Nucleation and growth of {101¯1} compression twin in Mg single crystals. (November 2022)

• Record Type: Journal Article
• Authors: Li, Xin-Yao; Guo, Ya-Fang; Mao, Yong; Tang, Xiao-Zhi
• Is Part Of: International journal of plasticity. Volume 158(2022)
• Publication Date: 2022-11
• Subjects: Compression twin -- Nucleation -- 〈a〉 dislocation -- Molecular dynamics -- Mg; Plasticity -- Periodicals; Plasticité -- Périodiques; Plasticity; Periodicals; 620.11233
• DOI: 10.1016/j.ijplas.2022.103437
• Languages: English
• ISSNs: 0749-6419

Abstract

Highlights: A novel nucleation mechanism of { 10 1 ¯ 1 } twin associated with the cross-slip of 〈a〉 dislocation is proposed based on MD simulations. A 4-layer height { 10 1 ¯ 1 } twin embryo forms via 〈a〉 dislocation slip in pyramidal plane combined with twinning shear in 〈 10 1 ¯ 2 〉 direction. The formation of basal SFs in a twin embryo can greatly reduce the required atomic shuffling and facilitate the development of a twin embryo. The { 10 1 ¯ 1 } twinning shear is consistent with the irrational shear of b2 TD, which is not influenced by the existence of basal SFs. Abstract: The { 10 1 ¯ 1 } compression twin is more commonly observed under a -axis tension rather than c -axis compression in hexagonal close-packed (hcp) Mg single crystals both in experiments and atomistic simulations. In this work, molecular dynamics simulations are applied to investigate the nucleation and growth of { 10 1 ¯ 1 } twin in Mg single crystal, which is crucial for a comprehensive understanding of the plasticity of hcp metals. A { 10 1 ¯ 1 } twin embryo with 4-layer height is found to be naturally nucleated at the free surface via 〈a〉 dislocation slip in Mg single crystal. The nucleation of the { 10 1 ¯ 1 } twin embryo involves the cross-slip of the nucleated prismatic 〈a〉 dislocation onto pyramidal { 10 1 ¯ 1 } plane, which is achieved by slip of 〈a〉 dislocation and shear along the 〈 10 1 ¯ 2 〉 direction. Basal stacking faults (SFs) forms in twin embryo and grows with the migration of { 10 1 ¯ 1 } twin boundary. The formation of basal SFs in { 10 1 ¯ 1 } twin embryo can greatly reduce the required atomic shuffling in 〈 1 2 ¯ 10 〉 direction, thus facilitate the development of a { 10 1 ¯ 1 } twin embryo. The basal SFs inside { 10 1 ¯ 1 } twin are anomalous SFs without dislocation activities involved, thus the { 10 1 ¯ 1 } twinning shear is not influenced by the existence of basal SFs, which is consistent with the irrational shear of 2-layer twinning dislocation.