Jafar Khalil-Allafi | Sahand University of Tec. (original) (raw)
Papers by Jafar Khalil-Allafi
Social Science Research Network, 2022
Transactions of The Institute of Metal Finishing, Jun 22, 2023
Biomaterials advances, Jul 1, 2023
Philosophical Magazine, 2003
Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been ra... more Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been rationalized on the basis of dislocation stress fields, coherency stress fields around Ni 4 Ti 3 precipitates and evolving Ni concentrations between precipitates during ageing. ...
Social Science Research Network, 2022
In this paper, microstructure characterization of friction stir welding (FSW) joint of 7055-T6 al... more In this paper, microstructure characterization of friction stir welding (FSW) joint of 7055-T6 aluminum alloy was performed via scanning electron microscope, electron backscatter diffraction, and transmission electron microscope technology. The nanomechanical behavior of FSW joint was systematically studied using nanoindentation technique. The relationship between microstructure and nanomechanical behavior was established and the nanohardness and microhardness were analyzed. The results show that FSW led to grain refinement of aluminum alloy and continuous dynamic recrystallization and geometric dynamic recrystallization were the primary mechanisms of grain refinement. The precipitated phase dissolved and coarsened during FSW, which led to a decrease in the microhardness of the joint. The nano-hardness of each zone of the joint displayed indentation size effect. The creep behavior at room temperature conformed to the Voigt model, and dislocation glide was the primary creep mechanism. The stir zone (SZ) and thermo-mechanically affected zone (TMAZ) had high nano-hardness and elastic modulus, while TMAZ and heat-affected zone (HAZ) had high creep resistance at room temperature. The nanomechanical behavior was mainly affected by precipitation in the grain interior.
Philosophical Magazine, 2003
Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been ra... more Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been rationalized on the basis of dislocation stress fields, coherency stress fields around Ni 4 Ti 3 precipitates and evolving Ni concentrations between precipitates during ageing. ...
International Journal of Engineering, Jul 1, 2013
The aim of the present research is to convert bioinert surface of NiTi to bioactive and biocompat... more The aim of the present research is to convert bioinert surface of NiTi to bioactive and biocompatible surface. In order to develop a bioactive and corrosion resistant film on NiTi, electrophoretic deposition process was done and TiO2 particles were deposited on the NiTi surface. Suspensions including TiO2 particles were prepared using a mixture of acetone and n-butanol (0%, 30%, 60%, 80% and 100% acetone) without using any dispersant. Sedimentation test was used to characterize the suspensions. SEM investigations on surface morphology of coatings shows deposition within 0% acetone cause to crack-free and dense coating with relatively coarse grains and high corrosion resistance.
Journal de physique, Oct 1, 2003
Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiom... more Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiometric Heusler-type Ni 2:16 Mn 0:78 Ga 1:06 single crystal (conduction electron-to-atom ratio = 7.56). The splitting of a cubic (020) peak on a reciprocal lattice c Ã-plane was traced with decreasing temperature from 400 to 37 K. It was found that an orthorhombic structure (a > b > c) appears slightly below the transformation temperature as a metastable transient precursor structure before the formation of a final stable tetragonal structure (a ¼ b < c). The modes of deformation from cubic to orthorhombic are (i) simple shrinking and elongation of two cubic axes or (ii) a shuffling-like deformation along the cubic h110i direction on one of the cubic planes. The mode of deformation from orthorhombic to tetragonal is a shuffling-like deformation along the orthorhombic h110i direction on the orthorhombic c-plane. Both shuffling-like deformations originate from tilting deformations that preserve the common h111i direction.
International Journal of Materials Research, Jun 1, 2004
The size distributions and volume fractions of Ni4Ti3 precipitates in Ni-rich Ni –Ti shape memory... more The size distributions and volume fractions of Ni4Ti3 precipitates in Ni-rich Ni –Ti shape memory alloys affect their mechanical and functional properties. In the present work precipitate sizes and volume fractions were measured after various thermo-mechanical treatments using transmission electron microscopy (TEM) in combination with quantitative metallography. TEM tilting experiments revealed that the Ni4Ti3 particles have a disk-like shape with a disk diameter D and a disk thickness t. These two parameters together with the number density of particles per unit volume were determined after stress-free and stress-assisted aging at 400, 500 and 530 °C. Volume fraction results are presented after different thermo-mechanical treatments and our quantitative metallographic procedure is documented.
Surface & Coatings Technology, Sep 1, 2022
مواد و فناوری های پیشرفته, Jun 22, 2009
Materials Science and Engineering: C, Jul 1, 2017
The present study deals with pulse electrochemical deposition of HA on NiTi alloy and invitro eva... more The present study deals with pulse electrochemical deposition of HA on NiTi alloy and invitro evaluation of coatings. At first step, a thermo-chemical surface modification process was applied to control the Ni release of the alloy. The electrochemical deposition of CaP coatings were examined at both dilute and concentrated solutions. The morphology and the composition of coatings were studied using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Plate like and needle like morphologies were formed for dilute and concentrated solution respectively and HA phase was formed by increasing the pulse current density for both electrolyte. The thickness of the samples was measured using cross sectioning technique. Fibroblast cell culture test on the coated samples revealed that the HA coating obtained by dilute solution shows the best biocompatibility. Also, MTT assay showed the highest cell density and cell proliferation after 5 days for the HA coating of dilute solution. The contact angle of samples was measured and the coated samples showed a hydrophilic surface. Soaking the sample in SBF revealed that the crystallization rate of calcium-phosphate compounds is higher on the plate like HA coating as compared to the needle like morphology. The P release of the HA coated samples were measured in a physiological saline solution and the results show that the ions releasing in the plate like
Journal of Welding Science and Technology of Iran, Jan 10, 2020
اﺳﺪي ﺳﻌﯿﺪ ﻫﻤﮑﺎران و ﻧﺸﺮ ، ﯾ ﻪ ﻓﻨﺎور و ﻋﻠﻮم ي ﺟﻮﺷﮑﺎر ي ا ﯾ ﺮان، ﺳ... more اﺳﺪي ﺳﻌﯿﺪ ﻫﻤﮑﺎران و ﻧﺸﺮ ، ﯾ ﻪ ﻓﻨﺎور و ﻋﻠﻮم ي ﺟﻮﺷﮑﺎر ي ا ﯾ ﺮان، ﺳﺎل ﭘﻨﺠﻢ ﺷﻤﺎره ، 2 ، زﻣﺴﺘﺎن و ﭘﺎﯾﯿﺰ 1398 ﺻﻔﺤﻪ ، 152-141 142 (0.635 × 0.432 mm) were selected and the laser welding technique was used to connect the wires. The microstructure, chemical composition and phasesin the weld zone of the joints werestudied with Optical microscopy (OM), Scanning electron microscopy (SEM) equipped with EDS analysis system, focused X-ray diffraction (Micro-XRD).Also, the mechanical properties of the weld zone were investigated by using Vickers microhardness test. Microstructure investigation showed that the obtained microstructure from the laser weld of these alloys has a dendritic and nonhomogeneous structure. According to XRD analysis, brittle intermetallic compounds such as Fe 2 Ti, Cr 2 Ti, TiNi 3 , and Ti 2 Ni wereformed during laser welding in the weld zone. Formation of these brittle intermetallics caused increasing the hardness of the weld zoneabout 800 HV. and decreasing the mechanical properties. Also, Fe 2 Ti intermetallic particles mainly formed in the weld region near the NiTi fusion zone which results in stress concentration, micro-cracks formation and dropping joints mechanical properties. Therefore, a suitable modification process is required to control the chemical composition of the weld zone and improving the joint properties of dissimilar laser welded archwires of these alloys.
Journal of Materials Engineering and Performance, 2016
Metals and Materials International, Jan 31, 2021
In this study, the influences of the stress aging process on the electrochemical behaviors toward... more In this study, the influences of the stress aging process on the electrochemical behaviors toward evaluating corrosion resistance of NiTi shape memory alloys in the in-vitro condition have been investigated. For this approach, the samples have been manufactured by introducing multiple precipitation morphology in the alloy structure via applying different levels of stresses during the aging process. The samples were characterized using multiply electron microscopy, electrochemical methods, X-ray diffraction, and differential scanning calorimetry. Results show that by prolonging aging time from 1 to 5 h and increasing the stress aging level (15–60-150 MPa) the corrosion resistance improves, which is implied a better formation of a protective layer. It seems that homogeneous precipitation of Ni-rich phases under the stress aging process improves the corrosion resistance of the alloy.
Journal of Manufacturing Processes, Jul 1, 2020
In this study, dissimilar laser welding of NiTi to stainless steel (SS) orthodontic archwires was... more In this study, dissimilar laser welding of NiTi to stainless steel (SS) orthodontic archwires was investigated. As a novel and more operational approach, Ni powder was used as a weld filler metal to improve the properties of joints in laser welding of these alloys. Therefore, welding was performed in two conditions, with and without Ni powder addition, and the results were compared. Optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and focused X-ray diffraction (micro-XRD) analysis were used to study the microstructure, chemical composition and phase characteristics of joints. The Fe-Ni-Ti ternary phase diagram was used as a tool to analyze the phase changes in weld zone with chemical composition variations in two conditions. Results showed that brittle intermetallics such as Fe 2 Ti and Cr 2 Ti were formed in zones close to NiTi weld interface in joints without Ni powder addition. However, Ni powder had favorable effects on microstructure, chemical composition and mechanical properties of laser welded joints. In fact, use of Ni powder changed primary solidifying phase region from Fe 2 Ti to ductile phases of Ni 3 Ti and γ, and consequently promotes the formation of these ductile phases in the weld zone. Moreover, as a result of chemical composition dilution by Ni, the microstructure of weld zone changed from dendrite to dendrite-cellular structure by suppressing the constitutional undercooling in Ni powder added condition. Furthermore, microhardness tests revealed that the addition of Ni powder caused the average hardness of weld zone to decrease from 580 HV down to 325 HV due to aforementioned intermetallic phase replacement. On the other hand, tensile properties of joints were improved and reached to a tensile strength of 300 MPa and a fracture strain of 2.9 % by adding Ni powder. These values for the welding without Ni powder addition were 150 MPa and, 1.8 %, respectively.
Surface & Coatings Technology, Oct 1, 2023
Journal of Materials Engineering and Performance, Jul 1, 2020
This paper presents the results from validation of models for prediction of chloride ingress in c... more This paper presents the results from validation of models for prediction of chloride ingress in concrete exposed in de-icing salt road environment. Three models including the simple error-function complement (ERFC) model, the DuraCrete model and the ClinConc model, were evaluated using the measurement data collected from both the field exposure site after over ten years exposure and the real road bridges after 25-30 years in service. The sensitivity of input parameters in each model is analysed. The results show that, among different input parameters, the age factor is the most sensitive one. The simple ERFC model significantly overestimates chloride ingress. The DuraCrete model, if the input parameters are properly selected, may give a reasonably good prediction, otherwise often underestimates chloride ingress. The ClinConc model in general gives fairly good predictions for chloride ingress in de-icing salt road environment with heavy traffic at high speed.
Journal of Materials Science, Jul 1, 2010
NiTi-shape memory alloys have superior-shape memory effect and super elastic behavior because of ... more NiTi-shape memory alloys have superior-shape memory effect and super elastic behavior because of the thermo-elastic and the reversible martensitic transformation [13]. The high-temperature phase austenite with the B2 struc-ture, on cooling, transforms to low-temperature phase ...
Materials & Design, Mar 1, 2018
Influence of stress aging process on variants of nano-Ni4Ti3 precipitates and martensitic transfo... more Influence of stress aging process on variants of nano-Ni4Ti3 precipitates and martensitic transformation temperatures in NiTi shape memory alloy. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Jmade(2017),
Social Science Research Network, 2022
Transactions of The Institute of Metal Finishing, Jun 22, 2023
Biomaterials advances, Jul 1, 2023
Philosophical Magazine, 2003
Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been ra... more Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been rationalized on the basis of dislocation stress fields, coherency stress fields around Ni 4 Ti 3 precipitates and evolving Ni concentrations between precipitates during ageing. ...
Social Science Research Network, 2022
In this paper, microstructure characterization of friction stir welding (FSW) joint of 7055-T6 al... more In this paper, microstructure characterization of friction stir welding (FSW) joint of 7055-T6 aluminum alloy was performed via scanning electron microscope, electron backscatter diffraction, and transmission electron microscope technology. The nanomechanical behavior of FSW joint was systematically studied using nanoindentation technique. The relationship between microstructure and nanomechanical behavior was established and the nanohardness and microhardness were analyzed. The results show that FSW led to grain refinement of aluminum alloy and continuous dynamic recrystallization and geometric dynamic recrystallization were the primary mechanisms of grain refinement. The precipitated phase dissolved and coarsened during FSW, which led to a decrease in the microhardness of the joint. The nano-hardness of each zone of the joint displayed indentation size effect. The creep behavior at room temperature conformed to the Voigt model, and dislocation glide was the primary creep mechanism. The stir zone (SZ) and thermo-mechanically affected zone (TMAZ) had high nano-hardness and elastic modulus, while TMAZ and heat-affected zone (HAZ) had high creep resistance at room temperature. The nanomechanical behavior was mainly affected by precipitation in the grain interior.
Philosophical Magazine, 2003
Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been ra... more Multiple-step martensitic transformations in Ni-rich NiTi shape memory alloys have so far been rationalized on the basis of dislocation stress fields, coherency stress fields around Ni 4 Ti 3 precipitates and evolving Ni concentrations between precipitates during ageing. ...
International Journal of Engineering, Jul 1, 2013
The aim of the present research is to convert bioinert surface of NiTi to bioactive and biocompat... more The aim of the present research is to convert bioinert surface of NiTi to bioactive and biocompatible surface. In order to develop a bioactive and corrosion resistant film on NiTi, electrophoretic deposition process was done and TiO2 particles were deposited on the NiTi surface. Suspensions including TiO2 particles were prepared using a mixture of acetone and n-butanol (0%, 30%, 60%, 80% and 100% acetone) without using any dispersant. Sedimentation test was used to characterize the suspensions. SEM investigations on surface morphology of coatings shows deposition within 0% acetone cause to crack-free and dense coating with relatively coarse grains and high corrosion resistance.
Journal de physique, Oct 1, 2003
Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiom... more Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiometric Heusler-type Ni 2:16 Mn 0:78 Ga 1:06 single crystal (conduction electron-to-atom ratio = 7.56). The splitting of a cubic (020) peak on a reciprocal lattice c Ã-plane was traced with decreasing temperature from 400 to 37 K. It was found that an orthorhombic structure (a > b > c) appears slightly below the transformation temperature as a metastable transient precursor structure before the formation of a final stable tetragonal structure (a ¼ b < c). The modes of deformation from cubic to orthorhombic are (i) simple shrinking and elongation of two cubic axes or (ii) a shuffling-like deformation along the cubic h110i direction on one of the cubic planes. The mode of deformation from orthorhombic to tetragonal is a shuffling-like deformation along the orthorhombic h110i direction on the orthorhombic c-plane. Both shuffling-like deformations originate from tilting deformations that preserve the common h111i direction.
International Journal of Materials Research, Jun 1, 2004
The size distributions and volume fractions of Ni4Ti3 precipitates in Ni-rich Ni –Ti shape memory... more The size distributions and volume fractions of Ni4Ti3 precipitates in Ni-rich Ni –Ti shape memory alloys affect their mechanical and functional properties. In the present work precipitate sizes and volume fractions were measured after various thermo-mechanical treatments using transmission electron microscopy (TEM) in combination with quantitative metallography. TEM tilting experiments revealed that the Ni4Ti3 particles have a disk-like shape with a disk diameter D and a disk thickness t. These two parameters together with the number density of particles per unit volume were determined after stress-free and stress-assisted aging at 400, 500 and 530 °C. Volume fraction results are presented after different thermo-mechanical treatments and our quantitative metallographic procedure is documented.
Surface & Coatings Technology, Sep 1, 2022
مواد و فناوری های پیشرفته, Jun 22, 2009
Materials Science and Engineering: C, Jul 1, 2017
The present study deals with pulse electrochemical deposition of HA on NiTi alloy and invitro eva... more The present study deals with pulse electrochemical deposition of HA on NiTi alloy and invitro evaluation of coatings. At first step, a thermo-chemical surface modification process was applied to control the Ni release of the alloy. The electrochemical deposition of CaP coatings were examined at both dilute and concentrated solutions. The morphology and the composition of coatings were studied using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Plate like and needle like morphologies were formed for dilute and concentrated solution respectively and HA phase was formed by increasing the pulse current density for both electrolyte. The thickness of the samples was measured using cross sectioning technique. Fibroblast cell culture test on the coated samples revealed that the HA coating obtained by dilute solution shows the best biocompatibility. Also, MTT assay showed the highest cell density and cell proliferation after 5 days for the HA coating of dilute solution. The contact angle of samples was measured and the coated samples showed a hydrophilic surface. Soaking the sample in SBF revealed that the crystallization rate of calcium-phosphate compounds is higher on the plate like HA coating as compared to the needle like morphology. The P release of the HA coated samples were measured in a physiological saline solution and the results show that the ions releasing in the plate like
Journal of Welding Science and Technology of Iran, Jan 10, 2020
اﺳﺪي ﺳﻌﯿﺪ ﻫﻤﮑﺎران و ﻧﺸﺮ ، ﯾ ﻪ ﻓﻨﺎور و ﻋﻠﻮم ي ﺟﻮﺷﮑﺎر ي ا ﯾ ﺮان، ﺳ... more اﺳﺪي ﺳﻌﯿﺪ ﻫﻤﮑﺎران و ﻧﺸﺮ ، ﯾ ﻪ ﻓﻨﺎور و ﻋﻠﻮم ي ﺟﻮﺷﮑﺎر ي ا ﯾ ﺮان، ﺳﺎل ﭘﻨﺠﻢ ﺷﻤﺎره ، 2 ، زﻣﺴﺘﺎن و ﭘﺎﯾﯿﺰ 1398 ﺻﻔﺤﻪ ، 152-141 142 (0.635 × 0.432 mm) were selected and the laser welding technique was used to connect the wires. The microstructure, chemical composition and phasesin the weld zone of the joints werestudied with Optical microscopy (OM), Scanning electron microscopy (SEM) equipped with EDS analysis system, focused X-ray diffraction (Micro-XRD).Also, the mechanical properties of the weld zone were investigated by using Vickers microhardness test. Microstructure investigation showed that the obtained microstructure from the laser weld of these alloys has a dendritic and nonhomogeneous structure. According to XRD analysis, brittle intermetallic compounds such as Fe 2 Ti, Cr 2 Ti, TiNi 3 , and Ti 2 Ni wereformed during laser welding in the weld zone. Formation of these brittle intermetallics caused increasing the hardness of the weld zoneabout 800 HV. and decreasing the mechanical properties. Also, Fe 2 Ti intermetallic particles mainly formed in the weld region near the NiTi fusion zone which results in stress concentration, micro-cracks formation and dropping joints mechanical properties. Therefore, a suitable modification process is required to control the chemical composition of the weld zone and improving the joint properties of dissimilar laser welded archwires of these alloys.
Journal of Materials Engineering and Performance, 2016
Metals and Materials International, Jan 31, 2021
In this study, the influences of the stress aging process on the electrochemical behaviors toward... more In this study, the influences of the stress aging process on the electrochemical behaviors toward evaluating corrosion resistance of NiTi shape memory alloys in the in-vitro condition have been investigated. For this approach, the samples have been manufactured by introducing multiple precipitation morphology in the alloy structure via applying different levels of stresses during the aging process. The samples were characterized using multiply electron microscopy, electrochemical methods, X-ray diffraction, and differential scanning calorimetry. Results show that by prolonging aging time from 1 to 5 h and increasing the stress aging level (15–60-150 MPa) the corrosion resistance improves, which is implied a better formation of a protective layer. It seems that homogeneous precipitation of Ni-rich phases under the stress aging process improves the corrosion resistance of the alloy.
Journal of Manufacturing Processes, Jul 1, 2020
In this study, dissimilar laser welding of NiTi to stainless steel (SS) orthodontic archwires was... more In this study, dissimilar laser welding of NiTi to stainless steel (SS) orthodontic archwires was investigated. As a novel and more operational approach, Ni powder was used as a weld filler metal to improve the properties of joints in laser welding of these alloys. Therefore, welding was performed in two conditions, with and without Ni powder addition, and the results were compared. Optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and focused X-ray diffraction (micro-XRD) analysis were used to study the microstructure, chemical composition and phase characteristics of joints. The Fe-Ni-Ti ternary phase diagram was used as a tool to analyze the phase changes in weld zone with chemical composition variations in two conditions. Results showed that brittle intermetallics such as Fe 2 Ti and Cr 2 Ti were formed in zones close to NiTi weld interface in joints without Ni powder addition. However, Ni powder had favorable effects on microstructure, chemical composition and mechanical properties of laser welded joints. In fact, use of Ni powder changed primary solidifying phase region from Fe 2 Ti to ductile phases of Ni 3 Ti and γ, and consequently promotes the formation of these ductile phases in the weld zone. Moreover, as a result of chemical composition dilution by Ni, the microstructure of weld zone changed from dendrite to dendrite-cellular structure by suppressing the constitutional undercooling in Ni powder added condition. Furthermore, microhardness tests revealed that the addition of Ni powder caused the average hardness of weld zone to decrease from 580 HV down to 325 HV due to aforementioned intermetallic phase replacement. On the other hand, tensile properties of joints were improved and reached to a tensile strength of 300 MPa and a fracture strain of 2.9 % by adding Ni powder. These values for the welding without Ni powder addition were 150 MPa and, 1.8 %, respectively.
Surface & Coatings Technology, Oct 1, 2023
Journal of Materials Engineering and Performance, Jul 1, 2020
This paper presents the results from validation of models for prediction of chloride ingress in c... more This paper presents the results from validation of models for prediction of chloride ingress in concrete exposed in de-icing salt road environment. Three models including the simple error-function complement (ERFC) model, the DuraCrete model and the ClinConc model, were evaluated using the measurement data collected from both the field exposure site after over ten years exposure and the real road bridges after 25-30 years in service. The sensitivity of input parameters in each model is analysed. The results show that, among different input parameters, the age factor is the most sensitive one. The simple ERFC model significantly overestimates chloride ingress. The DuraCrete model, if the input parameters are properly selected, may give a reasonably good prediction, otherwise often underestimates chloride ingress. The ClinConc model in general gives fairly good predictions for chloride ingress in de-icing salt road environment with heavy traffic at high speed.
Journal of Materials Science, Jul 1, 2010
NiTi-shape memory alloys have superior-shape memory effect and super elastic behavior because of ... more NiTi-shape memory alloys have superior-shape memory effect and super elastic behavior because of the thermo-elastic and the reversible martensitic transformation [13]. The high-temperature phase austenite with the B2 struc-ture, on cooling, transforms to low-temperature phase ...
Materials & Design, Mar 1, 2018
Influence of stress aging process on variants of nano-Ni4Ti3 precipitates and martensitic transfo... more Influence of stress aging process on variants of nano-Ni4Ti3 precipitates and martensitic transformation temperatures in NiTi shape memory alloy. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Jmade(2017),