The effect of texture and microstructure on equibiaxial fracture in gallium embrittled aluminum sheet
Abstract
The effect of crystallographic texture and microstructure on intergranular fracture in embrittled aluminum sheets was examined using liquid metal embrittlement in biaxial fracture experiments. Liquid metal embrittlement was induced by contact and penetration with liquid gallium in rolled aluminum sheets possessing $\{112\} \langle 111\rangle$ primary recrystallization texture. After selective embrittlement, specimens were loaded in equibiaxial tension to brittle intergranular fracture. Primary radial cracks formed either approximately parallel or perpendicular to the sheet rolling direction. Secondary cracks formed nearly orthogonal to the primary crack direction. Possible mechanisms for both cases of crack directionality are discussed. In the gallium embrittled sheets, fracture propagated by the initiation and coalescence of multiple collinear cracks. Approximately two-dimensional microstructures were produced in aluminum sheets. They were similarly embrittled and fractured to study local microstructural effects on thru-thickness crack initiation and propagation. Grain boundary orientations were measured by the Kikuchi electron backscattering technique and the boundaries were analyzed by the Coincident Site Lattice (CSL) Model. Crack tip blunting events were observed in the 2D specimens when coalescing intergranular cracks intersected facets with $\Sigma$1 to $\Sigma$9 coincidence. In the textured specimens, similar blunting events were explained as the intersection of growing cracks with regions containing dense concentrations of low $\Sigma$ CSL grain boundaries. These boundaries were found highly resistant to gallium penetration and embrittlement relative to other grain boundaries.
Degree
Ph.D.
Advisors
Bowman, Purdue University.
Subject Area
Materials science|Metallurgy
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