The preparation, formation mechanism and magnetic properties of a Fe-Cr-Mn-N amorphous alloy

Abstract

In this paper, the amorphous phase formation process, formation mechanism and magnetic properties, during the mechanical alloying (MA), have been investigated in Fe60Cr15Mn10N15 alloy, respectively. The results obviously indicate that amorphous Fe60Cr15Mn10N15 with a wide supercooled liquid region (SCLR, 82 K) can be obtained via 40 h MA process. With the milling time increasing gradually, the microstructures evolve from the initial crystalline powder, to completely amorphous phase, and eventually to amorphous phase with embedded Cr2N. By calculation, the mixing chemical enthalpy ΔHchem and amorphous formation enthalpy ΔHform have been obtained as −0.24 kJ/mol and −6.610 kJ/mol, respectively, implying the existence of thermodynamic advantage for the amorphous phase formation. In addition, the effect of 7 at% B and 7 at% Mo addition on the amorphous phase formation have also been studied, however, the diffraction peaks corresponding to Mo (Cr2N) still appear after 120 h milling. Meanwhile, isothermal annealing experiments were conducted at different temperatures, obtaining the microstructure evolution as: amorphous → amorphous alloy + Cr2N → α-Fe + Cr2N → α-Fe + CrN + Cr2N. And the hysteresis loops in amorphous Fe60Cr15Mn10N15 undergoing both the MA process and isothermal annealing procedure provide us with the evidence that this alloy system can exhibit excellent soft magnetic properties.