Neutron diffraction study in amorphous Ni30Ta70 alloy powders by mechanical alloying

A mixture of elemental Ni and Ta powders with an atomic ratio of 3∶7 was subjected to mechanical alloying (MA). An amorphous Ni₃₀Ta₇₀ alloy was formed after 80 hrs of milling, the amorphization by rapid quenching technique of which has not been reported. The atomic structural changes were observed by neutron diffraction in the amorphization process during MA. The radial distribution function RDF(r) shows that peaks of fcc-Ni and bcc-Ta crystal broaden first and gradually approach those characteristic of an amorphous phase with increasing MA time. A local atomic environment around Ni and Ta atoms was studied by analyzing the first peak in the total pair distribution function g(r) after the completion of amorphization. We reach our conclusion from this analysis that the amorphization in the Ni₃₀Ta₇₀ alloy takes place by the penetration of smaller Ni atoms into the bcc-Ta lattice.     

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…     

Thermal stability of a Cu/Ta multilayer: an intriguing interfacial reaction

When a Cu/Ta multilayer is formed by sputtering, it is found that the Cu has the equilibrium f.c.c. structure whereas the Ta is in a metastable tetragonal (β-Ta) form. The transformation of the latter into the stable b.c.c. phase (α-Ta), in the presence of Cu, is the subject of the present study. We observed that for a Ta film alone without Cu, the phase transformation starts at about 800°C. In a Cu/β-Ta multilayer, we found from X-ray diffraction analysis that a large amount of β-Ta already transformed into b.c.c.-Ta upon annealing at 700°C, which is much lower than the transformation temperature of Ta by itself. Our transmission electron microscopy (TEM) analysis furthermore reveals that during annealing at around 600°C, small α-Ta grains nucleate at the Cu/β-Ta interface and grow into Cu. Annealing at 800°C results in a complete transformation of the multilayer into the agglomeration of separate Cu and α-Ta grains. Also, we observed that an amorphous layer about 2 nm thick forms upon annealing at 500°C in the Cu/β-Ta system, which has a slightly positive heat of mixing. In energy dispersive spectroscopy (EDS) analysis, the Cu/β-Ta interface of as-deposited samples is found to be chemically discrete, while the Cu/β-Ta interface of a 600°C annealed sample shows extensive interdiffusion and the amorphous layer formed at the interface is found to be a mixed layer of Cu and Ta. Upon annealing at a higher temperature (800°C), no amorphous layer appears and the interface is found to be chemically abrupt. We conclude that the microstructural change of the multilayer is the process of the Ta phase transformation and this occurs through the interaction with Cu. We, furthermore, discuss the amorphization in the Cu–Ta system based on a calculated free energy diagram.     

机械合金化制备W-Ni-Fe纳米-非晶材料

按照80．7W-13．2Ni-6．1Fe的原子分数．采用机械合金化(MA)方法，制备了W-Ni-Fe合金纳米晶和非晶相的混晶结构。结合XRD，利用近似内标法计算了球磨不同时间球磨粉中残留晶体W的体积分数和非晶相中的W含量，并分析了球磨过程中非晶形成的机制。结果表明：随球磨时间的延长，W晶粒不断细化．球磨60h，钨晶粒尺寸可达到10nm-20nm，非晶相的形成过程主要是Ni(Fe)首先溶入W中形成过饱和固溶体，球磨20h后形成W-Ni(Fe)非晶。过饱和固溶体的形成是由于携带较大晶界存储能的小粒子不断溶入W中，计算得到可固溶的临界Ni粒子尺寸约为3nm。由于Fe污染不断溶入W中，在球磨过程中，残留晶体W的体积分数不断减少．而非晶相中的W-Ni(Fe)比例基本保持恒定，为63W-37Ni(Fe)。     

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.     

Microstructural, thermal and magnetic properties of amorphous/nanocrystalline FeCrMnN alloys prepared by mechanical alloying and subsequent heat treatment

Amorphous FeCrMnN alloys were synthesized by mechanical alloying (MA) of the elemental powder mixtures under a nitrogen gas atmosphere. The phase identification and structural properties, morphological evolution, thermal behavior and magnetic properties of the mechanically alloyed powders were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively. According to the results, at the low milling times the structure consists of the nanocrystalline ferrite and austenite phases. By progression of the MA process, the quantity and homogeneity of the amorphous phase increase. At sufficiently high milling times (>120 h), the XRD pattern becomes halo, indicating complete amorphization. The results also show that the amorphous powders exhibit a wide supercooled liquid region. The crystallization of the amorphous phase occurs during the heating cycle in the DSC equipment and the amorphous phase is transformed into the crystalline compounds containing ferrite, CrN and Cr₂N. The magnetic studies reveal that the magnetic coercivity increases and then decreases. Also, the saturation magnetization decreases with the milling time and after the completion of the amorphization process (>120 h), the material shows a paramagnetic behavior. Although the magnetic behavior does not considerably change by heating the amorphous powders up to the crystallization temperature via DSC equipment, the material depicts a considerable saturation magnetization after the transformation of the amorphous phase to the nanocrystalline compounds.     

机械合金化及热处理对TiH2-Ni粉末结构和形貌的影响（英文）

研究机械合金化及热处理对TiH2-Ni粉末的结构和形貌的影响。在初始球磨阶段,Ni(Ti)固溶体形成。当球磨至60h时,非晶结构的TiH2-Ni粉末形成,粉末中还包含少量的纳米晶TiH2相,粉末内元素分布均匀。球磨60h的粉末经693K热处理,发生了非晶化反应;经1073K短时间热处理后,非晶相结晶,形成Ti2Ni、TiNi和TiNi3相;在相同热处理温度下进一步延长热处理时间可使富镍相析出以及在3种Ti-Ni相之间发生相转变。     

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.     

Nb含量对机械合金化Cu-Nb合金晶粒细化和力学性能的影响

采用机械合金化法制备了Cu-xNb(x=0-30%)合金粉末,通过X射线衍射仪(XRD)、金相显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)观察和显微硬度测量分析了Nb溶质含量对粉末晶粒细化过程以及力学性能的影响。结果表明,尽管Nb与Cu的平衡固溶度接近为0,经100h球磨后,Nb在Cu中的最大固溶量可达约11wt%。随着Nb含量的增加,Cu-Nb合金粉末的晶粒细化能力提高。这是由于随着偏析至位错处的溶质原子数量增加,合金的回复过程得到抑制,因此有利于晶粒尺寸的减小。Cu-30wt%Nb合金球磨100h后Cu相平均晶粒尺寸减小至约6nm。此外,球磨Cu-Nb合金粉末的显微硬度随着Nb含量的增加而提高,其强化机制主要为细晶强化和固溶强化。     

Structure and magnetostriction of Tb0.4Nd0.6(Fe0.8Co0.2)1.90 alloy prepared by solid-state synthesis

Mechanical alloying (MA) and subsequent solid sintering process was used to prepare the Nd-containing magnetostrictive Tb0.4Nd0.6(Fe0.8Co0.2)1.90 alloy. The structure, thermal stability and phase transformation were investigated as functions of composition, milling process and annealing temperature. An amorphous phase was formed by high-energy ball milling for 5 h with the ball-to-powder weight ratio of 20:1, which crystallized into MgCu2-type and PuNi3-type crystalline structure with different annealing temperatures. The magnetoelastic properties were investigated by means of a standard strain technique. The high Nd-content (Tb,Nd)(Fe,Co)2 Laves phase for the composition Tb0.4Nd0.6(Fe0.8Co0.2)1.90 was synthesized by MA process plus annealing at 500 ℃ for 30 min.     

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.     

The competing crystalline and amorphous solid solutions in the Ag–Cu system

Upon nonequilibrium processing using vapor quenching or mechanical alloying, the supersaturated fcc solid solution predominates over the amorphous solution in the Ag–Cu system. The thermodynamic and kinetic origins of this phase selection are explored. The enthalpy of formation of both solutions has been determined as a function of composition using calorimetry measurements and molecular dynamics (MD) simulations. The enthalpy of the fcc solution is found to be lower than that of the competing amorphous phase. The preference for the fcc crystalline state is enhanced by the low kinetic barrier to crystallization of the amorphous solution, which occurred during quenching even when high cooling rates were employed or during annealing at low temperatures. Consequently, the retention of an amorphous Ag–Cu solution required kinetic trapping using ultrahigh quenching rates achievable only under stringent vapor deposition conditions or in MD simulations. However, transmission electron microscopy revealed the presence of local regions of amorphous Ag–Cu after cold rolling of multilayers of elemental Ag and Cu foils at room temperature. This result of partial amorphization demonstrates the possibility of mechanically driven solid-state amorphization in a system with a positive heat of mixing.     

高能球磨工艺对Ti50Ni22Cu25Sn3组织演变的影响

用高能球磨法制备Ti50Ni22Cu25Sn3非晶粉末,并研究球磨工艺参数对Ti50Ni22Cu25Sn3非晶形成过程的影响。结果表明,球磨转速以及磨球直径对Ti50Ni22Cu25Sn3非晶相的形成效率具有十分重要的影响。较高的转速和合适的球径能有效促进该Ti基合金的非晶化,缩短合金非晶化的时间,当转速为400 r/min,球料比为20:1时,球磨时间约为30 h后,可得到完全的Ti50Ni22Cu25Sn3非晶粉末     

Mechanically induced crystalline–glassy phase transformations of mechanically alloyed Ta55Zr10Al10Ni10Cu15 multicomponent alloy powders

New multicomponent Ta-based glassy alloy powder was synthesized by mechanical alloying (MA) the elemental powders of Ta₅₅Zr₁₀Ni₁₀Al₁₀Cu₁₅ at room temperature, using a low-energy ball milling technique. During the early stage of milling the agglomerated crystalline powders are mechanically crushed and fresh surfaces are rapidly created. Kneading of such ground powders enhances the atomic diffusion and leads to local alloying. As the MA time increases, the number of vacancies in the Ta lattice (base material) increases so that the atoms of the alloying elements for Zr, Al, Ni and Cu tend to migrate to the open defected lattice of metallic Ta. The number of atoms of the alloying elements that migrate to the bcc lattice of the base material are increasing with increasing MA time and this leads to a monotonic expansion of the Ta lattice. Further milling time (86–130 ks) plays an important role in increasing the rate of diffusion and this leads to an increase in the number of migrated atoms of the alloying elements that pass into the Ta lattice. The a₀ of the yielded solid solution at this stage does not change anymore with increasing MA time and a homogeneous supersaturated bcc-solid solution is obtained after 130 ks of MA time. This solid solution, which is subjected to continuous imperfections, is gradually transformed into a glassy phase upon increasing the MA time. The glassy powders of the final-product (1080 ks) in which its glass transition temperature (T_g) lies at a high temperature (834 K), crystallize through a single sharp exothermic peak at 1004 K (T_x). The total enthalpy change of crystallization (ΔH_x) is −10.32 kJ/mol. The width of the supercooled liquid region before crystallization (ΔT_x) of the synthesized glassy powder shows the largest value (170 K) of any reported metallic glassy system.     

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.     

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.     

Crystallization of magnesium niobate from mechanochemically derived amorphous phase

The effect of high-energy ball milling and subsequent annealing on the mixture of MgO and Nb₂O₅ has been investigated. X-ray diffraction (XRD) measurement indicates that an amorphous phase is produced after milling for 5 h, while traces of MgNb₂O₆ crystallized from the amorphous phase during prolonged milling. Significant crystallization of MgNb₂O₆ from the amorphous state is observed after annealing at 500 °C, while the reaction of the remaining MgO and Nb₂O₅ does not take place at this temperature. Single phase MgNb₂O₆ can be achieved for all the milled samples at 700 °C. No significant grain growth is observed when the milled powders were annealed at temperature below 900 °C. Almost fully dense MgNb₂O₆ ceramics are obtained after annealing at 1100 °C from the as-milled powders.     

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.     

Effect of powder alloy composition on the microstructure and properties of kinetic sprayed Cu-Ga based coating materials

This study attempted to manufacture Cu-Ga coating materials via the kinetic spray process and examined the effect of powder alloy composition on the microstructure and properties of the kinetic sprayed Cu-Ga based coating materials. Cu-15 at%Ga, Cu-20 at%Ga, and Cu-30 at%Ga powders were prepared and used. Annealing heat treatments were conducted at 200 °C~800 °C. The results showed that the coating layers could be manufactured with Cu-15 at%Ga and Cu-20 at%Ga powders via the kinetic spray process, except for Cu- 30 at%Ga. A single phase of pure Cu was observed in the Cu-15 at%Ga coating layer and Cu and Cu₃Ga phases in the Cu-20 at%Ga coating layer. A small amount of Ga₂O₃ was also detected between deposited particles in both coating layers. It was difficult to obtain the coating layer due to the shattering of powders during the kinetic spraying with Cu-30 at%Ga powder, which is made up of a variety of inter-metallic compounds. Porosity and hardness decreased as the annealing temperature increased, and porosity decreased into 0.48% (Cu-15 at%Ga), 0.74%(Cu-20 at%Ga) at 800 °C. Annealing heat treatment appeared to be effective in enhancing the density of the coating layers without generating a new phase. This study also considered to suggest the optimal alloy composition of kinetic sprayed Cu-Ga based coating material for sputtering target.