Influence of initial state and heating rate on phase transformation in Fe66Ga34 alloy

The influence of phase composition and heating rate on the character of phase transformations and the composition of the resulting structural phases was analyzed using neutron diffraction. This comparative study were carried out on a pulsed neutron source CSNS (China) on the General Purpose Powder Diffractometer (GPPD). Phase transformations in the Fe₆₆Ga₃₄ alloy have been analyzed by in situ real-time neutron diffraction in the temperature range from 20 to 880°C with constant heating rates of 2 and 10 °C/min and temporal resolution of about 4 min. It is shown that a decrease in the cooling rate of the alloy leads to the formation of an equilibrium phase α-Fe₆Ga₅, the presence of which significantly affects the character of subsequent phase transformations. The maximum temperature of the metastable Fe₁₃Ga₉ phase existence does not depend on the presence or absence of the equilibrium α-Fe₆Ga₅ phase, but increases with increasing heating rate. The Curie temperature for the Fe₁₃Ga₉ phase has been estimated for the first time as T_C = 380°C. At this temperature a jump in the volume of the unit cell of this phase occurs, which may indicate the presence of negative spontaneous volume magnetostriction.