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Matrix Transformation in Boron Containing High-Temperature Co–Re–Cr Alloys
Pavel Strunz,Debashis Mukherji,Přemysl Beran,Ralph Gilles,Lukas Karge,Michael Hofmann,Markus Hoelzel,Joachim Rösler,Gergely Farkas 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.5
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect ofboron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr 2 Re 3 type) phases were measuredat ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diff raction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobaltand to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that thetransformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperaturedid not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm ofboron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which bindshcp-stabilizing elements (Cr and Re). Moreover, borides were identifi ed in alloys with high boron content.