M.h. Avazkonandeh-Gharavo, M. . Haddad-Sabzevar, H. Fredriksson,
Volume 13, Issue 2 (6-2016)
Abstract
Because the partition coefficient is one of the most important parameters affecting microsegregation, the aim of this research is to experimentally analyse the partition coefficient in Al-Mg alloys. In order to experimentally measure the partition coefficient, a series of quenching experiments during solidification were carried out. For this purpose binary Al-Mg alloys containing 6.7 and 10.2 wt-% Mg were melted and solidified in a DTA furnace capable of quenching samples during solidification. Cooling rates of 0.5 and 5 K/min were used and samples were quenched from predetermined temperatures during solidification. The fractions and compositions of the phases were measured by quantitative metallography and SEM/EDX analyses, respectively. These results were used to measure the experimental partition coefficients. The resultant partition coefficients were used to model the concentration profile in the primary phase and the results were compared with equilibrium calculations and experimental profiles. The results of calculations based on the experimental partition coefficients show better consistency with experimental concentration profiles than the equilibrium calculations.
E. Eshghi, M Kadkhodayan,
Volume 13, Issue 2 (6-2016)
Abstract
High speed and absence of a precise control over pressure distribution confine sheet Electromagnetic Forming into a die to simple shapes having shallow depth. It is possible to reach a higher depth by using a convex punch instead of a concave die. In this study, sheet Electromagnetic Forming on a punch and sheet Electromagnetic Forming into a die are investigated. The electromagnetic part of the study is investigated analytically and its mechanical part is studied numerically. In order to couple electromagnetic with mechanical parts, no-coupling method is used. The obtained results are verified by comparing the obtained results with previous experimental ones in literature. Rate-dependent and rate-independent hardenings are taken into consideration for the mechanical behavior for material of AAl1050. Using appropriate hardening model for material yields acceptable results. Moreover, a convex punch instead of a concave die is used to reach to a higher depth in sheet Electromagnetic Forming.
M. Rakhshkhorshid,
Volume 13, Issue 3 (9-2016)
Abstract
Till now, different constitutive models have been applied to model the hot deformation flow curves of different materials. In this research, the hot deformation flow stress of API X65 pipeline steel was modeled using the power law equation with strain dependent constants. The results was compared with the results of the other previously examined constitutive equations including the Arrhenius equation, the equation with the peak stress, peak strain and four constants and the equation developed based on a power function of Zener-Hollomon parameter and a third order polynomial function of strain power a constant number. Root mean square error (RMSE) criterion was used to assess the performance of the understudied models. It was observed that the power law equation with strain dependent constants has a better performance (lower RMSE) than that of the other understudied constitutive equations except for the equation with the peak stress, peak strain and four constants. The overall results can be used for the mathematical simulation of hot deformation processes
. S. Khani, . M. T. Salehi, . H. R. Samim, Prof. M. R. Aboutalebi, . H. Palkowski,
Volume 13, Issue 3 (9-2016)
Abstract
The evolution of microstructure and mechanical properties of a magnesium cast alloy (AZ31) processed by equal channel angular pressing (ECAP) at two different temperatures were investigated. The as-cast alloy with an average grain size of 360 was significantly refined to about 5 after four ECAP passes at 543 K. Grain refinement was achieved through dynamic recrystallization (DRX) during the ECAP process in which the formation of necklace-type structure and bulging of original grain boundaries would be the main mechanisms. ECAP processing at lower temperature resulted in finer recrystallized grains and also a more homogenous microstructure. The mechanical behavior was investigated at room temperature by tensile tests. The obtained results showed that the ECAP processing can basically improve both strength and ductility of the cast alloy. However, the lower working temperature led to higher yield and ultimate strength of the alloy.
N. Radhika, R. Raghu,
Volume 13, Issue 4 (12-2016)
Abstract
Functionally graded aluminium/zirconia metal matrix composite was fabricated using stir casting technique followed by horizontal centrifugal casting process and a hollow cylindrical functionally graded composite (150 x 150 x 16 mm) was obtained with centrifuging speed of 1200 rpm. The microstructural evaluation and hardness test was carried out on the outer and inner surface of the functionally graded composite at a distance of 1 and 13 mm from the outer periphery. In Response Surface Methodology, Central Composite Design was applied for designing the experiments and sliding wear test was conducted as per the design using a pin-on-disc tribometer for varying ranges of load, velocity and sliding distance. The model was constructed and its adequacy was checked with confirmation experiments and Analysis of Variance. The microstructural examination and hardness test revealed that the outer surface of FGM had higher hardness due to the presence of particle rich region and the inner surface had lesser hardness since it was a particle depleted region. The wear results showed that wear rate increased upon increase of load and decreased with increase in both velocity and sliding distance. Scanning Electron Microscopy analysis was done on the worn specimens to observe the wear mechanism. It was noted that wear transitioned from mild to severe on increase of load and the outer surface of FGM was found to have greater wear resistance at all conditions.
M. Mahmoudiniya, Sh. Kheirandish, M. Asadi Asadabad,
Volume 14, Issue 1 (3-2017)
Abstract
Nowadays, Ni-free austenitic stainless steels are being developed rapidly and high price of nickel is one of the most important motivations for this development. At present research a new FeCrMn steel was designed and produced based on Fe-Cr-Mn-C system. Comparative studies on microstructure and high temperature mechanical properties of new steel and AISI 316 steel were done. The results showed that new FeCrMn developed steel has single austenite phase microstructure, and its tensile strength and toughness were higher than those of 316 steel at 25, 200,350 and 500°C. In contrast with 316 steel, the new FeCrMn steel did not show strain induced transformation and dynamic strain aging phenomena during tensile tests that represented higher austenite stability of new developed steel. Lower density and higher strength of the new steel caused higher specific strength in comparison with the 316 one that can be considered as an important advantage in structural applications but in less corrosive environment
H. Torabzadeh Kashi, M. Bahrami, J. Shahbazi Karami, Gh. Faraji,
Volume 14, Issue 2 (6-2017)
Abstract
In this paper, cyclic flaring and sinking (CFS) as a new severe plastic deformation (SPD) method was employed to produce the ultrafine grain (UFG) copper tubes. The extra friction has eliminated in the CFS method that provided the possibility for production of longer UFG tubes compared to the other SPD methods. This process was done periodically to apply more strain and consequently finer grain size and better mechanical properties. The CFS was performed successfully on pure copper tubes up to eleven cycles. Mechanical properties of the initial and processed tubes were extracted from tensile tests in the different cycles. The remarkable increase in strength and decrease in ductility take placed in the CFS-ed tubes. The material flow behavior during CFS processing was analyzed by optical microscopy (OM), and a model was presented for grain refinement mechanism of pure copper based on multiplication and migration of dislocations (MMD). This mechanism caused that the initial grains converts to elongated dislocation cells (subgrains) and then to equiaxed ultrafine grains in the higher cycles. The CFS method refined the microstructure to fine grains with the mean grain size of 1200nm from initial coarse grain size of 40µm
N. Aboudzadeh, Ch. Dehghanian, M.a. Shokrgozar,
Volume 14, Issue 4 (12-2017)
Abstract
Recently, magnesium and its alloys have attracted great attention for use as biomaterial due to their good mechanical properties and biodegradability in the bio environment. In the present work, nanocomposites of Mg - 5Zn - 0.3Ca/ nHA were prepared using a powder metallurgy method. The powder of Mg, Zn and Ca were firstly blended, then four different mixtures of powders were prepared by adding nHA in different percentages of 0, 1, 2.5 and 5 %wt. Each mixture of powder separately was fast milled, pressed, and sintered. Then, the microstructure and mechanical properties of the fabricated nanocomposites were investigated. The XRD profile for nanocomposites showed that the intermetallic phases of MgZn2, MgZn5.31 and Mg2Ca were created after sintering and the SEM micrographs showed that the grain size of nanocomposite reduced by adding the nHA. The nano composite with 1wt. % nHA increased the density of Mg alloy from 1.73 g/cm3 to 1. 75 g/cm3 by filling the pores at the grain boundaries. The compressive strength of Mg alloy increased from 295MPa to 322, 329 and 318MPa by addition of 1, 2.5 and 5wt. % nHA, respectively.
H. Mirzakouchakshirazi, A. Eivani, Sh. Kheirandish,
Volume 14, Issue 4 (12-2017)
Abstract
Effects of annealing treatment after equal channel angular pressing (ECAP) on the interface properties and shear bond strength of Al/Cu bimetallic rods were investigated. For the as-deformed samples, the one with two passes of ECAP indicated higher shear bond strength. Formation of a layer of intermetallic compounds after annealing treatment is confirmed. In general, by increasing annealing temperature, thickness of intermetallic compounds at the interface increases. Shear bond strength was initially reduced by annealing at 200, 250 and 300 ͦ C and increased at 350 ͦ C. With further increase in annealing temperature to 400 ͦ C, shear bond strength slightly decreased which is correlated to the increased thickness of the intermetallic compounds.
A. Eivani, S.h. Seyedein, M. Aboutalebi,
Volume 15, Issue 1 (3-2018)
Abstract
In this research, samples of AlMg0.7Si aluminum alloy are deformed up to three passes using equal channel angular pressing (ECAP). Formation of a sub-micron structure after three passes of ECAP is demonstrated. Microstructural stability of the samples is investigated at temperatures of 300-500 °C. At 300 °C, fine recrystallized structure forms after 10 min which remains stable when the annealing proceeds up to 18 hrs. However, at 350 °C and higher, the microstructure is quite unstable. Even by 10 sec annealing, the samples exhibit recrystallized structure which turned to abnormal grain growth when temperature enhances to 500 °C and time up to 300 sec.
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. Gholami Shiri, Y. Palizdar, . A. Jenabali Jahromi, Eduardo F. de Monlevade,
Volume 15, Issue 3 (9-2018)
Abstract
The relation between microstructure and the fracture mechanisms of δ-TRIP steel with different Nb-content has been investigated using complementary methods of light microscopy, SEM, EDS, EBSD, X-ray phase analysis and tensile test. The results revealed a close dependency between the presences of constitutive phases i.e. ferrite, bainite, retained austenite and martensite and the mode and characteristics of fracture. All samples revealed almost different fractography pattern which could be associated to the effect of Nb microalloying element. The different fractography patterns were consisted of dimple rupture, riverside and Wallner lines pattern. The proportion of the cleavage fracture in comparison of dimple rapture increased by increasing the Nb-content due to the increase of primary martensite in the microstructure.
M. Fallah Tafti, M. Sedighi, R. Hashemi,
Volume 15, Issue 4 (12-2018)
Abstract
In this study, the microstructural variations, mechanical properties and forming limit diagrams (FLD) of Al 2024 aluminum alloy sheet with the thickness of 0.81mm are investigated during natural ageing (T4) treatment. The most formability in Al 2024 can be achieved just after solution treatment, and it is better to perform the forming process, on this aluminum alloy sheet, in this condition. However, in industrial applications, there is usually a postponement for some hours after solution treatment to begin the forming process that it means the forming process should be done at the natural ageing condition. This condition decreases the formability of Al 2024 sheets. To monitor the properties variations in natural ageing condition, FLDs are determined after specific times (e.g., 0.5, 1.5, 4 and 24 hours). The variations in micro-hardness, yield strength, ultimate tensile strength and elongation at break are observed with changing the ageing time. The scanning electron microscope (SEM) investigations illustrated that density and size of precipitates are changed with ageing time. Moreover, the Nakazima test is utilized to study the forming limits considering the natural ageing condition. Results show by increasing the ageing time, up to 4hr, the majority of properties variations could be seen, and from 4hr to 24hr, the variations are changed slower.
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. Sadeghi, M. Hadi, O. Bayat, H. Karimi,
Volume 17, Issue 1 (3-2020)
Abstract
In this paper a constitutive equation was considered for the isothermal hot compression test of the Mn-Ni-Cr alloy. The hot compression test was performed in the strain rate range of 0.001-0.1 s-1 and deformation temperature was varied from 700 to 900 °C. A considerable reduction in flow stress was observed regardless of the strain rate when temperature was increased from 700 to 750 °C. DTA and XRD evaluation revealed that the removal of Mn3Cr phase and formation of the single solid solution phase were the reason for the flow stress reduction. At the low deformation temperature (700°C) and the high strain rate (0.1 s-1), a partially recrystallized microstructure was observed; this was such that with increasing the temperature and decreasing the strain rate, a recrystallized microstructure was completed. Also, the relationships between flow stress, strain rate and deformation temperature were addressed by the Zener-Holloman parameter in the exponent type with the hot deformation activation energy of 301.07 KJ/mol. Finally, the constitutive equation was proposed for predicting the flow stress at various strain rates and temperatures.
I. Kakaravada, A. Mahamani, V. Pandurangadu,
Volume 17, Issue 1 (3-2020)
Abstract
In the present investigation, A356-TiB2/TiC composites with a various weight fractions (0, 2.5, 5 and 7.5%) were synthesized through a K2TiF6-KBF4-Graphite (C) reaction system. Formation of TiB2 and TiC particulates and their distribution are confirmed by various characterization techniques. The tensile properties such as ultimate strength, yield strength, young's modulus and percentage of elongation in addition to their failure behavior of these composites were studied at ambiance and high temperatures (100, 200 and 3000C). The increment in the volume fraction of the composite raises the hardness and the enhancement of hardness was reported up to 49% at 7.5% reinforced composite due to the strengthening effect. The density and porosity of fabricated composites were investigated. The rise in volume fraction of reinforcement phase declines the density and increase the porosity of composites. Further, the ultimate strength, yield strength, young's modulus is declining by raising the temperature. Result analysis illustrates that the 7.5% reinforced composite retaining the ultimate strength up to 84.4% and the ductility is raised by 27% at 3000C. Yield strength and young's modulus are also retained 74.31% and 71.09% respectively at the similar material and experimental conditions. The fracture surface analysis of the composites illustrates that, the ductile nature of failure appearance microscopically with the formation of fine dimples and voids on fracture surface at elevated temperatures. Cleavage facets and tear crumples observation indicates the brittle kind of failure at the ambient temperature. Findings from the experimental study provide the tensile behavior of the composites at the regular working temperature of the automobile engine piston.
S. Mortezaei, H. Arabi, H. Seyedein, A. Momeny, M. Soltanalinezhad,
Volume 17, Issue 3 (9-2020)
Abstract
Dynamic Recrystallization (DRX) is one of the likely mechanisms for fine-graining in metals and alloys. The dynamic recrystallization (DRX) phenomena occurs in different thermo-mechanical processing (TMP) conditions for various metallic materials. DRX depends on various materials and thermo-mechanical parameters such as temperature, strain rate, strain, stress and initial microstructure. in the present study, the restoration mechanism of the 17-7PH stainless steel has been investigated using a hot compression test under different conditions of thermo-mechanical treatment. The microstructural characteristics and the behavior of the hot deformation of the under study steel are investigated using flow curves and microstructure images obtained from optical microscopy. The results show that the maximum and steady state stresses are significantly affected by the strain rate and the deformation temperature. So that, the flow stress increases with decrease in the deformation temperature and increase in the strain rate. Microstructural studies confirm the occurrence of DRX as a restoration mechanism in the microstructure for the two phases of austenite and ferrite.
B. Mirzakhani, Y. Payandeh, H. Talebi, M. Maleki,
Volume 17, Issue 3 (9-2020)
Abstract
In this paper, the effect of two-step precipitation hardening on the mechanical properties of Al-3.7Cu-1Mg was investigated. For this meaning, some specimens were subjected to the first step aging at 175, 190 and 205°C for 2 h, once the samples solution treated at 500°C. To have stable precipitates uniformly distributed in the microstructure and to reduce the heat treatment time, the second step was implied at 65°C. The tensile and hardness tests were performed at ambient temperature immediately after aging. The results indicated that depending on the first step temperature, the second aging time affects the alloy mechanical behavior in different aspects. A factor named SNMP introduced to determine the cycle giving the best mechanical properties. The strength and elongation increase 1.5 and 2 times respectively; compared to the values reported in the DIN EN 755-2 standard by performing the two-step aging cycle, consisting of the first-stage at 175°C and the second step at 65°C for 10 hours. Moreover, using the proposed two-step aging, the heat treatment time was reduced considerably compared to the conventional precipitation hardening process.
Mahdi Behjati , Seyed Ali Asghar Akbari Mousavi , Yaser Vahidshad,
Volume 22, Issue 4 (12-2025)
Abstract
This work presents a comprehensive investigation of the high cycle fatigue behavior of Haynes 25 cobalt-based superalloy and its welds produced by pulsed continuous-wave (CW) laser welding. The alloy, manufactured through vacuum induction melting and electroslag remelting followed by rolling and annealing, exhibited a yield strength of 650 MPa, an ultimate tensile strength of 1050 MPa, and an outstanding elongation of 57% at room temperature. The fatigue limit was determined by test method as 200 MPa for lifetimes exceeding 10⁸ cycles, highlighting its excellent resistance to cyclic loading. For the weld zone, fabricated under optimized pulsed CW laser parameters, the yield and ultimate tensile strengths were 660 MPa and 965 MPa, respectively, with a fatigue limit of 175 MPa. Advanced microstructural analyses using OM, SEM, EBSD, and XRD revealed an austenitic FCC matrix with carbide precipitates, predominantly (W, Cr)₇C₃ and M₆C, decorating both the matrix and grain boundaries. Fatigue crack initiation in the base metal was associated with carbide clusters near the surface, while in the weld zone it was strongly linked to near-surface gas porosity defects. These findings not only establish fundamental fatigue benchmarks for Haynes 25 but also provide the first direct insights into the microstructural origins of fatigue damage in its laser-welded joints, thereby addressing a critical knowledge gap for its deployment in high-temperature and cyclic-loading environments.
Sahar Ziraki, Amir Moghaddam Kia, Ramin Ebrahimi,
Volume 22, Issue 4 (12-2025)
Abstract
In this study, an existing approach for estimating fatigue life using tensile data was extended and applied to 4340 steel under different temperature. The S-N and strain-life curves were plotted at 25, 200, and 350 ˚C. The Basquin and Coffin-Manson equation constants were determined based on the corrected true fracture stress and strain values. Moreover, the b constants were approximated as -0.065, -0.072, and -0.073 at 25, 200, and 350 ˚C, respectively. This was achieved by setting the alternating stress equal to the fatigue limit in an infinite number of cycles when b leveled off. The transition fatigue life of 1000 cycles was considered for 4340 steel to determine the c constants, which were determined to be -0.69, -0.7, and -0.699, at 25, 200, and 350 ˚C, respectively and the strain-life curves were plotted. Comparison of S-N curves obtained from both fatigue and tensile data revealed strong agreement, indicating that the tensile test is a simple and cost-effective method capable of providing a quick estimate of high- and low-cycle fatigue behavior and serving as a suitable alternative to conventional fatigue testing.
