Performance Characterization And Tensile Fracture Strength Of Fe-based/Ni-based Amorphous Wires

Magnesium alloys with high specific strength and low density have many excellent properties.However,the key issues such as low strength and room temperature brittleness of magnesium alloys limit their widely application.Adding the second phase to form a composite material is an important mean to improve the mechanical properties of magnesium alloys.Amorphous wires with small size are increasingly attracting attention as representatives of high strength materials.However,there is no extensive research on the preparation of amorphous enhanced magnesium-based composites so far.The Fe-based and Ni-based amorphous wires were selected because they were composed of all-metal components and have high crystallization temperatures.They are unlikely to crystallize after being heated and very possible to be successfully applied as a reinforcement phase to the preparation of magnesium matrix composite,which fine interface bonding and microscopic properties should be achieved.However,at present,there are very limited researches on the microstructure,mechanical properties and internal structure of two amorphous wires.Therefore,this study focused on two amorphous wires.Two kinds of amorphous wires were fabricated and their microstructures and mechanical properties were investigated by means of X-ray diffraction(XRD)?differential scanning calorimetry(DSC)?scanning electron microscope(SEM)? transmission electron microscope(TEM)and a micro-stretching machine.The effects of annealing on tensile strengths of amorphous wires were also studied.The melt extraction method is used to fabricate the Fe-based and Ni-based amorphous wires.Some defects caused by melt extraction method,such as Rayleigh waves and grooves,are avoided when the roller speed is 1700r/min and the feed speed is 30-70?m/min.The surface of the amorphous wires fabricated is smooth,and the average length of a single wire is up to 1 m.The cross section is round and the diameter is about 40 ?m with homogeneous chemical compositions distribution.The results of thermal analysis show that the glass transition temperature(Tg)of the Fe-based amorphous wires is 834 K and the Tg of the Ni-based amorphous wires is 966 K.There is a wide diffraction peak in the X-ray diffraction pattern of the amorphous wires,and there is no sharp crystallization peak,indicating that the fabricated wires have an amorphous structure.High resolution photographs in transmission electron microscopy have no crystalline phase,and the distribution of atoms is not regular.The selected-area diffraction pattern shows a typical amorphous diffraction ring with no diffraction spot.The magnetization curve of Fe-based amorphous wire shows a straight line with a fixed slope with no significant saturation magnetization.Thus,these reflect the special magnetic characteristics of the Fe-basedamorphous wires.The magnetization curve of Ni-based amorphous wire has a typical loop shape with a coercive force of 85 Oe.The stress-strain curve of the single amorphous wire shows a typically brittle fracture characteristic.No yield platform and necking are observed in the stress-strain.It fractures directly when the load is up to a breaking value.The surface morphologies of the tensile fractured show two typical characteristics.The first cross section type is a combination of a vein pattern zone and a smooth featureless zone,and the corresponding angle between the stress axis and the fracture surface is 54°.The second cross section is a radial fracture,and the corresponding angle between the stress axis and the fracture surface is 86°.The Fe-based and Ni-based amorphous wires have a tensile strength of about 3000 MPa,and the data of the Ni-based experimental sample are more concentrated.In the cyclic loading experiment,both of this two wires show a residual deformation on the stress-strain curves.Different strain rate experimental results show that the highest tensile strength of Fe-based wires occurs at a loading rate of 5×10-4 s-1,and the highest tensile strength of Ni-based wires occurs at 1×10-4 s-1.The tensile strength data of the Fe-based and Ni based amorphous wires show that the Ni-based wires exhibit higher safety and reliability.The three-parameter Weibull fitting results show that the fracture threshold of Fe-based amorphous wires is 1581.62 MPa and that of Ni-based amorphous wires is 2440.6 MPa.Obviously,the safety of Ni-based materials is high.The fracture threshold of Fe-based amorphous wires is low,and catastrophic fracture often occurs under low stress conditions.The fitting results based on the log-normal distribution show that the fitting coefficients of both are at a relatively high value close to 1,which are 0.9782(Fe-based)and 0.9589(Ni-based),respectively,indicating that the tensile strength data of melt extracted amorphous wires is suitable for log-normal distribution.The standard deviation coefficient characterizes the dispersion of the experimental data.The s-value(0.2643)of Fe-based amorphous wires is much larger than that of Ni-based wires(0.0724),indicating that the Fe-based wires are more discrete.?0 is the average characteristic stress,and the average stress of Fe-based wires and Ni-based wires is 2884.19 MPa and 2833.87 MPa.The log-normal fitting can be used to calculate the probability.For example,The probability of the tensile strength falls within 1000-3000 MPa is 0.559(Fe base)and 0.784(Ni base),respectively.No nanocrystallization occurs after annealed under Tg.However,the main diffraction peaks of X-ray diffraction of the annealed sample becomes higher and sharper.The high resolution transmission electron microscope(HRTEM)analyze showed that the degree of ordering of the sample after annealing changed(3.1%-7.8%).With increasing annealing temperature to 580 ?,the tensile strength of the Fe-based amorphous wires decreases from3000 MPa in the prepared state to about 1500 MPa.There is obvious effect of annealingtime on strength when annealing time is more than 20 min.The tensile strength of Ni-based amorphous wires is more sensitive to the annealing temperature,and decreases rapidly with increasing annealing temperature.Annealing time has no obvious effects on the tensile strength of Ni-based amorphous wires.