Microstructure of titanium alloy modified by high-intensity implantation of low- and high-energy aluminium ions

Abstract

This study focuses on the analysis of microstructural, elemental and phase compositions of surface and near-surface layers of titanium after the implantation of aluminium. A titanium alloy with a chemical composition close to commercially pure titanium (grade 2) was used as the target material. Ion implantation was performed using two modes of irradiation: 1. repetitively pulsed ion beams with a mean ion energy of 35 keV; 2. low-energy-focused ion beams of high intensity with a mean ion energy of 2.6 keV. The irradiation fluence reached 1.1 × 1018 ion/cm2 using the first mode and 1.6 × 1021 ion/cm2 using the second mode. In both cases, the beam itself heated the targets. The peak concentration of aluminium after the implantation of medium-energy ions was ~65 at.%, and the maximum depth of dopant penetration was 2.6 μm. On the contrary, in the case of high-intensity low-energy ion implantation, the surface concentration of dopant reached a maximum of 25 at.%, but the depth of penetration increased significantly and achieved 50 μm. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that fine-grained intermetallic phases, Ti3Al and TiAl, and solid solutions of various compositions were possibly formed after the medium-energy ion implantation. The mean grain size of the intermetallic phases was ~50 nm. XRD and TEM analyses in the case of low-energy high-intensity ion implantation demonstrated the formation of the ion-alloyed layer, which comprised intermetallic phase Ti3Al and solid solutions of aluminium in titanium. The grain size of Ti3Al phase can be 5 μm and more.