Shear band stability is measured for a Zr-based bulk metallic glass in compressive bending and compared with previous results in tension. Compressive failure is induced via bending of trapezoidal cross-section beams. This characterization is done at multiple fictive temperatures and compared with results in tension, revealing a compression-tension asymmetry in shear banding stability. Stability, indicated here as the ability to resist catastrophic shear bands in favor of stable, arrested shear bands, is higher in compression than tension at all measured fictive temperatures. This asymmetry suggests that shear band propagation is different in tension and compression, and possible mechanisms underlying this difference are suggested. Additionally, this stability measurement is shown to be consistent in uniaxial compression testing, demonstrating its potential for predicting a brittle vs. ductile response in different loading modes of bulk metallic glasses.

Calcium phosphates are the predominant type of mineral in humans. They are essential for the formation of bones and teeth but can also deposit in diseased tissues. Whitlockite, a calcium phosphate mineral, is almost exclusively found in diseased calcified lesions. Despite its significance, the crystal growth mechanisms of whitlockite under physiological conditions are poorly understood. To investigate this, we conducted a constant composition experiment and applied a growth kinetics model to study the growth of whitlockite and hydroxyapatite nanoparticles in simulated body fluid. Contrary to our expectations, whitlockite did not dissolve in the undersaturated simulated body fluid. Instead, whitlockite nanoparticles served as a substrate for the formation of poorly-crystalline apatite, resulting in increased particle size. Our findings may help explain the colocalisation of whitlockite particles and large poorly-crystalline apatite lesions in human diseases.