Ordered ? phases in a 4Zr–4Nb-containing TiAl-based alloy
A considerable amount of B2 phase with a cellular morphology is retained in a 4Zr–4Nb-containing TiAl-based alloy. Heterogeneous precipitation of ordered ? from B2 is found to occur readily after HIPping: B2 ? ? with the B82-structure in cell regions and B2 ? ? with the D88-structure in cell-wall regions. Congregated D88-? domains and particles form as a network surrounding the well-developed B82-? cells. The heterogeneous formation of different ? variants is caused by a heterogeneous distribution of Zr + Nb elements across B2, which plays an important role in stabilizing vacancies and promotes the formation of D88-?. Fine D88-? particles are also observed to precipitate from the B82-? cell matrix after ageing at 700 °C for 1000 h, showing a transformation path of ? ? B2 ? B82-? ? D88-? for the aged cells. The heterogeneous formation of a D88-? network and B82-? cells is found to be detrimental to ductility and fatigue strength. A very brittle fine-grained TiAl alloy is produced as a result.
Z.W. Huang aEmail:z.w.huang@bham.ac.uk
[a]School of Materials Science; Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, PR China;[b]Department of Metallurgy; Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
