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The magnetic susceptibilities and microstructures of Zr-Nb binary alloys were investigated to develop a new metallic biomaterial with a low magnetic susceptibility for magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, and the microstructure was evaluated with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). Zr-Nb alloys as-cast showed a minimum value of magnetic susceptibility between 3 and 9 mass% Nb, and the value abruptly increased up to 20 mass% Nb, followed by a gradual increase with the increase of the Nb content. XRD, OM, and TEM revealed that the minimum value of the susceptibility was closely related to the appearance of the athermal ! phase in the phase. Since the magnetic susceptibility of Zr-3Nb alloy consisting of an 0 phase was as low as that of Zr-9Nb alloy consisting of the and ! phases, that of the ! phase was lower than that of the 0 and phases. When Zr-16Nb alloy was heat-treated, the isothermal ! phase appeared, and, simultaneously, the magnetic susceptibility decreased. Therefore, the ! phase contributes to the decrease of the magnetic susceptibility, independently of the formation process of the ! phase. The magnetic susceptibility of the Zr-3Nb alloy as-cast was almost one-third that of Ti-6Al-4V alloy, which is commonly used for medical implant devices. Zr-Nb alloys are useful for medical devices used under MRI.

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