Deformation, mechanical properties, and fracture of titanium hydrides

This study investigates the deformation behavior and cracking mechanisms in titanium δ-hydrides through in-situ scanning electron microscopy (SEM) and in-situ electron backscatter diffraction (EBSD) tensile experiments. Two commercially pure titanium specimens were hydrided and then homogenized to have both intergranular and intragranular δ-hydrides, before being deformed to ∼14 % macroscopic tensile strain. Pre-deformation grain orientations and shapes were measured by EBSD and subsequently imported into a crystal plasticity finite element model to simulate the evolution of localized deformation fields and the formation of microcracks within hydrides. In addition, indentation experiments were performed to extract plastic properties of hydrides. Pre-deformation numerical and experimental results indicated that the formation of δ-hydrides, in the absence of external mechanical loads, induces lattice rotations up to 2° near hydride tips as well as at the intersection of intergranular and intragranular hydrides. With applying external mechanical loads, { 11 2 ̅ 2 } < 11 2 ̅ 3 ̅ > compression twins form in the titanium matrix, followed by the formation of secondary { 10 1 ̅ 2 } < 10 1 ̅ 1 ̅ > extension twins within compression twins. The interaction of hydrides with compression twins increase local rotations within hydrides up to 6°. Microcracks were detected in both intragranular and intergranular δ-hydrides, with a higher propensity measured within the former. These microcracks were observed to form at the intersections of compression twins and hydrides, on the crystallographic planes of hydrides. Numerical results confirm that the presence of twins affect the formation of microcracks. • In-situ SEM and in-situ EBSD tensile experiments are conducted to study deformation and fracture of titanium δ-hydrides. • CPFE modeling is used to study the micromechanics of crack initiation. • { 11 2 ̅ 2 } < 11 2 ̅ 3 ̅ > compression twins are observed to form in titanium, followed by secondary { 10 1 ̅ 2 } < 10 1 ̅ 1 ̅ > extension twins. • Interactions between compression twins and hydrides cause large, localized lattice rotations inside hydrides, reaching up to 6°. • Microcracks primarily form inside hydrides at intersections with { 11 2 ̅ 2 } < 11 2 ̅ 3 ̅ > compression twins.