Quantitative assessment of microstructure and its effects on compression behavior of aluminum foams via high-resolution synchrotron X-ray tomography

Abstract

Synchrotron X-ray microtomography has been used for the three-dimensional characterization of microstructure in the cell walls of aluminum foams. A combination of high-resolution phase contrast imaging technique and several application techniques has enabled the quantitative image analyses of microstructures as well as the assessment of their effects on deformation behaviors. The application techniques include local area tomography, microstructural gauging and in-situ observation using a specially designed material test rig. It has been clarified that ductile buckling of a cell wall occurs regardless of any of the microstructural factors in the case of a pure aluminum foam, while rather brittle fracture of a cell wall is induced by the existence of coarse micropores and their distribution independently of the intermetallic particles and the grain boundary in the case of aluminum foams alloyed with Zn and Mg. It has also been confirmed that coarse TiH 2 particles, which are a residual foaming agent added to alloy melts, remain intact during the deformation. When cooling rate during foaming is high, however, lower energy absorption might be attributable to the significant amount of residual TiH 2 particle and its inhomogeneous distribution. These tendencies are also confirmed by three-dimensional strain mapping by tracking internal microstructural features.

Quantitative X-ray tomography

“…Most of the research focuses on the mechanical/deformation behaviour but other properties are also considered. Amongst the recent studies, some are dedicated to cellular materials in general, 362,[376][377][378][379][380] others focus on specific types of cellular materials including metals, 372,[381][382][383][384][385][386][387][388][389][390] ceramics, 257,[391][392][393][394] polymers, [395][396][397] carbon, 398 nuclear graphite 399 and even bread. 400 In some cases FE simulations have been run side by side with in situ deformation under CT observation to compare their predictive capability both locally on a strut-by-strut basis and globally in terms of Poisson's ratio and Young's modulus, for example for conventional versus auxetic open cell foams.…”

Roles of Pre-Existing Hydrogen Micropores on Ductile Fracture

“…1,3) It has been clarified that percentage porosity depend on the hydrogen content in aluminum alloy, 4,5) strongly suggesting that micropores in aluminum alloys are filled with molecular hydrogen. Synchrotron X-ray microtomography has been applied to the observations of high-density micropores, [6][7][8][9][10][11][12] because this technique is especially effective for micropore observation, since micropores are easily filled with abrasive powders during sample preparation processes for observation, such as cutting and polishing.…”

In Situ Observation of Void Nucleation and Growth in a Steel using X-ray Tomography

“…Tensile test was performed at constant displacement rate (CHS = 0.0005 mm/s) at room temperature using a specially designed in situ testing machine installed on a highly precise rotation stage described in the references. 21,22) X-ray transparent tube was used to transmit the load between the upper and lower grips of the machine. During the in situ experiments, the samples are deformed in tension and the test interrupted at different strain levels (10 steps up to the strain of 64%) with planned interval in order to acquire tomograms sequentially, as shown in Fig.…”