Brittle–ductile transition during creep in nearly and fully lamellar high-Nb TiAl alloys

Abstract Nearly lamellar Ti 44Al 6Nb 1Cr 2V alloy (at.%) and fully lamellar Ti 47Al 6Nb-0.1C alloy were crept in air at 740–820 °C under 276 MPa, in order to study the brittle–ductile transition during creep (BDTC). The results show that the temperatures of BDTC are determined to be 760–780 °C in Ti 44Al 6Nb 1Cr 2V alloy and 780–800 °C in Ti 47Al 6Nb-0.1C alloy. During creep below the temperatures of BDTC, two alloys exhibit small creep strain and long creep life; the colony boundary sliding, the formation of voids and cracks contribute to main creep strain. During creep above the temperatures of BDTC, two alloys exhibit large creep strain and short creep life; the plastic deformation of lamellar structures contribute to main creep strain. The BDTC of nearly/fully lamellar TiAl alloys are mainly determined by the slip system in α2 lamellae. The significant increasing of creep strain reduces microstructural stability, and thus reduces creep properties.