Solidification of Ni-Re Peritectic Alloys

Differential thermal analysis (DTA) and microstructural and microprobe measurements of DTA and as-cast Ni-Re alloys with compositions between 0.20 and 0.44 mass fraction Re provide information to resolve differences in previously published Ni-Re phase diagrams. This investigation determines that the peritectic invariant between liquid, Re-rich hexagonal close packed and Ni-rich face center cubic phases, L + HCP → FCC, occurs at 1561.1 °C ± 3.4 °C (1σ) with compositions of liquid, FCC and HCP phases of 0.283 ± 0.036, 0.436 ± 0.026, and 0.828 ± 0.037 mass fraction Re, respectively. Analysis of the microsegregation in FCC alloys yields a partition coefficient for solidification, k = 1.54 ± 0.09 (mass frac./mass frac.). A small deviation from Scheil behavior due to dendrite tip kinetics is documented in as-cast samples. No evidence of an intermetallic phase is observed.

Analysis of 3D elemental mapping artefacts in biological specimens using Monte Carlo simulation

In this paper, we present Monte Carlo simulation results demonstrating the feasibility of using the focused ion beam based X-ray microanalysis technique (FIB-EDS) for the 3D elemental analysis of biological samples. In this study, we used a marine diatom Thalassiosira pseudonana as our model organism and NISTMonte for the Monte Carlo simulations. We explored several beam energies commonly used for the X-ray microanalysis to examine their effects on the resulting 3D elemental volume of the model organism. We also performed a preliminary study on the sensitivity of X-ray analysis for detecting nanoparticles in the model. For the conditions considered in this work, we show that the X-ray mapping performed using the 5 keV beam energy results in 3D elemental distributions that closely reflect the elemental distributions in the original model. At 5 keV, the depth resolution of the X-ray maps is about 250 nm for the model organism. We also show that the nanoparticles that are 50 nm in diameter or greater are easily located. Although much work is still needed in generating more accurate biological models and simulating experimental conditions relevant to these samples, our results indicate that FIB-EDS is a promising technique for the 3D elemental analysis of some biological specimens.