Showing 55 results for Microstructure
K. Tavighi, M. Emamy, A. R. Emami,
Volume 11, Issue 4 (12-2014)
Abstract
This study was undertaken to investigate the effects of Cu and solution heat treatment on the microstructure and hardness of cast Al-Al4Sr metal matrix composite. Different amounts of Cu (0.3, 0.5, 1, 3 and 5 wt.%) were added to the composite. Specimens were heat treated at 500 °C for 4 hours followed by water quenching. Microstructural studies were assessed by the use of optical microscope, scanning electron microscope (SEM) and x-ray diffractometry (XRD). The results showed that addition of 5 wt.% Cu reduces the length of large needle-like Al4Sr phase and refines the microstructure. In addition, the presence of Cu-intermetallics increases hardness of the composite. Cu mainly forms θ phase which segregates at the grain boundaries. Heat treatment partially dissolves Cu-intermetallics and homogenizes the distribution of θ phase in the matrix.
M. Siadat-Cheraghi, S. R. Allahkaram, Z. Shahri,
Volume 12, Issue 1 (3-2015)
Abstract
Pure cobalt coatings were electrodeposited on copper substrate by means of direct electric current in a
chloride solution at different current densities in the range of 10-70 mA cm
-2
. The surface morphology and
microstructure were investigated via X-ray diffraction analysis and scanning electron microscopy. Corrosion behavior
of cobalt coatings was also studied in a 3.5 wt% NaCl solution using potentiodynamic polarization and impedance
spectroscopy techniques. The results showed that corrosion resistance of deposits was strongly influenced by the
coating’s morphology. Co deposit obtained in lower current densities exhibited the highest corrosion resistance, due
to their lower grain boundaries and so the least density of active sites for preferential corrosion attacks
M. Amuei, M. Emamy, R. Khorshidi, A. Akrami,
Volume 12, Issue 3 (9-2015)
Abstract
In this study, Al2014 alloy refined with Al-5%Ti-1%B master alloy was prepared by strain-induced melt
activated (SIMA) process. The main variables of the SIMA process were cold working, holding time and temperature in
semi-solid state. Cold working was applied on specimens by upsetting technique to achieve 10%, 20% and 30% height
reduction. Cold worked specimens were heat treated in semi-solid state at 585 °C, 595 °C, 605 °C, 615 °C, 625 °C and
635 °C and were kept in these temperatures for different times (20 and 30 min). Observations through optical and
scanning electron microscopy were used to study the microstructural evaluation. The results revealed that fine and
globular microstructures are obtained by applying 30 % height reduction percentage and heat treating in 625 °C for
30 min. Comparison between refined and unrefined Al2014 alloy after applying SIMA process showed that Al-5%Ti-1%B master alloy has no significant effect on average globule size but makes the final structure more globular.
M. Alipour, M. Emami, R. Eslami Farsania, M. H. Siadati, H. Khorsand,
Volume 12, Issue 4 (12-2015)
Abstract
A modified strain-induced melt activation (SIMA) process was applied and its effect on the structural characteristics and hardness of the aluminum alloy Al–12Zn–3Mg–2.5Cu was investigated. Specimens subjected to a deformation of 40% at 300 °C were heat treated at various times (10-40 min) and temperatures (550-600 °C). Microstructural studies were carried out using optical and scanning electron microscopies (SEM). Results showed that the best microstructure was obtained at the temperature and time of 575 °C and 20 min, respectively. The hardness test results revealed superior hardness in comparison with the samples prepared without the application of the modified SIMA process.
T6 heat treatment including quenching to 25 °C and aging at 120 °C for 24 h was employed to reach to the maximum strength. After the T6 heat treatment, the average tensile strength increased from 231 MPa to 487 and 215 MPa to 462 for samples before and after strain-induced melt activation process, respectively. Ultimate strength of globular microstructure specimens after SIMA process has a lower value than as-cast specimens without SIMA process
M. Shahmiri,
Volume 14, Issue 1 (3-2017)
Abstract
In the present work microstructural evolution of A356 Aluminum alloy using an inclined cooling plate casting process for thixoforming feedstock production is investigated. The resultant microstructure was evaluated and compared with those of the same alloy produced by the conventional casting process, i.e. directly cast in the same mold without using an inclined cooling plate. It was found that when alloy melt poured over an inclined cooling plate and subsequently cast in semisolid condition into a metallic mould resulted in fine rosettes and nearly globular α-Al primary phase uniformly distributed in an Al +Si eutectic matrix. The effect of the processing parameters such as the lengths and angles of the inclined cooling plate and their combinations were identified to produce alloy ingot with the most suitable microstructural constituent for thixoforming process
M. Paidpilli, K. Verma, R. Pandey, A. Upadhyaya,
Volume 14, Issue 1 (3-2017)
Abstract
In the present work, one batch of prealloyed 6061Al powder was processed by mixing and another one was ball milled with varying amount of lead content (0-15 vol. %). These powders were compacted at 300MPa and sintered at 590˚C under N2. The instrumented hardness and the young’s modulus of as-sintered 6061Al-Pb alloys were examined as a function of lead content and processing route. The wear test under dry sliding condition has been performed at varying loads (10-40 N) using pin-on-disc tribometer. The microstructure and worn surfaces have been investigated using SEM to evaluate the change in topographical features due to mechanical alloying and lead content. The mechanically alloyed materials showed improved wear characteristics as compared to as-mixed counterpart alloys. Delamination of 6061Al-Pb alloys decreases up to an optimum lead composition in both as-mixed and ball-milled 6061Al-Pb alloys. The results indicated minimum wear rate for as-mixed and ball-milled 6061Al alloy at 5 and 10 vol. % Pb, respectively.
Z. Ghaferi, S. Sharafi, M.e. Bahrololoom,
Volume 14, Issue 2 (6-2017)
Abstract
In this research, nanocrystalline Co-Fe coatings were electrodeposited on copper substrate. The influence of current density on different properties of the films at two pH levels was investigated. All the coatings showed nodular structure with rougher morphology at higher current densities. Due to anomalous deposition at higher current density, the amount of iron content increased and reached its maximum value at about 50 wt.% for the coating obtained from pH 5. X-ray diffraction patterns showed hcp structure as the dominant phase. However, by increasing current density at lower pH value, a double phase structure containing fcc+hcp phases was detected. It was observed that current density has a positive effect on grain refinement. However, coarser grains would obtain at lower pH value. Microhardness measurements showed that, there is a direct relationship between grain size and microhardness. Moreover, microstructure in double phase structure films can influence microhardness more dominantly. Vibrating sample magnetometer (VSM) measurements indicated that the saturation magnetic is proportion to deposited iron content and reached its maximum value at about 1512 emu/cm3. It was cleared that grain size, phase structure and chemical composition can affect coercivity of the films effectively.
N. Nikoogoftar, S. H. Razavi, M. Ghanbari,
Volume 14, Issue 3 (9-2017)
Abstract
In this research, the effect of annealing and aging temperature as well as the effect of quenching media on the microstructure, hardness and dry sliding wear behavior of Ti-6Al-4V alloy has been studied. Cylindrical samples with the diameter of 10 mm and the height of 20mm were solutionized at 930˚C and 1060˚C for 600 seconds and then were quenched in the cold water and in the air. The samples were aged at different temperature of 480˚C, 550˚C and 610˚C for 360 s to increase the hardness. Heat treated samples were tested using standard pin-on-disc test machine at the applied loads of 100, 150 and 200 N. Microstructural investigations using scanning electron microscope revealed that for the samples solutionized at 930˚C and quenched in the water, the microstructure is composed of primary α and high volume fraction of martensitic α΄ phase with fine precipitated of β between martensitic lathes. In the case of air cooled samples, transformed β has also been appeared in the vicinity of primary α. For the samples solutionized at 1060˚C and quenched in the water, fully martensitic micro structure with fine β precipitates was observed. For the sample solutionized at 1060˚C and air quenched, plate like α and lamellar grain boundary β were detected. The maximum hardness value relates to the sample solutionized at 1060˚C and quenched in water which is equal to 433 HV. Different wear mechanisms, including oxidative wear, scratch, and delamination occurred at the worn surfaces at different applied loads. For the samples quenched in the water, the oxidative wear mechanism governing at low applied load and oxide debris was observed as separate or compacted particles which formed in the contact between pin and steel counter face detached from the sample. At higher applied loads, delamination and scratch mechanism was also observed and metallic plate like debris was detached from the sample. Mechanically mixed layer (MML) was formed on the surface of the pin at high applied loads and for the samples with low hardness value adhesion marks were also revealed on the steel disc. The minimum weight loss in the wear test is related to the sample quenched from the 1060ºC in the cold water and aged at 550 ºC .
M. Arockia Jaswin, D.m. Mohan Lal,
Volume 15, Issue 1 (3-2018)
Abstract
The behaviour of the cryogenically treated En52 martensitic valve steel has been experimentally analyzed in this paper. Material samples are subjected to deep cryogenic treatment after completing the regular heat treatment. The critical properties of the valve steel like wear resistance, hardness, tensile strength and impact strength are evaluated for the cryo treated En52 valve steel samples as per the ASTM standards. The microstructural changes and the mechanism behind the enhancement of the properties are examined and reported. The precipitation of fine carbides, transformation of retained austenite and refinement of carbides were the reasons behind the improvement of the mechanical properties. Deep cryogenic treatment process parameters are optimized for better wear resistance, hardness and tensile strength using grey Taguchi technique. Deep cryogenic treatment process greatly influences the wear resistance, a maximum enhancement of 54% is observed
M. Alvand, M. Naseri, E. Borhani, H. Abdollah-Pour,
Volume 15, Issue 1 (3-2018)
Abstract
Friction stir welding (FSW) is a promising technique to join aluminum alloys without having problems encountered during fusion welding processes. In the present work, the evolution of microstructure and texture in friction stir welded thin AA2024 aluminum alloy are examined by electron backscattered diffraction (EBSD) technique. The sheets with 0.8 mm thickness were successfully welded by friction stir welding at the tool rotational speeds of 500, 750, and 1000 rpm with a constant traverse speed of 160 mm/min. EBSD revealed that stir zones exhibited equiaxed recrystallized grains and the grain size increased with increasing the tool rotation rate. The fraction of high angle grain boundaries and mean misorientation angle of the boundaries in the FSW joints at 500 rpm were 63.6% and 24.96°, respectively, which were higher than those of the sample welded at 1000 rpm (53.6% and 17.37°). Crystallographic texture results indicated that the Cube {001}<100> and S {123}<634> textures in base metal gradually transformed in to Copper {112}<111> shear texture. It was found that with increasing the tool rotation rate, the intensity of Cube {001}<100>, Y {111}<112>, S {123}<634>, and Dillamore {4 4 11}<11 11 8> texture orientations increased and the intensity of Brass {011}<211> texture orientation decreased.
S. Kord, M. H. Siadati, M. Alipour, H. Amiri, P.g. Koppad, A. C. Gowda,
Volume 15, Issue 4 (12-2018)
Abstract
The effects of rare earth element, erbium (Er) additions on the microstructure and mechanical properties of Al-15Zn-2.5Mg-2.5Cu alloy have been investigated. This new high strength alloy with erbium additions (0.5, 1.0, 1.5 and 2.0 wt%) was synthesized by liquid metallurgy route followed by hot extrusion. Microstructural characterization was performed using scanning electron microscope and electron probe microanalysis. Significant amount of grain refinement was observed with erbium addition in the hot extruded and heat treated alloy. Tensile test was performed to investigate the effect rare earth on mechanical behavior of alloy in as cast and hot extruded condition before and after T6 heat treatment. The combined effect of erbium addition, hot extrusion and heat treatment significantly enhanced the tensile strength of alloy (602 MPa) when compared to the as cast alloy without erbium addition (225 MPa). The strengthening of the alloy was attributed to grain refinement caused by erbium along with hot extrusion and formation of precipitates after T6 heat treatment. Fractograhic investigations revealed that the hot extruded alloy with erbium addition after heat treatment showed uniformly distributed deep dimples exhibiting ductile behavior.
T. Ebadzadeh, S. Ghaffari, M. Alizadeh, K. Asadian, Y. Ganjkhanlou,
Volume 16, Issue 1 (3-2019)
Abstract
The densification behavior, structural and microstructural evolution and microwave dielectric properties of Li2TiO3 + xZnO (x = 0, 0.5, 1, 1.5, 2, 3, and 5 mol%) ceramics have been investigated using X-ray diffraction, Field Emission Scanning Electron Microscopy, Raman spectroscopy and microwave resonant measurement. The Maximum density of 3.33 g/cm3 was obtained in Li2TiO3 + 2ZnO ceramic at low sintering temperature of 1100˚C. SEM investigations revealed good close packing of grains when x = 2 and preferential grain growth when x ≥ 3. The maximum values of Q × f = 31800 GHz and εr = 22.5 were obtained in Li2TiO3 + 3ZnO and Li2TiO3 + 2ZnO compositions, respectively. The observed properties are attributed to the microstructural evolution and grain growth (first case) or high density of the obtained ceramic (second case).
M. Tavakoli Harandi, M. Askari-Paykani, H. Shahverdi, M. Nili Ahmadabadi,
Volume 16, Issue 1 (3-2019)
Abstract
One-step and two-step annealing techniques were used to examine the relationship between microstructure and mechanical properties during compression tests in iron-based ribbons and nanostructured 1- and 2.5mm cylindrical rods. The X-ray diffraction, microstructural, and mechanical results showed that substituting Nb for Fe had a minor effect on glass-forming ability but increased the formability index. The novel two-step annealing process resulted in a remarkable formability index of 16.62 GPa, yield stress of 2830 MPa, ultimate strength of 3866 MPa, and 4.3% plastic strain. A ductile nanosized α-Fe framework and boron-containing nano precipitations, which caused Zener pinning effect, were responsible for these novel mechanical properties.
M. Adineh, H. Doostmohammadi, R. Raiszadeh,
Volume 16, Issue 2 (6-2019)
Abstract
Relations between the microstructure, mechanical properties and machinability of as-cast 65Cu-35Zn brass with various amounts of Al from 0 to 4.72 and Si from 0 to 3.62 wt% were investigated. Both Si and Al initially enhanced the UTS and toughness of the brass samples, which led to improvement in machinability due to a reduction in the main cutting force. A duplex brass with random oriented α plates in β’ matrix was found to have the best machinability among the other microstructures. It was found that beside the presence of brittle phases, such as β’ phase in the microstructure, the morphology and hardness of the phases involved had significant influence on machinability.
I. Hajiannia, M. Shamanian, M. Atapour, R. Ashiri, E. Ghassemali,
Volume 16, Issue 2 (6-2019)
Abstract
In this study, the effects of the second pulse resistance spot welding on the microstructure and mechanical properties of TRIP1100 steel were evaluated. The thermal process after welding was designed to improve metallurgical properties with pulse currents of 6kA, 9kA and 12kA after initial welding with 10kA current. The effect of the second pulse on mechanical and microstructural properties was investigated. The fracture of the welds was for pulsed samples of 6kA and 9kA PO with CTS test. Due to existence of the microstructure including the equaxial dendritic and finer in FZ in the pulsed current 9kA, the maximum fracture energy and maximum force were observed. A significant decrease in the FZ hardness in 6kA current was observed in the nanohardness results, which was attributed to existence martensitic and ferrite temper. The highest ratio of CTS / TSS was obtained for 6kA and 9kA, respectively, and force displacement rate was maximum in 9kA. The fracture surfaces included dendrites and dimples. The results of partial fracture revealed separation in the coherent boundaries of the coarse grain of the annealed region.
A. Khakzadshahandashti, N. Varahram, P. Davami, M. Pirmohammadi,
Volume 16, Issue 3 (9-2019)
Abstract
The combined influence of both melt filtration and cooling rate on the microstructure features and mechanical properties of A356 cast alloy was studied. A step casting model with five different thicknesses was used to obtain different cooling rates. The effect of melt filtration was studied by using of 10 and 20 ppi ceramic foam filters in the runner. Results showed that secondary dendrite arm spacing decreased from 80 μm to 34 μm with increasing cooling rate. Use of ceramic foam filters in the runner led to the reduction of melt velocity and surface turbulence, which prevented incorporation of oxide films and air in the melt, and consequently had an overall beneficial effect on the quality of the castings. A matrix index, which is the representative of both SDAS and microporosity content, was defined to consider the simultaneous effect of melt filtration and cooling rates on UTS variations. Also, the fracture surface study of test bars cast using 10 and 20 ppi ceramic foam filters showed features associated with ductile fracture.
M. Demouche, E. H. Ouakdi, R. Louahdi,
Volume 16, Issue 3 (9-2019)
Abstract
In this study, high-carbon, chromium alloy steel (100Cr6) having the initial spheroidized microstructure was welded using the rotary friction welding method. The effects of process parameters such as friction time and friction force were experimentally investigated. The friction welded joints were produced of two 100Cr6 steel rods. In order to examine the microstructure and mechanical properties of the friction welded 100cr6 steel joints, tensile and hardness tests were conducted. The microstructure of weld zone was examined by optical microscopy. It was found that after cooling, martensitic structure is obtained at the core and periphery of the weld joint. It was found that the tensile strength of friction welded samples is increased with increasing time and force of friction up to a certain level and then decreases again. Hardness measurements show a higher hardness at the centre of the weld joint in comparison with its periphery.
H. Jafarian, H. Miyamoto,
Volume 17, Issue 1 (3-2020)
Abstract
In the present work, accumulative roll bonding (ARB) was used as an effective method for processed of nano/ultrafine grained AA6063 alloy. Microstructural characteristics indicate considerable
grain refinement leading to an average grain size of less than 200 nm after 7 ARB cycles. Texture analysis showed that 1-cycle ARB formed a strong texture near Copper component ({112}<111>). However, texture transition appeared by increasing the number of ARB cycles and after 7-cycle of ARB, the texture was mainly developed close to Rotated Cube component ({100}<110>). The results originated from mechanical properties indicated a substantial increment in strength and microhardness besides a meaningful drop of ductility after 7 ARB cycles.
M. Azadi, M. Ferdosi, H. Shahin,
Volume 17, Issue 1 (3-2020)
Abstract
In this paper, the effects of solutioning and various aging heat treatment processes on the microstructure, the hardness and electrochemical properties of a duplex stainless steel (DSS) were studied. The evaluation of the microstructure and phase compositions were carried out by the optical microscopy (OM) and the X-ray diffraction (XRD), respectively. Electrochemical behaviors of specimens were evaluated by both potentiodynamic polarization and electrochemical impedance spectra (EIS) tests at temperatures of 25 and 60 ºC. The obtained results showed that the solutioning heat treatment increased corrosion rates with respect to the blank specimen. The aging process at 490 ºC for 20 hrs increased the volume percent of the carbide phase to the highest value (25.1%) which resulted in an increase of the hardness value to 170 VHN. The specimen which was aged at 540 ºC for 10 hrs with the Cr7C3 size of 22.8 µm, exhibited the higher corrosion resistance at both temperatures of 25 and 60 ºC with respect to other aged specimens. In addition, the temperature of 60 ºC promoted the anodic reactions in 3.5 wt% NaCl solution which decreased impedance modulus values significantly. Consequently, the carbide size was more effective parameter than the carbide content in predicting electrochemical behaviors of such alloys.
R. Niazi, E. Tohidlou, H. Khosravi,
Volume 17, Issue 3 (9-2020)
Abstract
The effects of erbium (Er) addition at various weight percentages (0-0.6 wt.% at an interval of 0.2) on the microstructural characteristics, tensile response and
wear properties of as-cast Al-7.5Si-0.5Mg alloy were evaluated. The microstructure of samples was examined by X-ray diffraction, optical microscopy and scanning electron microscopy. The obtained results demonstrated that the incorporation of erbium obviously decreased the α-Al grain size and eutectic Si, and altered the Si morphology from plate to semi-globular. Further addition of erbium (> 0.2 wt.%) did not alter the eutectic morphology and size. Moreover, the Al
3Er phase was also observed in the eutectic region after modification. Out of the erbium contents used, 0.2 wt.% erbium showed the best influence on the tensile and wear properties. Compared with those of unmodified specimen, the values of ultimate tensile strength and elongation were enhanced by 31% and 39%, respectively with the introduction of 0.2 wt.% erbium. Additionally, a remarkable enhancement in the wear properties was observed with the addition of 0.2 wt.% erbium.
