The Interaction Between $$ \{ 10\bar{1}2\} $$ { 10 1
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IN magnesium and magnesium alloys with hexagonal close-packed structure, deformation twinning is an important deformation mode due to the limited available slip systems, especially at room temperature.[1–3] However, the activation of twinning brings about a serious tension-compression asymmetry of yield strength due to the unidirectional nature of the twinning.[4–7] Besides, the twins are considered as the origin of crack initiation,[8,9] which indicates that the occurrence of twinning has a detrimental influence on the formability of magnesium alloys. Therefore, restricting the activation of twinning, especially the f1012g twinning, is one of the available methods for the weakening of asymmetry and the improvement of formability.[10]
JIANBO SHAO, TAO CHEN, and CHUMING LIU are with the School of Materials Science and Engineering, Central South University, Changsha 410083, China; ZHIYONG CHEN is with the School of Materials Science and Engineering, Central South University and also with the School of Physics and Technology, Xinjiang University, Urumqi 830046, China. Contact e-mail: [email protected] Manuscript submitted June 24, 2020. accepted October 30, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Recently, magnesium alloys containing the LPSO phase have attracted great attention due to their excellent mechanical properties at room and elevated temperatures.[11–14] Different types of LPSO phases have been extensively observed in Mg-TM-RE (TM = Zn, Cu, Ni, Co; RE = Y, Dy, Ho, Gd, Tb, Er, Tm) alloys.[15,16] 14H and 18R are the most common types of LPSO phases for Mg-Zn-RE systems.[17] Nie and Zhu et al.[18,19] discovered that 14H and 18R LPSO phases have the same structural unit with ABCA stacking sequence. 14H LPSO phase contains two structural units and the two adjacent units are separated by three {0001} planes of magnesium matrix.[18] As for 18R, three structural units are separated by two {0001} planes of magnesium.[19] In wrought magnesium alloys, LPSO phases precipitate at the grain boundary in the form of bulk shape or along the basal plane of the matrix in the plate-like shape during the casting and heat treatments.[20] The inhibition of the intragranular LPSO phase on f1012g twinning is considered as an important strengthening mechanism.[21–23] As reported by Matsuda et al.,[21] the densely developed LPSO plates remarkably suppress the growth of f1012g twin. Shao et al.[24] found that the LPSO phase with a thickness over 12 nm cannot be twinned, and twin boundary shows great deviation away from the twinning plane when it encounters the
LPSO phase. In addition, the twinning is fully inhibited in the matrix lamella with a thickness smaller than 20 nm.[25] It is widely reported that basically no twins were present in magnesium alloys containing the LPSO phase.[26,27] However, Garces et al.[28] has emphasized that the plastic deformation in magnesium matrix can be still dominated by f10 12g twinning even considering the inhibiting effect of LPSO plates on f10 12g twinning. The thickness and distribu
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