Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2022, Materials Science and Engineering

This work investigates processing parameters for laser powder bed fusion (LPBF) additive manufacturing (AM) to produce bismuth telluride coupons. AM provides the ability to fabricate complex geometries, reduce material waste, and increase design flexibility. The processing parameters for LPBF were varied in single bead experiments guided by analytical modeling to identify conditions that result in uniform beads. Coupons were built using these processing parameters and the cross-sections characterized using optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). Porosity analysis using OM concluded most coupons had porosity levels less than 10% by area. SEM and EDS analysis revealed there were slight composition and microstructure variations throughout the cross-sections depending on the processing conditions. These results show that LPBF is a viable process for producing bismuth telluride coupons with low porosity. Investigations of the microstructure and composition of the coupons indicate further research opportunities.

Committee: Joy Gockel Ph.D. (Advisor); Henry D. Young Ph.D. (Committee Member); Raghavan Srinivasan Ph.D., P.E. (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science in Engineering, Youngstown State University, 2019, Department of Mechanical, Industrial and Manufacturing Engineering

Additive manufacturing is one of the more recent advances in manufacturing technology. Additive manufacturing processes allow for the creation of parts in a layer-by-layer fashion. There are several materials that can be used in additive manufacturing processes including metal, ceramic, and polymers which each presenting their own challenges. This work focuses on metal based additive manufacturing parts made out of AlSi10Mg using a process called laser powder bed fusion. Laser powder bed fusion is one of the three major metal additive manufacturing processes with the other two being multi-pass welding and direct energy deposition. One of many challenges that occur with the laser power bed fusion process is minimizing the residual stresses and distortion that are present in the part during and after the build. During the early days of additive manufacturing that was mostly done through a trial-and-error process where multiple version of a part would be printed until a desired outcome was achieved, and this was often very expensive, and time consuming. There has been plenty of research in developing simulation models in order to predict the distortions and stresses that developed during the additive manufacturing process. These simulations allowed engineers to optimize parts before they were printed, and thus reduce the number of wasted prints. This work demonstrates and validates use of a software package call Autodesk Netfabb Simulation in order to find the optimal orientation of a complex part. The optimal orientation was selected for three categories: distortion, stress, and printability. Optimal orientations were selected from a selection of 23 orientations that were simulated. To validate the simulations, two test parts along with three of the aforementioned orientations were printed and measured using 3D scanning while still the build plate. The result of this was that the optimal orientation was different for each of three criteria meaning it is up to the part (open full item for complete abstract)

Committee: Jason Walker PhD (Advisor); Brett Conner PhD (Committee Member); Virgil Solomon PhD (Committee Member) Subjects: Engineering; Mechanical Engineering; Metallurgy

MS, University of Cincinnati, 2018, Engineering and Applied Science: Materials Science

This study investigates the effects of laser shock peening (LSP) and ultrasonic nanocrystal surface modification (UNSM) on residual stress, near surface modification, and hardness of Inconel 718 (IN718) specimens manufactured by selective laser melting (SLM) techniques. IN718 is a nickel-based Ni-Cr-Fe superalloy. It has a unique set of properties that include good workability, corrosion resistance, high-temperature strength, favorable weldability, and excellent manufacturability. Additive manufacturing (AM) techniques, in particular, the laser assisted AM techniques have been developed and adopted in the industry in the past three decades. The LSP and UNSM are the recently developed mechanical surface treatment techniques that cause the severe plastic deformation on the surface. This in turn induces deep compressive stresses and forms a fine-crystalline surface layer in the specimen that improves the hardness, strength, and fatigue life. In this study, the SLM technique is used to manufacture IN718 super-alloy specimens. SLM parts are well known for their high tensile stresses in the as-built state, in the surface or subsurface region. These stresses have a detrimental effect on the mechanical properties, especially on the fatigue life. LSP and UNSM as a surface treatment method are applied on heat-treated specimens and as-built specimens. Heat-treated specimens are those samples which are fully annealed to relieve all the inbuilt stresses. They are heat treated at 955°C for one hour followed by furnace cooling. After LSP and UNSM treatment, optical microscope and electron back scattered diffraction (EBSD) is used to characterize the microstructures of both heat-treated and as-built specimens. A nanoindentation test is performed to determine the local properties like the hardness of as-built and heat-treated specimens. Afterward, the hardness along the distance from the LSP and UNSM treated surface is also defined. After UNSM treatment, compressive residual str (open full item for complete abstract)

Committee: Jing Shi Ph.D. (Committee Chair); Yao Fu (Committee Member); Vijay Vasudevan Ph.D. (Committee Member) Subjects: Materials Science

Master of Science in Mechanical Engineering, Cleveland State University, 2024, Washkewicz College of Engineering

Additively manufactured blocks of Stainless Steel 316L (SS316L) have been made using three different methods and forged for comparison of material properties before and after forging. The first method used for creating the blocks was Binder-Jetting (BJ), a low-heat powder bed metal additive technique that uses glue to hold the powder together before sintering. The second method was Selective Laser Melting (SLM), a powder bed metal additive technique that utilizes a laser to melt the metal powder each layer achieving high density parts out of the printer. The final method used to create the blocks was Wire Arc Additive Manufacturing (WAAM), a form of Directed Energy Deposition (DED) that utilizes an electrified rod of filler material to create an arc and melt the filler material to a substrate, building upon itself. BJ provides complex geometry and versatility. With the low-heat printing application, this method can be used for more than just metals and can be used for combinations of powdered materials. This also allows for various post-processing procedure can be made depending on desired output and material choice. SLM provides high density parts with complex geometry directly out of the printer with minimal post processing, allowing for easier industrial use. WAAM provides parts with low-moderate geometry complexity. However, this process allows for larger parts and a faster rate of printing than SLM and BJ. After printing, and any necessary post-processing, the blocks were forged in open-die forging. The BinderJet parts resulted in low density, only coming around 62% density, and thus had v additional mass loss during the forging process and provided the worst results. Both SLM and WAAM had densities around 99% and provided beneficial results when combined with forging, showing grain reduction and grain flow characteristics. With a 25.93% increase in Ultimate Tensile Strength (UTS) for SLM and 21.66% increase in UTS for WAAM; SLM performed (open full item for complete abstract)

Committee: Tushar Borkar (Advisor); David Schwam (Committee Member); Liqun Ning (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2023, Electrical Engineering

The development of patient-specific implants for reconstructive applications involving unique deformities or injuries has demonstrated the promise of additive manufacturing (AM) in the medical setting. Biomimetic lattice structures can facilitate internal bone growth due to their porous nature, which can reduce stress shielding and improve the lifespan of an implant. In addition, pulsed electromagnetic field therapy can be implemented to accelerate the osseointegration process internally in the lattice structures by improving cellular proliferation and attachment. In this research, cubic and body-centered cubic (BCC) unit cell geometries were 3D printed using selective laser melting and biocompatible Ti-6Al-4V feedstock powder. The lattices were designed with four different pore sizes (400, 500, 600, and 900 µm, representing 40-90% porosity in a 10 mm cube). Compression and tensile testing were performed to evaluate the mechanical properties of the lattice structures, with results compared to human cancellous bone. SEM microstructural characterization of the manufactured lattices exhibited deviations in AM pore sizes and strut diameters when compared to original CAD designs in nTopology. It was found that the elastic modulus of human cancellous bone (10 - 900 MPa) could be matched for both tensile (92.7 - 129.6 MPa) and compressive (185.2 - 996.1 MPa) elastic modulus of cubic and BCC lattices. BCC lattices exhibited higher compressive properties over cubic, whereas cubic lattices exhibited superior tensile properties over BCC. To determine the effects of porosity and unit cell geometry on the osteogenesis of human MG-63 osteoblastic cell lines in vitro, glucose consumption, alkaline phosphate (ALP), and end-of-culture cell count activity was analyzed as markers for osteogenic growth. The results indicated that lattices with a 900 µm pore size exhibited the highest glucose consumption and the greatest change in alkaline phosphate activity when compared to other pore (open full item for complete abstract)

Committee: Amy Neidhard-Doll (Committee Chair); Margaret Pinnell (Committee Member); Yvonne Sun (Committee Member); Dathan Erdahl (Committee Member); Guru Subramanyam (Committee Member) Subjects: Biology; Biomedical Engineering; Biomedical Research; Electrical Engineering; Electromagnetics; Mechanical Engineering

MS, University of Cincinnati, 2022, Engineering and Applied Science: Mechanical Engineering

The fickle nature of Selective Laser Melting (SLM) makes it exceedingly difficult to anticipate the outcome of a specific print. Physical and mechanical properties of the samples fabricated via SLM largely depend on processing parameters governing the print. Slight alterations to such process parameters are infamously linked with haphazard variations in aforementioned properties. Design engineers or operators must undergo a tedious optimization process to arrive at process parameters that result in desired outcomes. In the efforts to possibly avoid expensive resources and time required for redundant trail and errors, high-fidelity predictive models must be developed for SLM. In this study, robust and reliable supervised learning models based on Gaussian Process Regression (GPR) are established to model and predict physical and mechanical properties of as-built Ti-6Al-4V alloy manufactured via SLM. Properties such as density, surface roughness parameter Ra, and hardness are modeled based on most pertinent SLM input process parameters of laser power, scanning speed, hatch spacing, layer thickness and volumetric energy density. A comprehensive dataset is collected from literature published over last 15 years. Data are trained using ten-fold cross validation technique, and Hyperparameters optimization is performed for all three GPR models. Alongside GPR, Artificial Neural Network (ANN) models are also developed for all three properties, using same cross validation technique and data. As a benchmark tool, a traditional parametric modeling technique of Multiple Linear Regression (MLR) is employed as well. This is followed by Analysis of Variance (ANOVA) for collective dataset, revealing which factors and interactions are statistically significant to the studied physical properties. Use of statistical error metrics like MAE and RSME has been made throughout this multifaceted study. Finally, actual SLM experiments are performed, and developed models are deploy (open full item for complete abstract)

Committee: Jing Shi Ph.D. (Committee Member); Ashley Paz y Puente Ph.D. (Committee Member); Manish Kumar Ph.D. (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2022, Engineering and Applied Science: Mechanical Engineering

Additive manufacturing (AM) has been gaining attention thanks to its ability to manufacture complex parts in less time with satisfactory quality. Selective laser melting (SLM) is one of the most widely adopted AM technologies for metal alloys, and IN718 is one of the most common metallic materials used in SLM. Due to the complicated physical interactions during SLM process, there exists complex non-linear relationship between process parameters and material properties of obtained components, and thus it is critical to reveal such relationship for predicting property and obtaining desired quality of SLM-ed IN718. Literature data on process parameters and properties of SLM-ed IN718 are collected by exhaustively searching and mining from all related publications. The large amount of collected data is used for relationship modeling with characteristics of wide process parameter ranges and high model robustness under various settings. Meanwhile, SLM experiments using a design of experiment (DOE) method named Central Composite Design are carried out to systematically consider four major process parameters over relatively wide ranges. Relative density (RD), surface roughness (SR), hardness, and tensile properties of the obtained samples are measured and analyzed. Microstructure analysis is conducted by using OM, SEM, TEM, XRD, and fractography for understanding the cause of changes in properties. Such systematic experimentation with a comprehensive set of properties provides fairly comprehensive process-property knowledge of SLM-ed IN718. RD predictive modeling is attempted using DOE experiment data, followed by the response surface analysis. A statistical predictive model of RD with relatively high accuracy is derived, and a desired process window of RD greater than 98.5% is obtained. In addition, robust RD predictive models suitable for a wider range of process parameters are also built using back propagation neural network (BPNN) and genetic algorithm (GA) (open full item for complete abstract)

Committee: Jing Shi Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member); Jay Lee Ph.D. (Committee Member); Janet Jiaxiang Dong Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2021, Materials Engineering

Additive Manufacturing (AM) is a rapidly developing field that offers new possibilities for manufacturing with materials that are difficult to process with traditional manufacturing methods. This report will examine the application of selective laser melting in making magnetic cores out of Hiperco 50. The iron-cobalt family of alloys is known to offer the best magnetic properties of all soft magnetic materials but is extremely brittle. Additive manufacturing offers the opportunity to make high quality magnetic cores in unique geometries that traditional manufacturing is unable to replicate. To test the viability of this process three types of test specimens were built out of Hiperco 50 powder to examine key material properties. First 1 cm3 cube specimens were built to measure the density of the final parts, and they were also used to examine the porosity and microstructure. The second type of specimens were tensile bars, built in both vertical and horizontal orientations with respect to the build plate, to examine the mechanical properties of the final parts as well as the impact of build orientation. The final test specimens were magnetic toroids, comprised of cores to be wound with copper magnet wire and tested for magnetic permeability and remanence. Half of these specimens were also subjected to a final magnetic heat treatment cycle, which was the same as the cycle used for traditionally manufactured Hiperco 50 components, in order to determine the change in performance. These AM fabricated specimens showed a 1-5% decrease in density from traditionally manufactured Hiperco 50 parts, with the build parameters being the largest deciding factor of final density and porosity. These parts also had a poorly defined grain structure until subjected to a magnetic heat treatment. After undergoing the recommended heat-treatment, niobium precipitates were observed along the newly defined grain boundaries. However, there was a severe drop in mechanical performance, (open full item for complete abstract)

Committee: Donald Klosterman (Committee Chair); Zafer Turgut (Committee Member); Li Cao (Committee Member) Subjects: Electromagnetics; Electromagnetism; Materials Science

Doctor of Philosophy, Case Western Reserve University, 2021, EMC - Mechanical Engineering

We present a powder-scale computational framework to predict the microstructure evolution of metals in Powder Bed Fusion Additive Manufacturing (PBF AM) processes based on the Hot Optimal Transportation Meshfree (HOTM) method. The powder bed is modeled through Discrete Element Method (DEM) as discrete and deformable three-dimensional bodies by integrating statistic information from experiments, including particle size and shape, and powder packing density. Tractions in Lagrangian framework are developed to model the recoil pressure and surface tension. The laser beam is applied to surfaces of particles and substrate dynamically as a heat flux with user-specified beam size, power, scanning speed and path. The linear momentum and energy conservation equations are formulated in the Lagrangian configuration and solved simultaneously in a monolithic way by the HOTM method to predict the deformation, temperature, contact mechanisms and fluid-structure interactions in the powder bed. The numerical results are validated against benchmark tests and single track experiments. Various powder bed configurations, particle size distributions, laser powers and speeds are investigated to understand the influence of dynamic contact and inelastic material behavior on the deformation, heat transfer and phase transition of the powder bed. The formation of defects in the microstructure of 3D printed metals, including pores, partially and un-melted particles, are predicted by the proposed computational scheme.

Committee: Bo Li (Committee Chair); Yasuhiro Kamotani (Committee Member); John Lewandowski (Committee Member); Ya-Ting Liao (Committee Member) Subjects: Mechanical Engineering

Master of Science in Engineering, Youngstown State University, 2020, Department of Civil/Environmental and Chemical Engineering

As new influxes of aerospace technology are introduced, production of legacy system replacement parts is halted. For end-users of legacy systems, like the U.S. Air Force, selective laser melting (SLM) offers a unique solution to this problem by making highly specific and complex parts available without the lead time or cost associated with conventional acquisition methods. One major obstacle impeding full implementation of legacy aerospace parts is the need for understanding of failure behavior of 3D-printed metals. This knowledge is important in the development of quality control standards and maintenance protocols that ensure the safety of aircrafts in use. In this study, experiments were performed on AlSi10Mg to understand the corrosion behavior of this alloy in practical environments, when conceivable errors in fabrication result in defective parts. Three studies were performed to evaluate the effects of process parameters, defect size, and contamination levels of Inconel, on the corrosion behavior of AlSi10Mg. In the first study, galvanic corrosion was observed between α-aluminum and silicon coarsened in the heat-affected zone of characteristic SLM melt pools. In addition, a relationship between process parameters of laser power, laser velocity, and hatch spacing and corrosion was determined. In the second study, density of defects was determined to be a more pressing issue in the failure of corroded AlSi10Mg in an accelerated neutral salt fog. Finally, galvanic coupling between nickel and both aluminum and silicon was concluded to catastrophically accelerate the corrosion of the alloy.

Committee: Holly Martin Ph.D. (Advisor); Brett Conner Ph.D. (Committee Member); Pedro Cortes Ph.D. (Committee Member) Subjects: Aerospace Materials; Chemical Engineering; Engineering; Materials Science

Doctor of Philosophy, University of Toledo, 2020, Engineering

The standard of care for mandibular segmental defects is the use of Ti-6Al-4V (i.e. surgical grade 5 Titanium or Ti64) skeletal fixation plates and screws. There is a significant stiffness mismatch between the Ti64 skeletal fixation plates and the cortical bone. Although these high stiff Ti64 skeletal fixation plates provide enough immobilization immediately after the surgery, when the bones heal, the high level of stiffness disturbs the loading distribution. The result is stress shielding in the surrounding bone which may lead to bone resorption and eventually could lead to failure of the surgery. NiTi (i.e. Nickel-Titanium or Nitinol) is a biocompatible, shape memory alloy that offers interesting features, such as superelasticity. Additionally, NiTi has a lower stiffness than Ti64 which can be further reduced by imposing porosity. With the proper choice of the level and type of porosity, one can reduce the NiTi stiffness to that of the cortical bone. Thanks to the superelastic property of NiTi, the risk of stress concentration and increased strain levels due to imposing porosity does not lead to early failure of the porous NiTi structure than if it were formed from Ti64. Therefore, making superelastic NiTi a more suitable candidate for such applications. Additive manufacturing (AM) is a relatively new method of fabrication that enables the fabrication of parts directly from a CAD file. In this method, the CAD file is sliced into thin layers, and then the part is fabricated in a layer-by-layer approach. Recently, additive manufacturing has been used for the fabrication of NiTi parts. It is, therefore, possible to fabricate complex-shape porous NiTi components such as the devices for mandibular segmental repair surgery. As a solution to the stress shielding problem of the mandibular reconstruction surgery, in this work, we have introduced NiTi patient-specific, stiffness matched bone fixation plates. The proposed bone fixation plates are designed based on a (open full item for complete abstract)

Committee: Mohammad Elahinia (Committee Chair); David Dean (Committee Member); Matthew J. Franchetti (Committee Member); Mohammad Mahtabi (Committee Member); Reza Rizvi (Committee Member) Subjects: Biomechanics; Biomedical Engineering; Engineering; Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2020, Materials Science and Engineering

AlSi10Mg mechanical test samples were fabricated by selective laser melting (SLM). Samples were built in the Z and XY orientations and subjected to several different post processing combinations of stress relief (SR) heat treatment, T6 heat treatment, and hot isostatic pressing (HIP). Uniaxial tension testing, fatigue crack growth (FCG) testing, and fracture toughness testing were done to study the effects of different build orientations and post-process conditions on the resulting microstructure and properties. The FCG tests were conducted in three-point bending at stress ratio R = 0.1 and a frequency of 20 Hz. Fracture toughness testing was also conducted in three-point bending, and JIC values were determined. Metallography and fractography analysis were conducted using OM and SEM. Compared to conventional cast AlSi10Mg, SLM-processed AlSi10Mg had similar strength and improved ductility. Build orientation and post process conditions were observed to cause differences in microstructure, defect characteristics, resulting mechanical properties, and fracture behavior.

Committee: John Lewandowski (Committee Chair); William Baeslack (Committee Member); Clare Rimnac (Committee Member) Subjects: Aerospace Materials; Materials Science; Metallurgy

PhD, University of Cincinnati, 2018, Engineering and Applied Science: Mechanical Engineering

TiC nanoparticles (NPs) and GNPs(GNPs) are used to reinforce Inconel 718 (IN718) via selective laser melting process. Various post heat treatment methods with four levels of temperature, with or without the subsequent aging are carried out on the obtained pure IN718 and IN718-matrix nanocomposite materials. The effect of post heat treatment strategies on the microstructure and mechanical properties of the obtained materials is investigated. Meanwhile, multiscale simulation is performed to investigate the influence of laser parameters on the microstructure of SLM-processed Ni-Nb alloy, with the consideration of realistic thermal history and powder-to-dense phase transformation. The interaction between particle and solidification front is investigated, the engulfment/push behavior and overall distribution of TiC nanoparticles (NPs) in the dendrite solidification process of the binary alloy are revealed. It is found that with the increase of nTiC addition, the material microstructure is refined. Mechanical properties, including tensile, and anti-wear properties are effectively enhanced with the addition of external nano reinforcement. Multiscale numerical study proves that laser scan speed and degree of undercooling significantly affect the microstructure and overall distribution of NPs in a metal matrix. Higher laser scan speed results in higher cooling rate in the solidification region and alleviated micro-segregation ratio. A higher degree of undercooling leads to easier engulfment of NPs and overall more uniform distribution of NPs.

Committee: Jing Shi Ph.D. (Committee Chair); Jay Lee Ph.D. (Committee Member); Yijun Liu Ph.D. (Committee Member); Vijay Vasudevan Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science, University of Toledo, 2016, Mechanical Engineering

Mandibular reconstruction surgery is a part of treatment for cancer, tumor, and all the cases that involve segmental defects. One of the most common approaches for the reconstruction surgery is to resect the segmental defect and use a double barrel fibula graft to fill the resected region and recover the mandible's normal functions, such as chewing. The grafted bone is connected to the host mandible, using the standard of the care Ti-6Al-4V fixation plates. The fixation plates are available in the form of prefabricated plates and also patient-specific plates in the market. Due to the high stiffness of the Ti-6Al-4V plates in comparison with the mandible bone and the grafted bone, the loading distribution on the whole reconstructed mandible will be different from a healthy mandible. The high stiffness fixation hardware carries a great portion of the loading and causes stress shielding on the grafted bone and the surrounding host bone. Based on the bone remodeling theory, the stress shielding on the cortical bone causes bone resorption and may lead to implant failure. A solution to reduce the risk of implant failure is to use a low stiffness biocompatible material for the mandibular fixation plates. We have proposed the use of stiffness-matched, porous NiTi fixation plates either in the form of patient-specific or prefabricated, instead of the standard of the care Ti-6Al-4V plates. NiTi is a biocompatible material that has a low stiffness in comparison with Ti-6Al-4V and also benefits from the superelastic feature. Superelasticity, which can also be found in bone tissues, allows the material to recover large strains (up to 8%) and increases the shock absorption. In this thesis, we have evaluated the use of proposed fixation hardware by comparing it with a healthy mandible and a reconstructed mandible using the standard method. To this end, first different models including a healthy mandible, a reconstructed mandible using patient-specific Ti-6Al-4V fixation hardwa (open full item for complete abstract)

Committee: Mohammad Elahinia (Advisor); Mohammad Elahinia (Committee Chair); Mehdi Pourazady (Committee Member); Efstratios Nikolaidis (Committee Member) Subjects: Biomechanics; Biomedical Engineering; Materials Science; Mechanical Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering

Selective Laser Melting (SLM) is an additive manufacturing (AM) technique that creates complex parts by selectively melting metal powder layer-by-layer. In SLM, the process parameters decide the quality of the fabricated component. In this study, single beads of commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy are melted on a substrate of the same material as powder using an in-house built SLM machine. Multiple combinations of laser power and scan speed are used for single bead fabrication while the laser beam diameter and powder layer thickness are kept constant. This experimental study investigates the influence of laser power, scan speed and laser energy density on the melt pool formation, surface morphology, geometry (width, depth, and height) and hardness of melt pools. The results show that the quality, geometry, and hardness of melt pool is significantly affected by laser power, scanning speed and laser energy density. In addition, the observed unfavorable effects such as inconsistent melt pool formation, balling, porosity are discussed in detail. At the end, suggestions are provided to use optimal parameters to avoid such unfavorable effects.

Committee: Ahsan Mian Ph.D. (Advisor); Henry D. Young Ph.D. (Committee Member); Ha-Rok Bae Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science, University of Toledo, 2015, Mechanical Engineering

In recent years, shape memory alloys (SMAs) have entered a wide range of engineering applications in fields such as aerospace and medical applications. Nickel-titanium (NiTi) is the most commonly used SMAs due to its excellent functional characteristics (shape memory effect and superelasticity behavior). These properties are based on a solid-solid phase transformation between martensite and austenite. Beside these two characteristics, low stiffness, biocompatibility and corrosion properties of NiTi make it an attractive candidate for biomedical applications (e.g., bone plates, bone screws, and vascular stents). It is well know that manufacturing and processing of NiTi is very challenging. The functional properties of NiTi are significantly affected by the impurity level and due to the high titanium content, NiTi are highly reactive. Therefore, high temperature processed parts through methods such as melting and casting which result in increased impurity levels have inadequate structural and functional properties. Furthermore, high ductility and elasticity of NiTi, adhesion, work hardening and spring back effects make machining quite challenging. These unfavorable effects for machining cause significant tool wear along with decreasing the quality of work piece. Recently, additive manufacturing (AM) has gained significant attention for manufacturing NiTi. Since AM can create a part directly from CAD data, it is predicted that AM can overcome most of the manufacturing difficulties. This technique provides the possibility of fabricating highly complex parts, which cannot be processed by any other methods. Curved holes, designed porosity, and lattice like structures are some examples of mentioned complex parts. This work investigates manufacturing superelastic NiTi by selective laser melting (SLM) technique (using PXM by Phenix/3D Systems). An extended experimental study is conducted on the effect of subsequent heat treatments with different aging conditions on phase (open full item for complete abstract)

Committee: Mohammad Elahinia (Advisor); Mehdi Pourazady (Committee Member); Matthew Franchetti (Committee Member) Subjects: Mechanical Engineering