Influence of quenching rate and heat treatment on the magnetic properties and phase components of rapidly quenched Fe77.5Nd4B18.5 alloy

The magnetic properties and phase components of rapidly quenched Fe_77.5Nd₄B_18.5 alloy as a function of quenching rate and heat treatment were studied. X-ray diffraction and thermomagnetic measurements show that the Fe_77.5Nd₄B_18.5 ingot consists of Nd₂Fe₁₄B, Fe₂B and α-Fe. The X-ray diffraction patterns of optimally annealed samples show only metastable Fe₃B phase which decomposes into Fe₂B and α-Fe at T_a > 850 °C, but the thermomagnetic curves show the presence of the Nd₂Fe₁₄B phase. In the sample annealed at 950 °C for 60 min, Nd_1.1Fe₄B₄ appears in coexistence with Nd₂Fe₁₄B, Fe₂B and α-Fe. The Fe_77.5Nd₄B_18.5 alloy is found to have very good glass-forming ability. Samples prepared at quenching rates v_s ⩾ 6.6 m s⁻¹ are amorphous and magnetically soft. Annealing at about 650–670 °C gives the highest coercive field, which is nearly independent of quenching rate.