Effect of Addition of Rare Earth Elements on the Microstructure, Texture, and Mechanical Properties of Extruded ZK60 Alloy

S. Najafi,M. Sabbaghian,A. Sheikhani,P. Nagy,K. Fekete,J. Gubicza 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.6

Microstructure, texture and mechanical properties of extruded ZK60 alloys containing different rare earth (RE) elementswere studied. Two alloys containing 1 and 2 wt% Ce-rich lanthanides as well as two other alloys with 1 and 2 wt% Y wereprepared and denoted as ZK60–1RE, ZK60–2RE, ZK60–1Y and ZK60–2Y, respectively. The results showed that the additionof RE elements refined the grain size of the ZK60 alloy, and Y had a more significant effect on the grain size reduction. The finer grain size in the ZK60–1Y and ZK60–2Y alloys (2.3 and 2.1 μm, respectively) compared to ZK60–1RE andZK60–2RE alloys (6.2 and 3.7 μm, respectively) was attributed to the pinning effect of very fine secondary phases on grainboundaries. While the ZK60–1Y alloy exhibited a fiber texture with a slight rotation of < 1010 > poles around the extrusiondirection, the ZK60–1RE alloy showed a new texture component known as RE texture. Moreover, there were no changes inthe fiber-like texture component of ZK60–2RE and ZK60–2Y alloys. The mechanical properties of the alloys were assessedby shear punch test. Accordingly, the addition of RE and Y elements enhanced the shear strength, and the maximum ultimateshear strength of 176 MPa was obtained for the ZK60–2RE alloy. The higher dislocation density, the lower volume fractionof dynamically recrystallized regions compared to other alloys, and the large fraction of secondary phase particles wereresponsible for this high strength value.

Effect of Ce Addition on the Tribological Behavior of ZK60 Mg-Alloy

S. M. Banijamali,Y. Palizdar,S. Najafi,A. Sheikhani,M. Soltan Ali Nezhad,P. Valizadeh Moghaddam,H. Torkamani 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8

The present work aims to study the tribological behavior of an extruded ZK60 alloy in the presence of Ce; in a previous study, among ZK60 alloys with diferent Ce addition rates, an alloy with 3 wt% of Ce was found to exhibit the mostpromising mechanical (e.g., hardness and strengths) properties, while its wear behavior remained unknown. The results ofmicrostructural examinations by optical and electron microscopes show that Ce addition reduces the grain size from 6.1 to2.0 μm. Besides, in addition to the precipitates already distributed in the base alloy (Mg7Zn3), Ce could promote the formation of a new precipitate (MgZn2Ce), increasing the total fraction of the precipitates. These microstructural evolutionsenhance the strengths of the studied ZK60 alloy, as the yield and tensile strengths increase from 212 to 308 MPa and from297 to 354 MPa, respectively. A pin on disc tribometer was employed to study the wear behavior of the developed alloyunder diferent normal loads (5, 20, 40, and 60 N). The results show that the base and Ce-added alloys exhibit almost asimilar frictional behavior, while the wear resistance of the Ce-added alloy is higher within the load ranges applied: (i) inlow load conditions (5 and 20 N), where the abrasive wear is the active mechanism, the precipitates in the Ce-added alloycould enhance the wear resistance. (ii) Under the load of 40 N, oxidative wear is also an operative wear mechanism, leadingto a sharp increase in the wear rate of the alloys. In this condition, Ce could provide a protective oxide layer, which couldimprove the wear resistance of the alloy. (iii) At a load of 60 N, both studied alloys exhibit a similar wear rate due to a severeoxidation condition. Therefore, beyond this loading condition, the microstructural evolutions (e.g., change in precipitationbehavior) caused by Ce addition can no longer contribute to the enhancement of wear resistance.

The Effect of Manual Acupressure (Point BL32) on Pain Associated with Intramuscular Injections of Magnesium Sulfate

Seyed S. Najafi,Setareh Nazaribin,Marzieh Momennasab,Amin Kordi Yoosefinejad 사단법인약침학회 2019 Journal of Acupuncture & Meridian Studies Vol.12 No.02

The aim of this study was determining the effect of acupressure on the severity of pain associated with intramuscular injections of magnesium sulfate administered by the Ztrack technique in patients with eclampsia and preeclampsia. Forty-eight patients participated in this single-group clinical trial, which was conducted in three stages. For each patient, three intramuscular injections were administered by the Z-track technique. The first injection was administered by the conventional method. The second injection at a sham control point and the third injection using acupressure (BL32) were administered. Pain severity was measured on a visual analogue scale. The mean pain intensity was 7.22 in the first, 4.75 in the second and 1.94 in the third injections (p < 0.001). The results of the study showed that acupressure at the BL32 point before intramuscular injection of magnesium sulfate significantly reduced the injection-related pain.

Numerical solution of non-Fourier heat transfer during laser irradiation on tooth layers

S. Falahatkar,A. Nouri-Borujerdi,M. Najafi,A. Mohammadzadeh 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.12

This study reports on the simulation of temperature distribution of human tooth under a laser beam based on non-Fourier models. The temperature in the tooth depth that directly results from the conduction heat transfer process is caused by the lengthy thermal relaxation time in the tooth layers. A detailed tooth composed of enamel, dentin, and pulp with unstructured shape, uneven boundaries, and realistic thicknesses was considered. A finite difference scheme was separately adopted to solve time-dependent equations in solid layers and soft tissue of the tooth. In this study, a dual-phase-lag non-Fourier heat conduction model was applied to evaluate temperature distribution induced by laser irradiation. Results show that for the laser-irradiated tooth, the phase lag time of heat flux (τ q ) greatly affects the temperature of the early stage, whereas the phase lag time of the temperature gradient (τ T ) significantly influences the temperature of the later stage. Prediction of temperature profile in the tooth based on this investigation is more real using the non-Fourier model (i.e., τ q = 16 and τ T = 2 millisecond) compared with experimental studies. Meanwhile, the Fourier model (τ q = τ T ) or classical Fourier form (τ q = τ T = 0) and the thermal wave model (τ q = 16 and τ T = 0) led to unreal heated point on the enamel. The effects of laser parameters, such as laser exposure time and laser intensity on the pulp, were also investigated. Increasing the laser duration and simulation time after laser irradiation was a logical approach to pulp ablation compared with increasing the laser intensity.

Enhanced triisopropylbenzene cracking and suppressed coking on tailored composite of Y-zeolite/amorphous silica–alumina catalyst

M.S. Aghakhani,A.A. Khodadadi,Sh. Najafi,Y. Mortazavi 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.5

Catalytic composites of Y-zeolite-amorphous silica–alumina (ASA) were prepared by four different methods to enhance pre-cracking and cracking of triisopropylbenzene (TIPB). TIPB cracking on composite catalysts were compared with a conventionally prepared catalyst. The samples were characterized by FESEM, XRD, N2-adsorption and NH3-TPD. The catalysts performance was evaluated by triisopropylbenzene cracking at 350˚ C in a fixed bed reactor. The coke content of the catalysts was measured by TPO. Compared to the conventional catalyst, significantly deeper cracking to benzene of about 117% higher, up to 62% lower amount of coke, and lower deactivation rate are observed for the composite catalysts.

Synthesis of nanostructured CuInSe2 (CIS) powder via solvothermal processing using diethylamine as a solvent

M. Najafi,M. R. Vaezi,S. K. Sadrnezhaad 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.6

In this paper, CuInSe2 nanostructures have been synthesized via a solvothermal method using diethyamine as a solvent. Various morphologies of CuInSe2 were obtained from the reaction of cupric chloride, indium chloride and selenium powder by changing the solvothermal conditions. The effect of the experimental parameters such as reaction time, temperature and concentration of the selenium powder were studied. The crystalline structures and morphologies of the products were characterized by means of X- ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) techniques,respectively. The results show that the morphology and dimensions of the CIS nanostructures obtained can be controlled through selective processing conditions. The optical properties and band gaps were estimated with a UV-Vis spectrophotometer. The electrical resistances of the samples were recorded by using four point probes.

Order of N Complexity Transform Domain Adaptive Filters : Software and Hardware Implementation

A. Najafi,B. Farhang Boroujeny,G. S. Samudra 대한전자공학회 1993 JTC-CSCC : Joint Technical Conference on Circuits Vol.- No.-

Prediction of Scour in Plunge Pools below Outlet Bucket Using Artificial Intelligence

B. Lashkar-Ara,S. M. H. Ghotbi,L. Najafi 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.7

Accurate prediction of sediment scour hole dimensions downstream of hydraulic structures, e.g. the outlet bucket, is a complex and not straight forward engineering problem encountered worldwide. Dimensions of a scour hole are usually determined by empirical equations which their validation is limited by experimental conditions. As constructing physical models has its own difficulty, determining of scour hole parameters has been applied in this paper for a collection of previous experimental studies. Two artificial intelligence techniques (ANN & ANFIS) are used and the results are compared with empirical equation for maximum scour holes using nonlinear regression method. Artificial Neural Network (ANN) simply represents interconnection of neurons, each of which carries out the task of combining the input, determining its strength by comparing the combination and finding out the result. On the other hand, ANFIS is a hybrid scheme which uses the learning capability of the ANN to derive the fuzzy rules with membership functions. The results showed that maximum error caused by applying ANFIS techniques in estimating scour hole dimensions was 5.2 percent while the error in neural network model was 10.38 percent. The significance of different parameters was discussed and a simple, innovative formula was proposed. This formula is an interesting tool for the engineering community due to its preferences for estimating the parameters of complex phenomena like erosion procedures. It has been established that scour estimations could be improved if soft computation is used in place of the traditional formulae.

Modelling Spatial, Altitudinal and Temporal Variability of Annual Precipitation in Mountainous Regions: The Case of the Middle Zagros, Iran

Rashid Saeidabadi,Mohammed S. Najafi,GholamReza Roshan,Jennifer M. Fitchett,Shoaieb Abkharabat 한국기상학회 2016 Asia-Pacific Journal of Atmospheric Sciences Vol.52 No.5

Relationships between precipitation and elevation are difficult to model for mountainous regions, due to complexities in topography and moisture sources. Attempts to model these relationships need to be tested against long-term location specific meteorological data, and hence require a case-study approach. This study uses artificial neural networks to model these relationships for the Middle of Zagros region, in semi-arid western Iran. Precipitation data for the region were collected for 1995-2007. Annual precipitation was designated as the target variable for the network, which additionally included variables significantly related to precipitation for the region, including longitude, latitude, elevation, slope, distance from the ridge, and relative distance from moisture. Long-term changes in annual precipitation for the region are investigated for 1961-2010. The artificial neural network (ANN) model explains 76% of the spatial variability of precipitation in the Middle Zagros. Precipitation predominantly increases with elevation on the windward slope, to a maximum height of 2500 m.asl, and thereafter either remains constant or decreases slowly to the ridge. Precipitation in the region has decreased significantly over the study period, with fluctuations driven by AO, NAO, ENSO and variability in the strength of pressure centers. Spectral analysis reveals significant oscillations of 2-4 and 5 yr periods, which correspond temporally with cycles in macro-scale circulation, ENSO and the Mediterranean Low pressure.

Adsorption of malachite green from aqueous solution by carboxylate group functionalized multi-walled carbon nanotubes: Determination of equilibrium and kinetics parameters

M. Rajabi,B. Mirza,K. Mahanpoor,M. Mirjalili,F. Najafi,O. Moradi,H. Sadegh,R. Shahryari-ghoshekandi,M. Asif,I. Tyagi,S. Agarwal,Vinod Kumar Gupta 한국공업화학회 2016 Journal of Industrial and Engineering Chemistry Vol.34 No.-

MWCNTs functionalized with the carboxylate group are used as efficient adsorbent for the rapid removaland fast adsorption of malachite green from the aqueous solutions. The optimized contact time and pHwere 10 min and 9, respectively. The effect of temperature revealed that the adsorption capacity ofmalachite green (MG) dye increased with increasing contact time, temperature and pH of the workingsolution. The adsorption equilibrium and kinetic data was well fitted and found to be in good agreementwith the Langmuir isotherm model and pseudo second order kinetic model respectively with highcorrelation coefficient.