Abstract:Microstructures and magnetic properties of Fe₈₄Nb₇B₉, Fe₈₀Ti₈B₁₂ and Fe₃₂Ni₃₆(Nb/V)₇Si₈B₁₇ powders and their bulk alloys prepared by mechanical alloying(MA) method and hot-press sintering were studied. The results show that: 1) After MA for 20 h, nanocrystalline bcc single phase supersaturated solid solution forms in Fe₈₄-Nb₇B₉and Fe₈₀
Ti₈B₁₂alloys, amorphous structure forms in Fe₃₂Ni₃₆Nb₇Si₈B₁₇ alloy, duplex microstructure composed of nanocrystalline γ-(FeNi) supersaturated solid solution and trace content of Fe₂B phase forms in Fe₃₂Ni₃₆-V₇Si₈B₁₇alloy. 2) The decomposition process of supersaturated solid solution phases in Fe₈₄Nb₇B₉and Fe₈₀Ti₈B₁₂alloys happens at 710-780℃, crystallization reaction in Fe₃₂Ni₃₆Nb₇Si₈B₁₇alloy happens at 530℃(the temperature of peak value) and residual amorphous crystallized further happens at 760℃(the temperature of peak value), phase decomposition process of supersaturated solid solution at 780℃(the temperature of peak value) and crystallization reaction at 431℃(the temperature of peak value) happens in Fe₃₂Ni₃₆V₇Si₈B₁₇ alloy. 3) under 900℃, 30 MPa, 0.5 h hot-press sintering conditions, bulk alloys with high relative density(94.7% 95.8%) can be obtained. Except that the grain size of Fe₈₄Nb₇B₉ bulk alloy is large, superfine grains (grain size 50 200 nm) are obtained in other alloys. Except that single phase microstructure is obtained in Fe₈₀Ti₈B₁₂ bulk alloy, multi-phase microstructures are obtained in other alloys. 4) The magnetic properties of Fe₈₀Ti₈B₁₂ bulk alloy(Bs=1.74 T,Hc=4.35 kA/m) are significantly superior to those of other bulk alloys, which is related to the different phases of nanocrystalline or amorphous powder formed during hot-press sintering process and grain size.

Key words: Fe-based soft magnetic alloys; high energy milling; hot-press sintering; amorphous phase; magnetic properties