Brittle‐to‐ductile transition temperature and its controlling mechanism in ti‐47Al‐2Mn‐2Nb alloy

Abstract

Brittle‐to‐ductile transition (BDT) temperature (T_BD) has been evaluated according to temperature dependence of tensile properties under different strain rates from 10^‐5 to 10^‐1 s^‐1 in a two‐phase Ti‐47Al‐2Mn‐2Nb alloy with near lamellar microstructure. Tensile fractography was observed using a scanning electron microscope while deformation substructures were investigated using a transmission electron microscope. It was found that T_BD, when defined as the temperature corresponding to 7.5% elongation, increases from 1023K to more than 1373K, the strain rate increases from 10^‐5 to 10^‐1 s^‐1. Based on the strain rate dependence of T_BD (and using the Zener‐Hollomon factor) an apparent activation energy of 324kJ/mol was obtained, which is approximate to the self‐ and inter‐diffusion activation energies in the y‐TiAl phase. Transgranular fracture and dimple fracture were found to dominate in fracture surfaces below and above T_Bd, respectively. Furthermore, the most popular 1/2<110] ordinary dislocations were found to begin to climb around T_BD. All this evidence, as well as a theoretical calculation using the Nabarro Model, add up to a conclusion that the BDT of the alloy is controlled by dislocation climbing.

Key words:

• TiAl alloy
• tensile properties
• brittle‐to‐ductile transition temperature
• strain rate

Notes

Invited paper

Correspondence addressee