High temperature mechanical properties of vanadium alloyed γ base titanium-aluminides

Plastic-flow and microstructure evolution during hot deformation of a gamma titanium aluminide alloy

“…This structure is similar to the globularized microstructures obtained in fully lamellar, two-phase (␥ ϩ ␣ 2 ) titanium aluminides upon extensive hot working. [1,12,15] The high level of ductility obtained at 1350 ЊC and 0.1 s Ϫ1 can thus be attributed to the following: (1) at low strain levels, the dynamic precipitation of coherent ␣ laths provides an efficient means of energy dissipation generally known as transformation toughening; (2) at intermediate strain levels, contiguous, intragranular deformation and rotation of the ␥ ϩ ␣ grains with little or no grain boundary sliding prevents nucleation and growth of cavities; and (3) at high strain levels, dynamic globularization of the fibrous structure delays the onset of cavitation or cracking. Eventually, the specimen fails by delamination cracks formed along the fibrous interfaces.…”

“…The wrought microstructure enables dynamic recrystallization to commence at low strain levels during tension tests and thereby prevents/retards the growth of wedge cracks as well as intergranular cavities, resulting in improvements in ductility. The influence of the gamma grain size on ductility of gamma titanium aluminides has been investigated in detail by several researchers, including Imayev et al, [13] Nobuki et al, [15] and Tsuzuku and Sato. [17] Indeed, Imayev et al have demonstrated that an alloy containing 90 pct ␥ and 10 pct ␣ 2 can be rendered superplastic with fracture elongations higher than 300 pct at 900 ЊC and ϳ0.001 s Ϫ1 if the gamma grain size can be refined to ≤2 m.…”

“…However, when the grain size is smaller (i.e., ≤10 m), m for relatively low strain rates increases dramatically with grain refinement. [13][14][15][16][17][18] Plots of log p vs reciprocal temperature shown in linear plots in Figure 4(a) varies from 3350 to 5500 K depending on the strain rate. An apparent activation energy, Q, can be calculated as Q ϭ 2.303 RS/m, where R is the universal gas constant.…”

“…Tensile deformation and fracture of near gamma titanium aluminide alloys at elevated temperatures have been investigated extensively. [1,2,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] These investigations can be broadly classified into two groups: (a) studies devoted to the evaluation of tensile properties of different alloys containing a variety of microstructures under potential service conditions, i.e., at temperatures below 1000 ЊC and at a fixed strain rate of ϳ10 Ϫ4 s Ϫ1 ; [4][5][6][7][8][9][10][11] and (b) studies dealing with superplasticity and related phenomena in wrought alloys containing fine, equiaxed aggregates of ␥, ␣ 2 , and ␤ 2 phases. [12][13][14][15][16][17][18] Accordingly, the latter group of studies includes tension tests conducted at temperatures ranging from 900 ЊC to 1250 ЊC and strain rates varying from 10 Ϫ5 to 10 Ϫ2 s Ϫ1 .…”

“…[12][13][14][15][16][17][18] Accordingly, the latter group of studies includes tension tests conducted at temperatures ranging from 900 ЊC to 1250 ЊC and strain rates varying from 10 Ϫ5 to 10 Ϫ2 s Ϫ1 . In contrast, only a few investigations [2,15,19,20] have focused on the tensile flow and fracture of gamma titanium aluminides under conventional, hot working conditions, namely, at high temperatures and high strain rates.…”