Structural, microstructural and magnetic properties of amorphous/nanocrystalline Ni63Fe13Mo4Nb20 powders prepared by mechanical alloying

This paper focuses on the magnetic, structural and microstructural studies of amorphous/nanocrystalline Ni₆₃Fe₁₃Mo₄Nb₂₀ powders prepared by mechanical alloying. The ball-milling of Ni, Fe, Mo and Nb powders leads to alloying the element powders, the nanocrystalline and an amorphization matrix with Mo element up to 120 h followed by the strain and thermal-induced nucleation of a single nanocrystalline Ni-based phase from the amorphous matrix at 190 h. The results showed that the saturation magnetization decreases as a result of the electronic interactions between magnetic and non-magnetic elements and finally increases by the partial crystallization of the amorphous matrix. The coercive force increases as the milling time increases and finally decreases due to sub-grains formation.     

Fabrication of Ti-Cu-Ni-Al amorphous alloys by mechanical alloying and mechanical milling

Ti-based amorphous alloy powders were synthesized by the mechanical alloying (MA) of pure elements and the mechanical milling (MM) of intermetallic compounds. The amorphous alloy powders were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Scanning electron micrographs revealed that the vein morphology of these alloy powders shows deformation during the milling. The energy-dispersive X-ray spectral maps confirm that each constituent is uniformly dispersed, including Fe and Cr. The XRD and DSC results showed that the milling time required for amorphization for the MA of pure elements was longer than that of the MM for intermetallic compounds. The activation energy and crystallization temperature of the MA powder are different from those of the MM powder.     

Microstructural characterization and amorphous phase formation in Co40Fe22Ta8B30 powders produced by mechanical alloying

In this work, microstructural evolution and amorphous phase formation in Co₄₀Fe₂₂Ta₈B₃₀ alloy produced by mechanical alloying (MA) of the elemental powder mixture under argon gas atmosphere was investigated. Milling time had a profound effect on the phase transformation, microstructure, morphological evolution and thermal behavior of the powders. These effects were studied by the X-ray powder diffraction (XRD) in reflection mode using Cu Kα and in transmission configuration using synchrotron radiation, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results showed that at the early stage of the milling, microstructure consisted of nanocrystalline bcc-(Fe, Co) phases and unreacted tantalum.Further milling, produced an amorphous phase, which became a dominant phase with a fraction of 96 wt% after 200 h milling. The DSC profile of 200 h milled powders demonstrated a huge and broad exothermic hump due to the structural relaxation, followed by a single exothermic peak, indicating the crystallization of the amorphous phase. Further XRD studies in transmission mode by synchrotron radiation revealed that the crystalline products were (Co, Fe)_20.82Ta_2.18B₆, (Co, Fe)₂₁ Ta₂ B₆, and (Co, Fe)₃B₂. The amorphization mechanisms were discussed in terms of severe grain refinement, atomic size effect, the concept of local topological instability and the heat of mixing of the reactants.     

A comparative study of mechanical alloying and mechanical milling of Nd8Fe88B4

A comparative study was made of structure and magnetic properties of Nd₈Fe₈₈B₄ prepared by mechanical alloying (MA) using elemental powders as starting materials and by mechanical milling (MM) of the alloy. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) combined with transmission electron microscopic (TEM) studies revealed that both milling procedures resulted in a mixture of α-Fe and an amorphous phase. The thermal stability of the as-milled powders produced by MA was comparable to that of the as-milled powders produced by MM. Heat treatment of the milled powders above the crystallization temperature resulted in the formation of a nanocrystalline mixture of Nd₂Fe₁₄B and α-Fe, but annealed MA powders demonstrated a somewhat coarser structure in comparison with annealed MM powders. Therefore, higher remanences and coercivities were obtained by MM.     

Structural characteristics and magnetic properties of bulk nanocrystalline Fe_(84)Zr_2Nb_4B_(10) alloy prepared by mechanical alloying and spark plasma sintering consolidation

Magnetic properties of Fe84Zr2Nb4B10 sample were investigated. The sample was produced from nanocrystalline powders made by the mechanical alloying (MA) and consolidation using the spark plasma sintering (SPS) technique. Effects of milling time on phase transformation, structural characteristics, and magnetic properties of powders were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and physical property measure system (PPMS), respectively. Results show that nanostructured α-Fe supersaturated solid solution is obtained in the final MAed products. The saturation magnetization (Ms) increased with increasing milling time and became constant at 130 h, but the coercivity (Hc) increased firstly and then decreased. The consolidated bulk sample exhibited a high density of 6.893 g·cm-3, there was no phase change during SPS process, and the saturation magnetization and susceptibility of the SPSed bulk sample improved in comparison with the milled powders. The variation of magnetic parameters can be explained by nano-scale effect and Herzer model.     

Preparation and magnetic properties of amorphous Co–Cu–B alloy nano-powders

Magnetic Co–Cu–B powders were successfully prepared by the reduction of copper chloride and cobalt chloride in an aqueous solution of sodium borohydride. Using X-ray diffraction (XRD), selective area electronic diffraction (SAED), differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS) it was shown that, when Co²⁺/Cu²⁺ ratio in the original mixed solution was greater, the resultant powders were amorphous alloy powders, having a nearly spherical morphology with diameters <50 nm. DSC trace of the as-prepared Co–Cu–B ultrafine amorphous alloy powders showed only one exothermic peak, and no sharp glass transition temperature could be identified. From the room-temperature magnetic hysteresis loops measured by vibrating sample magnetometer, it was found that the Co–Cu–B amorphous alloy powders exhibited hard magnetic behavior, and the saturation magnetization could be further improved by crystallization.     

Kinetics and formation mechanism of amorphous Fe52Nb48 alloy powder fabricated by mechanical alloying

A single phase amorphous Fe₅₂Nb₄₈ alloy has been synthesized through a solid state interdiffusion of pure polycrystalline Fe and Nb powders at room temperature, using a high-energy ball-milling technique. The mechanisms of metallic glass formation and competing crystallization processes in the mechanically deformed composite powders have been investigated by means of X-ray diffraction, Mössbauer spectroscopy, differential thermal analysis, scanning electron microscopy and transmission electron microscopy. The numerous intimate layered composite particles of the diffusion couples that formed during the first and intermediate stages of milling time (0–56 ks), are intermixed to form amorphous phase(s) upon heating to about 625 K by so-called thermally assisted solid state amorphization, TASSA. The amorphization heat of formation for binary system via the TASSA, ΔH_a, was measured directly as a function of the milling time. Comparable with the TASSA, homogeneous amorphous alloys were fabricated directly without heating the composite multilayered particles upon milling these particles for longer milling time (86 ks–144 ks). The amorphization reaction here is attributed to the mechanical driven solid state amorphization. This single amorphous phase transforms into an order phase (μ phase) upon heating at 1088 K (crystallization temperature, T_x) with enthalpy change of crystallization, ΔH_x, of −8.3 kJ mol⁻¹.     

放电等离子烧结制备Fe75Zr3Si13B9磁性材料

采用机械合金化技术制备Fe75Zr3Si13B9非晶合金粉体,利用SPS放电等离子烧结技术在不同烧结温度下将非晶合金粉体制备成d20 mm×7 mm的块体非晶纳米晶合金。采用XRD和DSC分析了Fe75Zr3Si13B9非晶合金粉体的相组成、玻璃转变温度Tg、开始晶化温度Tx和晶化峰温度Tp。然后利用XRD、SEM、Gleeble3500、VSM分析不同烧结温度下块体的相转变、微观形貌、力学性能和磁性能。研究表明,在500 MPa的烧结压力下,随着烧结温度的升高,非晶相开始晶化形成非晶纳米晶双相结构,同时,样品的致密度、抗压强度、微观硬度、饱和磁化强度均显著提高。最后在500 MPa的烧结压力和863.15 K的烧结温度下,获得密度6.9325 g/cm3、抗压强度1140.28 MPa、饱和磁化强度1.28 T的非晶纳米晶磁性材料。     

Mechanical alloying characteristic and thermal stability of Al_(78)Fe_(20)Zr_2 amorphous powders

The powders of pure Al, Fe, and Zr for preparing Al78Fe20Zr2 were subject to a high-energy planetary ball milling.The microstructure evolution of the mixtures at the different intervals of milling was characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM) and differential scanning calorimetry(DSC).It was found that a nearly complete amorphization could be achieved in the mixtures after ball milling for 23 h.Further ball milling led to the crystallization of the amorphous powders.A long time ball milling, e.g., 160 h, led to a complete crystallization of the amorphous powders and the formation of Al3Zr and Al13Fe4.The crystallization products caused by ball milling are almost the same as that produced by isothermal annealing of the amorphous powders in vacuum at 800 K for 1 h.     

Mechanical alloying characteristic and thermal stability of Al<Subscript>78</Subscript>Fe<Subscript>20</Subscript>Zr<Subscript>2</Subscript> amorphous powders

The powders of pure Al, Fe, and Zr for preparing Al₇₈Fe₂₀Zr₂ were subject to a high-energy planetary ball milling. The microstructure evolution of the mixtures at the different intervals of milling was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). It was found that a nearly complete amorphization could be achieved in the mixtures after ball milling for 23 h. Further ball milling led to the crystallization of the amorphous powders. A long time ball milling, e.g., 160 h, led to a complete crystallization of the amorphous powders and the formation of Al₃Zr and Al1₃Fe₄. The crystallization products caused by ball milling are almost the same as that produced by isothermal annealing of the amorphous powders in vacuum at 800 K for 1 h.     

AMORPHIZATION TRANSFORMATION BY MECHANICAL ALLOYING IN THE Mo-Si SYSTEM

1.IntroductionInrecelltyears,MoSiZhasattractedconsiderableattentionasapotentialhigh-temperaturestructuralmaterial.Thecombinationofhighmeltingpoint(2030"C),moderatedensity(6.24gcm--'),excellentoxidationresistance,andhighmodulusatelevatedtemperaturemakesMoSiZoneofthemostpromisingmatrixphasetobeusedattemperaturesupto1600oC[l].Anothermolybdenumsilicide,Mo5Si3,hasbeenproposedasapotentialreinforcementforMoSt,[1,2].AmongawidevarietyofprocessingtechniquesutilizedtosynthesizeMoSt2,mechanicalalloy…     

High-pressure sintering and magnetic properties of Fe86Zr11-xNbxB3 （x=5.5, 6） amorphous alloys

1 INTRODUCTION Fe-based nanocrystalline soft magnetic alloys become the focus in the world because of their ex- cellent soft magnetic properties and high saturation induction.In engineering applications , soft mag- netic alloys are usually used in bulk form with complex shape . However , nanocrystalline soft magnetic alloys in engineering applications are pre- pared through the crystallization of amorphous al- loy which is controlled by melt spinning, accord- ingly the shape and size of th…     

Nd56Fe30Al10Dy4大块非晶合金晶化过程中磁性及微观结构的研究

采用铜模吸铸法制备Nd56Fe30Al10Dy4大块非晶合金,利用差示扫描量热仪(DSC)、振动样品磁强计(VSM)、X射线衍射仪(XRD)和扫描电镜(SEM)研究了该合金晶化过程中磁性及微观结构的变化。结果表明,铸态下合金表现为明显的硬磁性,在765 K退火后,合金中有少量晶态相产生,内禀矫顽力和饱和磁化强度略有下降。随着退火温度升高,合金中晶态相的相对含量逐渐增加,非晶相的相对含量逐渐减少,饱和磁化强度逐渐降低,但其内禀矫顽力变化不大。810 K退火后,合金完全晶化,铁磁性消失。结合合金的磁性能、微观结构、铁磁交换耦合作用的结果分析,Nd基大块非晶合金的矫顽力来源于合金中非晶相,但非晶相的相对含量却对矫顽力影响不大,这可以用强钉扎机制进行解释。     

Mechanical alloying and magnetic saturation of tungsten–nickel powders

Alloying mechanism and magnetic saturation of tungsten and W-40 wt.% Ni milled powders were investigated using XRD, SEM and saturation magnetisation techniques. Mechanical alloying was proceeded by deformation of FCC Ni toward FCT phase and BCC to BCT in W, hence formation of supersaturated tetragonal Ni(W) solid solution. Milling of pure W yielded a product comprised of magnetic BCT and non-magnetic nanocrystalline BCC W powders. The magnetic saturation of W increased at the early milling stage and decreased later due to the transition of the BCC W structure toward anisotropic close packed crystal structure and formation of nanograins with high specific surface. Magnetic saturation of W–Ni powders decreased with milling time but increased after forming a metastable tetragonal solid solution.     

Amorphization and magnetic properties of Fe62Nb38 mechanically alloyed powders

The amorphization and magnetic properties of Fe62Nb38 mechanically alloyed powders were investigated. In the initial mechanical alloying processes, the lattice structure of pure Fe is destroyed due to the cold-welding and fracturing, accompanying the reduction of ferromagnetic properties. The Ms value of Fe62Nb38 powders with ball-milling time t=6 h is only 48.1 A.m^2/kg. With prolongating of mechanical alloying processes, a solid state amorphization reaction (SSAR) takes place and the Fe-Nb ferromagnetic amorphous phase is formed. With the milling time increasing from 6 to 18 h, the saturation magnetization of Fe62Nb38 powders increases with enhancement of the proportion of ferromagnetic amorphous phase in milled powders. The Ms value of the Fe62Nb38 amorphous powders is 98 A.m^2/kg, which is very close to the value estimated from dilute model. However, the Curie temperature of the Fe62Nb38 amorphous phase is only 206℃, which is much smaller than that of the pure Fe. This implies that the exchange interaction between Fe atoms in amorphous alloyed Fe62Nb38 becomes weak due to the Nb dilution. Investigation shows that the variation of magnetic properties of milled powders is one of important tools for describing the amorphization by mechanical alloying.     

Amorphization process induced by mechanical alloying in the immiscible Cu-Ta system

The mechanism for the amorphization induced by mechanical alloying (MA) has been studied in the immiscible Cu- Ta system. A mixture of copper and tantalum powders at a composition ratio of Ta: Cu = 7:3 was used. The first 30 h of milling essentially results in the reduction in Ta and Cu grain size down to ∼10 nm without measurable formation of an amorphous phase. The thermally assisted amorphization (TAA) becomes noticeable after 60 h of milling. The higher the ambient temperature, the faster the amorphization proceeds. The TAA effect is also observed by annealing a partially amorphous MA powder. The microstructure after 30 h of milling is such that fine Cu crystallites are embedded in a fine- grained Ta matrix. Here an interfacial energy contribution is large enough to raise the Gibbs energy to that of an amorphous phase. Now high temperature milling or annealing allows an energetically downhill process to occur. This is most likely responsible for the observed TAA effect in the Cu- Ta system characterized by a positive heat of mixing.     

Ti—Fe机械合金化中氢致非晶化的研究

研究了氢原子对Ｔｉ－Ｆｅ系机械合金化的影响,应用 ＸＲＤ,ＤＳＣ,ＴＥＭ等方法测试了Ｔｉ－Ｆｅ系和Ｔｉ－Ｆｅ－ＴｉＨ２系的机械合金化反应过程和产物结构的特征。研究结果表明,氢原子在机械合金化过程中诱导非晶ＴｉＦｅ相的形成,由于氢原子的影响,非晶ＴｉＦｅ相的结构弛豫温度和晶化温度低于机械合金化得到的非晶ＴｉＦｅ相相应的温度。     

Synthesis and characteristics of W-Ni-Fe nano-composite powders prepared by mechanical alloying

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The synthesis of nanocrystalline Ni75Nb12B13 alloys by high energy ball milling of elemental components

Ni₇₅Nb₁₂B₁₃ alloys were synthesized by mechanical alloying (MA) of individual Ni, Nb and B components. X-ray investigation showed the formation of Ni (Nb, B) solid solution and amorphous phase at the intermediate stage of milling. Metastable phases formed by MA turned into Ni (Nb), Ni₂₁Nb₂B₆ and Ni₃Nb stable phases during heating up to 720 °C. The exothermal effects on DSC curves were caused with these processes. The disintegration of Ni (Nb, B) solid solution and crystallization of an amorphous phase resulted in the stable phases formation during the milling prolongation as well as after thermal treatment.     

Formation of crystalline and amorphous solid solutions of W–Ni–Fe powder during mechanical alloying

The tungsten heavy alloy with the composition of 76.6W–17.3Ni–6.1Fe in atom percent was mechanically alloyed (MA) from the elemental powders of W, Ni and Fe. Nanocrystalline supersaturated solid solutions and amorphous phase were obtained during MA. Phase evolution, grain size and lattice distortion of these powders were determined and discussed. A thermodynamic model was developed based on semi-experimental theory of Miedema to calculate the driving force for phase evolution. The thermodynamic analysis showed that there is no chemical driving force to form the solid solution and the amorphous phase. The effect of the work of milling on the amorphization during MA was discussed and the model of multilayer amorphization during MA was applied to illustrate the feasibility of amorphization of powder with neither ΔH_mix0 nor D_BD_A. The driving force for amorphization is provided not by the negative heat of mixing or the stored energy in the grain boundaries but by the sharp concentration gradients in this system. Amorphization is mechanically driven and not by the negative heat of mixing. Crystallization is suppressed by sharp concentration gradients.