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

Abstract

The high-temperature mechanical properties of directionally solidified (DS) ingots of binary and some ternary MoSi2/Mo5Si3 eutectic composites with a script lamellar structure have been investigated as a function of loading axis orientation and growth rate in a temperature range from 900 to 1500°C. These DS ingots are plastically deformed above 1000 and 1100 °C when the compression axis orientations are parallel to [10]MoSi2 (nearly parallel to the growth direction) and [001]MoSi2, respectively. [10]MoSi2-oriented DS eutectic composites are strengthened so much by forming a script lamellar microstructure and they exhibit yield stress values several times higher than those of MoSi2 single crystals of the corresponding orientation. The yield stress values increase with the decrease in the average thickness of MoSi2 phase in the script lamellar structure, indicating that microstructure refinement is effective in obtaining better high-temperature strength of these DS eutectic composites. Among the four ternary alloying elements tested (V, Nb, Ta and W), Ta is found to be the most effective in obtaining higher yield strength at 1400 °C.

Creation of High-Temperature Heat-Resistant Alloys Based on Refractory Matrices and Natural Composites

“…Depending on the composition, the structure of molybdenum alloys obtained by the above methods [55-57, 59, 60] In the directional solidification of eutectics of the MoSi 2 -Mo 5 Si 3 system, it was possible to obtain a lamellar microstructure of silicide phases located in the direction of heat removal [57,58].…”

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

“…MoSi2-based alloys have been considered as promising candidates for high-temperature structural application owing to its high melting point, good oxidation resistance, relatively low density [1][2][3][4]. Directionally-solidified MoSi2/Mo5Si3 spontaneous composite is of particular interest because of its better creep property than other MoSi2-based composites [5] [6]. However, its fracture toughness at room temperature is still insufficient for practical application.…”

“…However, its fracture toughness at room temperature is still insufficient for practical application. As this shortage is believed to be overcome by microstructure refinement and morphology control [6] [7], it is quite important to elucidate the formation mechanism of the MoSi2/Mo5Si3 microstructure, which has an exotic eutectic pattern, the so-called script lamellar pattern (Fig. 1a).…”

“…The PF model should also be able to reproduce the spacing transition phenomena observed in the experiment and predicted by theory [13]. Secondly, the two-dimension model is extended to a three-dimension one in order to output microstructure images comparable to experimental results in [6]. Then, a nucleation functionality is incorporated into this eutectic model.…”

“…Comparison of microstructure between phase-field simulation (upper row: 3D bird'-eye view, center row: horizontal cross-section, red:MoSi2, blue:Mo5Si3) results and experimental results (bottom row, dark:MoSi2, grey:Mo5Si3 after Matsunoshita et al[6])) for three growth rates of 10 mm·h -1 (left) , 50 mm·h -1 (center) and 100 mm·h -1 (right).…”