A new approach to develop palladium-modified Ti-based alloys for biomedical applications

A new powder mixing/coating technique combined with selective laser melting (SLM) or hot isostatic pressing has been used to modify Ti-6Al-4V (Ti64) with Pd with the aim of further improving its corrosion resistance. The modified alloy samples were characterised in terms of porosity, surface structure, microstructure and composition using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and electron microprobe analysis (EPMA). Their corrosion properties were evaluated via electrochemical tests and the mechanical properties measured via tensile tests. Using a new physical powder mixing technique, Pd was homogeneously distributed among the base Ti alloy powder particles without damaging their sphericity. After HIPing Pd is mainly located at grain boundaries while during SLM Pd has dissolved into the matrix. The porosity in the as-SLMed samples and surface roughness both increase continuously with increased laser scanning speed. Pd did not cause significant improvement in tensile properties but did enhance corrosion resistance in 2 M HCl by shifting the corrosion potential into the passive region of Ti64. The current work suggested that the new approach is a feasible route of synthesising modified alloys with both chemical and microstructural homogeneity as well as improved performance for biomedical application

Carbon uptake and distribution in Spark Plasma Sintering (SPS) processed Sm(Co, Fe, Cu, Zr)z

Spark Plasma Sintering (SPS) rapidly consolidates high-melting point powders between carbon dies, but carbon can pose a risk for many materials. Carbon uptake in SPS and conventional, pressure-less sintered (CS) Sm(Co, Fe, Cu, Zr)z has been analysed using Electron Probe Micro-Analysis (EPMA) to produce high-detail elemental distribution maps. Field's metal was used as mounting material to avoid introducing carbon into the samples. The distribution maps show high surface carbon levels in the SPS-processed Sm(Co, Fe, Cu, Zr)z to a depth of 10 μm. Much less carbon was observed in CS Sm(Co, Fe, Cu, Zr)z. Furthermore, elemental carbon analysis (LECO-C) confirmed carbon was most abundant at the surface in SPS-processed Sm(Co, Fe, Cu, Zr)z but also at higher levels internally, when compared to the CS sample. It is inferred that the carbon contamination is due to the contact between the powder and the graphite die/paper at elevated temperatures during SPS process. The measured levels of carbon in the SPS-processed sample are not expected to significantly impact the magnetic properties of Sm(Co, Fe, Cu, Zr)z. These results may have implications for other powder materials processed by SPS with properties sensitive to carbon