Sudhanshu S. Singh

In situ experimental techniques to study the mechanical behavior of materials using X-ray synchrotron tomography

In situ X-ray synchrotron tomography is an excellent technique for understanding deformation behavior of materials in 4D (the fourth dimension here is time). However, performing in situ experiments in synchrotron is challenging, particularly in regard to the design of the mechanical testing stage. Here, we report on several in situ testing methods developed by our group in collaboration with Advanced Photon source at Argonne National Laboratory used to study the mechanical behavior of materials. The issues associated with alignment during mechanical testing along with the improvements made to the in situ mechanical testing devices, over time, are described. In situ experiments involving corrosion-fatigue and stress corrosion cracking in various environments are presented and discussed. These include fatigue loading of metal matrix composites (MMCs), corrosion-fatigue, and stress corrosion cracking of Al 7075 alloys.

In situ investigation of high humidity stress corrosion cracking of 7075 aluminum alloy by three-dimensional (3D) X-ray synchrotron tomography

In situ X-ray synchrotron tomography was used to investigate the stress corrosion cracking behavior of under-aged Al–Zn–Mg–Cu alloy in moisture. The discontinuous surface cracks (crack jumps) mentioned in the literature are actually a single continuous and tortuous crack when observed in three dimension (3D). Contrary to 2D measurements made at the surface which suggest non-uniform crack growth rates, 3D measurements of the crack length led to a much more accurate measurement of crack growth rates.

Modeling Anisotropic Multiphase Heterogeneous Materials via Directional Correlation Functions: Simulations and Experimental Verification

The effective properties of heterogeneous materials critically depend on their complex microstructure. In this article, by successfully reconstructing the three-dimensional microstructure of a multiphase alloy with orientated anisotropic inclusions from two-dimensional slices, we show that such materials can be modeled by the two-point correlation functions of the inclusion phases along the three orthogonal characteristic directions of the inclusions. The reconstructions are compared to the actual microstructure obtained from high-resolution X-ray tomography experiments by quantifying certain directional cluster statistics associated with the microstructures.

In situ tensile testing of tin (Sn) whiskers in a focused ion beam (FIB)/scanning electron microscope (SEM)

Abstract Tin and tin-alloyed electroplated films are known to be susceptible to whisker growth under a range of conditions, many of which result in the generation of compressive stresses in the film. Compressive stress is considered to be one of the primary causes for whisker nucleation and growth. While extensive investigations have been performed on whisker growth, there have been few studies on the mechanical properties of tin whiskers themselves. We report on the tensile behavior of tin whiskers that were obtained by indentation and furnace aging of electroplated tin films on copper disks. Tensile tests of the whiskers were conducted in situ in a dual beam focused ion beam (FIB)-scanning electron microscope (SEM) system using a micro electro-mechanical systems (MEMS) based tensile testing stage. The strength of the whiskers was found to decrease with an increase in gage length and aged whiskers were found to be weaker than their indented counterparts. The observed gage length effect can be attributed to the probability of finding more defects as the whisker length increases. The effect of processing on the observed strength variation was investigated by analyzing the oxygen content in the whiskers via energy dispersive spectroscopy and the microstructure through transmission electron microscopy (TEM). The deformation mechanisms of whiskers were also inferred using post-mortem TEM. It was observed that the whiskers grown by indentation were dislocation free both before and after deformation. In contrast, whiskers grown by aging showed notable dislocation content (arranged in low energy configurations) even before deformation.

Automated Correlative Tomography of an Aluminum 7075 Alloy Spanning Length Scales and Modalities

The recent confluence of advanced computing power with new 3D characterization approaches has yielded great enthusiasm in the materials science community to pursue new scientific pathways, supported by the ‘materials by design’ approach. It has become clear that one technique by itself cannot span all of the necessary length-scales in materials characterization nor provide a complete set of modalities. There is need in several areas such as energy materials, electronics, and metals, where the combination of two or more techniques is required to obtain a fundamental understanding of the microstructure [1].