RESUMEN
Magnesium-zinc-calcium (Mg-Zn-Ca) alloys as a biomaterial have attracted much attention recently, owing to their excellent biocompatibility, similar mechanical properties to natural bone, and biodegradable properties. Despite the numerous advantages of MgZnCa alloys, the rapid degradation of magnesium proved challenging as the implant in unable to retain its structural integrity for a sufficient duration of time. For metallic glasses, the capability to produce a bulk sample that is sufficiently large for useful applications have been far less successful owing to challenging processing parameters that are required for rapid cooling. In this study, Mg65Zn30Ca5 melt-spun ribbons were produced using melt-spinning followed by spark plasma sintering under high pressure (60 MPa) at different temperatures (130-170 °C) to provide an insight into the consolidation, mechanical, and corrosion behavior. Microstructural interfaces were characterized using scanning electron microscopy while the thermal stability of the amorphous phase was characterized using differential scanning calorimetry and X-ray diffraction. Here, pellets with 10 mm diameter and 10 mm height with a complete amorphous structure were achieved at a sintering temperature of 150 °C with densification as high at ~98%. Sintering at higher temperatures, while achieving higher densification, resulted in the presence of nano-crystallites. The mechanical properties were characterized using microhardness and compression tests. The hardness values of the sintered products were relatively higher to those containing crystallite phases while the ultimate compressive strength increased with increasing sintering temperature. Bio-corrosion properties were characterized via electrochemical testing with PBS as the electrolyte at 37 °C. The corrosion results suggest that the sintered samples have a significantly improved corrosion resistance as compared to as-cast samples. More notably, SPS150 (samples sintered at 150 °C) exhibited the best corrosion resistance (35× compared to as-cast in the context of corrosion current density), owing to its single-phase amorphous nature. This study clearly shows the potential of spark plasma sintering in consolidating amorphous ribbons to near-full density bulk pellets with high corrosion resistance for bio-applications.
RESUMEN
Diffraction data were collected using synchrotron X-ray scattering (sXRD) and electron back-scattered diffraction (EBSD) during in situ tensile-compressive deformation of Mg alloy AZ31B dogbone samples. The onset and evolution of twinning and detwinning were monitored based on intensity changes in sXRD 2D scattering patterns (which also provided average elastic strain values through the calculation of orientation-specific lattice spacing changes), and EBSD, that revealed the micro-scale grain morphology changes. The observations were interpreted and analysed with the help of crystal plasticity finite element modelling (CP-FEM), as reported in the published article (https://doi.org/10.1016/j.ijplas.2019.02.018).
RESUMEN
High energy 2D X-ray powder diffraction experiments are widely used for lattice strain measurement. The 2D to 1D conversion of diffraction patterns is a necessary step used to prepare the data for full pattern refinement, but is inefficient when only peak centre position information is required for lattice strain evaluation. The multi-step conversion process is likely to lead to increased errors associated with the 'caking' (radial binning) or fitting procedures. A new method is proposed here that relies on direct Digital Image Correlation analysis of 2D X-ray powder diffraction patterns (XRD-DIC, for short). As an example of using XRD-DIC, residual strain values along the central line in a Mg AZ31B alloy bar after 3-point bending are calculated by using both XRD-DIC and the conventional 'caking' with fitting procedures. Comparison of the results for strain values in different azimuthal angles demonstrates excellent agreement between the two methods. The principal strains and directions are calculated using multiple direction strain data, leading to full in-plane strain evaluation. It is therefore concluded that XRD-DIC provides a reliable and robust method for strain evaluation from 2D powder diffraction data. The XRD-DIC approach simplifies the analysis process by skipping 2D to 1D conversion, and opens new possibilities for robust 2D powder diffraction data analysis for full in-plane strain evaluation.
