Multiscale In Situ Characterization of Deformation Dynamics in hcp Metals

This study thoroughly examines the activation and evolution of deformation mechanisms in selected hexagonal close-packed metals - Mg, Ti, and Co - utilizing a unique combination of in-situ experimental techniques at various temporal and spatial scales. Namely, the acoustic emission (AE) technique is capable of capturing local stress/strain bursts (i.e. the acoustic signatures of dislocation avalanches, twinning, phase transformation, etc.) from the entire volume of the tested material at time scales approaching nanoseconds. The digital image correlation (DIC) technique used in this work combines ultra-high-speed cameras and various optical setups (including light microscope) to provide, at the same time, sub-micrometer and sub-microsecond resolutions. The AE and DIC recording is applied in-situ, simultaneously, during the actual deformation test. On top of that, for the examination of yet more detailed microstructure evolution, in-situ and ex-situ scanning electron microscopy (SEM), including backscatter electron diffraction (EBSD) observations, is applied. The studied materials, apart from sharing the same type of crystalline lattice, feature different properties such as c/a ratio and stacking fault energies, resulting in dissimilar responses to the applied load. Along these lines, the results are discussed in terms of the underlying microstructure-deformation behavior relations in these materials with an emphasis on the fundamental avalanche-like deformation characteristics. The results bring about the apprehension of the microstructure-mechanical performance relationship in hcp metals which, in turn, can be utilized for the systematized design of new materials with desired properties.