Effects of ternary additions on the microstructure and thermal stability of directionally-solidified MoSi2/Mo5Si3 eutectic composites

Abstract

Effects of ternary additions on the microstructure and thermal stability of directionallysolidified MoSi 2 /Mo 5 Si 3 eutectic composites have been studied for twelve different elements (Ti, V, Cr, Fe, Co, Ni, Nb, Ta, W, Ir, B and C) paying special attention to the variation of lattice misfits and interface segregation behavior with ternary additions. Among six elements (type-1: Ti, V, Cr, Nb, Ta and W) with a relatively high solubility in MoSi 2 and Mo 5 Si 3 , Ta and W are found to be beneficial to microstructure refinement. All other six ternary elements (type-2: Fe, Co, Ni, Ir, B and C) with a negligibly low solubility in MoSi 2 and Mo 5 Si 3 exhibit a strong tendency to segregate on MoSi 2 /Mo 5 Si 3 interfaces, resulting in both microstructure refinement and the modification of the interface morphology.

Pattern formation mechanism of directionally-solidified MoSi2/Mo5Si3 eutectic by phase-field simulation

“…It can be claimed that the origin of the interface instability is due to the complex crystal structure for both MoSi2 and Mo5Si3 phases. In a crystallographic analysis [7], MoSi2 and Mo5Si3 have bodycentered tetragonal structures with the types of C11b and D8m, respectively. The ( 0 1 1 ) plane of MoSi2 and (0 0 1) plane of Mo5Si3 are found to be nearly perpendicular to the temperature gradient or growth direction.…”

“…The frequency of nucleation is increased to 50 s -1 . (a-c) the simulated pattern became more discontinuous and intersected; (d) Experimentally observed pattern in MoSi2/Mo5Si3 eutectic alloyed with 0.1 at% Co (after Fujiwara et al [7]).…”

“…To answer the first question, crystallographic analysis and experimental observation should be considered. Based on lattice parameters at the eutectic temperature (1900˚C), as illustrated in Fig.11, the mismatch between the two crystals of MoSi2 and Mo5Si3 can be eliminated by formation of ledgeterrace structure with a set of the atomic arrangement parameters, including the inclination angle θ having a value of 13.9˚ [7]. In the experimental observation by high-resolution TEM (Fig.1b), there is also a ledge-terrace structure at the interface, which has an inclination angle of 13.5˚, almost equal to the analysis result.…”

Plastic deformation of directionally solidified ingots of binary and some ternary MoSi2/Mo5Si3 eutectic composites

“…The loading axis orientations tested are [10] MoSi2 and [001] MoSi2 , which are nearly parallel to and perpendicular to the growth direction of the DS ingots, respectively. [17] Crystallographic orientations of these DS ingots are hereafter referred to those of the MoSi 2 matrix and are indicated with a subscript ‘MoSi 2 ’ unless otherwise stated.…”

“…[17] The data in Table 1 are estimated using Ta L and W L lines instead of Ta M and W M lines that seriously overlapped with Si K line resulting in relatively large measurement errors in our previous results.…”