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The laser ablation of microparticle aerosol (LAMA) process was used to direct-write nanostructured, patterned films of silver with thicknesses in the range 20–200 μm at room temperature. A critical difference between the LAMA process and conventional processes for depositing patterned, thick films is that the LAMA process does not require surfactants that can interfere with post-deposition sintering. Thus, LAMA-produced films allow the intrinsic sintering of nanoparticulate films to be studied directly. Post-deposition sintering was conducted over a range of temperatures (100–175 °C) and compression loads (25–600 N) and the strength and electrical resistivity of the sintered samples were measured. The samples were characterized using optical microscopy, profilometry, SEM, and XRD and the density of the deposits were determined from the grain size, resistivity and known relationships between these parameters and density. LAMA-produced films were found to sinter to produce high strength, high conductivity films at temperatures 50–100 °C lower than conventional processes that use organic additives. Mechanisms for the low-temperature sintering of the nanostructured films are discussed and compared with established theory for pressure-assisted sintering.
Al2O3/Y-TZP particulate composites and particulate laminates with varying compositions and ratios of layer thickness were fabricated by tapecasting, lamination, and sintering. Tensile strain-rate-change (SRC) tests were conducted on the particulate composites and particulate laminates at a temperature of 1350 °C and compared to previous results where tests were conducted in compression. Stress exponents for particulate composites and laminates were measured to be approximately two in both tension and compression. The observed similarity of SRC data suggests that a common deformation mechanism exists in tension and compression. Elongation-to-failure tests were also conducted at 1350 °C at a constant true-strain rate of 10−4 s−1. It was found that the elongation-to-failures of particulate laminates are lower than for particulate composites with similar overall compositions because of interlayer constraint in the particulate laminates which induces cavitation in the harder layer. The increase in flow stress from dynamic grain growth was used to determine that flow stress depends on grain size to approximately the 1.5 power. Elongations for fine grained particulate composites produced by pressureless sintering were similar to those described in the literature for hot-pressed particulate composites of similar composition, but with slightly coarser grain sizes.
Al2O3/Y-TZP particulate composites with compositions of between 20 and 80 vol.% Y-TZP were produced by tapecasting, lamination, and sintering. The processing methods employed resulted in fine grain sizes with only small variations between the composites produced. The resulting particulate composites were tested in compression at a temperature of 1350 °C over strain rates from 10−5 to 3.16×10−4 s−1. Microstructural changes during testing were minor. Stress exponents were measured to the range from approximately two to three, which are consistent with published data on similar materials from tensile experiments. Models of composite creep behavior are compared to the experimental data over the full range of compositions studied. A constrained isostrain model is found to provide better predictive capabilities than either an unconstrained model, an isostress model, or a rheological model. Furthermore, the constrained isostrain model provides the most reasonable predictions for creep rates of 100% Al2O3 and 100% Y-TZP materials.
