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The mechanism of fatigue-induced interface damage in Cu/V nanoscale metallic multilayers was systematically investigated using the state-of-the-art in situ transmission electron microscopy. Upon cyclic compression, Cu/V nanoscale metallic multilayers show an interface-controlled fatigue deformation, and the interface morphology of Cu/V nanopillars changes significantly after 200 cyclic loadings. Cyclic deformation induced nanoscale intrusions/extrusions on the bimetal interface, while no sign of persistent slip bands or crack was observed. Formation of the nano-intrusions/extrusions can be attributed to the reciprocating defect motion and severe defect-interface interactions during the fatigue testing. This study provides a unique mechanistic understanding on the fatigue damage in metallic multilayers at nanoscale and sheds light on tailoring the damage tolerance of heterostructures via interface engineering.

We have investigated limited angle transmission tomography to estimate speed of sound (SOS) distributions for breast cancer detection. That requires both accurate delineations of major tissues, in this case by segmentation of prior B-mode images, and calibration of the relative positions of the opposed transducers. Experimental sensitivity evaluation of the reconstructions with respect to segmentation and calibration errors is difficult with our current system. Therefore, parametric studies of SOS errors in our bent-ray reconstructions were simulated. They included mis-segmentation of an object of interest or a nearby object, and miscalibration of relative transducer positions in 3D. Close correspondence of reconstruction accuracy was verified in the simplest case, a cylindrical object in homogeneous background with induced segmentation and calibration inaccuracies. Simulated mis-segmentation in object size and lateral location produced maximum SOS errors of 6.3% within 10 mm diameter change and 9.1% within 5 mm shift, respectively. Modest errors in assumed transducer separation produced the maximum SOS error from miscalibrations (57.3% within 5 mm shift), still, correction of this type of error can easily be achieved in the clinic. This study should aid in designing adequate transducer mounts and calibration procedures, and in specification of B-mode image quality and segmentation algorithms for limited angle transmission tomography relying on ray tracing algorithms.

Leukotriene B4 1 was prepared from two chiral synthons 8 and 14. The chiral secondary alcohols of 8 and 14 were constructed by BINOL/Ti(OiPr)4 catalyzed enantioselective alkynylzinc addition to aldehydes.

Selective laser melting technique was employed to fabricate a step-wise compositionally graded Fe–Al alloy coupon using the in-situ alloying of blended powders. Microstructural characterization of the fabricated coupons shows a columnar to equiaxed grain structure transition with increasing Al content along the building direction, along which the laser scan speed is increased. In the low Al content regions, the absence of constitutional undercooling (CUC) allows columnar grain growth against the macroscopic thermal gradients, whereas dominance of CUC in high Al regions leads to fully equiaxed and refined microstructures. Nanoindentation studies show a linear increase in hardness and reduction in elastic modulus for Al content up to ~20 at.%; no significant anisotropy in these properties could be seen.

Long periodic stacking ordered phases (LPSOs), consisting of various configurations of stacking faults, play an important role in developing ultrastrong Mg alloys with moderate ductility. However, their formation mechanisms are far from clear as no apparent defects are introduced during their formation as it is commonly believed that stacking faults are induced by defects. Here, we present the atomic and electronic basis for lattice-distortion-mediated formation of stacking faults, i.e., localized face-centred-cubic (FCC) structures, within a Mg-Zn-Y alloy with a hexagonal close-packed (HCP) structure. The atomic motion trajectories from ab-initio molecular dynamic simulations show that the Mg atoms occupying the nearest neighbour positions of Zn and Y solute atoms undergo a local HCP-to-FCC transition. It is revealed that a local lattice distortion caused by the solute atoms enables the Mg atoms to move and rearrange into a local FCC configuration, which is validated by high resolution scanning transmission microscopy and in-situ synchrotron X-ray diffraction. Our simulations provide profound insight into the formation mechanism of stacking faults in HCP Mg and their physical nature of phase transformations; this is not only critically important because conventional defects, such as dislocations and vacancies, are important to deformation are rare for Mg and its alloys, but also because they serve as a potential new approach to the design of advanced Mg alloys when defects are actually phase transformations.