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Nanoindentation experiments were conducted on a Ni+ ion-irradiated Zr-based bulk metallic glass (BMG). The irradiation was carried out using 2.5, 5, 10 and 15 MeV ions and a flux of similar to 10(16) ions/cm(2). Post mortem imaging of the indents reveals a transition in the deformation mechanism of the irradiated regions from heterogeneous shear banding to homogeneous flow. Additionally, the load-displacement curves exhibit a transition from serrated to continuous flow with increasing severity of irradiation damage. The stress-strain response obtained from micro-pillar compression experiments complements the indentation response exhibiting a decrease in the flow stress and an `apparent' strain hardening at the lowest irradiation damage investigated, which is not observed in the as-cast alloy. (C) 2011 Elsevier B.V. All rights reserved.

Structural relaxation behavior of a rapidly quenched (RQ) and a slowly cooled Pd40Cu30Ni10P20 metallic glass was investigated and compared. Differential scanning calorimetry was employed to monitor the relaxation enthalpies at the glass transition temperature, T g , and the Kolrausch–Williams–Watts (KWW) stretched exponential function was used to describe its variation with annealing time. It was found that the rate of enthalpy recovery is higher in the ribbon, implying that the bulk is more resistant to relaxation at low temperatures of annealing. This was attributed to the possibility of cooling rate affecting the locations where the glasses get trapped within the potential energy landscape. The RQ process traps a larger amount of free volume, resulting in higher fragility, and in turn relaxes at the slightest thermal excitation (annealing). The slowly cooled bulk metallic glass (BMG), on the other hand, entraps lower free volume and has more short-range ordering, hence requiring a large amount of perturbation to access lower energy basins.

The fatigue lives of a Zr-based bulk metallic glass (BMG) in the as-cast and shot-peened conditions were evaluated. Results suggest that shot peening does not cause significant enhancement of the fatigue performance of the BMG. Cracks were observed to nucleate in subsurface regions. This was attributed to the domination of the compressive residual stress field on the surface over deformation-induced plastic flow softening that otherwise leads to easy nucleation of shear bands which act like microcracks.

The mechanical behavior of single crystalline hydroxyapatite is examined through instrumented nano- and microindentation experiments on prism and basal planes. The results indicate that the c-axis orientation is stiff and hard, and significant anisotropy in properties was found. Nanoscale plasticity is observed in the form of pile-up along the nanoindentation edges and manifests as discrete displacement bursts in the load vs. depth of penetration curves. Toughness also shows significant anisotropy and is lower compared with the values reported for the polycrystalline hydroxyapatite.

The constraint factor, C , given by the hardness to the yield strength ratio and an indirect measure of the pressure sensitivity of plastic flow in amorphous alloys, of a Zr-based bulk metallic glass was measured as a function of temperature. Results show that, contrary to expectations, C increases linearly from ∼3.2 to 3.5 within the 300–525 K range. Gradual transition in the shear band-dominated deformation mechanism was suggested as a possible reason for the observed increase in C .