Linear-chain configuration of precipitates in Mg-Nd alloys

The linear-chain distribution of precipitates, resembling the characteristic features of bamboo, in a Mg-3 wt.% Nd alloy, aged at 250 °C for 10 h, has been examined using high-angle annular dark-field scanning transmission electron microscopy. The configuration consists of bamboo trunks of β1 variants and trunk connections of a hitherto unreported phase designated β2 in this work. The β2 phase has a hexagonal lattice (space group P6¯, a = 0.523 nm and c = 0.963 nm), and its orientation relationship with the Mg matrix phase is such that 〈112¯0〉β2//[0 0 0 1]α and {1¯100}β2//{11¯00}α. The β2 phase is metastable, but it is induced to form and is stabilized by the stress fields of the two adjacent β1 particles. The β2 particle either has a substructure of (0001)β2 planar faults, or is free of the planar faults, depending on whether the two β1 precipitates connecting it are of the same variant or not. A minor fraction of bamboos also have leaf-like β1 particles attached to the connection point of the bamboo trunks. The formation of the leaf-like particles is analyzed by interaction energy calculation and phase-field simulation.