Structural transformations and wear resistance of abrasive-affected amorphous Fe- and Co-based alloys

The abrasive wear resistance of the Fe₆₄Co₃₀Si₃B₃, Fe_82.6Nb₅Cu₃Si₈B_1.4, Co_86.5Cr₄Si₇B_2.5, and Fe₈₁Si₄B₁₃C₂ amorphous alloys (ribbon 30 μm thick) has been investigated upon sliding over fixed abrasives (corundum and silicon carbide). The character of fracture of the surface and structural transformations initiated in these materials by the abrasive action have been studied by the metallographic, X-ray diffraction, and electron-microscopic methods. It has been shown that the abrasive wear resistance of the amorphous alloys is smaller by a factor of 1.6–2.9 than that of the Kh12M and U8 tool steels possessing approximately the same level of hardness. A pronounced softening of the surface layer of the amorphous alloys in the process of wear, which is characterized by a decrease in their microhardness reaching 12.5%, has been found. It has been shown that in the surface layer of these amorphous alloys upon wear there arises a small amount (on the order of several volume percent) of the nanocrystalline structure, which does not exert a marked effect on the microhardness and wear resistance of the alloys. In the alloys under study, the main factor that is responsible for their comparatively low abrasive wear resistance is their local softening in the process of wear caused by specific features of deformation processes occurring heterogeneously under the action of high shear contact stresses.     

Relating residual stress and microstructure to mechanical and giant magneto-impedance properties in cold-drawn Co-based amorphous microwires

The effect of cold-drawing on the tensile property and giant magneto-impedance (GMI) effect of melt-extracted Co-based amorphous microwires was evaluated through detailed analyses of the distribution of residual stress and microstructural evolution. The tensile ductility and tensile strength increased gradually with cross-sectional area reduction ratio (R) until 51%, and decreased with further deformation. The microwire with R = 51% exhibits the highest tensile ductility of 1.09% and tensile strength of 4320 MPa. Structural and thermodynamic analyses reveal that it is the mechanical deformation rather than thermal activation that induces the precipitation of nanocrystals and arrests the quick extension of shear bands leading to the enhanced ductility. Interestingly, the GMI effect also attains the maximum value of 160% at 10 MHz when R = 51% (30% larger than that of the as-cast wires), before decreasing with further cold-drawing. Such an identical evolution trend of both tensile and GMI properties can be ascribed to two underlying mechanisms: the generation of longitudinal and circumferential residual stresses and the growth of deformation-induced nanocrystals during cold-drawing. The role of residual stress is established herein not only as a trigger to accelerate the amorphous-to-nanocrystalline phase transformation but also as a decisive contributor to the mechanical and GMI performance. The unique simultaneous improvement of both mechanical and GMI properties of cold-drawn Co-based microwires opens up new possibilities for a variety of engineering applications, such as high-performance magnetic, stress and biological sensors.     

Magnetic models of cast amorphous microwires

A theory of a magnetic domain model for glass-coated amorphous microwires is studied. The obtained theoretical results are confirmed by experiments. Cast glass-coated amorphous microwires with positive magnetostriction have a rectangle hysteresis loop, which is characterized by a coercive-force stable magnitude. The coercive-force magnitude and the fluctuations of this magnitude are of theoretical and practical interest. The theory of the relaxation mechanism of magnetic reversal is constructed. For the more precise comparison of the theory and the experiment, a series of experimental measurements is needed, which are also discussed in the paper.     

Temperature changes for the hysteresis loop of an amorphous magnetic microwire in a glass shell

We investigated the hysteresis loop of an Fe_72.Si₁₃B₁₅ microwire in a glass shell characterized by a rectangular hysteresis loop. The gel covering of the outer surface of the microwire transforms it into an hysteresis-free loop.     

Magnetic and microwave properties of glass-coated amorphous ferromagnetic microwires

Glass-coated amorphous FeCuNbSiB microwires were prepared by Taylor-Ulitovsky technique. X-ray diffractometry and scanning electron microscopy were used to investigate the microstructure and morphology of the glass-coated microwires respectively. The vibrating sample magnetometer and vector network analyzer were used to study the magnetostatic and microwave properties of glass-coated microwires. The experimental results show that the effective anisotropy of an array of 150 microwires of 10 mm in length is large than that of one microwire of 10 mm in diameter and an array of 150 microwires of 1 mm in diameter. The natural ferromagnetic resonance takes place as the microwave magnetic component is perpendicular to the microwires axis, and the electric dipole resonance takes place as the microwire is long or the short microwire concentration is moderate. The natural ferromagnetic resonance shifts to higher frequency with the larger microwire concentration. The electric dipole resonance is governed by the microwires length and concentration. The glass-coated FeCuNbSiB microwires can be used to design EMI filters and microwave absorbing materials.     

Giant magneto-impedance effect of two paralleled amorphous microwires

Giant magneto-impedance（GMI）is effectively enhanced by the mutual magnetic interaction between two amorphous microwires.A comparative study on GMI properties of a single wire and two wires arranged in parallel mode was reported in this work.Two-peak（TP）of impedance characteristic is presented when the dc external field changed from 0 to 320 A m^-1in two-wire system,which is attributed to successive magnetization process in two wires induced by their magnetic interaction.And the evolution of single peak to TP phenomenon,when the distance between two wires is upto 8 mm,evidences a distance dependence of transformation from successive magnetization to simultaneous via a corresponding distance dependence of magnetostatic interactions.It is proposed that the recombination of magnetic interaction and the shielding effect results in a distance dependency of GMI response.When the distance is 8 mm,the magnetization process is close to synchronous between two wires,which give rises to higher circular permeability and better GMI response.The impedance ratio DZ/Z increases from74.5 % of single wire to 172.4 % at 10 MHz.However,when the distance is upto 12 mm,the magnetic interaction is weak and magnetization process is completely independent,and GMI response decreases,relatively.This indicates that the GMI response could be effectively improved in a two-wire connection with an opticaldistance,which is promising and useful for the application of high-performance GMI sensors.     

预退火时间对Cu50Zr42Al8玻璃转变及晶化行为的影响

采用示差扫描量热(DSC)分析方法,研究了预退火处理对Cu50Zr42Al8块状非晶合金的玻璃转变温度Tg、起始晶化温度Tx、以及玻璃转变过程中的比热容变化的影响.结果表明:Cu50Zr42Al8块状非晶合金在2～64h的预退火处理下,其焓弛豫峰的变化趋势与玻璃转变过程中的比热变化△Cp,g和玻璃转变温度Tg的变化一致,都是随预退火时间的增加先增加后减少.而其起始晶化温度Tx随着预退火时间的延长而减小.基于有序原子团簇引起微观结构变化,利用结构弛豫理论讨论了预退火时间影响玻璃转变和晶化过程的机理.     

Sc对Zr基块体非晶合金晶化动力学的影响

以海绵锆为原材料,利用浇包型坩埚电弧炉倾斜铸造法制备Zr52.5Cu17.9Ni14.6Al10Ti5五元块体非晶合金楔形试样,研究活性元素Sc对合金玻璃形成能力及晶化动力学参数的影响。结果表明:Sc的加入可显著增大合金的最大非晶形成厚度,但对合金过冷液相区温度范围所表征的热稳定性影响较小。Sc虽然使合金的晶化激活能降低,但使晶化孕育期时间常数增大,晶化频率因子减小,二者的综合作用使合金晶化孕育期延长,过冷倾向增大,玻璃形成能力提高。     

Dimensional absorption high-frequency properties of the cast glass coated microwires

Correlation between frequency of natural ferromagnetic resonance of the cast glass coated amorphous microwires and high-frequency absorption of a composite material from this microwire is investigated. The article is published in the original.     

Effects of La content on the glass transition and crystallization process of Al–Ni–La amorphous alloys

Effects of La content on the glass transition and crystallization process of Al_94−xNi₆La_x (x = 3–9) amorphous alloys were investigated by X-ray diffraction and differential scanning calorimeter. The results show that the thermal stability increases with increasing the La content. The crystallization changes from a two-stage process without glass transition at x = 3–6 to a three-stage one with obvious glass transition at x = 7–9. The first crystallization process results in precipitation of single fcc-Al at x = 3–5, fcc-Al plus metastable phase(s) at x = 6 and 7, and single metastable phase at x = 8 and 9. The first crystallization process at x = 4 and 5 is the growth of quenched-in nuclei, whereas that at x = 6, 7 and 9 is the diffusion-controlled growth with a decreasing, constant and increasing nucleation rate, respectively. The activation energy for the first crystallization process is larger in the eutectic reaction than that in the primary reaction, and is the highest when the number of the products is the most.     

Effect of Te additions on the glass transition and crystallization kinetics of (Sb15As30Se55)100−xTex amorphous solids

Differential scanning calorimetry results under non-isothermal conditions of chalcogenide (Sb₁₅As₃₀Se₅₅)_100?xTe_x (where 0 ≤ x ≤ 10 at.%) glasses are reported and discussed. The dependence of the characteristic temperatures “glass transition temperature (T_g), the crystallization onset temperature (T_c) and the crystallization temperature (T_p)” on the heating rate (β) utilized in the determination of the activation energy for the glass transition (E_g), the activation energy for crystallization (E_c), the glass thermal stability (ΔT = T_c ? T_g) and the Avrami exponent (n). The composition dependence of the T_g, E_g, and E_c were discussed in terms of the chemical bond approach, the average heats of atomization and the cohesive energy (CE). The diffractogram of the transformed material shows the presence of some crystallites of AsSb, Sb₄Te₆, As₂Se₃ and Sb₂Se₃ in the residual amorphous matrix.     

Boron content dependence of crystallization, glass forming ability and magnetic properties in amorphous Fe-Zr-B-Nb alloys

The glass forming ability (GFA) was investigated in Fe_91−xZr₅B_xNb₄ alloys with B contents of 0–36 at.%. The GFA changes with B content, and fully amorphous alloys were prepared by melt spinning for B contents between 5 and 30 at.%. The amorphous alloys crystallize with a primary crystallization mode in the low B content range of 5≤x≤20 at.%, but in the eutectic mode in the high B content range of 20<x<30 at.%. A single new metastable Fe-Zr-B-Nb cubic phase with a lattice constant of 1.0704 nm, a saturation magnetization of 137 emu/g and a coercivity of 7.3 Oe at room temperature is formed when crystallizing in a polymorphous mode at x=30 at.%. The glass transition temperature (T_g), crystallization temperature (T_x), Curie temperature (T_c) and saturation magnetizations (M_s) of the amorphous alloys increase with increasing B content, but the coercivity (H_c) decreases. As the B content exceeds 20 at.%, not only increase the T_g, T_x and GFA sharply, due to the change of crystallization mode, but also the concentration dependence of the T_c and M_s changes. It is concluded that the amorphous alloys have better GFA, thermal stability and soft magnetic properties for the high B contents of 25–30 at.% than for the low B contents of 5–20 at.%.     

Cu添加对FeCoZrB非晶合金热稳定性和晶化过程的影响

本文选择在低B含量的Fe₄₂Co₄₂Zr₇B₉合金和高B含量的Fe₃₉Co₃₉Zr₇B₁₅合金基础上添加1at.%Cu,制备Fe_41.5Co_41.5Zr₇B₉Cu₁和Fe_38.5Co_38.5Zr₇B₁₅Cu₁非晶合金,利用同步热分析仪(STA), X射线衍射(XRD)和透射电镜(TEM)测试分析合金的晶化曲线及晶化相的结构,研究Cu添加对Fe₄₂Co₄₂Zr₇B₉和Fe₃₉Co₃₉Zr₇B₁₅非晶合金热稳定性和晶化过程的影响。结果表明,Cu添加稍微提高了Fe₄₂Co₄₂Zr₇B₉非晶合金的热稳定性,明显提高了Fe₃₉Co₃₉Zr₇B₁₅非晶合金的热稳定性。对于Fe₄₂Co₄₂Zr₇B₉和Fe₃₉Co₃₉Zr₇B₁₅非晶合金,晶化初期XRD存在明显的峰位移动;对于添加Cu后的Fe_41.5Co_41.5Zr₇B₉Cu₁和Fe_38.5Co_38.5Zr₇B₁₅Cu₁合金,晶化过程中几乎没有峰位移动。TEM测试表明Cu添加改善了纳米晶粒分布的均匀度。Cu添加对高B含量Fe₃₉Co₃₉Zr₇B₁₅合金热稳定性和晶化过程的影响大于低B含量的Fe₄₂Co₄₂Zr₇B₉合金。     

电脉冲孕育处理对Zr基块体非晶热稳定性及退火晶化的影响

通过先对Zr55Ni5Al10Cu30合金熔体施加脉冲电流处理,再利用非真空吸铸法制备出Zr55Ni5Al10Cu30块体非晶合金的方式,研究了电脉冲孕育处理对非晶热稳定性及退火晶化的影响。差分扫描量热(DSC)及X射线衍射(XRD)分析结果表明:经电脉冲孕育处理后Zr55Ni5Al10Cu30块体非晶合金的玻璃转变温度上升,晶化温度降低,过冷液相区变窄,同时玻璃转变激活能和晶化激活能有所减少。电脉冲孕育处理没有改变Zr55Ni5Al10Cu30块体非晶合金退火晶化相演变过程,但提高了非晶退火晶化率。电脉冲孕育处理对Zr55Ni5Al10Cu30块体非晶合金的晶化起到了促进作用。     

Surface magnetic properties and giant magnetoimpedance effect in Co-based amorphous ribbons

Correlationship between surface magnetic properties studied using the MOKE technique and giant magnetoimpedance effect (GMI) of nearly-zero magnetostrictive Co_66.5Fe_3.5Si_12.0B_18.0 amorphous ribbons in as-cast state has been investigated in the frequency range of 10 MHz–1.5 GHz. It was found that the surface anisotropy is different in the sides of the ribbon: it is transversal to the ribbon axis with multiple domain walls in one side and axial with a single domain wall in the other. The effect of permanent bias current on surface domain structure was investigated and it was found that the multidomain transversal is very sensitive to the bias current while the axial anisotropy is practically not affected by the applied bias current. This finding can be applied in design of highly sensitive material for magnetic sensors.     

Nd对块体Mg-Cu-Y-Nd非晶合金玻璃形成能力的影响

在非真空熔炼条件下采用工业纯原材料和负压铜模吸铸法制备Mg65Cu25Y10-xNdx(x=0,2,4,6,8,10)棒状试样,利用差示扫描量热(DSC)和X射线衍射(XRD)等方法分析Nd对Mg-Cu-Y-Nd非晶合金玻璃形成能力的影响。结果表明:Nd的含量(x)为0,4,6成分的合金试样具有完全非晶态组织,且x=4时具有最大的玻璃形成能力,其约化玻璃转变温度(Trg)为0.592,过冷液相区宽度(ΔTx)高达66 K;当x为2,8,10时,由于合金成分明显偏离共晶成分,玻璃形成能力降低,试样只含有少量非晶,且主要呈晶体组织特征。     

钛渣中TiO2作晶核剂对玻璃晶化的影响

制备了以钛渣和铁尾矿为主要原料,以钛渣兼作晶核剂的微晶玻璃材料,研究了Ｔｉ２含量变化对玻璃晶化的影响。采用ＤＴＡ,ＳＥＭ,ＸＲＤ等技术对该体系的晶化机理进行探讨。结果表明,当ＴｉＯ２含量小于１０％时仅产生表面晶化。而当ＴｉＯ２含量为１０％时可发生整体晶化,其活化能为１９０．６ｋｊ．ｍｏｌ＾－１,动力学参数ｍ＝３,晶体从晶界面呈三维生长。ＴｉＯ２、Ｆｅ２Ｏ３能共同促进晶化,晶体从相界面处生长,析出的     

Dynamic mechanical behavior of a Zr-based bulk metallic glass during glass transition and crystallization

The dynamic mechanical behaviors of the Zr41Ti14Cu12.5Ni8Be22.5Fe2 bulk metallic glass (BMG) during continuous heating at a constant rate were investigated. The glass transition and crystallization of the Zr-based BMG were thus characterized by the measurements of storage modulus E and internal friction Q-1. It was found that the variations of these dynamic mechanical quantifies with temperature were interre-lated and were well in agreement with the DSC trace obtained at the same heating rate. The origin of the first peak in the internal friction curve was closely related to the dynamic glass transition and subsequent primary crystallization. Moreover, it can be well described by a physical model, which can characterize atomic mobility and mechanical response of disordered condense materials. In comparison with the DSC trace, the relative position of the first internal friction peak of the BMG was found to be dependent on its thermal stability against crys-tallization.