Microstructural studies of in-situ formed MgB2 phases in a Mg alloy matrix composite

The microstructure of in-situ formed MgB2 phases in a Mg alloy matrix composite was studied by means of transmission electron microscopy and high-resolution electron microscopy. The MgB2 phases have hexagonal plate-like morphology with a remarkable interfacial energy anisotropy. The interfaces between MgB2 and Mg are sharp without any intermediate layer. The interfaces are semi-coherent with a regular arrangement of misfit dislocations. Dislocation loop and 60° dislocation are observed in the MgB2 phases. A phase transformation from MgB2 to Mg is observed and a structural model is proposed to describe the phase transformation process.