In order to complete the equilibrium diagram of the iron-aluminium system, the authors have very carefully studied the alloys between O and 42 per cent of aluminium by differential -dilatometric, , magnetic, and X-ray analysis and also by microscopic examination. From the results of this investigation a new diagram has been established as shown in Fig. 2, which may be summarized as follows; in the diagram, three compounds, a2, a3 and a4, are added which have newly found by the authors.
(1) The a1 phase (Fe3Al, a super-structure of a-iron already found by Bradly and Jay) is formed at a temperature of 570° by the following peritectoid reaction, a+a2_??_a1, its homogeneous range is 7.5 per cent at room temperature.
The Curié point of this phase is measured to be 510° at Fe3Al composition.
(2) The a2 phase has a new super-structure and is formed at a composition of Fe5Al3 (22.5 per cent aluminium) and a temperature of 1050° by the following peritectoid reaction, a+a3_??_a2.
(3) The a3-phase being also a super-structure is probably formed at the composition FeAl, 32.6 per cent aluminium, by the following peritectic reaction, melt+a_??_a3, and is stable only at high temperature:-this phase decomposes into a4 and θ phase at 35 per cent aluminium and 670° by the following eutectoid reaction, a3_??_θ+a4.
(4) The a4-phase shows a super-structure having same composition as the a3-phase, but it is stable at temperature below 780° and is formed by the following reaction, a3+a2_??_a4.
(5) ε-phase is formed by the peritectic reaction, a3+melt_??_ε and not by a+melt_??_ε, and it decomposes to θ+a3 at a temperature of 1080°, not to θ+a.
(6) The lattice constant-concentration curves of a, a1, a2, a4, and a3 phases are shown in Fig, 8.
(7) The curié point-concentration curves of a and a1, phases are given in. Fig, 5.
(8) The space group adopted for the phase, Fe5Al3 is any one among Th5 O15, Oh2 and Oh3 and 2 atoms being included in its unit cell.
(9) The phases a3 and a4 have the same chemical composition, and the space group determined for one of them is Th7 or T5 with 8 molecules of FeAl including in its unit cell, and Oh1 for the other with one molecule of FeAl, and the exact space groups to be adopted for the phases a3 and a4 could not be determined, as their difference in atomic structure and calculated and actual spectrum lines was very little.