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Abstract:
Due to their finely balanced strength and density, hexagonal close-packed (hcp) metals such as Ti and Mg are perceived as potential prime elements for the production of new light, and strong alloys essential for the sustainable development of green technologies oriented towards a reduction in mass in all transport sectors. Nevertheless, the conscious design of materials requires information on the relationship between alloy elements and individual deformation mode activity. Such complex knowledge in the context of hcp systems remains a challenge, seriously hampering our ability to anticipate the strength and ductility of new materials developed. In general, hcp metals and alloys suffer from limited cold workability arising from reduced crystal symmetry (compared to cubic crystals) and from the geometrical relations between their dislocation glide planes. On the other hand, the unique properties of single phase hcp materials, such as great strength and reasonable ductility of α-Ti+O solutions and a pronounced solution softening of α-Mg+Y alloys demonstrate the great potential of this groups of materials. All these aspects provide incentive for exploring the physics of plastic deformation and solution strengthening theories.

Keywords:
Hexagonal Ti alloys, solid solution strengthening, Peierls barriers, screw dislocations, first principles calculations

Abstract:
Stacking faults are the special regions of the crystal structure that exhibit non-uniform structure and diversified stability. Energy of this defects determines configurations of dislocation cores and type of predominant plastic deformation mechanism. In this study we focus on the generalised stacking fault energy computations of multi-slip-system hexagonal Ti alloys in the context of solution strengthening effect and the atomic as well as electronic structure identification of the analysed planar defects. The far reaching goal is to provide the physical and theoretical basis to answer the still unresolved question concerning the initiation of a micro-shear band in metallic solid.

Keywords:
stacking faults, hexagonal Ti alloys, instability of crystal lattice, solution strengthening, micro-shear band