Deformation mechanisms of basal slip, twinning and non-basal slips in Mg–Y alloy by micropillar compression

Abstract

Micropillar compression technique was employed to study the microscale deformation mechanisms of basal slip, twinning and non-basal slips at selected grains in a Mg-2 wt.% Y alloy. The results suggest a critical resolved shear stress (τCRSS) for basal slip 12.5 ± 1.7 MPa, and for twin nucleation and twin growth 38.5 ± 1.2 MPa and 33.8 ± 0.7 MPa, respectively. The higher values compared to those in pure Mg suggests a more balanced deformation in Mg alloy with Y addition. The activation of <c+a> dislocations in the twinned orientation is highlighted, which leads to strong work hardening in twinned favorable orientation [101‾0]. In addition, at prismatic-slip favorable orientation [112‾0], a twinning-to-prismatic slip transition was observed when elevating temperature from 25 °C to 100 °C and 250 °C. Specially at 250 °C, twinning was completely prohibited, and pure prismatic slip was triggered. The measured τCRSS for prismatic slip at 250 °C was 39.7 ± 0.3 MPa, much higher than that for pure Mg at the same temperature. Finally, at pyramidal-slip favorable orientation [0001], an abnormal strengthening was observed at 100 °C and 250 °C due to activation of pyramidal slips. Decompositions of <c+a> dislocations and Y segregation at stacking faults are the main mechanisms leading to the high-temperature strengthening in Mg–Y alloy.