The low fracture toughness of MoSi2 at ambient temperature has prompted investigations into new processing methods in order to impart some degree of fracture toughness into this inherently brittle material. In the following investigation, low pressure plasma spraying was employed as a fabricating technique to produce spray-formed deposits of MoSi2 and ductile reinforced MoSi2 composites containing approximately 10 and 20 vol.\% of a discontinuous tantalum lamelli reinforcement. Fracture toughness K1C measurements of MoSi2 and the MoSi2-Ta composites were done using a chevron notched four-point bend fracture toughness test in both the as-sprayed condition and after hot isostatic pressing at 1200-degrees-C and 206 MPa for 1 h. Results from the ductile reinforced MoSi2-Ta composites have shown that fracture toughness increases on the order of 200\% over the as-sprayed MoSi2 (4.50 +/- 0.173 MPa m1/2 to 9.97 +/- 0.25 MPa m1/2). In addition, a marked anisotropy in fracture toughness was observed in the spray-formed deposits owing to the layered splat structure produced by the low pressure plasma spray process.

The preferred orientation of a series of laser deposited superconducting thin films of YBa2Cu3O7-delta on LaAlO3 substrate has been examined. X-ray measurements (pole figures, chi-scans, omega-scans, rocking curves) reveal an increasingly strong preferred orientation of the polycrystalline material with c-axes perpendicular to the substrate surface as deposition temperature increases. At low temperatures c-axes are predominantly parallel to the substrate surface. Characteristic parameters of the texture types were derived from those measurements. With higher temperatures twinning on (110) was observed. The different texture types are interpreted in terms of a layered film structure.

Two-dimensional Monte Carlo simulations of recrystallization have been carried out in the presence of incoherent and immobile particles for a range of different particle fractions, a range of stored energies and a range of densities of potential nuclei (embryos). For stored energies greater than a critical value (H/J > 1) the recrystallization front can readily pass the particles leading to a random density of particles on the front and a negligible influence of particles on the recrystallization kinetics. At lower stored energies the particles pin the recrystallization front leading to incomplete recrystallization. However at very low particle fractions, when the new grain has grown much larger than the matrix grains, before meeting any particles, the new grains can complete the consumption of the deformed grains giving complete recrystallization by a process that appears to be similar to abnormal grain growth. Particles are, as reported previously, very effective at pinning grain boundaries, both of the deformed and recrystallized grains, when boundaries migrate under essentially the driving force of boundary energy alone. Such boundaries show a density of particles that rises rapidly from the random value found at the start of the simulation. As a consequence, particles very strongly inhibit normal grain growth after recrystallization. Such growth can only occur if the as-recrystallized grain size is less than the limiting grain size seen in the absence of recrystallization. Under these circumstances a small increment of grain growth occurs until the grain boundaries once again acquire a higher than random density of particles.

A Monte Carlo model for dynamic recrystallization has been developed from earlier models used to simulate static recrystallization and grain growth. The model simulates dynamic recrystallization by adding recrystallization nuclei and stored energy continuously with time. The simulations reproduce many of the essential features of dynamic recrystallization. The stored energy of the system, which may be interpreted as a measure of the flow stress, goes through a maximum and then decays, monotonically under some conditions and in an oscillatory manner under others. The principle parameters that were studied were the rate of adding stored energy, DELTA-H, and the rate of adding nuclei, DELTA-N. As DELTA-H increases, for fixed DELTA-N, the oscillations decay more rapidly and the asymptotic energy rises. As DELTA-N increases, again the oscillations decay more rapidly but the asymptotic stored energy decreases. The mean grain size of the system also oscillates in a similar manner to the stored energy but out of phase by 90-degrees. The flow stress oscillations occurred for conditions which lead to both coarsening and refinement of the initial grain size. Necklacing of the prior grain structure by new grains were observed for low DELTA-H and high DELTA-N; it is, however, not an invariable feature of grain refinement. The initial grain size has a profound influence on the microstructure that evolves during the first cycle of recrystallization but at long times, a mean grain size is established which depends on the values of DELTA-H and DELTA-N alone. Comparison of the relationships between the energy storage rate, maximum and asymptotic stored energy and the grain size suggest that in physical systems the energy storage rate and the nucleation rate are coupled. Comparison of the simulation results with experimental trends suggests that the dependence of nucleation rate on storage should be positive but weak. All of these results were obtained without the addition of special parameters to the model.

The preferred orientation of a series of laser deposited superconducting thin films of YBa2Cu3O7-delta on LaAlO3 substrate has been examined. X-ray measurements (pole figures, chi-scans, omega-scans, rocking curves) reveal an increasingly strong preferred orientation of the polycrystalline material with c-axes perpendicular to the substrate surface as deposition temperature increases. At low temperatures c-axes are predominantly parallel to the substrate surface. Characteristic parameters of the texture types were derived from those measurements. With higher temperatures twinning on (110) was observed. The different texture types are interpreted in terms of a layered film structure.