Microstructural observations revealed that, after homogenization at 1000 to 1360C, both binary and B-doped Ni3Al alloys without pre-strain exhibited annealing twins only on the Al-rich side of stoichiometry below 1200C. Above 1200C, annealing twinning could also take place on the Ni-rich side of stoichiometry in the binary alloy system, but no twins were found in the γ+γ’ 2-phase field. In contrast to the plentiful annealing twins in binary alloys, the addition of B greatly decreased the number of twins. An addition of 0.2at% significantly decreased the frequency of twinning events, and no twins appeared above 1200C. The addition of 0.5at%B removed almost all twins from the microstructure. Annealing twinning was supposed to be completed by 2 processes: including the sweeping of 1/3<211> super-partial dislocations on successive (111) planes, and the simultaneous diffusion of B atoms into the energetically favoured octahedral interstices that were surrounded by six Ni atoms. The B acted as a strong obstacle to the movement of super-partial dislocations, and greatly increased the difficulty of annealing twinning.

Annealing Twinning in Boron-Doped Ni3Al. Wei, F.G., Mishima, Y.: Materials Transactions, 2002, 43[6], 1283-90