Creep-deformation behavior of (Mo0.85Nb0.15)Si2 lamellar-structured C40/C11b two-phase crystals

Abstract

The creep-deformation behavior of (Mo0.85Nb0.15)Si2 crystals that were composed of C40 and C11b two-phases with an oriented lamellar microstructure was examined over 1200–1400 °C under compression. The creep behavior of the crystals varied greatly depending on the orientation of the loading axis with respect to the lamellar interfaces. The steady-state creep strain rate (SSCR) when the loading orientation was parallel to the lamellar interfaces (0°-orientation) was approximately 2 orders of magnitude lower than that when the loading orientation was inclined by 45° (45°-orientation). Creep tests were performed also with single crystals of C40-single-phase (Mo0.85Nb0.15)Si2, and proved that the C40-phase effectively acts as a strengthening phase in the creep behavior of the C40/C11b duplex-phase crystals. The variant-1-type C11b phase grains, which have a loading orientation parallel to [001], were also found to act as an effective strengthening component. The SSCR of the 0°-orientation was succeeded to be further decreased by controlling the lamellar microstructure via the addition of Cr. The SSCR of the 1 at.%-Cr-added lamellar-structured crystal under 300 MPa in the 0°-orientation was approximately a third of that of the non-added ternary crystal.