Growth of Crystals and Formation of C40/C11_b Lamellar Structure in (Mo_0.85Nb_0.15)Si₂

Abstract

In this paper, high-quality single crystals of (Mo0.85Nb0.15)Si2, around 8 mm in diameter and 90 mm in length, have been grown by optical heating floating zone method. Effects of chemical composition and growth rate on forming C40 structured single crystal were studied. Aligned C40/C11b lamellar structured can be formed in the as-grown crystals after post annealing at temperatures between 1473 and 1873 K. Chemical composition as well as annealing temperature are found to be two important factors to form C11b lamellae in the C40 matrix. Fully C40/C11b lamellar structure was formed after annealing at 1873 K in the present work. The aligned C40 and C11b lamellae follow a crystallographic orientation relationship of (0001)C40//(110)C11b. Dislocations were observed in some coarse C11b lamellae but never in C40 lamellae of the duplex structure. This is probably due to accumulation of misfit strain during formation of C40/C11b lamellae.

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

“…The FZ method can be used to avoid the peritectic reaction and ensure the growth of a single crystal; however, the growth conditions should be carefully controlled according to the alloys' compositions. When the alloy was composed of (Mo 0.85 Nb 0.15 )Si 2 , C40 single-phase single crystals were obtained at a growth rate of 2.5 mm/h; on the other hand, when the alloy was composed of (Mo 0.90 Nb 0.10 )Si 2 , single crystals were not obtained even at the same growth rate [4,8].…”