Influence of implantation on the grain size and structural-phase state of UFG-titanium

Abstract

Transmission electron microscopy (TEM) investigations were carried out to study the structural-phase state of ultra-fine grained (UFG) titanium with the average grain size of ∼0.2 and 0.3 µm, implanted with aluminium ions. MEVVA-V.RU ion source was used for ion implantation under room temperature, exposure time of 5.25 h, at ion implantation dosage of 1×1018 ion/cm2. UFG-titanium was obtained by means of multiple uniaxial compacting with multipass rolling in grooved rolls and further annealing at 573 K during 1 hour to reach the average grain size of ∼0.2 µm, and annealing at 623 K during 1 hour to reach the size of ∼0.3 µm. The study revealed that in alloy with the average grain size of ∼0.2 µm implantation results in a decrease in longitudinal grain size of α-Ti (from 1.9 to 0.7 µm), however lateral size in its turn changed insignificantly (from 0.15 to 0.12 µm). Grain anisotropy factor decreased by 3 times. In the alloy with the average grain size of ∼0.3 µm both longitudinal and lateral grain sizes decreased (from 0.33 to 0.19 µm and from 2.1 to 0.8 µm correspondingly). The studies also showed that implantation of titanium with aluminium has led to the formation of a number of phases, such as: β-Ti, TiAl3, Ti3Al, TiC and TiO2. Their places of concentration, sizes, distribution density and volume ratios were determined. TiAl3 and Ti3Al phases were established to be ordered ones, formed within the conditions of ion exposure along the boundaries of α-Ti grains. Conducted calculations demonstrated that implantation contributed to the alloy strengthening, i.e. in alloy with the average grain size of ∼0.2 µm the value of yield stress increased by 2 times, and in the alloy with the average grain size of ∼0.3 µm—by 4 times.