FIRST PRINCIPLES SLAB RELAXATION STUDY OF THE TiFe(001) SURFACE

We have performed Density Functional Theory calculations in the Generalized Gradients Approximation for the (001) surface of the intermetallic compound TiFe . We have focused on the interplay between spin polarization and surface relaxations, and the influence of the chemical species at the surface. We found that the surface shows a magnetic ordering. The magnetic moment at the surface layer depends strongly on the surface termination, being much larger for the case of Fe than Ti termination (3.11 and 0.29 μB/atom, respectively). The magnetic moments show an alternating behavior with a slow decaying as we go inside the material. On the other hand, the modification of the atomic positions due to the surface relaxation results in a very small influence on the magnetic moment with respect to the ideal, nonrelaxed configuration.

Investigation of the structure and properties of hypereutectic Ti-based bulk alloys

ABSTRACTStructure and mechanical properties of binary Ti-TM (TM-other transition metals) and ternary Ti-Fe-(TM, B or Si) alloys produced in the shape of the arc-melted ingots of about 25 mm diameter and 10 mm height are studied. The formation of high-strength and ductile hypereutectic alloys was achieved in the Ti-Fe, Ti-Fe-Cu and Ti-Fe-B systems. The structures of the high-strength and ductile hypereutectic alloys studied by X-ray diffractometry and scanning electron microscopy were found to consist of the primary cubic Pm3 m intermetallic compound (TiFe-phase or a solid solution on its base) and a dispersed eutectic consisting of this Pm3m intermetallic compound + BCC Im 3 m β-Ti supersaturated solid solution phase. The hypereutectic Ti-Fe alloy showed excellent compressive mechanical properties. The addition of Cu improves its ductility. B addition increased mechanical strength. Ni, Cr and Mn additions caused embrittlement owing to the formation of alternative intermetallic compounds. The deformation behaviour and the fractography of the Ti-based alloys were studied in details. The reasons for the high strength and good ductility of the hypereutectic alloys are discussed.