test, standard metallography technique, and micro-hardness test were employed. The results showed a profound effect of carbon content of the solid steel on the diffusion bonding process. It is suggested...
Nano-precipitation in if steel by the use of hot compression test
, Article 1st International Conference on Industrial Processes for Nano and Micro Products, London, 3 April 2007 through 4 April 2007 ; 2007 , Pages 203-210 ; 1855980827 (ISBN); 9781855980822 (ISBN) ; Aboutalebi, S. H ; Amin, M ; Baghaei Lakeh, R ; Khezr Seddigh Mazinani, S ; Sharif University of Technology
2007
Abstract
One of the methods to increase the hardness of metals, mostly used in aerospace and automobile industries, where light parts with high strength is needed, is precipitation hardening. Nano-precipitates can strongly influence the mechanical properties of materials, especially in a dynamic case. In the present work, attempts have been made so as to make Nano-particles dynamically precipitate in IF steels. Investigating the structure by the means of SEM and AFM resulted in understanding that the precipitates were in nano-size. The micro-hardness of samples was measured as well. © BHR Group 2007 Industrial Processes for Nano and Micro Products
Failure analysis of a gas turbine marriage bolt
, Article Journal of Failure Analysis and Prevention ; Volume 7, Issue 2 , 2007 , Pages 81-86 ; 15477029 (ISSN) ; Salimi, H. R ; Sharif University of Technology
2007
Abstract
A gas turbine which output 18MW power exploded after 3h of ordinary operation and after 4,785 starts. The turbine's rotor had undergone repair after 77,000 operating hours. A piece was cut from the failed marriage bolt and tested using atomic absorption spectrometry in order to know the grade of the alloy. It was found that the marriage bolt is made from ASTM A193 B16 steel which is suitable. Hardness and microhardness measurement was also determined and showed that it was within the range of the specified hardness for ASTM A193 B16 steel. The marriage bolt's mechanical properties also meet technical specifications and showed that it contained anti-corrosion properties. Visual examination...
Adhesive and cohesive properties by indentation method of plasma-sprayed hydroxyapatite coatings
, Article Applied Surface Science ; Volume 253, Issue 11 , 2007 , Pages 4960-4965 ; 01694332 (ISSN) ; Ziaei Moayyed, A. A ; Mesgar, A. S. M ; Sharif University of Technology
Elsevier
2007
Abstract
Adhesive and cohesive properties of the plasma-sprayed hydroxyapatite (HA) coatings, deposited on Ti-6Al-4V substrates by varying the plasma power level and spray distance (SD), were evaluated by an indentation method. The crystallinity and the porosity decreased with increasing both of these two parameters. The microhardness value, Young's modulus (E) and coating fracture toughness (K C ) were found to increase with a combinational increase in spray power and SD. The Knoop and Vickers indentation methods were used to estimate E and K C , respectively. The critical point at which no crack appears at the interface was determined by the interface indentation test. This was used to define the...
Effect of sintering atmosphere and carbon content on the densification and microstructure of laser-sintered M2 high-speed steel powder
, Article Materials Science and Engineering A ; Volume 403, Issue 1-2 , 2005 , Pages 290-298 ; 09215093 (ISSN) ; Simchi, A ; Sharif University of Technology
2005
Abstract
In the present work, the role of graphite addition and sintering atmosphere on the laser sintering of M2 high-speed steel (HSS) powder was studied. The test specimens were produced using a continuous wave CO2 laser beam at power of 200 W and at varying scan rate ranges from 50 to 175 mm s-1 under nitrogen and argon atmospheres. It was found that laser scan rate and sintering atmosphere strongly influence the densification of M2 HSS powder. Opposite to the conventional sintering that the sinterability of HSS is improved by graphite addition, the result of this work demonstrated that graphite addition decreases the sintered density of M2 HSS at relatively low laser scan rates, i.e. <100 mm...