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Prof. Mohammad Elahinia
Dynamic and Smart Systems Laboratory, Department of Mechanical Industrial and Manufacturing Engineering, The University of Toledo, OH 43606, USA

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Research Keywords & Expertise

0 Additive Manufacturing
0 Design Engineering
0 Design Optimization
0 Electrical Engineering
0 Finite Element Analysis

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Additive Manufacturing
Shape Memory Alloys
Medical Devices
Finite Element Analysis
3D printing
MR fluids
Machining
Materials engineering

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Journal article
Published: 12 August 2021 in Journal of Manufacturing and Materials Processing
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In this study, depth-sensing indentation creep response of cast and additively manufactured (laser powder bed fusion) NiTi alloys in heat-treated conditions have been investigated at ambient temperature. Indentation creep tests were evaluated with the help of a dual-stage approach comprising a loading segment with a subsequent constant load-holding stage and an unloading phase afterward. The investigation was carried out at a maximum load of 50 mN along with a holding time of 600 s. Different creep parameters comprising indentation creep displacement, creep strain rate, creep stress exponent as well as the indentation size effect have been analyzed quantitatively for the employed materials. In addition, microstructural analysis has been performed to ascertain the processing–microstructure–creep property correlations. A substantial indentation size effect was seen for both cast and printed NiTi samples in heat-treated conditions. According to the creep stress exponent measurements, the dominant mechanism of rate-dependent plastic deformation for all NiTi samples at ambient temperature is attributed to the dislocation movement (i.e., glide/climb). The outcome of this investigation will act as a framework to understand the underlying mechanisms of ambient-temperature indentation creep of the cast and printed NiTi alloy in conjunction with heat-treated conditions.

ACS Style

Minhazul Islam; Parisa Bayati; Mohammadreza Nematollahi; Ahmadreza Jahadakbar; Mohammad Elahinia; Meysam Haghshenas. Ambient-Temperature Indentation Creep of Shape Memory NiTi Alloys: Additively Manufactured versus Cast. Journal of Manufacturing and Materials Processing 2021, 5, 87 .

AMA Style

Minhazul Islam, Parisa Bayati, Mohammadreza Nematollahi, Ahmadreza Jahadakbar, Mohammad Elahinia, Meysam Haghshenas. Ambient-Temperature Indentation Creep of Shape Memory NiTi Alloys: Additively Manufactured versus Cast. Journal of Manufacturing and Materials Processing. 2021; 5 (3):87.

Chicago/Turabian Style

Minhazul Islam; Parisa Bayati; Mohammadreza Nematollahi; Ahmadreza Jahadakbar; Mohammad Elahinia; Meysam Haghshenas. 2021. "Ambient-Temperature Indentation Creep of Shape Memory NiTi Alloys: Additively Manufactured versus Cast." Journal of Manufacturing and Materials Processing 5, no. 3: 87.

Journal article
Published: 07 April 2021 in Journal of Alloys and Compounds
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This study is the first study on the compressive and tensile stress-strain revealing the deformation anisotropy among laser powder bed fusion NiTi parts fabricated with the same process conditions. We investigated the effects of building orientation on the microstructure and the resulting shape memory properties. To this end, three orientations were selected, namely 0, 45, and 90-degree, measured from the build plate and fabricated with the same process parameters. A strong (001) texture was formed along the building direction for all of the samples; a different texture could however be observed along the loading direction (LD). Samples fabricated with 45-degree showed a texture of (110) along the LD, as conformed through X-ray diffraction and backscattered diffraction while 0 and 90 samples still had the (001) texture along with the LD. These texture variations created anisotropic compression-tension behaviors with deformation patterns consistent with single crystals. The (001) -textured parts showed higher strength and lower transformation strain (2.87% @ 200 MPa in tension for 0 ͦ) while the (110) samples showed higher transformation strain at lower stresses (5.31% @ 150 MPa in tension for 45 ͦ).

ACS Style

Mohammadreza Nematollahi; Sayed Ehsan Saghaian; Keyvan Safaei; Parisa Bayati; Paola Bassani; Carlo Biffi; Ausonio Tuissi; Haluk Karaca; Mohammad Elahinia. Building orientation-structure-property in laser powder bed fusion of NiTi shape memory alloy. Journal of Alloys and Compounds 2021, 873, 159791 .

AMA Style

Mohammadreza Nematollahi, Sayed Ehsan Saghaian, Keyvan Safaei, Parisa Bayati, Paola Bassani, Carlo Biffi, Ausonio Tuissi, Haluk Karaca, Mohammad Elahinia. Building orientation-structure-property in laser powder bed fusion of NiTi shape memory alloy. Journal of Alloys and Compounds. 2021; 873 ():159791.

Chicago/Turabian Style

Mohammadreza Nematollahi; Sayed Ehsan Saghaian; Keyvan Safaei; Parisa Bayati; Paola Bassani; Carlo Biffi; Ausonio Tuissi; Haluk Karaca; Mohammad Elahinia. 2021. "Building orientation-structure-property in laser powder bed fusion of NiTi shape memory alloy." Journal of Alloys and Compounds 873, no. : 159791.

Short communication
Published: 10 March 2021 in Materials Letters
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Besides the possibility of fabricating complex geometries, a major advantage of additive manufacturing is tailoring the microstructure and consequently properties of the parts. By changing the process parameters (PPs). Functionally graded systems can be achieved without the need for post-processing or joining. In this study, fabrication of a functionally graded NiTi using selective laser melting was investigated. Using two different sets of PPs resulted in a part with two different functional properties. Several characterization methods were employed to study microstructural distribution. Thermomechanical full-field strain tests showed a novel behavior, a combination of superelastic and shape memory effects at room temperature.

ACS Style

Mohammadreza Nematollahi; Keyvan Safaei; Parisa Bayati; Mohammad Elahinia. Functionally graded NiTi shape memory alloy: Selective laser melting fabrication and multi-scale characterization. Materials Letters 2021, 292, 129648 .

AMA Style

Mohammadreza Nematollahi, Keyvan Safaei, Parisa Bayati, Mohammad Elahinia. Functionally graded NiTi shape memory alloy: Selective laser melting fabrication and multi-scale characterization. Materials Letters. 2021; 292 ():129648.

Chicago/Turabian Style

Mohammadreza Nematollahi; Keyvan Safaei; Parisa Bayati; Mohammad Elahinia. 2021. "Functionally graded NiTi shape memory alloy: Selective laser melting fabrication and multi-scale characterization." Materials Letters 292, no. : 129648.

Review
Published: 24 January 2021 in International Materials Reviews
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In the current review, an exceptional view on the multi-scale integrated computational modelling and data-driven methods in the Additive manufacturing (AM) of metallic materials in the framework of integrated computational materials engineering (ICME) is discussed. In the first part of the review, process simulation (P-S linkage), structure modelling (S-P linkage), property simulation (S-P linkage), and integrated modelling (PSP and PSPP linkages) are elaborated considering different physical phenomena (multi-physics) in AM and at micro/meso/macro scales (multi-scale modelling). The second part provides an extensive discussion of a data-driven framework, which involves extracting existing data from databases and texts, data pre-processing, high throughput screening, and, therefore, database construction. A data-driven workflow that integrates statistical methods, including ML, artificial intelligence (AI), and neural network (NN) models, has great potential for completing PSPP linkages. This review paper provides an insight for both academic and industrial researchers, working on the AM of metallic materials.

ACS Style

Seyed Mahdi Hashemi; Soroush Parvizi; Haniyeh Baghbanijavid; Alvin T. L. Tan; Mohammadreza Nematollahi; Ali Ramazani; Nicholas X. Fang; Mohammad Elahinia. Computational modelling of process–structure–property–performance relationships in metal additive manufacturing: a review. International Materials Reviews 2021, 1 -46.

AMA Style

Seyed Mahdi Hashemi, Soroush Parvizi, Haniyeh Baghbanijavid, Alvin T. L. Tan, Mohammadreza Nematollahi, Ali Ramazani, Nicholas X. Fang, Mohammad Elahinia. Computational modelling of process–structure–property–performance relationships in metal additive manufacturing: a review. International Materials Reviews. 2021; ():1-46.

Chicago/Turabian Style

Seyed Mahdi Hashemi; Soroush Parvizi; Haniyeh Baghbanijavid; Alvin T. L. Tan; Mohammadreza Nematollahi; Ali Ramazani; Nicholas X. Fang; Mohammad Elahinia. 2021. "Computational modelling of process–structure–property–performance relationships in metal additive manufacturing: a review." International Materials Reviews , no. : 1-46.

Journal article
Published: 17 November 2020 in Metals
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Laser powder bed fusion has been widely investigated for shape memory alloys, primarily NiTi alloys, with the goal of tailoring microstructures and producing complex geometries. However, processing high temperature shape memory alloys (HTSMAs) remains unknown. In our previous study, we showed that it is possible to manufacture NiTiHf HTSMA, as one of the most viable alloys in the aerospace industry, using SLM and investigated the effect of parameters on defect formation. The current study elucidates the effect of process parameters (PPs) on the functionality of this alloy. Shape memory properties and the microstructure of additively manufactured Ni-rich NiTiHf alloys were characterized across a wide range of PPs (laser power, scanning speed, and hatch spacing) and correlated with energy density. The optimum laser parameters for defect-free and functional samples were found to be in the range of approximately 60–100 J/mm3. Below an energy density of 60 J/mm3, porosity formation due to lack-of-fusion is the limiting factor. Samples fabricated with energy densities of 60–100 J/mm3 showed comparable thermomechanical behavior in comparison with the starting as-cast material, and samples fabricated with higher energy densities (>100 J/mm3) showed very high transformation temperatures but poor thermomechanical behavior. Poor properties for samples with higher energies were mainly attributed to the excessive Ni loss and resultant change in the chemical composition of the matrix, as well as the formation of cracks and porosities. Although energy density was found to be an important factor, the outcome of this study suggests that each of the PPs should be selected carefully. A maximum actuation strain of 1.67% at 400 MPa was obtained for the sample with power, scan speed, and hatch space of 100 W, 400 mm/s, and 140 µm, respectively, while 1.5% actuation strain was obtained for the starting as-cast ingot. These results can serve as a guideline for future studies on optimizing PPs for fabricating functional HTSMAs.

ACS Style

Mohammadreza Nematollahi; Guher P. Toker; Keyvan Safaei; Alejandro Hinojos; S. Ehsan Saghaian; Othmane Benafan; Michael J. Mills; Haluk Karaca; Mohammad Elahinia. Laser Powder Bed Fusion of NiTiHf High-Temperature Shape Memory Alloy: Effect of Process Parameters on the Thermomechanical Behavior. Metals 2020, 10, 1522 .

AMA Style

Mohammadreza Nematollahi, Guher P. Toker, Keyvan Safaei, Alejandro Hinojos, S. Ehsan Saghaian, Othmane Benafan, Michael J. Mills, Haluk Karaca, Mohammad Elahinia. Laser Powder Bed Fusion of NiTiHf High-Temperature Shape Memory Alloy: Effect of Process Parameters on the Thermomechanical Behavior. Metals. 2020; 10 (11):1522.

Chicago/Turabian Style

Mohammadreza Nematollahi; Guher P. Toker; Keyvan Safaei; Alejandro Hinojos; S. Ehsan Saghaian; Othmane Benafan; Michael J. Mills; Haluk Karaca; Mohammad Elahinia. 2020. "Laser Powder Bed Fusion of NiTiHf High-Temperature Shape Memory Alloy: Effect of Process Parameters on the Thermomechanical Behavior." Metals 10, no. 11: 1522.

Journal article
Published: 16 October 2020 in Engineering Structures
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The large reversible strain upon heating (shape memory effect) or unloading (superelasticity), high power-to-weight ratio, good functional stability, compact size, and lightweight make the rotary NiTi shape memory alloys actuators an interesting candidate for various engineering applications. Additive manufacturing (AM) provides a single step freeform manufacturing process that not only fabricates the complex geometries but also tailors the properties of the printed parts profoundly. In the selective laser melting (SLM) technique, the process parameters (PPs) and scanning strategy show the remarkable effect on the microstructure, the properties, and the size accuracy of as-built parts. Impurity pick-up during the AM process is an unintended incident altering the microstructure and thermomechanical properties of fabricated parts significantly. In this paper, slightly Ni-rich NiTi powder is utilized to fabricate the NiTi tubes with three different thicknesses via the SLM method. It is shown that the bidirectional scanning strategy results in the size deviation of thin-wall tubes. Transformation temperatures (TTs) of the as-fabricated samples are assessed and compared with those of the starting powder. A large shift in TTs is found between the powder and the SLM tubes. The x-ray diffraction pattern shows the martensite phase at room temperature for the starting powder, while the as-built tubes are in the austenite phase coexisting with a secondary phase of Ti-rich oxide. Scanning electron microscopy (SEM) confirms Ti-rich Ti4Ni2Ox precipitates form along the grain boundaries. The characterization of tubes under pure torsional loading shows the localized shear strain on the tube surface. The thermomechanical behavior of the as-fabricated tubes is investigated and shown to exhibit superelastic response with a stable transformation strain of 2.3% after 10 cycles.

ACS Style

Keyvan Safaei; Mohammadreza Nematollahi; Parisa Bayati; Hediyeh Dabbaghi; Othmane Benafan; Mohammad Elahinia. Torsional behavior and microstructure characterization of additively manufactured NiTi shape memory alloy tubes. Engineering Structures 2020, 226, 111383 .

AMA Style

Keyvan Safaei, Mohammadreza Nematollahi, Parisa Bayati, Hediyeh Dabbaghi, Othmane Benafan, Mohammad Elahinia. Torsional behavior and microstructure characterization of additively manufactured NiTi shape memory alloy tubes. Engineering Structures. 2020; 226 ():111383.

Chicago/Turabian Style

Keyvan Safaei; Mohammadreza Nematollahi; Parisa Bayati; Hediyeh Dabbaghi; Othmane Benafan; Mohammad Elahinia. 2020. "Torsional behavior and microstructure characterization of additively manufactured NiTi shape memory alloy tubes." Engineering Structures 226, no. : 111383.

Review
Published: 20 September 2020 in Progress in Materials Science
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NiTi alloys have recently attracted significant attention in aerospace and biomedical applications due to their excellent properties such as high corrosion resistance, proper biocompatibility, superior mechanical properties, and particular functional features like their shape memory effect and superelasticity. Among different manufacturing processes, special attention has been paid to powder metallurgy (PM) techniques such as additive manufacturing (AM) methods due to their advantages. A summary of all PM methods and their pros and cons are provided. This paper provides a comprehensive review of effective parameters on the microstructure and final properties of NiTi manufactured parts through PM methods. The warm and cold green compactions are compared, whereas the effect of alloying elements on the properties is discussed. Besides, the results of employing different processing parameters such as sintering time, temperature, atmosphere, heating rate, building orientation, and energy density are reviewed. In the end, two novel functional structures are considered, and the corresponding studies are summarized. The main objective of this research is to wrap up the main and novel achievements of the recent works on the correlation between process parameters and properties of NiTi parts manufactured by PM processes to give the readers a better understanding of this issue.

ACS Style

Soroush Parvizi; Seyed Mahdi Hashemi; Fatemeh Asgarinia; Mohammadreza Nematollahi; Mohammad Elahinia. Effective parameters on the final properties of NiTi-based alloys manufactured by powder metallurgy methods: A review. Progress in Materials Science 2020, 117, 100739 .

AMA Style

Soroush Parvizi, Seyed Mahdi Hashemi, Fatemeh Asgarinia, Mohammadreza Nematollahi, Mohammad Elahinia. Effective parameters on the final properties of NiTi-based alloys manufactured by powder metallurgy methods: A review. Progress in Materials Science. 2020; 117 ():100739.

Chicago/Turabian Style

Soroush Parvizi; Seyed Mahdi Hashemi; Fatemeh Asgarinia; Mohammadreza Nematollahi; Mohammad Elahinia. 2020. "Effective parameters on the final properties of NiTi-based alloys manufactured by powder metallurgy methods: A review." Progress in Materials Science 117, no. : 100739.

Review
Published: 31 July 2020 in Corrosion and Materials Degradation
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Biodegradable metals have been under significant research as promising alternatives to the currently in-use nonbiodegradable materials in the field of supportive medical implants. In this scope, magnesium and its alloys were widely investigated due to their superior biocompatibility over other metals. Most of the research effort in the literature has been focused on assuring the biocompatibility, improving mechanical properties, and tailoring the corrosion rate of magnesium-based implants. Furthermore, considerable research was done to develop numerical models towards an inexpensive and fast designing tools capable of simulating the degradation/corrosion behavior of magnesium-based implants. Due to the complexity of the degradation process and the various factors that can be involved, several hypotheses were introduced to provide a realistic simulation of the corrosion behavior in vitro and in vivo. A review of the current literature hypothesis and different modeling constitutive equations for modeling the corrosion of magnesium alloys along with a summary of the supplementary experimental methods is provided in this paper.

ACS Style

Moataz Abdalla; Alexander Joplin; Mohammad Elahinia; Hamdy Ibrahim. Corrosion Modeling of Magnesium and Its Alloys for Biomedical Applications: Review. Corrosion and Materials Degradation 2020, 1, 219 -248.

AMA Style

Moataz Abdalla, Alexander Joplin, Mohammad Elahinia, Hamdy Ibrahim. Corrosion Modeling of Magnesium and Its Alloys for Biomedical Applications: Review. Corrosion and Materials Degradation. 2020; 1 (2):219-248.

Chicago/Turabian Style

Moataz Abdalla; Alexander Joplin; Mohammad Elahinia; Hamdy Ibrahim. 2020. "Corrosion Modeling of Magnesium and Its Alloys for Biomedical Applications: Review." Corrosion and Materials Degradation 1, no. 2: 219-248.

Journal article
Published: 01 May 2020 in Materials
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In this study, the effect of the addition of Hf on the oxidation behavior of NiTi alloy, which was processed using additive manufacturing and casting, is studied. Thermogravimetric analyses (TGA) were performed at the temperature of 500, 800, and 900 °C to assess the isothermal and dynamic oxidation behavior of the Ni50.4Ti29.6Hf20 at.% alloys for 75 h in dry air. After oxidation, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to analyze the oxide scale formed on the surface of the samples during the high-temperature oxidation. Two stages of oxidation were observed for the NiTiHf samples, an increasing oxidation rate during the early stage of oxidation followed by a lower oxidation rate after approximately 10 h. The isothermal oxidation curves were well matched with a logarithmic rate law in the initial stage and then by parabolic rate law for the next stage. The formation of multi-layered oxide was observed for NiTiHf, which consists of Ti oxide, Hf oxide, and NiTiO3. For the binary alloys, results show that by increasing the temperature, the oxidation rate increased significantly and fitted with parabolic rate law. Activation energy of 175.25 kJ/mol for additively manufactured (AM) NiTi and 60.634 kJ/mol for AM NiTiHf was obtained.

ACS Style

Hediyeh Dabbaghi; Keyvan Safaei; Mohammadreza Nematollahi; Parisa Bayati; Mohammad Elahinia. Additively Manufactured NiTi and NiTiHf Alloys: Estimating Service Life in High-Temperature Oxidation. Materials 2020, 13, 2104 .

AMA Style

Hediyeh Dabbaghi, Keyvan Safaei, Mohammadreza Nematollahi, Parisa Bayati, Mohammad Elahinia. Additively Manufactured NiTi and NiTiHf Alloys: Estimating Service Life in High-Temperature Oxidation. Materials. 2020; 13 (9):2104.

Chicago/Turabian Style

Hediyeh Dabbaghi; Keyvan Safaei; Mohammadreza Nematollahi; Parisa Bayati; Mohammad Elahinia. 2020. "Additively Manufactured NiTi and NiTiHf Alloys: Estimating Service Life in High-Temperature Oxidation." Materials 13, no. 9: 2104.

Journal article
Published: 19 January 2020 in Metals
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The use of titanium bone fixation plates is considered the standard of care for skeletal reconstructive surgery. Highly stiff titanium bone fixation plates provide immobilization immediately after the surgery. However, after the bone healing stage, they may cause stress shielding and lead to bone resorption and failure of the surgery. Stiffness-modulated or stiffness-matched Nitinol bone fixation plates that are fabricated via additive manufacturing (AM) have been recently introduced by our group as a long-lasting solution for minimizing the stress shielding and the follow-on bone resorption. Up to this point, we have modeled the performance of Nitinol bone fixation plates in mandibular reconstruction surgery and investigated the possibility of fabricating these implants. In this study, for the first time the realistic design of stiffness-modulated Nitinol bone fixation plates is presented. Plates with different levels of stiffness were fabricated, mechanically tested, and used for verifying the design approach. Followed by the design verification, to achieve superelastic bone fixation plates we proposed the use of Ni-rich Nitinol powder for the AM process and updated the models based on that. Superelastic Nitinol bone fixation plates with the extreme level of porosity were fabricated, and a chemical polishing procedure used to remove the un-melted powder was developed using SEM analysis. Thermomechanical evaluation of the polished bone fixation plates verified the desired superelasticity based on finite element (FE) simulations, and the chemical analysis showed good agreement with the ASTM standard.

ACS Style

Ahmadreza Jahadakbar; Mohammadreza Nematollahi; Keyvan Safaei; Parisa Bayati; Govind Giri; Hediyeh Dabbaghi; David Dean; Mohammad Elahinia. Design, Modeling, Additive Manufacturing, and Polishing of Stiffness-Modulated Porous Nitinol Bone Fixation Plates Followed by Thermomechanical and Composition Analysis. Metals 2020, 10, 151 .

AMA Style

Ahmadreza Jahadakbar, Mohammadreza Nematollahi, Keyvan Safaei, Parisa Bayati, Govind Giri, Hediyeh Dabbaghi, David Dean, Mohammad Elahinia. Design, Modeling, Additive Manufacturing, and Polishing of Stiffness-Modulated Porous Nitinol Bone Fixation Plates Followed by Thermomechanical and Composition Analysis. Metals. 2020; 10 (1):151.

Chicago/Turabian Style

Ahmadreza Jahadakbar; Mohammadreza Nematollahi; Keyvan Safaei; Parisa Bayati; Govind Giri; Hediyeh Dabbaghi; David Dean; Mohammad Elahinia. 2020. "Design, Modeling, Additive Manufacturing, and Polishing of Stiffness-Modulated Porous Nitinol Bone Fixation Plates Followed by Thermomechanical and Composition Analysis." Metals 10, no. 1: 151.

Journal article
Published: 12 December 2019 in Scripta Materialia
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This study investigates the high-temperature shape memory behavior of NiTiHf alloys fabricated via selective laser melting process. Specifically, the effects of laser power (100 W and 250 W) on their transformation temperatures, strain, and microstructure were investigated and compared to the ingot. The transformation temperatures of SLM fabricated alloys increased from 150 °C to 350 °C with elevated laser power due to Ni evaporation. The sample fabricated with 100 W showed sharp transformation peaks, good shape memory behavior with recoverable strain of 1.67% and superelasticity. The sample fabricated with 250 W had broad transformation peaks with low recoverable strain of 0.7% during thermal cycling.

ACS Style

Guher P. Toker; Mohammadreza Nematollahi; Sayed E. Saghaian; Keyvan S. Baghbaderani; Othmane Benafan; Mohammad Elahinia; Haluk E. Karaca. Shape memory behavior of NiTiHf alloys fabricated by selective laser melting. Scripta Materialia 2019, 178, 361 -365.

AMA Style

Guher P. Toker, Mohammadreza Nematollahi, Sayed E. Saghaian, Keyvan S. Baghbaderani, Othmane Benafan, Mohammad Elahinia, Haluk E. Karaca. Shape memory behavior of NiTiHf alloys fabricated by selective laser melting. Scripta Materialia. 2019; 178 ():361-365.

Chicago/Turabian Style

Guher P. Toker; Mohammadreza Nematollahi; Sayed E. Saghaian; Keyvan S. Baghbaderani; Othmane Benafan; Mohammad Elahinia; Haluk E. Karaca. 2019. "Shape memory behavior of NiTiHf alloys fabricated by selective laser melting." Scripta Materialia 178, no. : 361-365.

Journal article
Published: 20 September 2019 in Materials
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Nitinol has significant potential for biomedical and actuating-sensing devices, thanks to its functional properties. The use of selective laser melting (SLM) with Nitinol powder can promote novel applications aimed to produce 3D complex parts with integrated functional performances. As the final step of the production route, finishing processing needs to be investigated both for the optimization of the surface morphology and the limit alteration of the Nitinol functional properties. In this work, the effect of an advanced method of surface modification, ultrasonic nanocrystal surface modification (UNSM), on the martensitic transformation and microstructure of SLM built Ni50.8Ti49.2 (at.%) was investigated. Scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry indicated that the UNSM process can generate stress-induced martensite, at least partially suppressing the martensitic transformation. The microhardness profile indicates that the UNSM process can affect the mechanical properties of the SLMed Nitinol sample in a range of up to approximately 750 μm in depth from the upper surface, while electron backscatter diffraction analysis highlighted that the initial austenitic phase was modified within a depth below 200 μm from the UNSMed surface.

ACS Style

C.A. Biffi; P. Bassani; M. Nematollahi; N. Shayesteh Moghaddam; A. Amerinatanzi; M.J. Mahtabi; M. Elahinia; A. Tuissi. Effect of Ultrasonic Nanocrystal Surface Modification on the Microstructure and Martensitic Transformation of Selective Laser Melted Nitinol. Materials 2019, 12, 3068 .

AMA Style

C.A. Biffi, P. Bassani, M. Nematollahi, N. Shayesteh Moghaddam, A. Amerinatanzi, M.J. Mahtabi, M. Elahinia, A. Tuissi. Effect of Ultrasonic Nanocrystal Surface Modification on the Microstructure and Martensitic Transformation of Selective Laser Melted Nitinol. Materials. 2019; 12 (19):3068.

Chicago/Turabian Style

C.A. Biffi; P. Bassani; M. Nematollahi; N. Shayesteh Moghaddam; A. Amerinatanzi; M.J. Mahtabi; M. Elahinia; A. Tuissi. 2019. "Effect of Ultrasonic Nanocrystal Surface Modification on the Microstructure and Martensitic Transformation of Selective Laser Melted Nitinol." Materials 12, no. 19: 3068.

Editorial
Published: 09 June 2019 in Bioengineering
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This special issue is dedicated to the simulation as well as experimental studies of biomechanical behavior of biomaterials, especially those that are used for bone implant applications

ACS Style

Mohammad Elahinia; Hamdy Ibrahim; Mohammad Javad Mahtabi; Reza Mehrabi. Engineering Bone-Implant Materials. Bioengineering 2019, 6, 51 .

AMA Style

Mohammad Elahinia, Hamdy Ibrahim, Mohammad Javad Mahtabi, Reza Mehrabi. Engineering Bone-Implant Materials. Bioengineering. 2019; 6 (2):51.

Chicago/Turabian Style

Mohammad Elahinia; Hamdy Ibrahim; Mohammad Javad Mahtabi; Reza Mehrabi. 2019. "Engineering Bone-Implant Materials." Bioengineering 6, no. 2: 51.

Journal article
Published: 02 May 2019 in Materials Science and Engineering: C
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While potentially strong enough for load-bearing skeletal reconstruction applications, the corrosion (biodegradation) rate of biocompatible Mg-Zn-Ca-based alloys still presents. The present work reports on the use of heat treatment (strengthening and resorption delaying) and micro arc oxidation (MAO) coating (corrosion delaying) processes which were developed to induce desirable corrosion rates which are essential to maintaining the mechanical integrity of Mg-Zn-Ca-based alloys during the bone healing period. Three Mg-x%Zn-0.5%Ca (wt%) alloys with different levels of Zn content (1.2, 1.6 and 5 wt%) were prepared and heat-treated at different age hardening temperatures (100, 150, 200 and 250 °C). In order to further decrease the corrosion rate and improve the bioactivity, samples of the heat-treated Alloy I (Mg-1.2wt%Zn-0.5wt%Ca) at the optimized age-hardening conditions were successfully coated with a biocompatible composite coating without and with HA/β-TCP nanoparticles by using an MAO process. The microstructure, morphology and the composition of the heat-treated and coated materials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). Hardness and compression tests were conducted, while a corrosion investigation of heat-treated and coated samples was performed using potentiodynamic polarization (PDP) and a mechanical integrity immersion test. The results confirmed that Zn content and age hardening temperature have significant effects on the mechanical and corrosion properties of heat-treated Mg-Zn-Ca-based alloys. Alloy I, which has 1.2 wt% Zn content and was aged at 200 °C, showed the best combination of corrosion (slowest) and mechanical (highest) properties. The MAO (HA/β-TCP) composite coating significantly improved corrosion resistance compared to the uncoated heat-treated alloy, with only 11.3% reduction in the compressive strength after 8 weeks of immersion.

ACS Style

Hamdy Ibrahim; Alan Luo; David Dean; Mohammad Elahinia. “Effect of Zn content and aging temperature on the in-vitro properties of heat-treated and Ca/P ceramic-coated Mg-0.5%Ca-x%Zn alloys”. Materials Science and Engineering: C 2019, 103, 109700 .

AMA Style

Hamdy Ibrahim, Alan Luo, David Dean, Mohammad Elahinia. “Effect of Zn content and aging temperature on the in-vitro properties of heat-treated and Ca/P ceramic-coated Mg-0.5%Ca-x%Zn alloys”. Materials Science and Engineering: C. 2019; 103 ():109700.

Chicago/Turabian Style

Hamdy Ibrahim; Alan Luo; David Dean; Mohammad Elahinia. 2019. "“Effect of Zn content and aging temperature on the in-vitro properties of heat-treated and Ca/P ceramic-coated Mg-0.5%Ca-x%Zn alloys”." Materials Science and Engineering: C 103, no. : 109700.

Review
Published: 29 April 2019 in Bioengineering
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Shape memory alloys (SMAs) have found widespread applications as biomedical devices. Biocompatibility, corrosion resistance, and ductility make these alloys attractive for medical devices such as stents and filters. For these implants, the superelastic property is the primary function of SMAs. Additionally, these alloys, such as NiTi as the prime example, can be used for actuation. Several modes of actuation such as displacement control, force control, and compliance control have been used as harnesses with SMA devices. These two unique properties have opened another application in the form of neurosurgery and robot-assisted surgery devices, as well as controlled assistive and rehabilitation devices. This paper reviews the state of the art of application of SMAs in the latter category where control is applied to harness innovative medical devices. To this end, two major subsets of these devices: prosthesis and orthosis which take the advantage of SMAs in assistive and rehabilitation devices are studied. These devices are further categorized to hand prosthetics, elbow, knee and ankle orthotics. In most of these designs, SMA wires act as artificial muscles to mimic the motion of limbs in the target joints. The evolution of each category is explained, and the specific results of them are reported. The paper also reviews the SMA applications for neurological and neuromuscular rehabilitation. To this end, different categories of rehabilitation devices as a passive and aided exercise for the ankle, knee, and elbow are highlighted. The SMA actuator in these devices can be EMG-controlled to improved patient outcome. In addition to providing a comprehensive overview of the biomedical devices, this paper identifies several possible future directions of SMA related research in the area of assistive and rehabilitation devices.

ACS Style

Mohammadreza Nematollahi; Keyvan Safaei Baghbaderani; Amirhesam Amerinatanzi; Hashem Zamanian; Mohammad Elahinia. Application of NiTi in Assistive and Rehabilitation Devices: A Review. Bioengineering 2019, 6, 37 .

AMA Style

Mohammadreza Nematollahi, Keyvan Safaei Baghbaderani, Amirhesam Amerinatanzi, Hashem Zamanian, Mohammad Elahinia. Application of NiTi in Assistive and Rehabilitation Devices: A Review. Bioengineering. 2019; 6 (2):37.

Chicago/Turabian Style

Mohammadreza Nematollahi; Keyvan Safaei Baghbaderani; Amirhesam Amerinatanzi; Hashem Zamanian; Mohammad Elahinia. 2019. "Application of NiTi in Assistive and Rehabilitation Devices: A Review." Bioengineering 6, no. 2: 37.

Journal article
Published: 27 February 2019 in Shape Memory and Superelasticity
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In this work, the effects of process parameters on the fabrication of NiTiHf alloys using selective laser melting are studied. Specimens were printed using bidirectional scanning pattern and with various sets of process parameters of laser power (100–250 W), hatch spacing (60–140 µm), and scanning speed (200–1000 mm/s). Cracking and delamination formation, dimensional accuracy, density, and transformation temperatures were examined. Despite the brittle nature of the alloy, fully dense parts have been produced. Laser scanning speed and volumetric energy density were found to be the most influential process parameters on fabricating defect-free samples. It was shown that transformation temperatures are highly dependent on the process parameters. By proper choice of parameters, it is possible to tailor the austenite finish temperature from 100 to 400 °C. The most influential factors on transformation behavior were found to be the laser power and energy density. It is worth noting that these two parameters at higher levels resulted in high process temperatures and therefore a larger level of Ni evaporation. Among the four parameters that constitute the energy density, the hatch spacing does not significantly affect the transformation temperatures. These findings serve as the foundation of developing HTSMA devices with desired geometrical and functional properties.

ACS Style

M. Nematollahi; G. Toker; S. E. Saghaian; J. Salazar; M. Mahtabi; O. Benafan; H. Karaca; M. Elahinia. Additive Manufacturing of Ni-Rich NiTiHf20: Manufacturability, Composition, Density, and Transformation Behavior. Shape Memory and Superelasticity 2019, 5, 113 -124.

AMA Style

M. Nematollahi, G. Toker, S. E. Saghaian, J. Salazar, M. Mahtabi, O. Benafan, H. Karaca, M. Elahinia. Additive Manufacturing of Ni-Rich NiTiHf20: Manufacturability, Composition, Density, and Transformation Behavior. Shape Memory and Superelasticity. 2019; 5 (1):113-124.

Chicago/Turabian Style

M. Nematollahi; G. Toker; S. E. Saghaian; J. Salazar; M. Mahtabi; O. Benafan; H. Karaca; M. Elahinia. 2019. "Additive Manufacturing of Ni-Rich NiTiHf20: Manufacturability, Composition, Density, and Transformation Behavior." Shape Memory and Superelasticity 5, no. 1: 113-124.

Metals
Published: 30 January 2019 in Journal of Materials Science
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Nickel–titanium (NiTi) alloys have recently attracted considerable attention due to their unique properties, i.e., shape memory effect and superelasticity. In addition, these promising alloys demonstrate unique biocompatibility, represented in their high stability and corrosion resistance in aqueous environments, qualifying them to be used inside the human body. In recent years, additive manufacturing (AM) processes have been envisioned as an enabling method for the efficient production of NiTi components with complex geometries as patient-specific implants. In spite of its great capabilities, AM as a novel fabrication process may reduce the corrosion resistance of NiTi parts leading to the excess release of the harmful Ni ions as the main corrosion byproducts. The main goal of this study is to create and evaluate a micro-arc oxidation (MAO) coating in order to enhance the corrosion resistance of additively manufacture NiTi medical devices. To this end, the process voltage and electrolyte used to produce MAO coating have been investigated and optimized. The corrosion characteristics of the MAO-coated specimens revealed that the proposed coating methodology significantly improves the corrosion resistance of NiTi parts produced using AM process.

ACS Style

Amir Dehghanghadikolaei; Hamdy Ibrahim; Amirhesam Amerinatanzi; Mahdi Hashemi; Narges Shayesteh Moghaddam; Mohammad Elahinia. Improving corrosion resistance of additively manufactured nickel–titanium biomedical devices by micro-arc oxidation process. Journal of Materials Science 2019, 54, 7333 -7355.

AMA Style

Amir Dehghanghadikolaei, Hamdy Ibrahim, Amirhesam Amerinatanzi, Mahdi Hashemi, Narges Shayesteh Moghaddam, Mohammad Elahinia. Improving corrosion resistance of additively manufactured nickel–titanium biomedical devices by micro-arc oxidation process. Journal of Materials Science. 2019; 54 (9):7333-7355.

Chicago/Turabian Style

Amir Dehghanghadikolaei; Hamdy Ibrahim; Amirhesam Amerinatanzi; Mahdi Hashemi; Narges Shayesteh Moghaddam; Mohammad Elahinia. 2019. "Improving corrosion resistance of additively manufactured nickel–titanium biomedical devices by micro-arc oxidation process." Journal of Materials Science 54, no. 9: 7333-7355.

Journal article
Published: 10 January 2019 in Scientific Reports
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Shape memory alloys (SMAs), such as Nitinol (i.e., NiTi), are of great importance in biomedical and engineering applications due to their unique superelasticity and shape memory properties. In recent years, additive manufacturing (AM) processes have been used to produce complex NiTi components, which provide the ability to tailor microstructure and thus the critical properties of the alloys, such as the superelastic behavior and transformation temperatures (TTs), by selection of processing parameters. In biomedical applications, superelasticity in implants play a critical role since it gives the implants bone-like behavior. In this study, a methodology of improving superelasticity in Ni-rich NiTi components without the need for any kind of post-process heat treatments will be revealed. It will be shown that superelasticity with 5.62% strain recovery and 98% recovery ratio can be observed in Ni-rich NiTi after the sample is processed with 250 W laser power, 1250 mm/s scanning speed, and 80 µm hatch spacing without, any post-process heat treatments. This superelasticity in as-fabricated Ni-rich SLM NiTi was not previously possible in the absence of post-process heat treatments. The findings of this study promise the fast, reliable and inexpensive fabrication of complex shaped superelastic NiTi components for many envisioned applications such as patient-specific biomedical implants.

ACS Style

Narges Shayesteh Moghaddam; Soheil Saedi; Amirhesam Amerinatanzi; Alejandro Hinojos; Ali Ramazani; Julia Kundin; Michael J. Mills; Haluk Karaca; Mohammad Elahinia. Achieving superelasticity in additively manufactured NiTi in compression without post-process heat treatment. Scientific Reports 2019, 9, 1 -11.

AMA Style

Narges Shayesteh Moghaddam, Soheil Saedi, Amirhesam Amerinatanzi, Alejandro Hinojos, Ali Ramazani, Julia Kundin, Michael J. Mills, Haluk Karaca, Mohammad Elahinia. Achieving superelasticity in additively manufactured NiTi in compression without post-process heat treatment. Scientific Reports. 2019; 9 (1):1-11.

Chicago/Turabian Style

Narges Shayesteh Moghaddam; Soheil Saedi; Amirhesam Amerinatanzi; Alejandro Hinojos; Ali Ramazani; Julia Kundin; Michael J. Mills; Haluk Karaca; Mohammad Elahinia. 2019. "Achieving superelasticity in additively manufactured NiTi in compression without post-process heat treatment." Scientific Reports 9, no. 1: 1-11.

Journal article
Published: 29 November 2018 in Bioengineering
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Magnesium (Mg) and its alloys can degrade gradually up to complete dissolution in the physiological environment. This property makes these biomaterials appealing for different biomedical applications, such as bone implants. In order to qualify Mg and its alloys for bone implant applications, there is a need to precisely model their degradation (corrosion) behavior in the physiological environment. Therefore, the primary objective develop a model that can be used to predict the corrosion behavior of Mg-based alloys in vitro, while capturing the effect of pitting corrosion. To this end, a customized FORTRAN user material subroutine (or VUMAT) that is compatible with the finite element (FE) solver Abaqus/Explicit (Dassault Systèmes, Waltham, MA, USA) was developed. Using the developed subroutine, a continuum damage mechanism (CDM) FE model was developed to phenomenologically estimate the corrosion rate of a biocompatible Mg–Zn–Ca alloy. In addition, the mass loss immersion test was conducted to measure mass loss over time by submerging Mg–Zn–Ca coupons in a glass reactor filled with simulated body fluid (SBF) solution at pH 7.4 and 37 °C. Then, response surface methodology (RSM) was applied to calibrate the corrosion FE model parameters (i.e., Gamma (γ), Psi (ψ), Beta (β), and kinetic parameter (Ku)). The optimum values for γ, ψ, β and Ku were found to be 2.74898, 2.60477, 5.1, and 0.1005, respectively. Finally, given the good fit between FE predictions and experimental data, it was concluded that the numerical framework precisely captures the effect of corrosion on the mass loss over time.

ACS Style

Amirhesam Amerinatanzi; Reza Mehrabi; Hamdy Ibrahim; Amir Dehghan; Narges Shayesteh Moghaddam; Mohammad Elahinia. Predicting the Biodegradation of Magnesium Alloy Implants: Modeling, Parameter Identification, and Validation. Bioengineering 2018, 5, 105 .

AMA Style

Amirhesam Amerinatanzi, Reza Mehrabi, Hamdy Ibrahim, Amir Dehghan, Narges Shayesteh Moghaddam, Mohammad Elahinia. Predicting the Biodegradation of Magnesium Alloy Implants: Modeling, Parameter Identification, and Validation. Bioengineering. 2018; 5 (4):105.

Chicago/Turabian Style

Amirhesam Amerinatanzi; Reza Mehrabi; Hamdy Ibrahim; Amir Dehghan; Narges Shayesteh Moghaddam; Mohammad Elahinia. 2018. "Predicting the Biodegradation of Magnesium Alloy Implants: Modeling, Parameter Identification, and Validation." Bioengineering 5, no. 4: 105.

Journal article
Published: 03 July 2018 in Mechanics of Materials
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NiTi, known as Nitinol, is the most common shape memory alloy which offers relatively low modulus of elasticity, shape memory properties, superelastic behavior, biocompatibility and low corrosion rate. In some applications, such as actuators and biomedical implants, it is common to use cellular lattice structure (CLS) to decrease the weight as well as equivalent modulus of elasticity (i.e., stiffness). The focus of this research is to model, at macro scale, the behavior of NiTi CLS (e.g., BCC and BCC-Z) processed through selective laser melting (SLM) additive manufacturing (AM) process. First, BCC and BCC-Z structures were fabricated and subjected to thermomechanical experiment to investigate their shape memory properties. Next, finite element analysis was performed using unit a cell model with appropriate boundary conditions. The model is based on a three -dimensional constitutive model derived from the Souza theory. Finally, the stress-strain curves obtained from finite element simulations were compared with those generated from mechanical tests. The comparison showed good agreement between the model prediction and experimental results for BCC (R>0.98, RMSE=1.79 MPa, p0.97, RMSE=6.28 MPa, p<0.05) structures. It was also revealed that the developed model was computationally more efficient, than other multi-cell models.

ACS Style

Mohammad Javad Ashrafi; Amirhesam Amerinatanzi; Zohreh Saebi; Narges Shayesteh Moghaddam; Reza Mehrabi; Haluk Karaca; Mohammad Elahinia. Shape memory response of cellular lattice structures: Unit cell finite element prediction. Mechanics of Materials 2018, 125, 26 -34.

AMA Style

Mohammad Javad Ashrafi, Amirhesam Amerinatanzi, Zohreh Saebi, Narges Shayesteh Moghaddam, Reza Mehrabi, Haluk Karaca, Mohammad Elahinia. Shape memory response of cellular lattice structures: Unit cell finite element prediction. Mechanics of Materials. 2018; 125 ():26-34.

Chicago/Turabian Style

Mohammad Javad Ashrafi; Amirhesam Amerinatanzi; Zohreh Saebi; Narges Shayesteh Moghaddam; Reza Mehrabi; Haluk Karaca; Mohammad Elahinia. 2018. "Shape memory response of cellular lattice structures: Unit cell finite element prediction." Mechanics of Materials 125, no. : 26-34.