Effect of Ta content on the magnetic susceptibility of Zr–Ta binary alloys preventing artefacts for MRI

Abstract

The microstructures and magnetic properties of Zr–Ta binary alloys were examined in the study presented here. The Zr–Ta alloys (Zr-(0–50) mass% Ta) were prepared from 99.5 mass% zirconium and 99.5 mass% tantalum by arc melting in an Ar atmosphere. Magnetic susceptibility was evaluated in air at room temperature. The phase constitutions were identified using an X-ray diffractometer (XRD), a scanning electron microscope (SEM), and a transmission electron microscope (TEM). The acicular martensitic phase formed mainly in the lower Ta composition. In Zr-25Ta and above, the volume fraction of the β-Ta phase increased as Ta concentrations increased. TEM observations showed phase separation due to spinodal decomposition in Zr-20Ta and 30Ta. The diffraction patterns for Zr-20Ta showed spots associated with the ω phase. Magnetic susceptibility gradually declined as Ta was added, falling to a minimum twice: near Zr-20Ta and 50Ta. The former minimum resulted from the high volume fraction of the ω phase having lower magnetic susceptibility than that of other phases. The latter resulted from the formation of the β-Ta phase with magnetic susceptibility lower than the β-Zr phase. As a result, Zr–Ta alloys showed about three times lower magnetic susceptibility than Ti alloys and would be suitable for use with medical devices in MRI environments.

Keywords:

• Zr alloy
• microstructure
• phase separation
• ω phase
• spinodal decomposition
• magnetic susceptibility
• MRI artefact