Deformation and fracture mechanisms of Ti-55531 alloy with a bimodal microstructure under the pre-tension plus torsion composite loading
Feiyu Huang, Chaowen Huang, Hongtao Zeng, Yang Jiang, Tao Wang, Mingpan Wan, Dan Liŭ, JI Sheng-li, Weidong Zeng
Abstract
The deformation and fracture behavior of the Ti-55531 alloy with a bimodal microstructure (BM) under the pre-tension plus torsion composite loading were systematically investigated at room temperature. The results indicate that the pre-tension loading dramatically reduces the subsequent torsional strength of the alloy, while its torsional plasticity is almost not affected. A ( 10 1 ¯ 0 ) prismatic slip is initiated inside the primary equiaxed α (α p ) phase during the pre-tension stage. Subsequently, several dislocation jogs form inside the α p particles due to the crossing of the (0002)[ 1 ¯ 2 1 ¯ 0] basal and ( 1 1 ¯ 01 ) [ 1 ¯ 2 1 ¯ 0] pyramidal slip systems during the torsion deformation stage, which may be a novel deformation mechanism of the Ti-55531 alloy. Moreover, the α p particles are cut by numerous parallel slip bands, resulting in ladder-like structures be formed at the α p /β trans (β transformed microstructure) interface, which can promote microcrack initiation at the α p /β trans interfaces. Furthermore, { 10 1 ¯ 1 } α deformation twins are only detected inside secondary α (α s ) phase just during the subsequent torsion deformation stage. In the main bearing phase, the α p particles elongate along specific directions in different deformation regions due to a change in the maximum shear stress. Thus, the cross-section profile from the surface to the center of the specimens after the pre-tension plus torsion deformation can be divided into three regions: torsion, tension plus torsion, and tension deformation regions. These findings can provide a theoretical basis for understanding the deformation damage of aerospace components under complex loads and optimizing their structural design. • The equiaxed α p particle plays a essential role in the pre-tension or pre-tension plus torsion deformation of the Ti-55531 alloy with a bimodal microstructure. • The pre-tension plus torsion load induces the crossing of (0002)[ 1 ¯ 2 1 ¯ 0] basal and ( 1 1 ¯ 01 ) [ 1 ¯ 2 1 ¯ 0] pyramidal slip systems to form ( 1 1 ¯ 03 ) [ 1 ¯ 2 1 ¯ 0] dislocation jogs. • ( 1 1 ¯ 03 ) [ 1 ¯ 2 1 ¯ 0] dislocation jogs formed inside α p particles leads to local hardening and eventually to microcrack initiation inner α p phases.