Order-disorder andα−γtransitions in FeCo

Electrical resistivity ($\rho$) measurements in an FeCo alloy (with 47.63-wt.% of Co) in the temperature range of 500-1350 °K are reported. Special attention is given to the temperature regions of 900-1100 °K and 1160-1300 °K. A change in the slope of the $\rho$ vs $T$ curve, associated with the order-disorder transition, yields a $\lambda$-type anomaly in $\frac{\partial \rho }{\partial T}$ with maximum at $T\simeq 1006$ °K. Comparison with the specific heat $C\left(T\right)\mathrm{}$ data of Orehotsky and Schröder shows that $\frac{\partial \rho }{\partial T}$ is proportional to $C\left(T\right)\mathrm{}$ in the critical region similar to the observations in $\beta$ brass. Near 1230 °K, a discontinuous change in resistivity of about 20% with hysteresis of about 12 °K, is observed. This first order transition is associated with the $\alpha -\gamma$ transition.