in situ Deformation Studies with Scanning Nanobeam Electron Diffraction

In this dissertation, experimental methods and data processing techniques are developed for nanobeam electron diffraction and applied to both crystalline and amorphous materials. Nanobeam electron diffraction is a technique in which a small electron probe is used to acquire diffraction patterns as the beam is rastered across the sample. We develop methods to use nanobeam electron diffraction during in situ deformation in the scanning transmission electron microscope. First, we describe the sample preparation methods used to create samples with the correct geometry for in situ experimentation. We compare and contrast in situ deformation techniques, including holders and experimental data obtained. We then develop and benchmark variations on cross-correlation algorithms for nanobeam electron diffraction strain mapping on simulated and real data. We find that Sobel filtered cross-correlation and "hybrid" correlation minimize the amount of error when diffraction patterns have uneven illumination. We also show that binning can reduce error when signal to noise is low in the diffraction patterns. We use this result to analyze in situ nanobeam electron diffraction strain mapping on a sample of 321 stainless steel being deformed in tension. We observe the motion of the first dislocation in a planar slip band, and measure the resulting lattice expansion in situ. This result is the first direct confirmation of such phenomena, and is theorized to be the reason why planar as opposed to wavy slip occurs. We then develop methodology to measure both strain and local order in amorphous materials, and demonstrate the technique on Cu46Zr46Al8 bulk metallic glass. We observe strains in excess of 2% before the sample fractures along a shear band, small amounts of plasticity, as well as a decrease in local order at high strains in areas where the sample fractured. This is supported by molecular dynamics simulations, and experimentally supports the shear transformation zone model of metallic glass deformation. As a whole, this dissertation presents method developments in in situ nanobeam electron diffraction for both crystalline and amorphous samples, as well as practical results of interest to the materials science community