Deformation Behavior of α2-Lamellae in Fully Lamellar Ti-48Al-2Mn-2Nb at Room Temperature

Slip Transfer Across Hetero-Interfaces in Two-Phase Titanium Aluminum Intermetallics

“…These yield stresses are almost twice as high as those recorded for the A-type orientations. [22] These mechanical characteristics of the PST-TiAl are consistent with previous reports and confirm the anisotropic behavior for the two different types of hard orientations. [3,10] B. TEM Observations At all levels of plastic straining normal to the lamellar interfaces, the c-phase lamellae accommodated most strain in the PST-TiAl compression coupons by activating dislocation glide and mechanical twinning systems experiencing high-resolved shear stresses, which are associated with Burgers vectors and twinning shears with components normal to the interfaces, whereas the a 2 lamealle appeared relatively defect free in comparison.…”

“…Observations related to the c-phase deformation have been reported previously. [22] In concert with previous work, we did not observe a h i-dislocations with b ¼ a h i after N-orientation loading of PST-TiAl. [3,10] After 1 pct of nominal plastic compressive strain, the TEM observations the a 2 lamellae remained essentially defect free with limited and localized deformation involving short segments of hook-shaped c-component dislocations, typically in the vicinity of stress concentrations associated with translamellar mechanical twins in the adjacent c lamellae (e.g., labels A and B in Figure 2).…”

“…Smaller magnitudes of Db are considered energetically more favored, and hence, direct slip transfer is more likely to occur on systems that require smaller Db. [10][11][12][13][14][15][16][17][18][19][21][22][23] Which product slip system will be activated by direct slip transfer depends essentially onto which system a higher shear stress is transferred and on the conservation of Burgers vector. However, generally and locally, the resolved shear stress must exceed the critical resolved shear stress for any activated slip system in the a 2 phase independent of whether slip transfer occurred by direct slip or by activation of local sources.…”

“…Pyramidal slip of c þ a=2 h i dislocations occurred inhomogeneously (i.e., slip on p 2 planes occurs more frequently than on p 1 planes, in slip bands associated with hard mode deformation twins impinging on the lamellar interfaces [also Figure 5]), confirming previous reports. [10,11,15,22,23] The graphics in Figure 4(a) depict the two possible geometries of the two pyramidal systems and the twin shear system across the (111)-lamellar heterophase interface. The p 1 planes 2 " 201 È É have a common traces, namely 1 " 10 ; with the hard mode octahedral slip and twinning planes, 11 " 1 È É ; of the c phase (Figure 4(a)), whereas those of p 2 planes 1 " 211 È É are rotated by 30 deg to those of the 11 " 1 È É planes (Figure 4(b)).…”

“…[9,10,21] Because of the multitude of different types of possible (c/c) and (c/a 2 ) interfaces, it is difficult to assess their precise roles for the mechanical properties of lamellar TiAl. [5,22] It has been speculated that different micro-mechanisms may exist for each individual type of hard mode deformation system and for each type of lamellar interface. [22] In the 0001 f g 11 " 20 and 1 " 100 È É 11 " 20 slip systems involving dislocations with Burgers vectors of the type b = 1/3 11 " 20 ¼ a h i; the a-dislocation slip can be activated with relative ease in Ti 3 Al, whereas the c-component dislocation slip, involving dislocations with Burgers vectors b = 1/3 11 " 26 ¼ 2c þ a h i gliding on first-order pyramidal planes, or p 1 planes 2 " 201 È É…”