| Among the eveloped amorphous alloy systems, Fe-based amorphous alloys which possess relatively low material cost and broad application of steel materials, have been considered to have an important value of engineering application. In order to obtain good glass forming ability(GFA) and then to prepare Fe-based amorphous alloys with larger size, usually one or more type of metalloid elements(B, Si, C, P and so on) have been added in Fe-based amorphous alloys. But all these Fe-based amorphous alloys show great brittleness, such as almost no plastic deformation in compression test, and their elastic deformation ability is also limited. Study on the brittleness of Fe-based amorphous alloy ribbons and bulks showed that their brittleness is closely related with types, content and distribution of metalloid elements. At present, Fe-based amorphous alloys without metalloid is rarely reported.In this dissertation, the chemical composition of Fe-based amorphous alloys without metalloid were designed by considering Inoue empirical criterion, binary deep eutectic rule, large atomic cluster and similar element substitution and FeCoNiCrZr and FeCoMoCrZr amorphous alloy ribbons were prepared successfully. The GFA, thermal stability, crystallization kinetics, precipitated phase, magnetic properties and mechanical properties of these two new Fe-based amorphous alloy systems were investigated by X-ray diffriction(XRD), differential scanning calorimetry(DSC), scanning electron microscopy(SEM), atomic force microscopy(AFM), vibrating sample magnetometer (VSM), It is expected to be able to lay the theoretical foundation for producing good plastic deformation ability or good magnetic properties of Fe-based bulk metallic glasses without metalloid. The main results and conclusions are as follows:1)(Fe0.52Co0.48-xNix)73Cr17Zr10(x=0.06,0.18,0.30) amorphous alloy ribbons were successfully prepared. With increasing the Co/Ni ratio, all the characteristic temperatures including onset of glass transition temperature(Tg)、onset of crystallization temperature (Tx、 peak of crystallization temperature(Tp) move towards to the higher temperature regions, the supercooled liquid region(△Tx) increases firstly, and then decreases. When x=0.18, amorphous alloy has the most wide△TX(△TX=41.5℃). The activation energies calculated by the Kissinger and Ozawa equations show good agreement, and all amorphous alloys have the same law: Eg> Ex> Ep. With increasing the Co/Ni ratio, the crystallization activation energy Ex increases firstly and then decreases, the maximum of local crystallization activation energies(Ec(x) decreases. When x=0.18, crystallization is the most difficult. With the increase of crystallization volume fraction(x), the Ec(x) of all amorphous alloys gradually increases to the maximum and then gradually decreases to the end of crystallization.2)(Feo.58Coo.42)73Mo17-xCrxZr10(x=9,12,17) amorphous alloy ribbons were successfully prepared. With increasing the Cr/Mo ratio, all the characteristic temperatures including Tg、 Tx、Tp move towards to the low temperature regions,△TX increases slowly. When x=17, amorphous alloy has the most wide△TX(△TX=41.5℃). All amorphous alloys have the same law:Ex> Eg≈Eg. With increasing the Cr/Mo ratio, Ex and Ep increases, the maximum of Ec(x) also increases. When x=17, crystallization is the most difficult. With the increase of crystallization volume fraction(x), the Ec(x) of all amorphous alloys were gradually increases to the maximum and then gradually decreased until the end of crystallization.3) Study on the non-isothermal crystallization kinetics of (Fe0.52Co0.30Nio.0.18)73C17Zr10amorphous alloy showed that the non-isothermal crystallization mechanism is composed of two processes, namely the nucleation-and-growth mode and normal grain growth kinetic law. The isothermal crystallization kinetics showed that the phase transformation mechanism depends on annealing temperature. As the isothermal annealing temperature increases, the nucleus growth mechanism changes from diffusion-controlled growth to interface-controlled growth. The calculated Ec(x) indicates that along with the crystallization evolution the isothermal crystallization becomes more difficult, whereas the non-isothermal crystallization becomes easier,4) The saturation magnetization(Ms) of FeCoNiCrZr and FeCoMoCrZr amorphous alloys at cast state are relatively low. The annealing temperature (Ti) pays an obvious effect on the type and grain size of precipitated phases in these alloys then cause the magnetic property to change significantly. The crystallization process of (Feo.52Coo.48-xNix)73Cri7Zr10(x=0.18,0.30) amorphous alloy is showed as Am'α-Fe(Co)+Am’'α-Fe(Co)+Cr2Ni3+Fe3Ni2+Cr2Zr+unknown phase. The crystallization process of (Feo.58Coo.42)73Mo5Cr12Zr10amorphous alloy is showed as Am'α-Fe(Co)+CrFe4+Fe23Zr6+Cr2Mo. The crystallization process of (Feo.58Co0.42)73Cr17Zr10amorphous alloy is showed as Am'α-Fe(Co)+Am’'a-Fe(Co)+CrFe4+Fe3Ni2+Cr2Zr+unknown phase. When Ti is lower than Tg, Ms increases slightly for all annealed amorphous ribbons as a result of relaxation of the internal stress of the as-quenched amorphous alloy. When Ti is in between Tx1and Tp1, the Ms significant increases due to the partial crystallization of amorphous precursors to create a homogeneous distribution of a-Fe(Co) nanocrystals within a residual amorphous matrix. When Ti is higher than Tp1, the Ms drops rapidly, which may be caused by the grain growth and the formation of paramagnetic phase.(Feo.58Coo.42)73Cr17Zr10amorphous alloy after annealed at565℃for40min has the best magnetic property(Ms=126.2emu/g). The results of AFM observation showed that in the annealed amorphous ribbons the grain size mesured from AFM graphs is much larger than that of the a-Fe(Co) nanocrystalline size caculated by Scherrer method, which is a typical phenomenon of coated grain.5) All the prepared amorphous ribbons show a certain tough in bending test. SEM graphs of bending fracture of (Feo.52Coo.3oNio.18)73Cr17Zr10amorphous ribbon showed that the fracture side has a great deal of shear steps and a larger number of vein patterns were distributed evenly on the fracture surface, which is a typical ductile fracture behaviour. When annealing temperature is blow Tg, due to the effect of structural relaxation on the amorphous alloy internal free volume, transition of ductile to brittle fracture was observed.6) The change of microhardness of (Fe0.52Co0.30Ni0.18)73Cr17Zr10amorphous ribbon with annealing temperature and annealing time was studied. The results show that the microhardness declines firstly, then rises and then declines with the rise of annealing temperature. In low-temperature annealing, the microhardness rises firstly, and then declines with the time, in high-temperature annealing, the microhardness rises all the time until to equilibrium. The variation of microhardness reflects the internal structural change of amorphous alloy.7) After vickers indentation deformation, the free deformation zone of (Feo.52Co0.30Ni0.18)73Cr17Zr10amorphous alloy consists of alternate semi-circular shear bands and radial shear bands. With the increasing load(P), the average indentation diagonal length(D) and the distance(R) from indentation center to free deformation edge increase, R/D is independent of P. The semi-circular shear bands transfer discontinuiousely, but the radial shear bands transfer continuitious, which indicates that the semi-circular shear bands form earlier than radial shear bands. The angle(20) between radial shear bands and the tangent direction of semi-circular shear bands change between about89～90°, which indicates that the shear deformation is controlled by the maximum shear stress and approximately follows the Von Mises yield criterion.8)(Fe0.52Co0.30Ni0.18)73Cr17Zr10amorphous ribbons under the tensile strain rate of2.0×10-3s-1show brittleness at room temperature, its tensile strength is1320MPa and elastic strain is about2.1%. A larger number of vein patterns and other type of patterns on the fracture surface show that plastic deformation occurs at microscopic. Due to the plastic deformation is confined to localized shear bands, the rapid expansion of local shear bands lead to brittle fracture of alloy at macroscopic. |
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