Deformation behaviour and 6H-LPSO structure formation at nanoindentation in lamellar high Nb containing TiAl alloy

Microstructure and deformation mechanisms at a nanoindentation in the lamellar colony of high Nb containing TiAl alloy have been studied using the focused ion beam and the transmission electron microscopy. Considerable deformation twins are observed around the nanoindentation, and a strain gradient is generated. A continuous change in the bending angle of the lamellar structure can be derived, and a strain-induced grain refinement process is observed as various active deformations split the γ grains into subgrains. In addition to all possible deformation mechanisms (ordinary dislocation, super-dislocation and deformation twining) activated due to the heavy plastic deformation, a 6-layer hexagonal (6H) long-period stacking ordered structure is identified for the first time near the contact zone and is thought to be closely related to the glide of partial dislocations.     

Local chemistry of a nanocrystalline high-strength Mg 97 Y 2 Zn 1 alloy

The local chemistry of a high-strength nanocrystalline Mg 97 Y 2 Zn 1 alloy produced by a rapidly solidified powder metallurgy process has been characterized by a three-dimensional atom probe (3DAP). The consolidated and extruded rod consists of hcp Mg grains of approximately 150nm size with their basal planes normal to the radial direction of the rod. 3DAP results revealed that the Y and Zn contents vary depending on the grains. Y- and Zn-depleted grains have a hcp structure, while Y- and Zn-enriched grains have a unique long-period stacking of the basal plane designated as 6H-Mg. In the 6H-Mg phase, the enrichment of Y and Zn occurs in one or two atomic layers in the unit cell. The chemical composition of the solute-enriched layer was estimated to be approximately 10 at.% Y and 3 at.% Zn using the 3DAP.