Some amorphous alloys in Zr-Ru-Mo and Zr-Ru-W systems prepared by rapid solidification

All binary systems of the ternary systems Zr-Mo-Ru and Zr-W-Ru show at least one eutectic point. This indicates the existence of low melting eutectic alloys in these ternary systems (∼ 1200–1300°C). As starting materials, homogeneous Zr-Mo-Ru and Zr-W-Ru samples of different compositions were prepared by rapid solidification (∼10⁶Ks⁻¹) in a splat-cooling apparatus with a rf levitation coil and a high-velocity two-piston arrangement driven by solenoids. The possibility of obtaining alloys in amorphous state from low-melting areas of these ternary systems with the addition of boron or silicon has been investigated.     

Structure of nanocomposites of Al-Fe alloys prepared by mechanical alloying and rapid solidification processing

Structures of Al-based nanocomposites of Al-Fe alloys prepared by mechanical alloying (MA) and subsequent annealing are compared with those obtained by rapid solidification processing (RSP). MA produced only supersaturated solid solution of Fe in Al up to 10 at.% Fe, while for higher Fe content up to 20 at.% the nonequilibrium intermetallic Al₅Fe₂ appeared. Subsequent annealing at 673 K resulted in more Al₅Fe₂ formation with very little coarsening. The equilibrium intermetallics, Al₃Fe (Al₁₃Fe₄), was not observed even at this temperature. In contrast, ribbons of similar composition produced by RSP formed fine cellular or dendritic structure with nanosized dispersoids of possibly a nano-quasicrystalline phase and amorphous phase along with α-Al depending on the Fe content in the alloys. This difference in the product structure can be attributed to the difference in alloying mechanisms in MA and RSP.     

Synthesis by ball milling and characterization of Al-Zn alloys

Mechanical ball milling is a useful technique for systems with positive enthalpy of mixing. With this technique solubility of a solute in a solid solution can be enhanced. Al-Zn system has positive heat of mixing. High energy ball milling has been employed to produce four alloys of Al with 2.5 to 10 wt% Zn. Powders of Al (1–125 m) and Zn (0.7–5.0 m) were mixed together in the desired proportion and milled with a powder to ball weight ratio of 1:20. The size and shape of the particles of as-received and alloy powders were examined in a scanning electron microscope (SEM) while their microanalysis was performed by energy dispersive system (EDS) attached with SEM. It has been observed that 120 h of milling of the powders produced homogeneous alloys. X-ray diffraction (XRD) patterns confirm complete solubility up to 10 wt% Zn in Al. Using the quasi-chemical theory of binary solid solutions, the enthalpy of mixing of 10 wt% Zn in Al has been determined to be 276 cals/mol. It is shown that stress exerted by very high density of dislocations, generated by mechanical milling, plays a major role in the enhancement of solubility. Hardness has been measured and it increases with increasing solute content.     

Nanostructure cathode materials prepared by high-energy ball milling method

We prepare Li₂MnO₃ and LiNi_0.5Mn_0.3Co_0.2O₂ as nanostructure cathode materials using a high-energy ball milling method with bulk-type electrodes. The nanostructure electrodes prepared by the ball milling exhibit much smaller particle sizes in diameter than those of bulk-type electrodes. The 1st charge–discharge capacitance and efficiency of the nanostructure cathode materials are superior to those of the bulk-type electrodes.     

Fast diffusion in nanocrystalline ceramics prepared by ball milling

Nanocrystalline materials can show enhanced diffusivity compared to their microcrystalline counterparts due to the large fraction of atoms or ions located in interfacial regions. In the case of ceramics, resulting properties with potential applications are, e.g., fast ionic conductivity, high mechanical creep rate and increased catalytic activity. Different nanocrystalline ceramic materials were prepared by high-energy ball milling of coarse grained source materials. The samples were characterized by XRD, TEM, BET method and IR spectroscopy. These measurements show that the primary crystallites form larger agglomerates with internal interfaces and that the reduction of the crystallite size is accompanied by a structural degradation of the surface zone. An example is the partial amorphization observed for LiBO₂ by IR spectroscopy. The diffusivity and ion conductivity in these materials was studied by NMR relaxation, NMR line shape and impedance spectroscopies. It was possible to discriminate between highly mobile ions in the interfacial regions and immobile ions in the grains. In general diffusion in the nanocrystalline systems was found to be fast compared to that in the corresponding microcrystalline source materials.     

Sm-Co hard magnetic nanoparticles prepared by surfactant-assisted ball milling

Hard magnetic nanoparticles based on the Sm(2)Co(17) and SmCo(5) systems have been successfully produced using a surfactant-assisted ball milling technique. A size-selection process has been developed to obtain nanoparticles of different sizes with narrow size distribution. Significant room-temperature coercivity up to 3.1?kOe has been achieved with the Sm(2)Co(17)-based nanoparticles of an average size of 23?nm. It has been found that surfactants play multifold roles in the processing.     

球磨Mg0.97La0.03Ni合金的热稳定性及电性能研究

采用XRD、DTA、SEM及电池性能测试仪等对球磨Mg0.97La0.03Ni合金的结构、形貌、活化性能、热稳定性、电化学稳定性及容量衰减机理等进行了详细的研究。结果表明：样品的热稳定性及循环稳定性随着球磨时间的延长而增加。经400r／min球磨50h的样品在第二次活化时即达到最大值450mAh／g．经25次循环充放电后．该样品的容量与其最大值相比下降了53％．容量衰减的主要原因有：在循环充放电过程中．非晶体逐渐分解生成Mg2NiH4和Ni等晶体相，同时在颗粒表面形成腐蚀产物Mg(OH)2等。     

Synthesis and structural evolution of tungsten carbide prepared by ball milling

Tungsten carbide has been synthesized directly by ball-milling tungsten powder and activated carbon in vacuum. The structural development of the WC phase with milling times up to 310 h has been followed using X-ray, neutron diffraction and scanning electron microscopy. Subsequent annealing (at 1000 °C for 1 and 20 h) of material milled for 90 h or longer, results in samples comprising almost entirely crystalline WC. The production of WC itself during milling results in enhanced iron contamination from the steel mill and balls on extended milling which were monitored by energy-dispersive X-ray and Mossbauer spectroscopies. This revised version was published online in November 2006 with corrections to the Cover Date.     

Development and application of ferromagnetic alloys made by rapid solidification

Abstract

Amorphous alloys, made by rapid solidification, were first introduced in 1960 and precipitated a major new field of research in metallurgy. A part of this new field, dating from around 1975, involves magnetic alloys made by rapid solidification. These new magnetic alloys are critically assessed against the background of existing Si–Fe alloys and the new developments in high induction Si–Fe. It is concluded that these new alloys, of potentially very low cost, may be important in the highly automated manufacture of small transformers and small electricals machines.

MST/726     

Al-based nanocrystalline composites by rapid solidification of Al-Ni-Sm alloys

Nanophase composites (Al-based materials with α-Al particles dispersed in an amorphous matrix) can be produced by melt spinning and annealing Al₈₈Ni_{12 − x}Sm_x (x = 2 to 10 at%) master alloys. The structures and the thermal stability of the ribbons obtained, asquenched and after annealing, are characterised by X-ray diffraction and differential scanning calorimetry. The mechanical properties of these composites, including hardness and abrasive wear resistance, are measured as a function of the volume fraction of α-Al nanocrystals in the amorphous matrix. The properties of these nanophase composites are compared with other industrial alloys in the aluminium family and show an exceptional hardness and wear resistance.     

Corrosion resistance enhancement of marine alloys by rapid solidification

Copper-nickel alloys used in marine applications, are known for their anti-fouling properties. However, they are generally of low strength and are moderately susceptible to corrosion when used in a marine environment. Attempts at adding iron to Copper-nickel alloys by conventional ingot metallurgy, to improve their mechanical and corrosion resistant properties, have met with limited success. In this work, rapid solidification technology was employed to produce rapidly solidified (RS) Cu-10Ni and Cu-10Ni-8Fe. It was found that both the RS Cu-10Ni and Cu-10Ni-8Fe exhibited superior mechanical and corrosion resistant properties, compared with their sand-cast counterparts. Furthermore, the addition of iron to Cu-10Ni alloy, produced by RS, increased the corrosion resistance of the alloy, whereas the addition of iron to Cu-10Ni alloy produced by conventional means, had an adverse effect.     

Transformation behavior and thermal stability of Al-based systems prepared by ball milling

Transmission electron microscopy, X-ray diffraction, scanning electron microscopy, differential thermal analysis, and differential scanning calorimetry were used to investigate the transformation behavior of (Al_0.88Ni_0.08Co_0.04)_100−x,Zr_x, (wherex = 0 to 5 at. %) alloys during ball milling, and the thermal stability during the reverse process of return to equilibrium. The results have shown that the crystalline to amorphous transformation occurs only in compositions containing Zr. Mechanical grinding is shown to easily amorphize the Al₃Zr compound which enters in equilibrium with the fcc-Al and (Co, Ni)₂Al₉ phases for the compositions studied. The formation of an amorphous phase at the fcc-Al and Co₂Al₉ grain boundaries leads to a wetting transition, and with decreasing grain size the initially nanostructured Al₈₈Ni₈Co₄ alloy was found to progressively transform to an amorphous alloy. The crystallization temperature, the activation energy, and the crystallization enthalpy increase, while the melting temperature of the quaternary alloys decrease with increasing Zr substitution up to 5 at. %.     

Microstructure and electrical properties of ZnO-based varistors prepared by high-energy ball milling

ZnO-based varistor ceramics were prepared at sintering temperatures ranging from 900 °C to 1,300 °C, by subjecting the mixed oxide powders to high-energy ball milling (HEBM) for 0, 5, 10 and 20 h, respectively. Varistor ceramics prepared by HEBM featured denser body, better electrical properties sintered at low-temperature than at traditional high-temperature. The high density is due to the refinement of the crystalline grains, the enhanced stored energy in the powders coming from lattice distortion and defects as well as the promotion of liquid-phase sintering. Good electrical properties is attributed to proper microstructure formed at low-temperature and improved grain boundary characteristics resulting from HEBM. With increasing sintering temperatures, the electrical properties and density became worse due to the decrease in amount of Bi-rich phase. Temperature increased up to 1,200 °C or above, the Bi-rich phase vanished and the ceramics exhibited very low nonlinear coefficient.     

Microstructure and martensitic transformation in Si-coated TiNi powders prepared by ball milling

Si was coated on the surface of Ti–49Ni (at%) alloy powders by ball milling in order to improve the electrochemical properties of the Si electrodes of secondary Li ion batteries and then the microstructure and martensitic transformation behavior were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ti–Ni powders coated with Si were fabricated successfully by ball milling. As-milled powders consisted of highly deformed Ti–Ni powders with the B2 phase and amorphous Si layers. The thickness of the Si layer coated on the surface of the Ti–Ni powders increased from 3–5 μm to 10–15 μm by extending the milling time from 3 h to 48 h. However, severe contamination from the grinding media, ZrO₂ occurred when the ball milling time was as long as 48 h. By heating as-milled powders to various temperatures in the range of 673–873 K, the highly deformed Ti–Ni powders were recovered and Ti₄Ni₄Si₇ was formed. Two-stage B2–R–B19′ transformation occurred when as-milled Si-coated Ti–49Ni alloy powders were heated to temperatures below 873 K, above this temperature one-stage B2–B19′ transformation occurred.     

Microstructural and chemical properties of AlN-Cu nanocomposite powders prepared by planetary ball milling

Microelectronic circuits require contact with a high thermal conductivity, and controlled low coefficients of thermal expansion packaging materials for the high performance and reliability of the semiconductor chips. The present study was carried out to investigate the microstructural and chemical properties of AlN-Cu nanocomposite powders created by planetary ball milling. X-ray diffraction and scanning electron microscopy analysis of the obtained powders were performed. The residual oxygen and carbon in ball milled AlN-Cu powders were analyzed. AlN-Cu composite powders of 15 μm size and copper crystallites of 25 nm were obtained after milling for 8 h. The amount of residual oxygen was considerably reduced after exposure to hydrogen reduction treatment at 600°C for 2 h. More significantly, 97% of the residual carbon was removed regardless of milling time and alloy composition. Furthermore, residual carbon was removed as a gaseous mixture of carbon monoxide and carbon dioxide.     

Magnetic properties of iron nitride-silica nanocomposite materials prepared by high-energy ball milling

Powder mixtures of (FexN)y and (SiO2)1-y, with x between 3 and 4 and y equal to 0.2 or 0.6, were ball-milled for 4, 8, 16, 32, and 64 h. X-ray diffraction, thermal analysis, and magnetization measurements allowed an investigation of structural and magnetic properties to be carried out. The samples consist of nanostructured Fe3N and Fe4N particles in a SiO2 matrix. As the milling time increases, the Fe4N phase is eliminated from the particles in favor of Fe3N. Coercive fields as high as 270 and 84 Oe are obtained for (FexN)0.2(SiO2)0.8 at 5 and 300 K, respectively. This higher coercive field, upon cooling, indicates the presence of small superparamagnetic particles. The coercive field also increases with milling time, which is due to the reduced particle size and induced stain. The saturation magnetization decreases with increased milling time as a consequence of an increase in the superparamagnetic fraction and increased strain. Hard and soft magnetic properties are observed for y = 0.2 and y = 0.6 samples, respectively.     

Microstructural characterization of amorphous and nanocrystalline boron nitride prepared by high-energy ball milling

Microstructural parameters like crystallite size, lattice strain, stacking faults and dislocation density were evaluated from the X-ray diffraction data of boron nitride (BN) powder milled in a high-energy vibrational ball mill for different length of time (2-120 h), using different model based approaches like Scherrer analysis, integral breadth method, Williamson-Hall technique and modified Rietveld technique. From diffraction line-broadening analysis of the successive patterns of BN with varying milling time, it was observed that overall line broadening was an operative cause for crystallite size reduction at lower milling time (∼5 h), whereas lattice strains were the prominent cause of line broadening at higher milling times (>19 h). For intermediate milling time (7-19 h), both crystallite size and lattice strain influence the profile broadening although their relative contribution vary with milling time. Microstructural information showed that after long time milling (>19 h) BN becomes mixture of nanocrystalline and amorphous BN. The accumulations of defects cause this crystalline to amorphous transition. It has been found that twin fault (β′) and deformation fault (α) significantly contributed to BN powder as synthesized by a high-energy ball-milling technique. Present study consider only three ball-milled (0, 2 and 3 h) BN powder for faults calculation because fault effected reflections (1 0 1, 1 0 2, 1 0 3) disappear with milling time (>3 h). The morphology and particle size of the BN powders before and after ball milling were also observed in a field emission scanning electron microscope (FESEM).