Microstructural characterization of arc-melted and directionally solidified near-eutectic molybdenum–silicon–boron alloys

In situ Observation of Ternary Eutectic Growth in a Directionally Solidified Mo–Si–B Alloy Using High‐Energy Synchrotron X‐Rays

“…The average lattice parameters obtained from the in situ HEXRD measurements in Figure 4 are shown in Table 1 and compared with recent experiments on DSed and as‐cast Mo–17.5Si–8B. [ 33 ] The lattice parameter obtained recently at room temperature correlate quite well, whereas the slight differences may origin from different solidification velocities during solidification caused by the two different processing techniques. The higher lattice parameters obtained during the present in situ experiments are higher since they were taken from sample areas within the liquid–solid interface or from the already solidified crystals just below the melting point.…”

“…The diffraction rings were obtained within the liquid phase, the liquid-solid interphase and the solidified eutectic crystals by scanning multiple times through the observation volume of interest. It was found that: 1) During the liquid-solid transition, all three eutectic phases simultaneously form out of the solidifying liquid phase; 2) Independently from the fraction of the liquid phase that is present in the actually observed sample volume, the Mo SS , [33] showing preferential growth of the ternary eutectic of <001>Mo ss // <001>Mo 3 Si//<100]Mo 5 SiB 2 along the solidification direction.…”

“…A morphologically stable liquid-solid interface is formed in the coupled zone, which has slightly shifted toward the Mo SS phase with the highest melting point. [19,30,33] Hence, the liquid-solid interface is kept at a low curvature of cellular growth and with a low perturbation of local undercooling, so that the eutectic phases grow in a stable manner parallel to the direction of the unidirectional temperature gradient.…”

“…In combination with the SEM-BSE images (Figure 2), the eutectic cells have typical diameters between 10 and 50 μm and are elongated well over 100-150 μm which is in absolute with our recent investigations. [33] Figure 6 shows the pole figures of the longitudinal section of the DSed alloy Mo-17.5Si-8B. Please note that the color scaling is different for the three sets of pole figures.…”

“…The Mo 5 SiB 2 phase grew preferentially in the <100] direction with the {001} planes parallel to the growth direction, which is consistent with the microstructure reported by Uemura et al [35,36] The eutectic phases had the preferential growth of <001>Mo ss //<001>Mo 3 Si//<100]Mo 5 SiB 2 along the temperature gradient and the result agrees with texture recently evaluated. [33] In addition, the pole figures calculated from the texture analysis of the HEXRD data are shown in Figure 7. For better comparability, the same orientations were chosen as for the pole figures obtained by EBSD.…”