Sintering Behavior and Mechanical Properties of Magnesium/β-Tricalcium Phosphate Composites Sintered by Spark Plasma Sintering

Abstract

Mg/bioceramic composites fabricated by powder metallurgy technique have been explored for biodegradable load-bearing implants. Although sintering behavior including densi cation and reaction has a signi cant effect on mechanical properties of the composites, little studies have been conducted focusing on both sintering behavior and mechanical properties. In this study, Mg/10 and 20 vol.% β-tricalcium phosphate (β-TCP) composites were fabricated by spark plasma sintering, which achieved high densi cation. Distinct sintering behavior of Mg/β-TCP composites involving reaction was investigated by estimating relative densities during sintering, thermal analyses, X-ray diffractometry and auger electron spectroscopy. The results suggest that Ca solid diffusion into Mg during sintering resulted in melting and penetrating Mg into gaps between β-TCP particles, and nally led to high densi cation. The reaction between Mg and β-TCP produced MgO. Compression tests showed that Mg/β-TCP composites enhanced their mechanical properties compared with Mg sintered at the same route. That s because the high densi cation of Mg/β-TCP composites and high hardness of MgO potentially caused good load transfer from Mg-matrix to the formed MgO as reinforcement. The discoveries regarding the reactions can help the design of Mg/calcium phosphate composites including Mg/β-TCP composites.

Degradation behaviors and cytocompatibility of Mg/β‐tricalcium phosphate composites produced by spark plasma sintering

“…The non‐reacted β‐TCP is located inside the MgO formed. The MgO region did not show any electron discharging because conductive Mg was localized around MgO, as discussed in our previous study . Sintered Mg showed the boundaries of sintered Mg particles (Figure C).…”

“…When MgO formed, Ca diffused from β‐TCP phase into Mg‐matrix through the MgO layer, which reduced the melting point of Mg‐matrix according to Mg‐Ca phase diagram. Thus, melted Mg could penetrate into the gaps between β‐TCP particles and locally appear around the MgO, which was the expected sites for β‐TCP before sintering . The Mg‐matrix containing Ca solid‐solute was localized adjacent to the MgO region because of the short sintering time, as shown in Figure E,F.…”

“…Figure A shows XRD patterns of Mg/10% β‐TCP composite, Mg/20% β‐TCP composite, sintered Mg, and extruded Mg. Mg/β‐TCP composites showed Mg, β‐TCP, and small MgO peaks (Figure B). The MgO phase resulted from the reactions between Mg and β‐TCP during sintering . Sintered Mg and extruded Mg showed only Mg peak.…”

“…In this study, we adapted the same methods for preparing Mg/β‐TCP composites as previously published, and reprinted with permission from the Japan Institute of Light Metals …”

“…Mg alloys and Mg‐based composites have been explored to potentially address these problems. Previously, Mg/β‐tricalcium phosphate (β‐TCP) composites showed improvement of mechanical properties, when they were prepared using a powder metallurgy process coupled with spark plasma sintering (SPS) . Mg particles are difficult to sinter using conventional sintering methods due to an oxide layer on the surface of Mg particles, but SPS method can address this issue because of its unique combination of external pressure and direct current through the particles .…”