TECHNICAL: This SGER project will develop a new experimental technique to use in-situ x-ray and neutron diffractions to quantitatively characterize nanotwin microstructures and their real-time evolutions under applied stress, electric and/or magnetic fields. This is a high-risk and high-payoff research. The high risk lies in the untested and novel idea of extracting quantitative information of nanotwin microstructures (i.e., dominant thicknesses and variant volume fractions, and their statistical variations) from the diffraction patterns. Such a nanotwin microstructure is a highly heterogeneous system producing extraordinary diffraction patterns that cannot be explained by the conventional diffraction theory of coarse domains. The idea is motivated by a newly discovered, previously unexplored nanotwin diffraction phenomenon as recently revealed by the PI's preliminary nanotwin diffraction theory, which shows that the unusual position, shape, width and intensity of the superlattice reflection peaks contain the quantitative information about nanotwin microstructures and could be analyzed, thus creating a highly promising opportunity for the exploratory research to develop new nanotwin diffraction analysis technique. This SGER project will use the nanotwins of various periods (conventionally known as multiple long-period layered martensitic phases) in ferromagnetic shape memory alloy Ni-Mn-Ga as model system and perform small-scale critical experimental and theoretical/computational tasks, namely, high-resolution transmission electron microscopy (HRTEM), x-ray and neutron diffraction, nanotwin diffraction theory and computation, to benchmark the new experimental technique. NON-TECHNICAL: If successful, the payoff is high: it will develop a transformative experimental technique for quantitative nanotwin microstructure characterization by using simple in-situ diffraction, open a new direction for the "established" diffraction research, and catalyze rapid advances in experimental investigation of nanodomained materials. In particular, the new technique will use the much easier in-situ diffraction to at least partially replace HRTEM, which is currently the only tool capable of nanodomain characterization, but is painstaking, costly and time-consuming impractical for analyzing many samples. The new experimental technique will provide a new, powerful and convenient experimental tool for nanodomained materials characterization, which will, in turn, expedite our understanding of nanodomain phenomena in many important functional materials. The project will contribute to human resource development by providing opportunity for participants to work on state-of-the-art exploratory research.
