Abstract
Zr alloy is expected to decrease the artifact volume of magnetic resonance imaging (MRI) due to its relatively small magnetic susceptibility. To improve the mechanical properties of a Zr–1mass%Mo alloy that yielded a reduced artifact volume during MRI, the alloy was melted, hot-forged, and cold-swaged with area reduction ratios of 30%, 50%, 60%, 70%, and 84%. The effects of cold swaging on the microstructure, mechanical properties, and magnetic susceptibility of the alloy were investigated. Before cold swaging, the microstructure consisted of laminated and layered α- and β-phases; however, after cold swaging, the α- and β-phases were bent and distorted, and the α-phase became oriented along the {10 1¯ 0} plane. The ultimate tensile strength and elongation to fracture of the Zr–1Mo alloy after cold swaging with an 84% area reduction were 1001 MPa and 10.7%, respectively. The alloy only experienced work-hardening when subjected to large deformations. On the other hand, the change in magnetic susceptibility with cold-swaging was small, from 13.85 × 10−9 to 14.87 × 10−9 m3·kg−1. Thus, a good balance of mechanical properties and low magnetic susceptibility in the Zr–1Mo alloy was obtained by cold swaging. Therefore, this alloy is suitable for utilization in medical devices and is expected to decrease the artifact volume.
Highlights
Magnetic resonance imaging (MRI) is widely used in surgical diagnosis because it does not involve exposure to radiation, unlike X-ray imaging
With an area reduction ratio of 84%, all peaks except those attributable to α (1010) and α (2020) almost vanished
The microstructure consisted of laminated and layered α- and β-phases before cold swaging, but distorted and bent α- and β-phases appeared with the orientation to α {1010} after cold swaging
Summary
Magnetic resonance imaging (MRI) is widely used in surgical diagnosis because it does not involve exposure to radiation, unlike X-ray imaging. MRI is affected by artifacts, e.g., defects in the MR images caused by metallic devices implanted in the human body. These artifacts are caused by the differences in magnetic susceptibility of the implanted metallic devices and the surrounding human tissue. The artifact volume is related to the magnetic susceptibility of the implanted metallic devices. Metallic implant materials with low magnetic susceptibilities are required to reduce the artifact volume. For 316L-type stainless steel and Co–Cr alloys, the artifact volume is relatively large because the magnetic susceptibilities of the constituent elements, namely Fe, Ni, and Co, are quite high [1]
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