Fabrication of High-Strength Zr-Based Composites by Spark Plasma Sintering

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Fabrication of High-Strength Zr-Based Composites by Spark Plasma Sintering Tomoyuki Fujii

, Masaki Suzuki, Ryuki Matsubara, Keiichiro Tohgo, and Yoshinobu Shimamura

Submitted: 21 July 2020 / Revised: 9 October 2020 / Accepted: 24 October 2020 Zirconium (Zr) partially stabilized zirconia (PSZ) composites were fabricated using the spark plasma sintering technique with the aim of producing medical implants with reduced metal-related artifacts in magnetic resonance imaging. Composites with compositions ranging from 100% Zr to 100% PSZ were fabricated, and they exhibited high mechanical performance. Optical microscopy and density measurements revealed that dense composites were successfully produced, irrespective of the PSZ content. Hardness and bending tests were performed to evaluate the inﬂuence of the addition of PSZ on the mechanical properties of the composites. The results showed that the hardness and bending strength increased with increasing PSZ content. The elastic modulus of the composites was higher than that predicted by the rule of mixtures, and this was due to the formation of Zr oxide around the Zr phase during sintering. It was concluded that the mechanical properties of the composites could be controlled within the range of those of monolithic Zr and monolithic PSZ, and that the use of PSZ was effective for improving the mechanical properties. Keywords

biomaterials, composites, mechanical properties, powder metallurgy, spark plasma sintering

1. Introduction Biomaterials are required for medical applications such as stents, artiﬁcial bones, artiﬁcial joints, artiﬁcial heart valves, and dental implants. Since such materials are used in vivo, they must exhibit high levels of biocompatibility, stiffness, strength, toughness, hardness, wear resistance, and formability (Ref 1). For replacement of hard tissues, strength and toughness are especially required, and metallic biomaterials such as titanium (Ti) and its alloys, stainless steel, and cobalt-based alloys are widely used (Ref 2). To improve their mechanical properties, much attention has been paid to ceramic–metal composites (Ref 3-10) and functionally graded materials (Ref 11-17) because they exhibit both the characteristics of metals (high strength and toughness) and those of ceramics (high hardness and wear resistance, and biocompatibility). The magnetic susceptibility of biomaterials has also been of interest because magnetic resonance imaging (MRI) is widely used for noninvasive examination of nerves, organs, and bones (Ref 18-20). If a biomaterial with high magnetic susceptibility is present during MRI, clear images cannot be obtained due to metal-induced artifacts. Zirconium (Zr) has recently attracted attention as an implant material because it exhibits lower magnetic susceptibility than other typical biomaterials. The magnetic susceptibility of Zr is half and one-thirtieth of those of

Tomoyuki Fujii, Masaki Suzuki, Ryuki Matsubara, Keiichiro Tohgo, and Yoshinobu Shimamura, Department of Mechanical Engin

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