| Fe-based metallic glasses are emerging as one of the hot research frontiers in the field of metallic materials due to their excellent mechanical properties,good magnetic properties and low cost of raw materials.Therefore,in view of theoretical significance and practical application,it is essential to develop Fe-based metallic glasses with high glass forming ability(GFA)and excellent soft magnetic properties.In present thesis,Fe-Nb-B and(Fe,Co)-Nb-B metallic glasses were successfully fabricated by the combination use of melt purification and melt-spinning methods.Thermal properties,soft magnetic properties and electrical resistivity of these alloys were investigated by X ray diffractometer(XRD),differential scanning calorimetry(DSC),vibrating sample magnetometer(VSM),and four probe tester.The relationship between GFA and soft magnetic properties and alloy composition in the Fe97-xNb3Bx(x=16,18,20;at%)and Fe94-xNb6Bx(x=13,15,17;at%)alloys were investigated.Additionally,the effects of partial replacement of Fe by Co element on GFA.soft magnetic properties and electrical resistivity in the(Fe1-xCox)79Nb3B18(x=0.15,0.3,0.45,0.6,0.75;at%)metallic glasses were studied.Moreover,the crystallization behaviors of(Fe1-xCox)79Nb3B18 amorphous alloys were studied through isothermal annealing.The relationship between annealing processing was explored in order to provide a guidance to develop new type of Fe-based amorphous/nanocrystalline soft magnetic alloys.The main results can be drawn as follows.The variation of GFA,soft magnetic properties and electrical resistivity for Fe-Nb-B ternary alloys was explored.For Fe94-xNb6Bx(x=16,18,20;at%)metallic glasses,both GFA and thermal stability increases with increasing B content.It is reached that the optimized GFA can be found in the Fe77Nb6B17 alloys with ?Tx=48 K and Tx=864 K.These alloys exhibit excellent soft magnetic properties with high saturation magnetization(Ms)of 80?108 emu/g and low coercivity(Hc)of 0.03?7.76 Oe.With increasing B content,the saturation magnetization firstly increases and then decreases.Similar analyze were also performed on the Fe97-xNb3Bx(x=16,18,20;at%)metallic glasses.DSC results indicated that Tx and ?Tx increase from 815 K to 852 K and 12 K to 31 K,respectively,with the increase of B content,thus enhancing their GFA and thermal stability.The Ms value firstly decreases from 126 emu/g for alloys with x=16 to 122 emu/g for alloys with x=18,and then it increases to 139 emu/g for alloys with x=20.Room-temperature resistivity for the Fe94-xNb6Bx and Fe97-xNb3Bx metallic glasses is in the range 122?133 ?? cm and 118-151 ?? cm,respectively.The GFA and thermal stability firstly increases and then decreases with Co-substituted(Fe1-xCox)79Nb3B18 metallic glasses.It reaches the optimized GFA for alloys with x=0.45,and their thermodynamic parameters of ?Tx,Trg,and ? are found to be 60 K,0.538,and 0.377,respectively.As Co content increases,the saturation magnetization firstly increases and then decreaes,which is ascribed to atomic magnetic moment.VSM results showed that Ms value reaches the maximum value of 140 emu/g for alloys with x=0.45.However,the addition of Co element decreases electrical resistivity of the alloys.It decreases significantly from 124?? cm to 96 ?? cm,and then it remains constant around 70 ?? cm.Experimental results show that metallic glasses exhibit a correspondence between thermal stability and soft magnetic properties,while the electrical resistivity is not consistent with that of the variation of GFA and soft magnetic properties.The coexistence of ?-Fe(Co)+Fe23B6 phases firstly precipitate from the amorphous matrix,and then Fe23B6 phase decompose into Fe2B phase for the(Fe1-xCox)79Nb3B18 metallic glasses subjected to isothermal annealing treatment.The final crystalline product is composed of?-Fe(Co),Fe23B6,and Fe2B phases.Annealing treatment enhances the saturation magnetization and coercivity of the alloys.The saturation magnetization and coercivity are found to be 180 emu/g and 5.08 Oe,respectively,for alloys with x=0.45 annealed at 910 K for 1200 s,which is higher than that of the as-quenched samples.The soft magnetic properties of the metallic glasses are directly associated annealing temperature and time.The type,size and distribution of the precipitates can be precisely controlled by reasonable annealing process,which can provide a guidance to fabricate Fe-based amorphous/nanocrystalline alloys with excellent performance.When the(Fe0.4Co0.6)79Nb3B18 metallic glasses are isothermally treated between Tg and Tx1,the Ms value slowly increases from 113 emu/g to 132 emu/g with the increase of annealing time,while coercive force is not very sensitive to the annealing time.As the annealing temperature is higher than Tx1,the grain firstly reaches a stable size within a very short period of 30?60 seconds,then it decreases and increases with increasing annealing time.When the annealing temperature is Tg<Ta<Tx1,grain size firstly increases and then decreases with the increase of annealing time.Under the same annealing time of 90 seconds,grain size firstly decreases and then increases with is increasing Ta in the region between Tg and Tm.The existence of ?-Fe(Co)phase is benefit to enhance saturation magnetization,while Fe2B phase does harm to the magnetic properties of the(Fe0.4Ca0.6)79Nb3B18 metallic glasses. |
PDF Full Text Request