Structural And Magnetic Properties Of Iron-based Nanocrystalline And Amorphous Alloys Powders After Ball-milling

Solid-state cooling technology,based on magnetocaloric effect,is highly efficient and environmental-friendly,which contributes to reducing the amount of greenhouse gas emission.Developing magnetocaloric materials with high performance is currently the focus of research,and iron-based alloys are potential room-temperature magnetocaloric materials without rare-earth elements.In this thesis,the alloy composition of Fe₇₉Mo₁₀B₁₀Cu₁ was selected,and nanocrystalline alloy powder and amorphous alloy powder were successfully prepared by mechanical alloying and mechanical grinding under different conditions（ball milling time 1h～96h with or without ethanol addition）using a monolithic powder mixture and a fast-hardening alloy thin strip as raw materials.The results showed that the monolithic powder mixture formed a single-phaseα-（Fe,Mo）nanocrystalline structure after alloying in a high-energy ball mill for 15h,while the nanocrystalline powder obtained by alloying in a planetary ball mill for 72h consisted of bothα-（Fe,Mo）andα-Mo phases.The saturation magnetization intensity of the alloyed powder decreases with increasing ball milling time because the mechanical alloying makes the non-magnetic Mo elements solidly soluble in the ferromagneticα-Fe lattice,resulting in the magnetic dilution phenomenon.In the early stage of ball milling（<5h）,the magnetoelastic anisotropy is the dominant factor in the alloy coercivity,resulting in a paradoxical increase in the coercivity of the sample with decreasing grain size.The addition of ethanol to the ball mill as a process control agent further refined the particle size of the alloy powder（～3μm）,but slowed down the alloying process and increased the grain size.The magnetization strength of the alloy powder was increased and the coercivity was significantly reduced at the same time.Among all the ball milled alloy powders,the sample with the best magnetic properties has a low saturation magnetization strength（148 A·m²/kg）and a very high coercivity（2230 A/m）,which requires further optimization of the ball milling process and improvement of the soft magnetic properties.