Ni/Al reactive multilayer foils were fabricated by cold rolling method and self-propagating reactions in these foils were investigated. A two-stage phase formation process was observed in the ignition experiment. The first step is the lateral growth of Al3Ni phase from isolated nucleation sites and the following coalescence into a continuous layer; the second step is the growth of such Al3Ni layers in the perpendicular direction of the interface until all Al is consumed. As there is still Ni available, Al3Ni will continuously react with Ni until no Ni is left, and the final reaction product turns out to be ordered B2 AlNi compound. X-ray diffraction (XRD) experiments showed that the reaction product of the cold rolled foil was the same as the physical vapor deposition (PVD) foil. The reaction process was studied by differential scanning calorimetry (DSC). Three peaks can be identified from the DSC curve. Cold rolled foils were heated to different peak temperatures obtained from DSC curve with the same heating rate as DSC. XRD results for such foils showed that the first two peaks were the exothermic formation of Al3Ni, while the last one was for the formation of AlNi. The enthalpy of the reaction for the cold rolled foil was calculated to be -57.5 KJ/mol, which was in good agreement with the formation enthalpy of AlNi (-59 KJ/mol). The reaction velocities of the first formation stage were measured to be 7mm/s for cold rolled foils, which were much smaller than the reaction velocities of PVD foils (which range between 1-30 m/s).

The problems of the creation of composite polymer-based materials with the use of nanosized molybdenum and tungsten fillers with the particle size of less than 10 nm are considered. The copolymer of formaldehyde and dioxolane (CFD) and the polyphenylene sulphide (PPS) are chosen as polymeric matrixes. A comparative analysis of the tribological properties of composite materials with fine nanosized fillers (5-10 nm) and nanosized analogues (100-200) is made. It is determined that the use of nanosized isotropic structure Mo fillers leads to improved wear-resistance up to three times for CFD-based composites and up to four times for PPS-based. The highest hardness values were observed while using isotropic nanosized tungsten fillers. The nanosized crystalline fillers also give positive results, but the bigger sized fillers decrease the polymer hardness characteristics comparatively nanosize isotropic analogues.

Lenses and other transparent optical materials suffer rapid damage when subjected to blowing abrasive particulates. The time-scale of these impact event falls between typical scratch tests (less than 1m/s) and ballistic tests (100s of m/s) and has not been studied in depth to date. Polymeric lens materials like polycarbonate are usually treated with a scratch-resistant coating, which is commonly silica-based. The coating provides some protection, yet is not sufficient at resisting abrasion from blown sand in most commercial products. We demonstrate that silicone elastomeric coatings are superior to polycarbonate and silica glass at resisting damage by blown sand particles. Sand abrasion tests were conducted using a custom-built test apparatus that exposes the sample to 400 micron diameter quartz silica moving at 16.5 m/s (approx. 38 mph). Scanning electron microscopy revealed the presence of small cracks and pits in polycarbonate, coated polycarbonate, and silica glass after sand exposure. No such damage was observed in the silicone-coated samples after an identical exposure.

We speculate that the elastic tensile strain at the surface is an important predictor of the material response at the time-scale of the impact. A simple mathematical model was developed using a momentum balance pre- and post-impact, and was used to approximate the maximum deformation and impact time-scale. A semispherical interaction volume was used in the model with a radius of 1.5x the particle diameter, determined through profilometry experiments. The material’s resistance to deformation was measured experimentally through a static mechanical test using a spherical indenter to represent the particle. Tensile tests were performed on both materials to identify the maximum elastic strain.Additionally, dynamic mechanical tests were performed to confirm that the mechanical behavior at long time-scales was valid at shorter time-scales of the impacts. DMA curves were shifted using the WLF equation. Profilometry and scanning electron microscopy (SEM) imaging were used to confirm the presence or absence of blown-sand induced damage.

Alumina/SiC “nanocomposites" consist of a dispersion of submicron SiC particles in an alumina matrix. The resistance to severe wear of the nanocomposites and the surface finish produced by a given grinding treatment are strikingly superior to those of pure alumina with the same grain size. We have explored the reasons for this by correlating a wide range of variations in the basic microstructure with the wear behaviour observed, including both the wear rate, and quantitative surface fractography of the worn surfaces. These improved properties of the nanocomposites are shown to be a consequence of a reduction in surface grain pullout by brittle fracture. In “dilute” nanocomposites (<10% SiC), this is due largely to a reduction in size of the individual pullouts. With 10% SiC nanoparticles, however, there is also evidence that the SiC directly suppresses the nucleation of cracking by plastic deformation of the surface. The origin of these effects will be discussed.

Evaluation method for delamination strength of micro-sized materials has been developed using by FEM and measurement of load-displacement curve of micro-sized specimen. This evaluation method is applied to micro-sized cylindrical SU-8 specimens on Si substrate. The maximum shear stress between SU-8 and Si was analyzed with FEM. Fracture load required to delaminate the two materials was examined using a mechanical testing machine for micro-sized materials, which have been developed in our group. The delamination strength was determined from the maximum shear stress and the fracture load.

e have undertaken the exploration of the AlxSi1-x systems to discover new alloys with enhanced properties. We describe the mechanical properties of thin film AlxSi1-x alloys determined through indentation experiments. Combinatorial methods were used to systematically control thin film microstructure through variations in composition and growth temperature. Discrete libraries of compositionally graded films have been sputter deposited onto silicon substrates to produce two structural phase regions: amorphous Al-Si and amorphous Si plus crystalline Al. The mechanical properties of the thin films were determined by analyzing the load-displacement traces based on the Oliver-Pharr method. X-ray diffraction was used to investigate the microstructures and determine the crystallite sizes.

The national high magnetic field laboratory builds and uses various high field magnets for fundamental research. In building high field magnets, a variety of high strength composites are required because of the Lorentz stresses generated by high field exceeding the strength of most of the materials, particular conductors. For example, a field of 60 T can generate a magnetic pressure that corresponds to a stress in the conductor of 1.5 GPa, which is at the limit of known conducting materials with conductivity higher than 70% International Annealed Copper Standard and sizes suitable for building high field magnets. The design of high field magnets is limited by these forces and, consequently, by the available materials. At the same time, the materials need to have excellent physical properties. For instance, the conductors need to have high electrical conductivity and high specific heat and the superconductors should have high critical current in field and low alternative current losses. This paper outlines our requirements and research on metal matrix composite materials for building high field magnets. The discussions include both the macrocomposite and microcomposite. The scales of the structures in the composites are from millimeters to nanometers.

Batch-foaming of miscible, immiscible and compatibilized polymer blend systems over a wide compositional range was carried out using carbon dioxide as a physical blowing agent. The resulting foam morphology was characterized by a detailed evaluation of foam density as well as of the cellular parameters. With regard to multiphase blends, transmission electron microscopic observations further provided a detailed insight into the cell wall morphology. The role of the melt-elongational properties and of the glass transition behavior of the various blend systems on the foaming characteristics was systematically elucidated. While the miscible blends showed a simple additivity behavior with regard to their foaming characteristics and properties, a significant influence of the initial blend morphology is demonstrated for the multiphase blends.

The primary objective of the study is to investigate the impact of chemical structure at the interface on the interface strength of fiber/matrix composite. A solvent based method was used to deposit trichlorosilane on E-glass fiber surfaces followed by in situ modification of the deposited layer to prepare pure and mixed amine undecyl self assembled monolayer (SAM). The extent of fiber/matrix adhesion was determined by performing single fiber fragmentation test (SFFT). The SFFT data indicate that ≈ 85 % of fiber breaks obtained for epoxy composite occurs at a much lower mass fraction of amine coverage for SAM while a similar number of fiber breaks occur at a much higher mass fraction of amine coverage for aqueous solution deposited coupling agent system.

Nickel-base superalloys are an important class of metallic ‘nanocomposite’ structural materials known for their good strength retention abilities at high homologous temperatures for long service times. Literature on electrical resistivity studies of age-hardening superalloys is limited. The current work is focused on developing microstructure-electrical resistivity correlations in controlled Waspaloy microstructures. The microstructures are ‘controlled’ as the size distribution of g¢ precipitates is varied systematically. The microstructures are produced upon aging the initial homogenized alloy at nominal temperatures of 700°C, 800°C and 875°C for times up to 100 hrs. Resistivity measurements did not reveal a g¢ nucleation regime for the sampled aging intervals. The primary microstructural evolution mechanism contributing to the observed changes in resistivity was g¢ coarsening. Interestingly, the microstructures resulting from progressive aging at 700°C showed a slow transformation of etch-pits from perfect polygonal shapes to more irregular shapes.

The mechanical behavior of W/Cu multilayers with a period of 24 nm and a 1/3 W/Cu thickness ratio prepared by magnetron sputtering was analyzed using a method combining X-ray diffraction and tensile testing. Tests were performed both with a conventional and a synchrotron light source to analyze the elastic response of the system. Comparison between the strain-load curves obtained in both experimental conditions and estimated curves clearly shows that high quality synchrotron measurements are a preliminary condition for size-effect studies. Moreover, cyclic tests were used to determine the elastic domain of each material and compare their mechanical responses. Plastic strain was observed in copper while tungsten layers were still elastically strained until cracks appeared.

The primary objective of this study is to improve the thermal stability of clay and clay filled composite. An epoxy-clay composite has been prepared by dispersing 1-hexadecyl-3-(6-hydroxyhexyl)-2-methylimidazolium modified clay in an epoxy resin and cured with metaphenylene diamine (m-PDA) at 110.0 °C for 7 h and post cured at 140°C for 4 h. The thermal stability of the modified clay and clay filled epoxy composite was characterized via thermogravimetric analysis (TGA). The onset decomposition temperature of the imidazolium functionalized clay was 360°C. Transmission Electron Microscopy (TEM) of the composite showed mixed morphology with predominant fraction of intercalated clay platelets in the epoxy matrix. The onset decomposition temperature of the modified clay filled epoxy composite was found to be higher than that of pristine epoxy.

In metal matrix composites the nature of the reinforcement can influence the development of residual stresses not only as a result of the mismatch in the thermal expansion coefficient between the fiber and the matrix but also caused by the interface of the materials during the processing cycles. The residual stress can be minimized through controlling the processing path and the thermal environment. We studied the residual stress formation and evolution in gamma titanium aluminide (Ti-47AL-2Ta) matrix. The matrix was reinforced with three different types of fibers: Alumina, Sapphikon, and Tiboride through hot isostatic pressing. The composite was heat treated for various combinations of time: 100, 200 and 500 hours; and temperature: 590C, 815C and 982 C respectively. Residual stresses were measured in the gamma phase of the matrix using X-Ray diffraction

Periodic cellular metal (PCM) sandwich cores can be considered hybrids of the solid and gas type. These can be designed at both the architectural and microstructural levels. PCM cores with 95% open porosity have been constructed from perforated 6061 aluminium alloy (AA6061) sheets using a perforation-stretching method. This method places planar, periodically-perforated sheet metal in an alternating-pin jig. The pins apply force out-of-plane, plastically deforming the sheet metal into a truss-like array of struts (i.e. metal supports) and nodal peaks (i.e. strut intersections). The result is a non-uniform work-hardened profile exhibiting large deformation at the nodes and small deformation at the struts.

For identical PCM architectures, this study looks at the interaction of microstructural strengthening mechanisms and the resultant performance of PCM truss cores. Beginning with fabrication, work-hardening induced a subcell network of dislocation tangles within the AA6061 matrix. Following this stage, a variety of microstructures were created through recovery, recrystallization and precipitation mechanisms. Microhardness measurements and electron back-scattered diffraction (EBSD) characterization were employed through truss core cross-sections in order to study the microstructural gradients of subcell size as well as interaction between subcells and precipitates in the truss cores. To determine the effect of microstructure on mechanical performance, PCM cores were compressed to study deformation and collapse mechanisms.

The present data can be used to illustrate engineering at the architectural and microstructural levels to achieve a range of mechanical properties in a hybrid sandwich core.