Formation and development of C40/C11b lamellar structure in NbSi2/MoSi2 crystals

A (Mo0.85Nb0.15)Si2 crystal with an oriented, lamellar, C40/C11b two-phase microstructure is a promising ultrahigh-temperature (UHT) structural material, but its low room-temperature fracture toughness and low high-temperature strength prevent its practical application. As a possibility to overcome these problems, we first found a development of unique “cross-lamellar microstructure”, by the cooping of Cr and Ir. The cross-lamellar microstructure consists of a rod-like C11b-phase grains that extend along a direction perpendicular to the lamellar interface in addition to the C40/C11b fine lamellae. In this study, the effectiveness of the cross-lamellar microstructure for improving the high-temperature creep deformation property, being the most essential for UHT materials, was examined by using the oriented crystals. The creep rate significantly reduced along a loading orientation parallel to the lamellar interface. Furthermore, the degradation in creep strength for other loading orientation that is not parallel to the lamellar interface, which has been a serious problem up to now, was also suppressed. The results demonstrated that the simultaneous improvement of high-temperature creep strength and room temperature fracture toughness can be first accomplished by the development of unique cross-lamellar microstructure, which opens a potential avenue for the development of novel UHT materials as alternatives to existing Ni-based superalloys.

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First-principles investigation of phase stability and effects on ductility for MoSi₂ alloyed by Al and Nb

Wang

et al. 2023

Int. J. Mod. Phys. B

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In this paper, site preference, phase stability and elastic parameters of MoSi2 for Al and Nb addition are studied using first-principles calculation. The results show that alloying elements can cause MoSi2 to change from C11b to C40 phase and the phase transition is due to the activated 1/2[[Formula: see text]11](110) slip system for C11b. [Formula: see text] ratio reveals that the ductility is enhanced after phase transition. Ductile factor [Formula: see text] based on competitive processes between micro-crack opening and dislocations emission is defined to assess the ductility of MoSi2. Interestingly, the increased ductility is due to the activated dislocation emission but suppressed crack propagation. Finally, charge density and DOS indicate that the improved ductility is due to the weakened Mo-4d and Si-3p covalent interactions.

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Formation and development of C40/C11b lamellar structure in NbSi2/MoSi2 crystals

Cited by 4 publications

References 13 publications

Development of unique cross-lamellar microstructure, resulting in the drastic increase in fracture toughness in Cr/Ir-codoped (Mo 0.85 Nb 0.15 )Si 2 crystals

Development of unique cross-lamellar microstructure, resulting in the drastic increase in fracture toughness in Cr/Ir-codoped (Mo 0.85 Nb 0.15 )Si 2 crystals

Outstanding compressive creep strength in Cr/Ir-codoped (Mo0.85Nb0.15)Si2 crystals with the unique cross-lamellar microstructure

First-principles investigation of phase stability and effects on ductility for MoSi₂ alloyed by Al and Nb

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Formation and development of C40/C11b lamellar structure in NbSi2/MoSi2 crystals

Cited by 4 publications

References 13 publications

Development of unique cross-lamellar microstructure, resulting in the drastic increase in fracture toughness in Cr/Ir-codoped (Mo 0.85 Nb 0.15 )Si 2 crystals

Development of unique cross-lamellar microstructure, resulting in the drastic increase in fracture toughness in Cr/Ir-codoped (Mo 0.85 Nb 0.15 )Si 2 crystals

Outstanding compressive creep strength in Cr/Ir-codoped (Mo0.85Nb0.15)Si2 crystals with the unique cross-lamellar microstructure

First-principles investigation of phase stability and effects on ductility for MoSi2 alloyed by Al and Nb

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First-principles investigation of phase stability and effects on ductility for MoSi₂ alloyed by Al and Nb