Crystallographic characters of {11¯22} twin-twin junctions in titanium

Abstract

{112 ̅ 2} contraction twins that are commonly activated in α-titanium interact to each other and form three types of twin-twin junctions (𝐶 𝑖,𝑗+1 𝐼 , 𝐶 𝑖,𝑗+2 𝐼 , 𝐶 𝑖,𝑗+3 𝐼 TTJs) corresponding to the crystallography of six twin variants 𝐶 𝑖 𝐼 (i = 1,2, … , 6). We detected 243 {112 ̅ 2} TTJs in rolled pure α-titanium sheets. Electron backscatter diffraction analysis reveals that 𝐶 𝑖,𝑗+1 𝐼 TTJs are profuse, 79.8% among three types while 𝐶 𝑖,𝑗+2 𝐼 , and 𝐶 𝑖,𝑗+3 𝐼TTJs take up 17.7 and 2.5%. Twin transmission does not occur. Consequently, boundaries associated with twin-twin interactions block twin propagation and influence twin growth. We explain structural features of TTJs according to the Schmid factor analysis and the reaction mechanism of twinning dislocations. The knowledge regarding TTJs provides insight for improving the predictive capability of meso/macro-scale crystal plasticity models for hexagonal metals.

Resolving intragranular stress fields in plastically deformed titanium using point-focused high-energy diffraction microscopy

“…The activation of both plastic slip and deformation twinning is predicted using a critical resolved shear stress (CRSS) criterion that states that a specific plastic deformation mode will initiate when its unique CRSS value is exceeded: This is known as Schmid's law. For hcp materials, reports showing a breakdown of Schmid's law called non-Schmid behavior are prolific (e.g., [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]), with potentially both atomic-scale and microscale origins. At the atomic scale, conventional Schmid's law does not account for sensitivities to the full 3D stress state (i.e., beyond the RSS) in cases where non-glide stress components influence non-planar dislocation core structures.…”

Strain Accommodations among Twin Variants in Ti and Mg

“…The latter one, also named as the apparent SF, is more perceptive, because it plots the loading domain for a specific twin variant with all the possible SFs into an IPF, which is associated with a crystallographic coordinate system of parent grain. This method has advantages of calculating the SFs of the multigeneration of twinning [9][10][11]. The normalized SF, defined as the ratio of each SF to the highest SF, is also adopted in cases that the absolute values of SFs for most twin variants are relatively low due to grain orientation [12,13].…”

“…Later, a quantitative expression of strain accommodation in terms of displacement gradient accommodation (DGA) was reported by Ando et al [30], Martin et al [31] and Jonas et al [32], independently. The DGA calculation and its general form has been extensively used in interactions of twin-twin and twin-slip in both experiment analyses [10,29,33] and theoretical calculations [34].…”

Secondary twin variant selection in four types of double twins in titanium

“…The prevailed secondary twin variant is corresponding to the variant with relative high SFs in most of the primary loading domain. By comparing the SFs with the experiments [21],…”

“…Tension twinning introduces a tensile strain and compression twinning generates a compressive strain along the c-axis of the crystal. {10 1 ̅ 2}< 1 ̅ 011> tension twinning and {11 2 ̅ 2}<11 23 ̅̅̅ > compression twinning are commonly observed in α-titanium at room temperature [19][20][21] and are referred to as T i I and C i I , respectively, where the subscript represents variants from 1 to 6.…”