Experimental assessment of the microstructure evolution and liquidus projection in the Mo-rich Mo–Si–B system

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

“…With respect to experimental scatter, the volume fractions of the ternary eutectic are consistent with previous literature findings [17,34] and agree very well with the lever rule and volume fractions expected for the ternary eutectic point in the Mo-rich Mo-Si-B system located between 16-18 at% Si and 7-8 at% B. [12,17] It has to be noted here, that the FlexiDS device uses two pyrometers for process control during directionally growth. [24] However, the positions are fixed within the induction coil (liquid zone) and at 10 mm above the coil and are, thus, not linked to the coordinate system of the positioning stage that moves the whole device up and down relative to the synchrotron X-ray beam.…”

“…The Mo–17.5Si–8B master alloy was slightly hypereutectic showing very few primary Mo 5 SiB 2 phase regions surrounded by a binary Mo SS –Mo 5 SiB 2 eutectic. [ 17 ] Differences in the temperature gradient, degree of constitutional undercooling, and the growth velocity during the DS process have altered the established liquidus line, [ 12 ] leading to a fully eutectic growth. The liquidus‐surface asymmetry of the Mo–Si–B system at the ternary eutectic point regarding the Mo SS , Mo 3 Si, and Mo 5 SiB 2 phases also resulted in more‐complex solidification behavior of eutectic Mo–Si–B alloys.…”

“…The different slopes of the primary solidification surfaces of the phases will therefore have an influence on the coupled zone of the ternary eutectic growth. [12,30] The complex and dynamic phase transition during DS and growth of the ternary eutectic is the focus of the present in situ study using high-energy synchrotron radiation. According to Kurz and Fisher, [19] a large temperature gradient and a slow growth velocity promotes a stable growth of eutectic compositions.…”

“…Thus, a holistic approach considering the alloy composition (affecting the phase distribution and volume fraction of phases) and the alloys microstructure has to be pursued to achieve the desired mechanical and oxidation properties to tailor alloys for specific applications. [4] Hence, different manufacturing strategies have been developed over the years to produce various types of Mo-Si-B alloys including powder metallurgy (PM), with powders produced either via gas atomization (GA) [5][6][7] or mechanical alloying (MA), [8][9][10] ingot metallurgy (IM), [11,12] directional solidification (DS), [13][14][15][16][17] and very recently additive manufacturing (AM). [18] DS offers the possibility to directly control the growth morphology of the microstructure basically by two parameters: the DOI: 10.1002/adem.202100111 Herein, synchrotron-generated high-energy X-ray is used to study growth behavior at the liquid-solid transition of multicomponent alloys during in situ directional solidification experiments at Deutsche Elektronen-Synchrotron (DESY), Hamburg, Germany.…”

“…Thus, a holistic approach considering the alloy composition (affecting the phase distribution and volume fraction of phases) and the alloys microstructure has to be pursued to achieve the desired mechanical and oxidation properties to tailor alloys for specific applications. [ 4 ] Hence, different manufacturing strategies have been developed over the years to produce various types of Mo–Si–B alloys including powder metallurgy (PM), with powders produced either via gas atomization (GA) [ 5–7 ] or mechanical alloying (MA), [ 8–10 ] ingot metallurgy (IM), [ 11,12 ] directional solidification (DS), [ 13–17 ] and very recently additive manufacturing (AM). [ 18 ]…”