ABSTRACT
Biomedical Co-Cr-based alloys used in dental restorations are usually subjected to high-temperature treatments during manufacturing. Therefore, it is practically essential to characterise and control the oxide films formed on the surfaces of these alloys during heat treatment in terms of material loss, the accuracy of fit, and the aesthetics of dental restorations. In this work, the effects of boron doping on the surface oxide films formed on Ni-free Co-28Cr-9W-1Si (mass%) dental alloys under short-term exposure to high temperatures, which simulate the manufacturing process of porcelain-fused-to-metal (PFM) restorations, were investigated. The surface oxides primarily consisted of Cr2O3 in all prepared alloys. The chemical composition of these surface layers varies with the B concentration in the bulk, with the addition of boron stabilising the dense Cr2O3 phase in the oxide films. Nanoscale boron enrichment is clearly observed at the interface between the oxide films and the metal substrate, with the oxidation of boron atoms leading to the formation of a B2O3 layer. Since B2O3 and Cr2O3 prevent oxygen diffusion, the surface oxide films on the boron-containing alloys are thinner; however, no additional thinning was observed when increasing the boron content from 0.01 to 0.8 mass%. It was also found that a small amount of boron does not degrade the corrosion properties of the alloys in a 0.9% NaCl solution. The results obtained in this study will aid in the improvement of manufacturing processes, and ultimately, the performance of PFM restorations.
ABSTRACT
This paper investigated the effect of carbon addition on the microstructure and tensile properties of Ni-free biomedical Co-29Cr-6Mo (mass%) alloys containing 0.2 mass% nitrogen. The release of metal ions by the alloys was preliminarily evaluated in an aqueous solution of 0.6% sodium chloride (NaCl) and 1% lactic acid, after which samples with different carbon contents were subjected to hot rolling. All specimens were found to primarily consist of a γ-phase matrix due to nitrogen doping, with only the volume fraction of M23C6 increasing with carbon concentration. Owing to the very fine size of these carbide particles (less than 1 µm), which results from fragmentation during hot rolling, the increased formation of M23C6 increased the 0.2% proof stress, but reduced the elongation-to-failure. Carbon addition also increased the amount of Co and Cr released during static immersion; Co and Cr concentrations at the surfaces, which increased with increasing the bulk carbon concentrations, possibly enhanced the metal ion release. However, only a very small change in the Mo concentration was noticed in the solution. Therefore, it is not necessarily considered a suitable means of improving the strength of biomedical Co-Cr-Mo alloys, even though it has only to date been used in this alloy system. The results of this study revealed the limitations of the carbon strengthening and can aid in the design of biomedical Co-Cr-Mo-based alloys that exhibit the high durability needed for their practical application.
Subject(s)
Alloys/chemistry , Carbon/chemistry , Ions/chemistry , Metals/chemistry , Nitrogen/chemistry , Materials Testing/methods , Tensile StrengthABSTRACT
A novel and facile strategy is developed to fabricate highly nitrogen-doped graphene (N-graphene) based layered, quasi-two-dimensional nanohybrids with ultrathin nanosheet nanocrystals using a low-temperature, solution processing method for high-performance supercapacitor electrodes. High N doping can be achieved together with one of the lowest oxygen content in chemically reduced graphene and related nanohybrids at low temperature by large-scale residue defects of chemically reduced graphene. The layered, quasi-two-dimensional nanohybrids or heterostructures of ultrathin Ni(OH)2 nanosheet nanocrystal/N-graphene can be applied in supercapacitor electrodes with ultrahigh capacitances of â¼1551 F g(-1), excellent rate performance in the scan measurements (from 2 mV s(-1) to 100 mV s(-1)) and in the discharge tests (from 1.5 A g(-1) to 30 A g(-1)) and good cycling stability. Moreover, the capacitance of Ni(OH)2 nanosheet/N-graphene nanohybrids is two and one orders of magnitude higher than that for pure nanocrystals and for the physical mixture of nanocrystal/N-graphene, respectively. Electron transfer in supercapacitor electrodes based on nanohybrids is over 100 times faster than that in electrodes from pure nanocrystals and several tens of times faster than that in electrodes from nanocrystal/N-graphene mixtures. This low-temperature method may provide a low-cost, solution-processable and easily scalable route to high-performance graphene nanohybrid electrodes for energy applications.
ABSTRACT
Owing to recent progress in nanotechnology, the ability to tune the surface properties of metals has opened an avenue for creating a new generation of biomaterials. Here we demonstrate the successful development of a novel Ti-based nanoglass composite with submicron-nanometer-sized hierarchical glassy structures. A first exploratory study was performed on the application of the unique nanostructure to modulate osteoblast behaviors. Our results show that this Ti-based nanoglass composite, relative to conventional metallic glasses, exhibits significantly improved biocompatibility. In fact, a 10 times enhancement in cell proliferation has been achieved. To a great extent, this superior bioactivity (such as enhanced cell proliferation and osteogenic phenotype) is promoted by its unique hierarchical structures combining nanoglobules and submicron button-like clusters from collective packing of these nanoglobules. This nanoglass composite could be widely applicable for surface modifications by means of coating on various materials including BMGs, crystalline metals or ceramics. Therefore, our successful experimental testing of this nanostructured metallic glass may open the way to new applications in novel biomaterial design for the purpose of bone replacement.
