Titanium alloys can experience a cooling-induced phase transformation from a body-centred cubic phase into a hexagonal close-packed phase which occurs in 12 crystallographically equivalent variants. Among them, variant selection II, 60 degrees/< 1 (2) over bar 10 >, is very close to the orientation of {10 (1) over bar1} < 1 (2) over bar 10 > twins (57.42 degrees/< 1 (2) over bar 10 >). We propose that the cyclic thermal loading during additive manufacturing introduces large thermal stresses at high temperature, enabling grain reorientation that transforms the 60 degrees/< 1 (2) over bar 10 > variant boundaries into the more energetically stable 57.42 degrees/< 1 (2) over bar 10 > twin boundaries. This transformation twinning phenomenon follows a strain accommodation mechanism and the resulting boundary structure benefits the mechanical properties and thermal stability of titanium alloys. [GRAPHICS] . IMPACT STATEMENT A new twinning mechanism, transformation twinning, was discovered in a Ti- 6Al-4V alloy fabricated by selective laser melting. The resulting high density of transformation twins impact the global mechanical properties significantly.

Trace elements and isotopic signatures are continuously recorded in growing shells and are empirically applied to monitor or reconstruct past environmental and climatic conditions. However, the precondition to correctly apply these proxy records is our understanding how trace elements are incorporated into growing biominerals. Although this understanding is still limited, we know today that bivalve shells form via non-classical crystallization pathways involving amorphous calcium carbonate (ACC) nanoparticles that transform to stable polymorphs aragonite calcite applications general understanding of the nano-scale properties of nacre is still limited. aim to understand trace element incorporation and mechanics of bivalve shell nacre at the nano-scale.

AFRICA (NWA) 11522. L. Daly, M.R. Lee, B.E. Cohen, J. Cairney, K. Eder, L. Yang, M.A. Cox, and A.J. Cavosie. School of Geographical and Earth Sciences, Univesity of Glasgow, Glasgow, G12 8QQ, UK, luke.daly@glasgow.ac.uk, Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, 2006, NSW, Australia. School of Earth and Planetary Science, Curtin University, Bentley, 6102,WA, Australia.

The CV3 Allende is one of the most extensively studied meteorites in worldwide collections. It is currently classified as S1—essentially unshocked—using the classification scheme of Stöffler et al. (1991), however recent modelling suggests the low porosity observed in Allende indicates the body should have undergone compaction-related deformation. In this study, we detail previously undetected evidence of impact through use of Electron Backscatter Diffraction mapping to identify deformation microstructures in chondrules, AOAs and matrix grains. Our results demonstrate that forsterite-rich chondrules commonly preserve crystal-plastic microstructures (particularly at their margins); that low-angle boundaries in deformed matrix grains of olivine have a preferred orientation; and that disparities in deformation occur between chondrules, surrounding and non-adjacent matrix grains. We find heterogeneous compaction effects present throughout the matrix, consistent with a highly porous initial material. Given the spatial distribution of these crystal-plastic deformation microstructures, we suggest that this is evidence that Allende has undergone impact-induced compaction from an initially heterogeneous and porous parent body. We suggest that current shock classifications (Stöffler et al., 1991) relying upon data from chondrule interiors do not constrain the complete shock history of a sample.