In polycrystalline metallic materials, quantitative and statistical assessment of the plasticity in relation to the microstructure is necessary to understand the deformation processes during mechanical loading. Plastic deformation often localizes into physical slip bands at the sub-grain scale. Detrimental microstructural configurations that result in the formation and evolution of slip bands during loading require advanced strain mapping techniques for the identification of these atomically sharp discontinuities. A new discontinuity-tolerant DIC method, Heaviside-DIC, has been developed to account for discontinuities in the displacement field. Displacement fields have been measured at the scale of the physical slip bands over large areas in nickel-based superalloys by high resolution scanning electron microscopy digital image correlation (SEM DIC). However, conventional DIC methods cannot quantitatively measure plastic localization in the presence of discontinuous kinematic fields such as those produced by slip bands. The Heaviside-DIC technique can autonomously detect discontinuities, providing information about their location, inclination, and identify slip systems (in combination with orientation mapping). Using Heaviside-DIC, discontinuities are physically evaluated as sharp shear-localization events, allowing for the quantitative measure of strain amplitude nearby the discontinuities. Measurements using the new Heaviside-DIC technique are compared to conventional DIC methods for identical materials and imaging conditions.

The unique capabilities of ultrashort pulse femtosecond lasers have been integrated with a focused ion beam (FIB) platform to create a new system for rapid 3D materials analysis. The femtosecond laser allows for in situ layer-by-layer material ablation with high material removal rates. The high pulse frequency (1 kHz) of ultrashort (150 fs) laser pulses can induce material ablation with virtually no thermal damage to the surrounding area, permitting high resolution imaging, as well as crystallographic and elemental analysis, without intermediate surface preparation or removal of the sample from the chamber. The TriBeam system combines the high resolution and broad detector capabilities of the DualBeam(TM) microscope with the high material removal rates of the femtosecond laser, allowing 3D datasets to be acquired at rates 4-6 orders of magnitude faster than 3D FIB datasets. Design features that permit coupling of laser and electron optics systems and positioning of a stage in the multiple analysis positions are discussed. Initial in situ multilayer data are presented.

In this paper, we report the use of the feedback signal of an ultrasonic fatigue system to dynamically deduce fatigue damage accumulation via changes in the nonlinear ultrasonic parameter. The applicability of this parameter in comparison to the resonant frequency for assessment of fatigue damage accumulation in a wrought aluminum alloy has been demonstrated, without the need for coupling fluids or independent generation of incident ultrasonic waves. The ultrasonic nonlinearity increased and the resonant frequency of the system decreased with initiation and propagation of the major crack. The nonlinear ultrasonic parameter shows greater sensitivity to damage accumulation than the resonant frequency. The number of cycles for crack propagation, estimated based on the changes in the nonlinear ultrasonic parameter, is in very good agreement with calculated crack growth rates based on the fractography studies.

The effect of phase-segregated Heusler TiNi2Sn on high temperature thermoelectric properties of bulk half-Heusler TiNiSn has been studied. In samples expressed by the composition TiNi1+xSn, a significant decrease in thermal conductivity (between 10% and 30%) is observed for two-phase TiNi1.15Sn, despite the second-phase particles existing at the micrometer scale; a 50% increase in the electrical conductivity is also measured. These result in a maximum figure of merit, ZT, of 0.44 at 800 K, which is 25% greater than is observed for the x = 0 sample. Density functional calculations of TiNiSn and TiNi2Sn suggest that the latter should deplete carriers at 0 K.

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