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 b1 variants and trunk connections of a hitherto unreported phase designated b2 in this work. The b2 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 h1120ib2 //[0001]a and f1 1 0 0gb2 //f1100ga. The b2 phase is metastable, but it is induced to form and is stabilized by the stress fields of the two adjacent b1 particles. The b2 particle either has a substructure of ð0 0 0 1Þb2 planar faults, or is free of the planar faults, depending on whether the two b1 precipitates connecting it are of the same variant or not. A minor fraction of bamboos also have leaf-like b1 particles attached to the connection point of the bamboo trunks. The formation of the leaf-like particles is analyzed by nteraction energy calculation and phase-field simulation.