Electron Microscope Study of the Crystal Structure of the Martensite in a Copper-Aluminium Alloy

The crystal structure of β' martensite in a Cu–11.7% alloy has been studied by transmission electron microscopy and electron diffraction. The structure has a monoclinic lattice, whose unit consists of 6 close-packed layers having a superlattice. It can also be described as an orthorhombic lattice having lattice constants of a =4.49 Å, b =5.19 Å, c =38.2 Å, ( a : b : c =√3: 2: 18√23), and consisting of 18 layers A B ' C B ' C A ' C A ' B A ' B C ' B C ' A C ' A B ', where the positions of atoms in each layer ( a b plane) are (A) Al:(00); Cu:(012), (1214), (1234), (A')=(A)+(012), (B)=(A)+(130), (B')=(B)+(012), (C)=(A)+(230), (C')=(C)+(012), where ( A )+(130) means that all the atoms in layer ` A ' are displaced by the amount of vector (130).