Biomedical Engineering and Bioengineering Commons^™

Shape Memory Behavior Of Dense And Porous Niti Alloys Fabricated By Selective Laser Melting, Soheil Saedi

Theses and Dissertations--Mechanical Engineering

Selective Laser Melting (SLM) of Additive Manufacturing is an attractive fabrication method that employs CAD data to selectively melt the metal powder layer by layer via a laser beam and produce a 3D part. This method not only opens a new window in overcoming traditional NiTi fabrication problems but also for producing porous or complex shaped structures. The combination of SLM fabrication advantages with the unique properties of NiTi alloys, such as shape memory effect, superelasticity, high ductility, work output, corrosion, biocompatibility, etc. makes SLM NiTi alloys extremely promising for numerous applications.

The SLM process parameters such as laser power, …

Structure And Dynamics Of Charged Colloidal Disks In Colloid-Polymer Mixtures, Suhasini Kishore

Doctoral Dissertations

Complex fluid mixtures of colloids and polymers are extensively used in several conventional and emerging technological applications. Particles self-assemble under different conditions to form colloidal glasses and gels and it often leads to the development of unusual viscoelastic features. In the case of aspherical particles, shape anisotropy and physical aging effects add to the existing complexities so the implementation of a strategic formulation method to improve performance and stability remains a critical challenge. This thesis presents a comprehensive analysis of particle interactions in mixtures of charged disk-shaped colloids and weakly-adsorbing polymers like poly(ethylene oxide) (PEO). Here, we discuss the behavior …

Influence Of Nb On The Β → Α″ Martensitic Phase Transformation And Properties Of The Newly Designed Ti-Fe-Nb Alloys, Shima Ehtemam-Haghighi, Yujing Liu, Guanghui Cao, Lai-Chang Zhang

Research outputs 2014 to 2021

A series of Ti-7Fe-xNb (x = 0, 1, 4, 6, 9, 11 wt.%) alloys was designed and cast to investigate the β → α″ martensitic phase transformation, β phase stability, the resulting microstructure and mechanical properties. Phase analysis revealed that only Ti-7Fe-11Nb alloy shows a single body-centred cubic β phase microstructure while the others are comprised of β and orthorhombic α″ phases. Moreover, Nb addition up to 11 wt.% enhances the stability and volume fraction of β phase in the microstructure, hence reducing the propensity of the alloy system to form α″ phase during quenching. Compressive yield strength and hardness …

Regional Mechanical Properties And Microstructure Of Ovine Heart Chambers, Shahnaz Javani

Electronic Theses and Dissertations

Mechanical properties of cardiac tissue play an important role in the normal heart function. As a baseline for understanding of physiology and pathophysiology of the heart, and for development and validation of new therapies, it is crucial to first understand the mechanical behavior of the normal heart tissue. Although heart chambers have the same embryonic origin, differences in the development of mechanical properties are expected to manifest over time during the adulthood period. Therefore, the goal of this study was to determine the passive mechanical properties of all heart chambers through a paired comparison study in an ovine model. Ovine …

The Microstructure And The Electrochemical Behavior Of Cobalt Chromium Molybdenum Alloys From Retrieved Hip Implants, Christopher P. Emerson

FIU Electronic Theses and Dissertations

Because of their excellent mechanical, tribological, and electrochemical properties, Cobalt Chromium Molybdenum alloys have been used as the material for both the stem and head of modular hip implants. Corrosion is one mechanism by which metal debris, from these implants, is generated, which can lead to adverse events that requires revision surgery. Manufacturing process such as wrought, as-cast, and powder metallurgy influences the microstructure, material properties, and performance of these implants

The current research focuses on analyzing the microstructure of CoCrMo alloys from retrieved hip implants with optical and scanning electron microscopy. Additionally, energy disperse spectroscopy was utilized to determine …

Evaluation Of Corrosion Properties For Use Of Az31b In Bioabsorbable Stents And In Vivo Corrosion Rate Prediction Using Fea, Jared Vidales, Austin Schader, Jenna Jerman, Michael Turovskiy

Materials Engineering

AZ31B was heat treated to evoke more controlled and uniform corrosion. 1/16” diameter AZ31B wire was cut into six samples each 1” long. The samples underwent heat treatments following ASTM B661-06. Samples were weighed and placed into three different in vitro environments. In the first scenario two samples of each heat treatment were individually placed in 50 ml of saline solution at 0.9% sodium, in a static test tube at 37°C temperature. Two samples were placed in 100 ml of 0.9% saline solution in a 250 ml stirring beaker with an average whirlpool depth of 1”. Two of each sample …

Mechanical Properties Of Dendritic Pd-Cu-Ga Dental Alloys, Efstratios Papazoglou, Qiang Wu, William A. Brantley, John C. Mitchell, Glyn Meyrick

Cells and Materials

Three Pd-Cu-Ga dental alloys with very similar nominal compositions and dendritic as-cast microstructures were selected for study: Option (Ney Dental) and Spartan (Williams/lvoclar) contain a small amount of boron, while Spartan Plus (Williams/Ivoclar) is boron-free. Bars of each alloy were tested in tension for the as-cast and simulated porcelain-firing conditions, and values of mechanical properties were measured. Fracture surfaces and microstructures of axially sectioned and etched fracture specimens were observed with the scanning electron microscope (SEM). Except for the elastic modulus, significant differences were typically found in alloy properties. Heat treatment eliminated the dendritic microstructure, decreased strength and increased ductility. …

X-Ray Diffraction And Scanning Electron Microscopy Analyses Of A Gallium-Based Dental Restorative Alloy, Randa E. Shaker, William A. Brantley, Qiang Wu, John C. Mitchell

Cells and Materials

Specimens of a gallium-based dental alloy were prepared with different condensation techniques, with and without the removal of a surface layer, and after aging for 2 hours at 50°, 100° and 150°C. X-ray diffraction at times ranging from 10 minutes to 1 day showed the development of the four matrix phases (ß-Sn, CuGa₂, Ga₂₈Ag₇₂, and In₄Ag₉) during the setting reaction. Scanning electron microscope (SEM) examination of specimens loaded to failure revealed brittle fracture, with greater porosity for hand-condensed specimens, and provided insight into crack propagation processes. Aging increased …

Effects Of Casting Conditions And Annealing On Microstructures And Vickers Hardness Of Dendritic Pd-Cu-Ga Dental Alloys, William A. Brantley, Qiang Wu, Zhuo Cai, Stanley G. Vermilyea, John C. Mitchell, Michael C. Comerford

Cells and Materials

Three Pd-Cu-Ga alloys with as-cast dendritic microstructures and very similar compositions, two containing less than 1 wt% boron and the third boron-free, were cast with normal bench-cooling or rapid-quenching into water. Quenched specimens were also heat treated at temperatures of 1000°, 1200°, 1500° and 1800°F that span the firing cycles for dental porcelain. Similar values of Vickers hardness were observed for all three alloys, suggesting little effect from boron on yield strength. The hardness was relatively insensitive to the experimental conditions, except for heat treatment at 1500° and 1800°F where significant softening occurred with transformation of the microstructure to Pd …

Heat-Treatment Behavior Of High-Palladium Dental Alloys, Qiang Wu, William A. Brantley, John C. Mitchell, Stanley G. Vermilyea, Jianzhong Xiao, Wenhua Guo

Cells and Materials

Four high-palladium dental alloys were cast, quenched following solidification, and heat treated at temperatures ranging from 200° to 1,800°F. The Vickers hardness of each alloy was measured, and microstructural changes were studied by scanning electron microscopy (SEM). Phase transformations were investigated by thermomechanical analysis (TMA). Heat treatment at 1,600° and 1,800°F significantly decreased the hardness of one Pd-Cu-Ga alloy, compared to the as-cast condition, as did heat treatment at 1,800°F for the other Pd-Cu-Ga alloy and one Pd-Ga alloy, and yielded fine-grained microstructures of the palladium solid solution. There were generally no significant changes in the hardness of the other …

Mechanism For Formation Of Lamellar Constituents In Grain-Refined Pd-Cu-Ga Dental Alloys, William A. Brantley, Zhuo Cai, John C. Mitchell, Stanley G. Vermilyea

Cells and Materials

Grain-refined Pd-Cu-Ga dental alloys solidify with a lamellar microstructural constituent that affects a variety of clinically relevant properties. While formation of this constituent has been attributed to eutectic solidification, an alternative mechanism of discontinuous precipitation has been proposed. Using a representative grain-refined Pd-Cu-Ga dental alloy, casting procedures involving two different rates of solidification were used: (a) A standard thin-walled coping configuration for a metal-ceramic restoration was cast into a room temperature mold, followed by rapid quenching into an ice-water mixture. (b) A thin plate specimen was cast into a standard elevated-temperature mold, with the same subsequent rapid quenching procedure. Neither …

Effects Of Solidification Conditions And Heat Treatment On The Microstructure And Vickers Hardness Of Pd-Cu-Ga Dental Alloys, William A. Brantley, Zhuo Cai, Stanley G. Vermilyea, Efstratios Papazoglou, John C. Mitchell, Alan B. Carr

Cells and Materials

Two representative Pd-Cu-Ga dental alloys, one with a dendritic as-cast microstructure containing a eutectic interdendritic constituent and the other with an equiaxed fine-grained as-cast microstructure containing a near-surface eutectic constituent, have been subjected to rapid quenching following casting, in addition to the conventional bench cooling recommended by the manufacturers. The quenched alloys were subsequently heat treated at temperatures of 1200°, 1500° and 1800 op that span the range of the firing cycles for dental porcelain. Scanning electron microscopic examination showed that the lamellar eutectic constituents normally present in the microstructures of the as-cast and bench-cooled alloys persisted when the alloys …

A Microstructural Investigation Of Calcium Hydroxyapatites Synthesized From Cahpo4•2h2o And Ca4(Po4)2o, Kevor S. Tenhuisen, Boyd A. Clark, Maria Klimkiewicz, Paul W. Brown

Cells and Materials

This investigation determined the effects of reaction temperature and bulk composition on the microstructural features of hydroxyapatites (HAp) synthesized from reaction between particulate CaHPO₄·2H₂O and Ca₄(PO₄)₂O. These data were used in combination with previous work to further elucidate the mechanistic reaction path taken by these calcium phosphate cements. HAps having two different compositions (Ca/P = 1.50 and 1.67) were synthesized between 15.0 and 70.0°C. All reactions reached completion as indicated by X-ray diffraction. Single point nitrogen absorption was performed on all samples to determine specific surface areas. The HAp which …

Room Temperature Aging Of Pd-Cu-Ga Dental Alloys, William A. Brantley, Zhuo Cai, Qiang Wu, Alan B. Carr, John C. Mitchell

Cells and Materials

Specimens of three Pd-Cu-Ga dental alloys cast five years ago and subsequently stored at room temperature were reexamined and observed to have lower amounts of the eutectic constituents in the near-surface region than originally present, along with other microstructural changes. This previously unreported room temperature aging behavior of these alloys is attributed to the presence of high-diffusivity paths in the non-equilibrium ascast eutectic structures and to the essential role of the surface for the vacancy diffusion mechanism. These results may have important clinical significance for the ill vivo corrosion resistance and long-term biocompatibility of the Pd-Cu-Ga alloys.

Backscattered Electron Imaging To Enhance Microstructural Contrast In Poly(Methyl Methacrylate) Bone Cement Fracture Analysis, L. D. T. Topoleski, P. Rutledge, X. Lu

Cells and Materials

Poly(methyl methacrylate) (PMMA) bone cement is used as a grout to secure joint replacement prostheses into bone. It has a distinct microstructure made up of: prepolymerized beads, an interbead matrix polymer, a radiopacifier {barium sulphate (BaS04) or zirconium dioxide (Zr02)}, and pores or voids; the radiopacifier is found only in the interbead matrix of the cured bone cement. The mechanism of slow or fatigue crack growth appears to be initial micro-cracking through the interbead matrix, followed by coalescence of the microcracks to form a continuous crack. Thus, distinguishing the interbead matrix from the pre-polymerized beads is important for investigating fatigue …

Microstructural Enhancement Of Dental Composite And Ceramic Materials By Plasma Etching, H. J. Mueller, M. S. Bapna

Cells and Materials

Radio frequency plasma etching of a selected number of dental materials , including glass filled polymeric composites, alumina reinforced ceramic, glass ionomer, and zinc oxide eugenol enhanced microstructural detail for scanning electron microscopy analyses. All four plasmas, argon , oxygen, carbon tetrafluoride (CF4), and CF4 + 4% 0 2 , proved effective, but the latter was the most effective. The etching of all materials , except the ceramic, was accomplished by the selective removal of a polymeric component. For the glass filled composites , this involved removal of the Bis-GMA matrix resin, leaving the filler particles in relief. For a …

Metallurgical Structures Of As-Cast And Heat-Treated High-Palladium Dental Alloys, William A. Brantley, Zhuo Cai, Alan B. Carr, John C. Mitchell

Cells and Materials

Scanning electron microscope observations and energy-dispersive spectroscopic analyses have been performed on two first-generation and two second-generation high-palladium dental casting alloys. A specimen design simulating a maxillary central incisor coping was employed to conserve metal, while providing thin and thick sections to yield a range of solidification rates. The alloys were centrifugally cast in air, following standard dental laboratory techniques; three castings were prepared for each alloy. Each casting was sectioned to produce two mirror-image specimens, and one specimen received the appropriate oxidation heat treatment, followed by a simulated full porcelain firing sequence. After metallographic polishing, specimens were examined with …

Microstructure Of Mica Glass-Ceramics And Interface Reactions Between Mica Glass-Ceramics And Bone, W. Holand, W. Gotz, G. Carl, W. Vogel

Cells and Materials

This review paper characterizes glass-ceramics containing mica as main crystal phase. The phase formation reactions in dependence of the chemical composition and the microstructure are shown. Microstructure of mica glass-ceramics has been studied by electron replica and scanning electron microscopic (SEM) techniques.

Mica glass-ceramics have previously been developed in Si02-B20rA120rMgO-F--base glasses. The material is machinable because of the precipitation of micas of fluorophlogopite-type. Also, a machinable glass-ceramic for dental applications was developed based on KMg2_5(Si40 10)F2-micas. We developed mica glass-ceramics in the Si02-Al20rMgO-NaiO-K20-F glass system. Phase formation within these glasses was observed by SEM. A double controlled nucleation and crystallization …

Microstructural Changes In Retrieved Amalgam Restorations, Grayson W. Marshall Jr., D. D. Mccoy, John H. Kinney, Hugo Letzel, Sally J. Marshall

Cells and Materials

Many blended or dispersed phase high Cu amalgams show excellent clinical performance in long term clinical trials. However, little is known concerning the microstructural changes that occur during clinical use of these systems. This investigation sought to characterize some of the changes that occur in the Ag-Cu particles and their surrounding reaction zones based on a study by backscattered scanning electron microscopy (BSEM), energy dispersive spectroscopy and a new rnicroprobe technique called Colorad which assigns various colors to elements and element combinations and indicates changes in elemental concentration by changes in color value (brightness). Restorations were retrieved from clinical trials …