Grain-Size Effect on the Structural-Phase State of the Surface Layer of VT1-0 Alloy Implanted with Aluminum Ions.

In this paper, we study the structural-phase state of the surface layers of commercially pure titanium (VT1-0 alloy) implanted with aluminum ions by transmission electron microscopy and energy-dispersive X-ray spectroscopy. The samples are foils cut perpendicular to the treated surface. The samples are studied in three states (submicrocrystalline, ultrafine-grained, and fine-grained) obtained after a combined method of multiple uniaxial pressing (abc pressing) followed by multi-pass rolling in grooved rolls at room temperature and subsequent annealing at 573, 673, and 773 K, respectively, for 1 h. Ion implantation is carried out for 8 h 20 min at an irradiation dose of 10¹⁸ ions/cm² and 623 K. It is established that implantation led to the formation of a gradient structure consisting of five layers: (1) oxide layer, (2) ion-implanted layer, (3) layer with a crushed grain structure, (4) layer formed under the residual influence of implantation, and (5) layer corresponding to the nonimplanted state of the alloy. The structural-phase state of layers 1–3, where the concentration of implanted aluminum was maximum, is studied. For each layer, its thickness, phase composition, shape and arrangement of particles of the phases formed by the action of ion implantation are determined, and the sizes of α-Ti grains, sizes, distribution density, and volume fractions of precipitated particles are measured. It is established that the basis of layer 1 is aluminum and titanium oxides. The matrix of layer 2 is an α-Ti solid solution supersaturated with Al atoms, and that of layer 3 is a solid solution based on α-Ti. Aluminum implantation is found to lead to the formation of the intermetallic phases Ti₃Al and TiAl₃. The particles of these phases are present as separately located nanograins in layer 1, Ti₃Al particles have a lamellar shape and are located inside α-Ti grains in layers 2 and 3, and TiAl₃ particles have a rounded shape and are found both in the bulk and at the grain boundaries of α-Ti. The volume fractions of intermetallic phases in layer 3 are maximum. [ABSTRACT FROM AUTHOR]