Formation mechanism of micro/nano-structures through competitive reactions in Mg/Cu super-laminate composites during initial hydrogenation

Formation mechanism of micro/nano-structures through competitive reactions in Mg/Cu super-laminate composites (SLCs) during initial hydrogenation was investigated experimentally. Three types of MgCu2 structures, an open network, a sheathed network and a layer, were observed after initial hydrogenation of Mg/Cu SLCs under the conditions of 573 K, 86.4 ks in H2 atmosphere of 3.3 MPa. Hydrogenation of Mg (1) and alloying Mg with Cu to form Mg2Cu (2) followed by hydrogenation of Mg2Cu (3) should be competitive. It is proposed that an open network of MgCu2 can be formed when (1) occurs later than (3), a sheathed network when (1) occurs later than (2) and earlier than (3), and a layer when (1) occurs earlier than (2). However, the reaction of MgH2 to Cu under H2 atmosphere is not known in general. Therefore, in order to prove the existence and the generality of this reaction, pellets of MgH2 and Cu powder were heated under the condition of 673 K, 86.4 ks in H2 atmosphere of 8.0 MPa. The formation of a layer of MgCu2 was confirmed by SEM observations, EDS analyses and XRD measurements.