Effect of La addition on high-temperature order-disorder phase transformation in Fe − 18Ga alloy

Abstract

The microstructure, internal friction (IF) behavior spectra, heat flow curves, and mechanical strength of Fe-18Ga-xLa (x = 0.05, 0.1, 0.2, 0.5, and 1.0 at.%) alloys were systematically analyzed in this investigation. In the IF spectra, a relaxation IF peak (Labeled as P1) and a peak related to order-disorder phase transition (Labeled as Ptr) are observed in the temperature range of 400 °C–690 °C. It is found trace La doping has a significant effect on the Ptr peak. With the increase of the La-doped content, the peak of Ptr gradually shifts to a lower temperature and the net peak height decreases. Combining with phase diagram, DSC, Grazing Incidence X-ray diffraction (GI-XRD) spectra and SEM, the mechanisms of the reduction of both the critical temperature and the strength of Ptr peak for the Fe-18Ga-xLa alloy are ascribed to the precipitation of LaGa2 phase, which reduces the Ga content gradually in the matrix. Further, the mechanism is verified in Fe-18.1Ga alloy and Fe-19.3Ga alloy. In addition, the trace La doping can significantly improve the mechanical strength of the Fe − 18Ga alloy.