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Recently, zinc-based materials have been extensively investigated as materials suitable for the fabrication of biodegradable orthopedic implants. In this study, porous zinc was prepared as a material for implantation into trabecular bone using spark plasma sintering with different sizes of initial zinc powders, and microstructural, mechanical and corrosion characterizations of the prepared materials were performed. The porosity of the prepared porous samples was approximately 20%. The mechanical properties depended on the initial powder particle size, the pore size and distribution. By using a finer powder (FP), <100 μm in size, the compressive yield strength and the compressive modulus were approximately 31.2 MPa and 1.2 GPa, respectively. These values approach those of trabecular bone (1–12 MPa and 0.1–0.4 GPa). Moreover, the plastic deformation of FP materials occurred at almost constant stress similar to trabecular bone. The corrosion rates of the porous Zn were 0.6–0.8 mm/a and depended on the initial powder particle size, the pore size and distribution. After pre-incubation of the porous Zn in simulated body fluid (SBF), the Zn concentration in biological extracts was below the toxic limit of zinc for L929 cells. Based on the obtained results, we can estimate that the materials prepared from the finer zinc powder showed properties suitable for the fabrication of porous biodegradable orthopedic implants. [ABSTRACT FROM AUTHOR]

Recently, iron-based materials have been considered as candidates for the fabrication of biodegradable load-bearing implants. Alloying with palladium has been found to be a suitable approach to enhance the insufficient corrosion rate of iron-based alloys. In this work, we have extensively compared the microstructure, the mechanical and corrosion properties, and the cytotoxicity of an FePd2 (wt%) alloy prepared by three different routes — casting, mechanical alloying and spark plasma sintering (SPS), and mechanical alloying and the space holder technique (SHT). The properties of the FePd2 (wt%) were compared with pure Fe prepared in the same processes. The preparation route significantly influenced the material properties. Materials prepared by SPS possessed the highest values of mechanical properties (CYS ~ 750–850 MPa) and higher corrosion rates than the casted materials. Materials prepared by SHT contained approximately 60% porosity; therefore, their mechanical properties reached the lowest values, and they had the highest corrosion rates, approximately 0.7–1.2 mm/a. Highly porous FePd2 was tested in vitro according to the ISO 10993-5 standard using L929 cells, and two-fold diluted extracts showed acceptable cytocompatibility. In general, alloying with Pd enhanced both mechanical properties and corrosion rates and did not decrease the cytocompatibility of the studied materials. [ABSTRACT FROM AUTHOR]

Abstract: There has recently been an increased demand for porous magnesium materials in many applications, especially in the medical field. Powder metallurgy appears to be a promising approach for the preparation of such materials. Many works have dealt with the preparation of porous magnesium; however, the effect of sintering conditions on material properties has rarely been investigated. In this work, we investigated porous magnesium samples that were prepared by powder metallurgy using ammonium bicarbonate spacer particles. The effects of the purity of the argon atmosphere and sintering time on the microstructure (SEM, EDX and XRD) and mechanical behaviour (universal loading machine and Vickers hardness tester) of porous magnesium were studied. The porosities of the prepared samples ranged from 24 to 29 vol.% depending on the sintering conditions. The purity of atmosphere played a significant role when the sintering time exceeded 6h. Under a gettered argon atmosphere, a prolonged sintering time enhanced diffusion connections between magnesium particles and improved the mechanical properties of the samples, whereas under a technical argon atmosphere, oxidation at the particle surfaces caused deterioration in the mechanical properties of the samples. These results suggest that a refined atmosphere is required to improve the mechanical properties of porous magnesium. [Copyright &y& Elsevier]

Zinc and zinc alloys have been studied due to their corrosion properties as potentially biodegradable materials. In this study, a zinc/hydroxyapatite composite (Zn/HA) containing 16 wt % HA was prepared by spark plasma sintering and characterized in detail. The microstructure, mechanical and corrosion properties were studied and the mutual relations between properties and microstructure were found. The porosity was evaluated to be approximately 18%. The mechanical properties (ultimate compression strength = 65 MPa and ultimate flexural strength = 120 MPa) are sufficient for the potential scaffolding and augmentation of cancellous bone. The flexural properties of these materials were measured for the first time. Immersion tests and subsequent analyses confirmed no direct participation of hydroxyapatite in the corrosion process and an ideal corrosion rate of approximately 0.4 mm/year. The amount of released zinc was between 4–6 mg/day corresponding with the maximal usable surface area of 25 cm2. All the results suggest that the Zn/HA composite is suitable as a potential biodegradable material (from the point of view of mechanical and corrosion properties) for the replacement of cancellous bones. [ABSTRACT FROM AUTHOR]

An equiatomic CoCrFeNiMn high-entropy alloy was prepared by induction melting and a progressive combination of mechanical alloying and compaction via spark plasma sintering done at temperatures of 800 °C and 1000 °C. The chosen methods of preparation had a significant impact on the microstructure and mechanical properties of the alloy. In comparison, the as-cast alloy had a much coarser microstructure while simultaneously obtaining inferior mechanical properties compared to those of the 8-h mechanically alloyed and spark plasma sintered alloy compacted at 1000 °C, which achieved a hardness of 424 ± 7 HV, and the alloy compacted at 800 °C showed a lower but still highly comparable hardness of 352 ± 12 HV. Both alloys showed good thermal stability, as expressed by almost negligible hardness changes during 100 h of annealing at temperatures of 400 °C and 600 °C. The investigated alloys also showed their superiority during compressive stress-strain tests at ambient and elevated temperatures of 400 °C and 600 °C. At ambient temperature, the highest compressive yield strength of 1534 MPa was observed for the sample compacted at 800 °C. As the temperature of the compressive test increased, the investigated alloys reduced their compressive yield strengths. [ABSTRACT FROM AUTHOR]

In this work, the formation of intermetallics in Ni–Ti system by reactive sintering at 500 and 650 °C was studied. Mechanism and kinetics of the reactions leading to Ni–Ti phases were determined by DTA and the application of an experimental model consisted of nickel-plated titanium. It was found that Ti 2 Ni phase forms already at 500 °C. At 650 °C this phase undergoes a reaction with nickel to NiTi and Ni 3 Ti. The reactions were determined to be diffusion-controlled. The formation of Ni 3 Ti contributes to the porosity evolution during reactive sintering production of NiTi alloy. [ABSTRACT FROM AUTHOR]