STEADY-STATE GRAIN-SIZE AND THERMAL-STABILITY OF NANOPHASE NI3FE AND FE(3)X (X=SI, ZN, SN) SYNTHESIZED BY BALL-MILLING AT ELEVATED-TEMPERATURES

Ball milling of Ni3Fe and Fe(3)X (X = Si, Zn, Sn) was performed at tem peratures from 23 degrees C to 300 degrees C. X-ray diffractometry, tr ansmission electron microscopy, and differential scanning calorimetry were used to measure the average grain size, internal strain distribut ion, and thermal stability of the as-milled samples. It was found that the average grain size was larger at higher milling temperatures, and the strain distribution was smaller. The alloys of Fe3Sn and Fe3Zn we re single-phase after milling, showing that the milling process suppre ssed the formation of the equilibrium phases that would otherwise have formed at 300 degrees C. Upon annealing the as-milled materials, grai n growth and equilibrium phase formation occurred nearly simultaneousl y, probably because both are controlled by atomic diffusivity. The the rmal stability against grain growth and equilibrium phase formation wa s not affected by milling temperature. There were, however, significan t differences in the stabilities of the different alloys against grain growth and phase separation, and some controlling parameters are sugg ested.