Effects of Phase Constitution of Zr-Nb Alloys on Their Magnetic Susceptibilities

Abstract

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.

Enhancing Functionalities of Metallic Materials by Controlling Phase Stability for Use in Orthopedic Implants

“…7.9 [41]. As is seen, the magnetic susceptibility of Zr-Nb alloys varies as a function of Nb content, showing a local minimum for the Nb content of 3-9 mass% [41]. As Zr undergoes allotropic transformation similar to Ti, the concept of the phase stability in Zr alloys is similar to that of Ti alloys.…”

“…The dependence of magnetic susceptibility on the Nb content in Zr-Nb alloys is shown in Fig. 7.9 [41]. As is seen, the magnetic susceptibility of Zr-Nb alloys varies as a function of Nb content, showing a local minimum for the Nb content of 3-9 mass% [41].…”

“…The magnetic susceptibility of living tissues reveals diamagnetism, while that of water being À9 Â 10 À6 cm 3 g À1 [40]. On the other hand, Ti, being paramagnetic, has the magnetic susceptibility of 3.2 Â 10 À6 cm 3 g À1 [41]. This magnetic susceptibility of Ti is much lower than that of ferromagnetic iron (Fe) and Co, but still higher than that of water.…”

“…This magnetic susceptibility of Ti is much lower than that of ferromagnetic iron (Fe) and Co, but still higher than that of water. Therefore, Zr, which is a congener of Ti, also exhibits a smaller magnetic susceptibility of 1.3 Â 10 À6 cm 3 g À1 , [41]. This property has gained significant attention, and it forms the genesis for the recent developments of Zr alloys, such as Zr-Nb [41,42] and Zr-Mo [43,44] alloys.…”

“…Therefore, the phase stability of Zr alloys depends on the chemical composition. The allotropic transformation results in the formation of some intermediate phases, such as non-equilibrium α 0 and ω phases, in addition to the equilibrium α and β phases [41][42][43]. In Zr-Nb alloys, the magnetic susceptibility of Zr-(3-9)Nb alloys reveals local minimum with Zr-3Nb, Zr-6Nb, and Zr-9Nb alloys consisting of single α 0 phase, (α 0 + ω + β) phases, and (ω + β) phases, respectively.…”