Search

A study of hot pressed B4C-based laminates, after rolling and without rolling, has been performed to elucidate the existence of fracture resistance/crack length anisotropy induced by this processing technique. While the crack lengths/fracture resistance was affected significantly by the presence of the residual stresses in B4C/B4C-ZrB2 laminates, no differences in Vickers crack lengths were observed in B4C/B4C laminates prepared by rolling and hot pressing, as compared to the crack lengths seen in pure B4C ceramics prepared by hot pressing without rolling. X-ray diffraction analysis confirmed that no texture has been formed during the rolling and hot pressing of B4C

Responsive nanomaterials are being developed through interdisciplinary research to improve and evaluate the performance of engineering assets. An overview of the work is given here. Nanomaterials are defined as bulk materials that have nanoparticle components. Responsive materials are defined as having an intrinsic ability to sense their condition and potentially respond when performance of the material is being affected or degraded. Responsive nanomaterials are a new class of material being developed by integrating nanoscale particles into host materials to provide the properties that we want. Nanomaterials can have unique combinations of properties such as a high surface area to volume ratio of the nanophase components, improved stiffness and strength, supercapacitance, electrical conductivity, magnetic properties, lightweight, photonic, and other properties. The focus of this paper is on development of responsive materials based on commercially available nanoscale materials that can be put into applications now. The nanoscale materials considered are carbon nanofibres, carbon nanosphere chains, long carbon nanotubes, and the intermediate products of these materials. Nanoengineering of multifunctional responsive materials is predicted to open up many new opportunities in the field of condition monitoring and asset evaluation, not just for structures, but also for humans, electronics, and the environment. New classes of responsive nanomaterials such as piezoresponsive, magnetoresponsive, photoresponsive, thermoresponsive and others may eventually enable the design of engineering assets that are self-monitoring and partially self-repairable, thus making high technology machines, vehicles, and structures safer for society and safeguarded against misuse.

In recent years, magnesium (Mg) and its alloy are being studied for their potential use in orthopedic implants with the novel ability to biodegrade after the implant serves its therapeutic function. Pure Mg, by itself, would not be suitable for use in a load-bearing implant application, due to its high corrosion rate and poor tribological properties. However, through proper alloying, this degradable metal is capable of achieving good mechanical properties reasonably similar to bone, a retarded rate of corrosion and enhanced biocompatibility. Previous studies have shown that alloying Mg with aluminum, lithium, rare earth (RE), zinc (Zn), and calcium (Ca) result in lower corrosion rates and enhanced mechanical properties. Despite the growing popularity of Mg and it alloys, there is relatively little information in the literature on their wear performance. In this paper, we report on an investigation of the directional tribological properties of Mg and Mg-Zn-Ca-RE alloy fabricated via two different manufacturing processing routes: as-cast and hot-extruded after casting, with extrusion ratios of 10 and 50. Pure Mg was cast 350°C. After casting, Mg-Zn-Ca-RE alloy was heat-treated at 510°C. Another Mg-Zn-Ca-RE alloy was hot-extruded at 400°C. Dry sliding wear tests were performed on as-cast and hot-extruded pure Mg and Mg-Zn-Ca-RE alloys using a reciprocating test configuration. Wear rate, coefficient of friction and wear coefficient were measured under applied loads ranging from 0.5–2.5N at sliding frequency of 0.2 Hz for 120 cycles, using microtribometery. Wear properties of the extruded specimen were measured in cross-section and longitudinal section. In the longitudinal section studies, wear properties were investigated along the extrusion direction and the transverse direction. Hardness properties were evaluated using microindentation. Cross-section and longitudinal section were indented with a Vickers indenter under applied load of 2.94 N. Alloying and extrusion enhanced the mechanical properties significantly, increased hardness by 80% and wear resistance by 50% compared to pure Mg. Despite the low hardness in both Mg and the Mg alloy cross-sections, the cross-sections for both displayed higher wear resistance compared to the longitudinal section. In the longitudinal section, wear resistance was higher along the transverse direction of the longitudinal section for both Mg and the Mg alloy. The wear coefficient was used to evaluate how the wear behavior of the material varied with respect to alloying, fabrication process, and direction of wear. The wear coefficient of pure Mg decreased as the extrusion ratio increased, thus, increasing the specific wear rate. The opposite behavior was found in the Mg alloy: as the wear coefficient increases, the specific wear rate decreases. The active wear mechanisms observed on the worn surface of Mg were fatigue, abrasive, adhesive and delamination wear. The same wear mechanisms were observed in the Mg alloy except for fatigue wear. Surface microstructure and topographical characterization were conducted using optical microscopy, scanning electron microscopy mechanical stylus profilometry, and optical profilometry.Copyright © 2015 by ASME

In this study, Mg/SiO2 and MgO/SiO2 multilayer coatings with bilayer thicknesses (Λ) 10, 20, 40, 100, 200 and 1000 nm were deposited on glass substrates using DC and reactive pulsed DC magnetron sputtering processes. The aim of these coatings is to control the initial degradation and provide mechanical strength to magnesium implant during handling and installation. The initial thickness calibrations and deposition rates optimization were conducted using stylus profilometer. After deposition of the multilayer coatings, the values of their bilayer thicknesses (Λ) were obtained from X-ray reflectometery. The mechanical properties, surface morphology and roughness of multilayer coatings were studied using nanoindentation, SEM and AFM respectively. The nanoindentation results showed higher hardness of MgO/SiO2 multilayer coatings compared to single layer Mg. The roughness analyses showed improved roughness for bilayer thicknesses (Λ) less than 20 nm. It was observed from the SEM images that SiO2 coatings has pores. By adding Mg and/or MgO in the form of multilayers improves the pores significantly. The Mg/SiO2 multilayer coatings showed controlled degradation rate when immersed in saline solution compared to the monolithic SiO2 coating. In conclusion, conditions for depositing Mg/SiO2 and MgO/SiO2 multilayer coatings has been optimized. Alternating brittle SiO2 ceramic layers with soft and ductile Mg layers significantly improved the hardness of the Mg coating. Hardness of multilayer coatings can be fine-tuned by modifying bilayer thicknesses. Significant improvement in the corrosion and mechanical properties of the multilayer coatings can be used to protect surface of magnesium implant material during handling, storage and installation.Copyright © 2015 by ASME

The SiC/SiCwf laminate design has been targeted to achieve increased residual compressive stress in thin SiCwf layers and small residual tensile stress in thick SiC layers, that would lead to a significant increase of the apparent fracture toughness of the composite. The laminates have been manufactured using rolling and hot pressing techniques. The measured apparent fracture toughness of laminates showed a significant increase over the monolith SiC ceramics. Thus, while the intrinsic fracture toughness of pure SiC ceramics is in the range of 2–3 MPa m1/2, significant increase up to 6–8 MPa m1/2 was achieved for the layered ceramics. A crack shielding by compressive residual stress was a main mechanism responsible for the significant toughening of the SiC/SiCwf laminate.

Boron carbide-silicon carbide ceramic composites are very promising armor materials because they are intrinsically very hard. However, their fracture toughness is not very high. Their ballistic performance could be significantly increased if the brittleness of these materials could be decreased. Here we report development of boron carbide-silicon carbide layered ceramics with controlled compressive and tensile stresses in separate layers. Such B4C-SiC laminates with strong interfaces can provide high apparent fracture toughness and damage tolerance along with high protection capabilities. The theory of heterogeneous layered systems was used to develop optimal design parameters allowing the evaluation and maximization of apparent fracture toughness. The layered composites were designed in a way to achieve high compressive residual stresses in thin B4C-SiC based layers and low tensile residuals stresses in thick B4C layers. The residual stresses were controlled by the phase composition of layers and the layers thickness. The estimated apparent fracture toughness was calculated for both three layered and nine layered composites. B4C-30 wt%SiC/B4C laminates were made based on the optimized design for high apparent fracture toughness. Processing of laminates involved preprocessing of powders, forming green tapes and hot pressing. Work is in progress to measure fracture toughness of laminates, as well as their strength, hardness and the ballistic performance.

Thin film composites consisting of metallic nanocrystals embedded in an insulating host have been synthesized using alternating-target pulsed laser deposition of Ni and Al 2 O 3 on silicon (100) substrate. The evaluation of structural quality of the thin film composites using high resolution transmission electron microscopy and scanning transmission electron microscopy with atomic number contrast has revealed the formation of a biphase system with thermodynamically driven segregation of Ni and alumina during pulsed laser deposition. The best hardness values of the thin film composites, measured using nanoindentation techniques, were found to be 20–30% larger than pure alumina films fabricated under identical conditions. Fracture toughness measurements of the composite showed slight toughening due to embedding of Ni nanoparticles.

We report here a novel thin film processing method based upon pulsed laser deposition to process nanocrystalline materials with accurate size and interface control with improved magnetic properties. Using this method, single-domain nanocrystalline Fe and Ni particles in the 5–10 nm size range embedded in amorphous alumina as well as in crystalline TiN have been produced. By controlling the size distribution in confined layers, it was possible to tune the magnetic properties from superparamagnetic to ferromagnetic behavior. Magnetic hysteresis characteristics below the blocking temperature are consistent with single-domain behavior. The paper also presents our results from investigations in which scanning transmission electron microscopy with atomic number contrast (STEM-Z) and electron energy loss spectroscopy (EELS) were used to understand the atomic structure of Ni nanoparticles and interface between the nanoparticles and the surrounding matrices. It was interesting to learn from EELS measurements at interfaces of individual grains that Ni in alumina matrix does not form an ionic bond indicating the absence of metal–oxygen bond at the interface. The absence of metal–oxygen bond, in turn, suggests the absence of any dead layer on Ni nanoparticles even in an oxide matrix.

A liquid fuel combustion chemical vapor deposition technique had been developed for oxide thin film deposition. Yttria-stabilized zirconia thin films had been processed using this technique operated in open air. Combustion flame had been modulated for high-quality film deposition by studying the effect of the ratio of the oxidant gas to the liquid fuel. Another key processing parameter, i.e. the substrate temperature, had been investigated. The as-grown films were characterized with X-ray diffraction and scanning electron microscope. The phase and crystallinity of the films were found strongly dependent on the experimental variables. Moderate increase of the ratio of the oxidant gas to the liquid fuel can accelerate the decomposition of the fuel and improve the quality of the deposited film. Two film growth kinetic modes were found with the transition temperature at approximately 1343 K. The microstructural zone transition temperature from zone 1 to zone 2 was found to be at approximately 1473 K. The processing variables were optimized with regard to both the phase quality and the growth rate.

Atomic force microscopy (AFM) is powerful technique to study surface properties and processes in the μm- and nm-range. In-situ liquid AFM measurements were conducted to evaluate the surface degradation of two biocompatible metals: Ti as the most bio-inert (bio-stable) and Mg as the promising biodegradable metal. The pure Mg and Ti thin films were deposited using DC magnetron sputtering on glass substrates. The corrosion resistances of the samples were evaluated in in pure water and phosphate buffered saline (PBS). The results showed exponential decay of film thickness in water.Copyright © 2014 by ASME

Magnesium and its alloys have been found to potential candidates for biodegradable implant applications. However, magnesium and its alloys are broadly known to have poor tribological properties, but detailed specifics on wear performance are scarce. This research investigates the tribological characteristics on Mg-Zn-Ca-RE alloys and pure magnesium under as-cast and extruded conditions. Pure magnesium and Mg-Zn-Ca-RE alloys were hot extruded at 350°C and 400°C. Magnesium and Mg-Zn-Ca-Re alloy were also cast at 350°C and heat treated at 510°C. Directional wear properties were investigated using a CETR-UMT 2 microtribometer under unlubricated conditions in a reciprocating configuration for 120 cycles, with normal loads ranging from 0.5N–2.5N. Wear tests were conducted in directions: cross-sectional, longitudinal (along the extrusion direction) and transverse direction (perpendicular to the extrusion direction). Wear properties and friction properties were analyzed using a microtribometer, a mechanical stylus profiler, and microindentation. Surface morphology and microstructure were characterized using optical microscopy, scanning electron microscopy, and optical profilometry. The results show a lower wear rate in the transverse and cross-sectional direction compared to the longitudinal direction.

Magnesium has attracted a lot of attention over the last few decades, due to its light weight and potential use as biomaterial. However, the poor corrosion resistance of magnesium restricts its practical use for application where exposure to aggressive aqueous media is unavoidable. This paper describes the growth, characterization and corrosion analyses of Al2O3, MgO and ZrO2 coatings for slowing down the degradation of Mg. Different thicknesses of Al2O3, MgO and ZrO2 were deposited on pure magnesium (99.95%) substrates using pulsed-DC magnetron sputtering process. The phase composition and microstructure analyses were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The corrosion protection behavior of the Al2O3, MgO and ZrO2 coated samples were evaluated using electrochemical measurements as such open-circuit potential, potentiodynamics and EIS. The corrosion test were performed in 0.9 wt% saline solution. The results showed that the Al2O3-coated Mg alloy exhibit a much superior stability and lower corrosion rate. The surface analyses of the corroded samples showed that the coating improved the corrosion resistance, whereas the bare Mg suffered severe localized corrosion. Adhesion assay was performed on the Al2O3, MgO and ZrO2 coatings to determine their biocompatibility. The results showed significant cell attachment to the coating compare to the control (bare glass).Copyright © 2014 by ASME

Medical change is coming. Robots and tiny machines built using nanoscale materials are going to fundamentally change engineering at the microscale and medicine will be the first area to benefit. In tiny machine design, copper and iron are replaced with carbon nanotube superfiber wire and magnetic nanocomposite materials. Because of the small size of tiny machines, high magnetic fields can be generated and high-force, high-speed devices can be built. Tiny machines are still in the early stages of being built and this chapter describes their engineering design and the work underway to build them. The tiny machines will operate inside the body and detect disease at an early stage, then provide precise therapy or surgery. There will also be engineering applications for the tiny machines such as performing high-throughput manufacturing operations at the microscale. The design principles and materials processing techniques described herein will facilitate the development of nanomaterial robots and tiny machines for myriad applications ranging from miniaturized sensors, actuators, energy harvesting devices, high-performance electric motors, and energy storage devices to smart structures with built-in artificial responsive behavior.

Nanotubes are a unique class of materials because their properties depend not only on their composition but also on their geometry. The diameter, number of walls, length, chirality, van der Waals forces, and quality all affect the properties and performance of nanotubes. This dependence on geometry is what makes scaling-up nanotubes to form bulk material so challenging. Nanotubes are also unusual because they stick together to form bundles or strands. Nanotube superfiber materials are fibrous assemblages of nanotubes and strands. The hope and dream of researchers around the world is that nanotube superfiber materials will have broad applications and change engineering design. This chapter gives a perspective on nanotube superfiber development. This chapter discusses new applications—where we think we can go with the material properties and what applications will be enabled—and new techniques for developing superfiber material.

Structural and dynamical studies of Optically-induced effects in SmA and SmC* liquid crystals are presented. The smectic materials are doped with photosensitive molecules capable of trans-cis isomerization under light illumination. Laser irradiation leads to the formation of strongly scattering textures with periodical array of parabolic focal conic domains (PFCD's). What is most surprising is that the effect is caused by a low-power (≤ 10 mW) He-Ne laser beam; its efficiency is highest in the visible part of the spectrum. The written information can be erased by another beam with shorter wavelength, such as from an Ar laser or a UV source. The PFCD's lattice can be stabilized by a polymeric network. The most plausible mechanism of the light-induced effect is compression/dilation of smectic layers caused by phototransformation of the molecules.

Nanostructured magnesium coatings have the potential of enhancing the integration of implant to bone tissues due to their ability to regulate the functions of integrin, which modulates cell proliferation and differentiation. However, they are soft, ductile and have low wear resistance. These limitations prevent the practical use of Mg coatings for this application. However, application of Mg thin films in the form of nanolaminate coatings has been found to improve hardness as well as wear properties. In this study, Mg/MgO and Mg/Al2O3 nanolaminates with bilayer thicknesses (Λ) 10, 20, 40, 100, 200, 1000 nm were deposited on glass substrate using the reactive pulsed DC magnetron sputtering process. The Mg/MgO nanolaminates were developed from an Mg target. Λ was controlled by the duration of oxygen flow during the sputtering process. Values of Λ were obtained from low angle-XRD. We found that the rate of MgO deposition significantly depends on water vapor content in the chamber and that a partial base pressure of water below 10−8 Torr is required to achieve repeatable results. Structure and properties of multilayered coatings were studied by X-ray diffractometry, nanoindentation, SEM and AFM. At Λ < 100 nm, MgO and Mg have preferred orientations and respectively, while at higher Λ, other orientations are present in the XRD patterns. The nanoindentation results showed slightly higher hardness of Mg/MgO and Mg/Al2O3 nanolaminate coatings compared to that of pure Mg. Nanolaminates have high ductility compared to MgO and Al2O3. Nanolaminate coatings at Λ < 100 nm exhibit an improvement in the mechanical properties due to the presence of interfaces which act as barrier to dislocation movement.

Magnesium and its alloys are great candidates for uses in orthopedic implant applications due to their biocompatibility, mechanical properties and degradability. However, they are susceptible to accelerated degradation rates due to micro galvanic corrosion, which leads to unpredictable corrosion behavior. The poor corrosion resistance limitation restricts the practical use of Mg for implant application, where exposure to aggressive environment of body fluids is unavoidable. This paper describes the growth, characterization and corrosion analyses of MgO coatings which can slow down the degradation of Mg. Bilayer Mg-MgO system was prepared by pulse DC magnetron sputtering method and used as a model for evaluation of sustainability of MgO on Mg surface. Immersion tests were performed on Mg-MgO system with varying thicknesses using the optical density method. The tests were performed at room temperature and 37°C with deionized water, phosphate buffered saline, albumin, media, media with fetal bovine serum and saline solutions. The result showed that degradation rate of MgO on Mg substrate significantly depends on media.Copyright © 2012 by ASME

Quantification of apoptotic tissues during inflammatory processes induced by biomaterials is challenging in vivo. Here we present a non-invasive method using a fluorescence imaging system which facilitates intermittent snap shots of the current state of local apoptotic tissue. For this purpose, apoptotic cells around two different subcutaneously implanted materials (titanium discs and copper-coated titanium discs) in hairless but immunocompetent mice were quantified after 4, 8 and 23 days of implantation. For validation, the results of fluorescence signals were compared to the histology of the inflammatory tissue using apoptotic-specific TUNEL-, macrophage-specific F4/80-, neutrophile-specific NIMP-R14- and chloroacetate esterase-staining. We could demonstrate that the fluorescence signals were well suited to quantify the extent of apoptosis in vivo and this is a good indication for the biocompatibility of biomaterials. This study shows that non-invasive monitoring of tissue processes following the implantation of biomaterials is possible in vivo and may help to reduce the number of animals in studies addressing biocompatibility.

Quantitative investigations of E,Z-photoisomerization of chiral dopants (−)-2-arylidene-p-menthanones were carried out using solvents of different nature and various liquid crystalline matrices.

The molecular conformation of three newly synthesized, sterically hindered aryl derivatives of five-membered nitrogen-containing heterocyclicortho-analogs of POPOP were studied by X-ray analysis and vibrational spectroscopy. It was shown that molecules of the compounds in the crystalline state and in solution are non-planar and asymmetric.

Bulk nanostructured metallic alloys as well as coatings are being research closely for biomedical applications, especially for implants. Corrosion behavior is of particular interest, given the aggressive environment of body fluids that these metals experience. While weight loss measurement and electrochemical analysis are the two commonly used techniques for corrosion behavior evaluation, both have their own limitations with respect to characterizing the corrosion of films and coatings under a micron in thickness. This paper reports on a novel application of the optical density technique as a relatively faster yet accurate method to evaluate the corrosion of thin metallic films. With this technique, the survivability and/or resorption time of a pure metallic coating is evaluated by monitoring the changes in optical density (directly related to reduction in film thickness, and thereby to weight loss) of thin film immersed in a corrosive media. In our experiments, Mg, Cu and Ag thin films of a wide range of thicknesses were sputter-deposited on glass substrates and the corrosion kinetics of these metals in a simulated body fluid was studied at room temperature. The results were utilized to develop a resorption time model for the coating, which can be used to predict the survivability of these metallic thin films.Copyright © 2011 by ASME

The phase composition and sintering behavior of two commercially available 10 mol % Sc 2 O 3 -1 mol % CeO 2 -ZrO 2 ceramics produced by Daiichi Kigenso Kagaku Kogyo (DKKK) and Praxair have been studied. DKKK powders have been manufactured using a wet coprecipitation chemical route, and Praxair powders have been produced by spray pyrolysis. The morphology of the powders, as studied by scanning electron microscopy, has been very different. DKKK powders were presented as soft (∼100 μm) spherical agglomerates containing 60-100 nm crystalline particles, whereas the Praxair powders were presented as sintered platelet agglomerates, up to 30 μm long and 3-4 μm thick, which consisted of smaller 100-200 nm crystalline particles. X-ray diffraction analysis has shown that both DKKK and Praxair powders contained a mixture of cubic (c) and rhombohedral (r) phases: 79% cubic +21% rhombohedral for DKKK powders and 88% cubic +12% rhombohedral for Praxair powders. Higher quantities of the Si impurity level have been detected in Praxair powder as compared to DKKK powder by secondary ion mass spectroscopy. The morphological features, along with differences in composition and the impurity level of both powders, resulted in significantly different sintering behaviors. The DKKK powders showed a more active sintering behavior than of Praxair powders, reaching 93-95% of theoretical density when sintered at 1300°C for 2 h. Comparatively, the Praxair powders required high sintering temperatures at 1500-1600°C. However, even at such high sintering temperatures, a significant amount of porosity was observed. Both DKKK and Praxair ceramics sintered at 1300°C or above exist in a cubic phase at room temperature. However, if sintered at 1100 °C and 1200°C, the DKKK ceramics exist in a rhombohedral phase at room temperature. The DKKK ceramics sintered at 1300° C or above exhibit cubic to rhombohedral and back to cubic phase transitions upon heating at a 300-500°C temperature range, while Praxair ceramics exist in a pure cubic phase upon heating from room temperature to 900° C. However, if heated rather fast, the cubic to rhombohedral phase transformation could be avoided. Thus it is not expected that the observed phase transitions play a significant role in developing transformation stresses in SCCeZrO 2 electrolyte upon heating and cooling down from the operation temperatures.

A biosensor is an electronic device that measures biologically important parameters. An example is a sensor that measures the chemicals and materials released during corrosion of a biodegradable magnesium implant that impact surrounding cells, tissues and organs. A responsive biosensor is a biosensor that responds to its own measurements. An example is a sensor that measures the corrosion of an implant and automatically adjusts (slows down or speeds up) the corrosion rate. The University of Cincinnati, the University of Pittsburgh, North Carolina A&T State University, and the Hannover Medical Institute are collaborators in an NSF Engineering Research Center (ERC) for Revolutionizing Metallic Biomaterials (RBM). The center will use responsive sensors in experimental test beds to develop biodegradable magnesium implants. Our goal is to develop biodegradable implants that combine novel bioengineered materials based on magnesium alloys, miniature sensor devices that monitor and control the corrosion, and coatings that slow corrosion and release biological factors and drugs that will promote healing in surrounding tissues. Responsive biosensors will monitor what is happening at the interface between the implant and tissue to ensure that the implant is effective, biosafe, and provides appropriate strength while degrading. Corrosion behavior is a critical factor in the design of the implant. The corrosion behavior of implants will be studied using biosensors and through mathematical modeling. Design guidelines will be developed to predict the degradation rate of implants, and to predict and further study toxicity arising from corrosion products (i.e., Mg ion concentrations, pH levels, and hydrogen gas evolution). Knowing the corrosion rate will allow estimations to be made of implant strength and toxicity risk throughout the degradation process.Copyright © 2009 by ASME

This chapter is an overview of potential applications of carbon nanotube smart materials in biology and medicine. Carbon nanotube arrays are forests of aligned nanotubes prepared on a substrate. The nanotubes have multifunctional properties that include high strength, sensing, actuation, and electronic properties. Several prototype smart material devices using nanotube arrays or nanotubes from the array are being developed by various groups that are co-authors of this chapter. The new devices include a biosensor, electrochemical actuator, nanotube probes, and a concept for a future in-body biosensor. Recently, aligned multi-wall carbon nanotube arrays over 1 cm tall were synthesized on large area substrates using a chemical vapor deposition process. The technique for growing nanotubes on large area substrates will open the door for low cost manufacturing of novel sensors, actuators, and devices for biology and medicine.

This research will specifically address the tensile of textile products employing high tenacity industrial quality multifilament twill textile yarns. The research report in this paper is directed toward developing a repeatable and reproducible test method for textile reinforcements. The p[paper will present a new testing technique, which uses pressure clamping systems as opposed to conventional roller grip systems. The pressure clamping system incorporates a technique used on other disciplines for very strong materials. This technique is the application of sacrificial tabs to the clamping area of the specimen, thus permitting very high jaw pressures without specimen damage. The specific concerns about testing reinforcing products expressed in the literature are: (1) the effect of sample gage (length) on reported values including tensile strength, extension and modulus, (2) the effect of test speed, i.e. strain rate on reported values: one specific issue is the difference between ASTM at 10% and ISO at 20% per minute, (3) the effect of jaw and grip types on reported values, (4) the control of sample slippage in grips, (5) the amount of tolerable slippage in clamping devices, (6) the accuracy of various extension measurement systems, (7) the effect of the extension measurement system on the reported values, (8) the effect of sample width on reported values, (9) the definition, measurement and reporting of modulus, (10) which modulus is important and (11) what portion of the sample does a reported modulus represent. The paper will focus on four of the concerns. The issue addressed are sample length and sample gage (area of extension measurement), method of extension measurement, test speed and modulus measurements.

Materials with nanoscale features have new or improved properties compared to bulk materials. These properties depend on the composition, size, and shape of the material, and include high specific strength and modulus, low melting point, high electrical and thermal conductivity, a large surface area to volume ratio, nearly defect-free structure, magnetic and optical properties, and sensing and actuation properties. This talk will discuss synthesis, processing, and application of nanoscale materials for engineering and medicine. Recent advances in nanoparticle synthesis include development of “Black Cotton TM ” which is centimeter long carbon nanotubes grown in arrays, improved carbon nanofiber material, and development of carbon nanosphere chain material which has the morphology of carbon onions chained together. Applications of these materials under development include spinning Black Cotton into thread to produce a new smart material with reinforcement, sensing, and actuation properties, use of nanotube arrays for electrodes and biosensors, catalyst loaded nanotubes for medical contrast agents, and nanosphere chains for manufacturing composite materials. Overall, this paper shows that “Nanoizing” materials and structures is a hot new technological science that is going to improve many aspects of our lives. These new materials are also generating intellectual property and new opportunities for small companies and universities. Key Words. Carbon Nanosphere Chain, Carbon Nanotube, Carbon Nanofiber, Black Cotton

Interfacial properties of boron nitride fiber coatings are studied in melt infiltrated Hi-Nicalon/BN(CVI)/SiC composites subjected to room temperature cyclic fatigue loading and long term annealing to 1000-1200°C in air. Interfacial shear strength was determined from single fiber push-out tests. Hi-Nicalon fibers with diameters of 13-14.5 μm were pushed out from specimens, with thicknesses ranging from 110-280 μm using a spherical tip with a 1 μm radius and 90° conical shape. Interfacial shear strength was calculated from sliding load, fiber diameter and specimen thickness. Due to significant scattering, 30 individual push tests in every sample were used to obtain the average interfacial shear strength. The virgin specimen has interfacial shear strength of 20 MPa which is higher than tensile tested specimens (12 MPa). It was shown that strength of room temperature tensile and fatigue tested samples correlates with their interfacial shear strength obtained from fiber push-out study. Annealing of a virgin specimen for 100 hours at 1000°C slightly increase shear strength up to 21.5 MPa while annealing at 1100°C and 1200°C led to significant increase of shear strength up to 29 and 39 MPa correspondingly. This effect is associated with BN degradation at temperatures >1000°C.

There is a wide spread interest in metal-ceramic nanocomposites due to their enhanced mechanical and magnetic properties when the size of metal particles is reduced to nano-scale. This paper presents results from our study of thin film ceramic-metal nanocomposites created by embedding nano-sized Ni metal particles in amorphous alumina matrix using pulsed laser deposition technique. Micro structural study of nanocomposites using high resolution transmission electron microscopy and scanning transmission electron microcopy with atomic number (Z) contrast (STEM-Z) have shown that nanocrystals of Ni are well separated from each other in alumina matrix. The size of nanoparticles is controlled by parameters of pulsed laser deposition method (deposition time and substrate temperature). Size of Ni nanoparticles is found to be 5-15 nm. Mechanical properties like hardness, elastic modulus and fracture toughness of samples having different particle size are investigated using nanoindentation continuous stiffness measurement (CSM) technique. Our results indicate that particle size has significant (up to 20 %) effect on hardness of thin film composites. Fracture toughness of these nanocomposites has been studied using Li-Bhushan method and a method relating fracture toughness and residual stress.

The tensile strengths of fiber tows and minicomposites based on Nextel 720 fiber were investigated at room temperature (RT) and at 1200°C (HT). Uncoated and monazite coated fibers were used, and the minicomposites were made with an alumina matrix. As-received ('unsoaked') and thermally soaked tows and minicomposites were used. It was found that uncoated fiber tows tested at RT have the highest strength and linear stress-strain curves with clearly-defined fracture. This was unlike coated fiber tows, which exhibit residual load-carrying capability beyond the maximum load point, because the fibers are not loaded equally during the tension test Soaked uncoated and coated tows tested at RT retained 30% and 73% of their corresponding unsoaked RT strengths. The protective effect of the coating on contact-related damage of tows appears to dominate over the damage caused by soaking at HT. On the other hand, uncoated, unsoaked tows tested at HT retained 32% of the RT average tensile strength of 544 MPa. Coated, unsoaked tows tested at HT retained 100% of their RT average strength of 312 MPa. Strength degradation of tows appears to originate from contact between fibers in a tow during testing. The beneficial effect of the coatings in reducing contact-related damage of tows during RT and HT testing can explain the identical results for RT and HT strengths of coated tows. Degradation of the monazite coating was observed after thermal soaking of minicomposites.

The tensile strengths of Nextel 720 fibers were measured at room temperature (RT) and 1200°C (HT) to study the effects of monazite (LdO 4 ) coating. Tests were conducted on as-received (unsoaked) materials as well as materials that had been thermally soaked at HT for 100 hours. There is close agreement between the Weibull modulus obtained from the statistical distribution of fracture strength and the Weibull modulus obtained from a study of the gage length dependence of strength. The monazite coating does not change the RT strength of unsoaked single fibers, but improves the HT strength retention capability of unsoaked fibers. The average strength retained by uncoated and coated fibers at HT is 54% and 74% of the RT value. This beneficial effect of the coating disappears after soaking - coated and uncoated fibers have an HT tensile strength of about 48% of RT value.

An one-pot procedure was developed for the synthesis of mesoporous silica containing bimetallic PdCo using Pd(NO3)2 and CoCl2, and cetyl trimethyl ammonium bromide (CTAB) as the templating agent, and tetramethoxy silane (TMOS) as the precursor. The materials were characterized using high resolution scanning transmission electron microscopy (HRSTEM), elemental analysis, X-ray diffraction (XRD), and magnetic measurements. The data indicate that the bimetallic Pd-Co nanoparticles are uniformly distributed on the inner pore walls of silica. The magnetic measurements of reduced Pd-Co nanoparticles (4-5 nm) in mesoporous silica reveal a typical ferromagnetic behavior up to 20 K and exhibit superparamagnetic properties above 30 K.

Scandia-doped zirconia is a very promising material for solid oxide fuel cells due to its high oxygen conductivity in the 700-850°C temperature range. 10 mol% Sc2O3 - 1 mol% CeO2 - ZrO2 ceramics were sintered at temperatures 1100-1600°C using different heating rates and dwell times. Ceramics sintered at temperatures higher 1300°C were found to exist in cubic phase at room temperature and exhibit slow phase transformation from cubic (c) to rhombohedral (beta) phase between 330 and 400°C. Analysis of c-β phase transition efficiency in the ceramics shows a strong correlation between the transition rate and sintering temperature. Kinetics of phase transitions were studied by high temperature X-ray diffractometry (HTXRD) and differential scanning calorimetry methods. The reversible c-β phase transition was found to have very wide hysteresis (45-70°C), which depends on sintering temperature and density. Coefficients of thermal expansion of c- and β-phases were calculated from temperature dependence of lattice parameters obtained by HTXRD in the temperature range of 25-800°C. Microstructural changes on the surface of the cubic phase due to c-β phase transition studied by SEM and AFM.

Phase transitions and CTE of 10mol%Sc2 O3 -1mol%CeO2 -ZrO2 ceramics sintered from two commercial powders produced by Praxair Surface Technologies, USA and DKKK, Japan are studied. Morphology of powders and grain structure of ceramics were studied by SEM and AFM. Ceramics produced from Praxair powder exist in cubic phase while DKKK-based ceramics exhibit slow phase transformation from cubic to rhombohedral (β) phase at temperatures 350–400°C. c-β Phase transition temperature is 440°C obtained by high temperature x-ray diffractometry (HTXRD) and differential scanning calorimetry. Coefficients of thermal expansion of cubic and β-phases were calculated from temperature dependence of lattice parameters obtained by HTXRD in the temperature range of 25–800°C. These results can be further used for the optimal design of SOFC layered structures as well as for determination of their reliability and durability under operational conditions.Copyright © 2007 by ASME

Multilayer and superlattice coatings of TiN/CrN coating are deposited on Si(100) substrate at different modulation wavelength by reactive unbalanced magnetron sputtering and characterized using X-ray diffraction, nanoindentation, AFM. Nano-roughness of films is in good correlation with hardness and modulus and this effect has been used for optimization of deposition parameters. Preliminary results have shown slightly better mechanical properties for multilayered TiN/CrN coatings compared to single layer TiN and CrN coatings. The XRD results have shown a preferred orientation in direction for TiN/CrN multilayer coatings at modulation wavelengths below 80 nm. At 100 nm layer thickness, TiN revealed small amount of crystals with orientation and their content significantly increases with increase in layer thickness while CrN layers only show preferred orientation of . Multilayered coatings exhibit better mechanical properties due to presence of large number of interfaces which act as barrier to dislocations. Fracture toughness and tribological properties of these coatings are also expected to show significant improvement and the investigation in this area is under progress.

(La0.9 Sr0.1 )0.95 Cr0.85 Mg0.10 Ni0.05 O3 (LSCMN) ceramics sintered at temperatures 1100–1700°C in air were characterized using powder x-ray diffraction, field emission scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, transmission electron microscopy, differential scanning calorimetry, and inductively-coupled plasma spectroscopic analysis. Pervoskite ceramics with the highest density (porosity between 2–5%) were sintered at 1650°C for 24 hours. Secondary phases at a level of 3–5% porousity have been detected in the LSCMN initial powder received and sintered samples. LSCMN initial powder and ceramics exist in orthorhombic phase at room temperature and exhibits a first order phase transition into rhombohedral phase in the temperature range 70–95°C. Temperature of phase transition depends on grain size. Hardness and fracture toughness of LSCMN were studied by nanoindentation and microindentation methods. At low indentation depths hardness values depend significantly on the number of grains effected by the indent and crack formation. Indentation size effect was quantified in terms of Nix-Feng and power-low models. At high loads the apparent hardness is almost two times less than hardness of LSCMN monocrystalls.Copyright © 2007 by ASME

Patterned multiwall carbon nanotube arrays up to four millimeters long were synthesized using chemical vapor deposition. Electrochemical actuation of a nanotube array tower was demonstrated in a 2 M NaCl solution at frequencies up to 10 Hz with 0.15% strain using a 2 V square wave excitation. The synthesis and electrochemical modeling approach outlined in the paper provide a foundation for the design of nanotube smart materials that actuate and are load bearing.

Highly aligned multi-wall carbon nanotube arrays up to 4 mm tall were synthesized on Si wafers using a chemical vapor deposition process with water delivery. Based on the long nanotube arrays, several prototype smart materials were developed including a biosensor, electrochemical actuator, and nanotube probes. The biosensor was formed by casting epoxy into a nanotube array and polishing the ends of the nanotubes. This electrode produced a near ideal sigmoidal cyclic voltammogram. Nanotube electrodes were then used to form a label-free immunosensor based on electrochemical impedance spectroscopy. The nanotube array immunosensor has good sensitivity, but decreasing the array size and improving the biofunctionalization is expected to dramatically increase the reproducibility and sensitivity. The electrochemical actuator was formed by bonding an electrode to a 1mm square by 4 mm long as-grown nanotube array post. The nanotube array actuator operated up to 10 Hz in a 2 M NaCl solution. With a driving voltage of 2 volts, the actuator produced 0.15% strain. Finally, nanotube bundles are being welded to tungsten tips and put inside glass needles for use as probes for biosensors and electrophysiology applications. All the smart materials applications discussed are recent, and further development is expected to yield improved performance and commodity level practical devices.

This paper describes progress in development of a sensor-actuator-nanoskin material based on multi-wall carbon nanotube arrays. This material can have individual sensing, actuation, or reinforcement properties, or the material may have combined multi-functional properties. The sensing and actuation properties are based on the theoretical telescoping property of multi-wall carbon nanotubes. The sensing property has been demonstrated in the literature. The actuation property is modeled in this paper but not demonstrated. Work is described that later may verify the actuation. Nanoskin samples are also fabricated and tested for mechanical, hydrophobicity, and capillarity properties. Overall, synthesis of dense arrays of long multi-wall carbon nanotubes is opening the door for the development of novel sensors, actuators, and multifunctional smart materials.

Publisher Summary Ceramics have found their use in numerous crosscutting industrial applications because of excellent hardness, wear, corrosion resistance, and ability to withstand high temperatures. The best approach to increasing the fracture toughness that enables the structural application of ceramics is through the development of ceramic composites. However, since these materials have a very high density of weak interfaces, they are not very strong. Several publications on ceramics show that the use of layered materials is the most promising method for controlling cracks by deflection, bifurcation, microcracking or internal stresses. Layered structures clearly offer a key to greater reliability at a moderate cost and new applications may result as more complex structures are tailored to specific applications. The way to achieve the highest possible mechanical properties is to control the level of residual stresses in individual layers. One can increase the strength and apparent fracture toughness of ceramics by creating a layer with compressive stresses on the surface. In such a way, surface cracks will be arrested and, therefore, higher failure stresses are achieved. The sign and value of residual stresses can be established by theoretical prediction. There have also been a number of experimental studies of laminated ceramics that were conducted using the models, attempting to maximize the mechanical properties. In the case of symmetrical laminates, it can be done by choosing layer compositions such that the Coefficient of Thermal Expansion (CTE) of the odd layers is smaller than the CTE of the even ones.

Recently we developed a new method to deposit YSZ thin films based on combustion chemical vapor deposition (CCVD) technique. YSZ thin films have been processed on polished silicon and MgO substrates from combustion of an aerosol jet. Thin and uniform films have been obtained. The film growth rate was greatly enhanced by utilizing high reagent concentrations, proper substrate temperature, and application of DC bias.

LaCrO3 based perovskites thin films are a prospective material as a protective coating against oxidation and corrosion of metallic interconnect for SOFCs. However, for RF magnetron sputtered LaCrO3 films, the microstructural development of amorphous films during annealing has not been reported, despite the importance of the crystallization processes as one of the factors determining the final properties of the film. SEM and TEM were employed to study the microstructure of the La-Cr-O thin films deposited by RF magnetron sputtering on the stainless steel substrate. The “as-deposited” La-Cr-O thin film was found to be X-ray amorphous with no visible spots in electron diffraction pattern, but after annealing in air, the film transforms first to LaCrO4 monazite type monoclinic phase at 495–530°C and further to the orthorhombic LaCrO3 perovskite at 800°C. In certain cases the second transition to the LaCrO3 perovskite occurred at 700°C. Formation of the porous self-organized LaCrO3 structure was studied by SEM and in-situ high temperature TEM. The effect of environment (air, vacuum, hydrogen) on the microstructural evolution of La-Cr-O thin films during annealing is reported.

Alumina is a widely used ceramic material due to its high hardness, wear resistance and dielectric properties. The study of phase transformation and its correlation to the mechanical properties of alumina is essential. In this study, interfacial adhesion properties of alumina thin films are studied using cross-sectional nanoindentation (CSN) technique. Alumina thin films are deposited at 200 and 700 °C, on Si (100) substrates with a weak Silica interface, using pulsed laser deposition (PLD) process. Effect of annealing on the surface morphology of the thin films is studied using atomic force microscopy. Xray diffraction studies revealed that alumina thin films are amorphous in nature at 200 °C and polycrystalline with predominant gamma alumina phase at 700 °C.Copyright © 2006 by ASME

The fiber-matrix interface between ceramic fibers and ceramic matrix plays a major role in the fatigue properties and toughness of continuous fiber reinforced ceramic matrix composites (CMCs). Boron Nitride (BN) is a widely used fiber coating material that provides a weak bond between the fiber and matrix. A weak fiber-matrix interface increases the strength and toughness of the overall CMC. Single fiber push-out tests were performed to study interfacial shear strength as a main parameter defining fatigue properties and toughness of SiC/SiC composites. The fiber-matrix interfacial shear strength was studied in melt infiltrated Hi-Nicalon/BN(CVI)/SiC composites exposed to various temperature and loading conditions, similar to those that are used in actual applications. Hi-Nicalon fibers with diameters of 13-14.5 μm were pushed out from samples with thicknesses ranging from 125-280 μm using a spherical tip with a 1 μm radius and 90° conical shape. Interfacial shear strength was calculated from sliding load, fiber diameter and sample thickness. Due to significant scattering, 30 individual push tests in every sample were used to obtain the average interfacial shear strength. The virgin sample has a shear strength of 20 MPa which is higher than tensile tested samples (12 MPa). Annealing of a virgin specimen for 100 hours at 1000°C slightly increased shear strength up to 21.5 MPa while annealing at 1100°C and 1200°C led to significant increase of shear strength up to 29 and 39 MPa correspondingly. This effect is associated with BN degradation at temperatures >1000°C.Copyright © 2006 by ASME