Search for: All records

Al-Mg alloy disks were produced from Mg sandwiched between Al through 100 turns of high-pressure torsion (HPT) at 6.0 GPa at room temperature, resulting in high microhardness of Hv 300–350 in regions experiencing a nominal shear strain >  ~ 390. While compositional mapping using scanning electron microscopy energy-dispersive spectroscopy (EDS) showed a uniform distribution of Mg through the disk thickness at 1.5 mm and 3.0 mm from the disk center, transmission electron microscopy EDS showed a heterogeneous distribution of Mg remained on the nanoscale. Although HPT induces enough mixing to result in face-center-cubic Al with supersaturations of Mg of up to ~ 20 at.% near the disk surfaces, β-Al3Mg2, γ-Al12Mg17 and Al2Mg intermetallic phases were identified by electron diffraction throughout the disk thickness even in regions experiencing high shear strain. This study visually captures detailed compositional heterogeneity throughout the sample thickness following intense mechanical alloying, nanoscale re-structuring and phase transformations. 

The amorphous-to-crystalline transition in TiO2 films upon annealing in air yields different polymorphs, depending on the oxygen partial pressure during the deposition of the amorphous precursor film. We further manipulate the resulting polymorph by introducing Sn into the system. By depositing a few nanometer-thick layer of metallic Sn between two layers of amorphous TiO2 prepared to yield the anatase polymorph of TiO2, we find that it results in the rutile polymorph if the content of Sn is high enough. If Sn is introduced as an oxide, no rutile is formed; anatase is by far the predominant phase (with a very small amount of brookite). This observation is consistent with scavenging of oxygen by elemental Sn at the Sn/TiO2 interfaces, stabilizing the rutile structure that can accommodate oxygen vacancies.