Phase equilibria and microstructural control of gamma TiAl based alloys

On the massive phase transformation regime in TiAl alloys: The alloying effect on massive/lamellar competition

“…3b. This effect of Nb on formation of massive g was observed earlier in Tie48Al based alloys by Takeyama et al [28]. By substituting 4%Nb with 4%Ta, the amount of massive g was increased to about 70 vol% (Fig.…”

Alloy design concepts for refined gamma titanium aluminide based alloys

“…As has been shown recently, one of the most promising alloying element in this respect is niobium, which can be dissolved in both the g and a 2 phases in an amount of about 10 at% [3,7,18,29e35]. Niobium additions increase considerably the activation energy of diffusion in the g and a 2 (a) phases [36,37] and make the a 0 g transformation sluggish [18]. It is also important that niobium additions lead to an improved corrosion resistance and high-temperature strength of g þ a 2 alloys and facilitate deformation twinning due to a decrease of the SISF (superlattice intrinsic stacking fault) energy in the g phase, which apparently increases the ductility of the alloys [3,34,36].…”

Creep behaviour and related high temperature microstructural stability of Ti–46Al–9Nb sheet material

“…Particles at colony boundaries that appear bright represent most likely the Ti and Nb-rich b/B2 phase, which was formed during dissolution of a 2 -lamellae. The appearance of b/B2 phase is not surprising, since it is well established that alloying with Nb extends the b/B2 phase field to higher Al concentrations [17,[34][35][36]. Although the amount of b/B2 phase at colony boundaries is rather small, its influence on the overall creep behaviour remains an open question.…”