Effects of ordering in Fe-xAl alloys

The evolution of the structurally different phases and of the microstructural state of Fe-xAl alloys is studied in neutron diffraction experiments performed in the high resolution and continuous temperature scanning modes. It is found that the D0$_3$ phase in a weakly nonequilibrium state of alloys occurring in the doping range from $x\approx23$ to $x\approx31$ at % has the form of nanoclusters $(L\approx100-800\,$Å) dispersed within a host material (matrix) such as the disordered (A2) or partially ordered (B2) phase. The B$2 \to\text{D0}_3\to \text{B2}\to\text{A2}$ phase transitions are accompanied by a decrease or increase in the lattice parameters of these phases in the course of ordering or disordering of the atomic structure, respectively. In this situation, the lattice parameters of both the matrix and clusters change simultaneously and a high degree of coherence of the crystal lattices of the matrix and clusters is observed.