Volume magnetic susceptibility design and hardness of Au–Ta alloys and Au–Nb alloys for MRI-compatible biomedical applications

The volume magnetic susceptibility (χv) and Vickers hardness (HV) of Au–Ta and Au–Nb alloys were investigated for use as magnetic resonance imaging (MRI)-compatible alloys for biomedical applications. χv of the Au–Ta alloys did not depend on the phase constitution but did depend on the alloy composition. Therefore, heat treatment hardly affected χv of the Au–Ta alloys, and only alloys with Ta contents near 15 were possibly MRI-compatible. In contrast, χv of the Au–Nb alloys depended on the phase constitution. Therefore, both the alloy composition and heat treatment can be used to widely control χv of Au–Nb alloys, and Au–xNb alloys (x≥6.8) can be made MRI-compatible by optimizing χv using heat treatment. HV of the Au–15Ta alloy was smaller than that of pure Ti even after heat treatment, whereas HV of the MRI-compatible Au–Nb alloys was possibly higher than that of pure Ti after heat treatment. The saturated χv values of the Au–Nb alloys after heat treatment at 800 °Care compatible with the hypothesis that χv of an alloy is the average χv of each phase of the alloy based on the rule of mixtures. This hypothesis supports the tailoring of χv by controlling the alloy composition and heat treatment.