It has recently been reported that some Cu-based metallic glasses containing a dispersion of embe... more It has recently been reported that some Cu-based metallic glasses containing a dispersion of embedded nanocrystals can sustain more than 50% room temperature compressive plastic strains. By carefully observing shear bands containing 3-8 nm crystallite particle dispersions using in situ deformation in tension in a transmission electron microscope, we have found and report here direct evidence of systematic shear delocalisation in the form of shear band thickening and zigzagging as well as crack blunting and zigzagging. Since it is well established that both temperature and free volume rise in active shear bands, it is found that the matter in shear bands containing such small nanoparticle dispersions deforms like a semi-solid slurry. The glassy matrix behaves liquid-like and the nanoparticles constitute a growing solid fraction. Shear delocalisation and crack blunting occur through sharp viscosity increase occurring as the crystallite (solid) fraction grows in the shear band slurry leading to the shear being displaced to neighbouring regions with lower crystalline volume fraction.
Reactive hydride composites are good candidates for solid hydrogen storage due to their high grav... more Reactive hydride composites are good candidates for solid hydrogen storage due to their high gravimetric capacity, cyclability, and suitable thermodynamic properties. The LiNH2–MgH2 system is promising as changes in stoichiometry and milling conditions may result in tailoring of these properties. In this work, LiNH2–MgH2 with different ratios (Li2:Mg, Li:Mg) and ball milling conditions (100, 600 rpm) were investigated. Thermal desorption profiles shows hydrogen release starting at 125 °C for Li2:Mg 600 sample and at 225 °C for Li:Mg 600 sample, while for Li:Mg 100 sample simultaneous hydrogen and ammonia release at 175 °C is observed. In-situ synchrotron X-ray diffraction shows the related structural transformations, such as formation of Mg(NH2)2 and allotropic transformation of α into β-Li2Mg(NH)2 for Li2:Mg 600 sample at 350 °C or direct formation of β-Li2Mg(NH)2 for Li:Mg 100 sample at 370 °C. Different polymorphs of the LiMgN phase were also observed during cooling for these two samples. For the Li:Mg 600 sample, transformation occurs in a unique reaction from an unknown phase into β-Li2Mg(NH)2 at 290 °C. The unknown phase is indexed as a Fm3m cubic similar to the high temperature γ-Li2Mg(NH)2.
It has recently been reported that some Cu-based metallic glasses containing a dispersion of embe... more It has recently been reported that some Cu-based metallic glasses containing a dispersion of embedded nanocrystals can sustain more than 50% room temperature compressive plastic strains. By carefully observing shear bands containing 3-8 nm crystallite particle dispersions using in situ deformation in tension in a transmission electron microscope, we have found and report here direct evidence of systematic shear delocalisation in the form of shear band thickening and zigzagging as well as crack blunting and zigzagging. Since it is well established that both temperature and free volume rise in active shear bands, it is found that the matter in shear bands containing such small nanoparticle dispersions deforms like a semi-solid slurry. The glassy matrix behaves liquid-like and the nanoparticles constitute a growing solid fraction. Shear delocalisation and crack blunting occur through sharp viscosity increase occurring as the crystallite (solid) fraction grows in the shear band slurry leading to the shear being displaced to neighbouring regions with lower crystalline volume fraction.
Reactive hydride composites are good candidates for solid hydrogen storage due to their high grav... more Reactive hydride composites are good candidates for solid hydrogen storage due to their high gravimetric capacity, cyclability, and suitable thermodynamic properties. The LiNH2–MgH2 system is promising as changes in stoichiometry and milling conditions may result in tailoring of these properties. In this work, LiNH2–MgH2 with different ratios (Li2:Mg, Li:Mg) and ball milling conditions (100, 600 rpm) were investigated. Thermal desorption profiles shows hydrogen release starting at 125 °C for Li2:Mg 600 sample and at 225 °C for Li:Mg 600 sample, while for Li:Mg 100 sample simultaneous hydrogen and ammonia release at 175 °C is observed. In-situ synchrotron X-ray diffraction shows the related structural transformations, such as formation of Mg(NH2)2 and allotropic transformation of α into β-Li2Mg(NH)2 for Li2:Mg 600 sample at 350 °C or direct formation of β-Li2Mg(NH)2 for Li:Mg 100 sample at 370 °C. Different polymorphs of the LiMgN phase were also observed during cooling for these two samples. For the Li:Mg 600 sample, transformation occurs in a unique reaction from an unknown phase into β-Li2Mg(NH)2 at 290 °C. The unknown phase is indexed as a Fm3m cubic similar to the high temperature γ-Li2Mg(NH)2.
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Papers by G. Vaughan