Metastable Ti---Ni---Fe---Si alloys prepared by mechanical alloying

The phase formation and physical properties of mechanically alloyed Ti₅₆Ni₁₈Fe₁₀Si₁₆ have been investigated. The as-milled samples are amorphous and undergo a transition to the icosahedral quasi-crystalline phase on annealing at about 1025 K. Mechanical alloying in the presence of an additive of 1% quasi-crystalline phase yielded the same phase directly. Alloys have been studied by X-ray diffraction. Mössbauer spectroscopy and magnetic susceptibility methods. These results may be compared with those in the literature for amorphous and quasi-crystalline alloys of similar composition prepared by rapid solidification from the melt. In all cases the alloys produced by mechanical alloying show a greater concentration of open volume defects and in the icosahedral phase, a greater degree of disorder and largerphason strains. Hydrogen diffusion studies of these alloys have shown that the mean interatomic distance increases for short hydrogenation times, but that for longer hydrogenation times the hydrogen increases local atomic order which results in a reduction of mean interatomic distances.     

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.     

Amorphization of Al---Cu---Fe quasicrystalline alloys by mechanical milling

The amorphous phase is formed from as-solidified Al---Cu---Fe alloy powder, which is mainly composed of the quasicrystalline phase, by mechanical milling. The structure and morphology of the milled powders were monitored by X-ray diffraction, scanning electron microscopy, and transition electron microscopy respectively. Experimental results indicate that quasicrystalline alloys are more easily amorphized than the corresponding crystalline alloys. No intermediate metastable phase appeared during the whole process. The crystallization behavior of the amorphous powders has been examined by thermal annealing and differential thermal analysis.     

Two milling time regimes in the evolution of magnetic anisotropy of mechanically alloyed soft magnetic powders

The milling time evolution of magnetic anisotropy of ball milled powders can be described considering two regimes. First, for short milling times, the main factor affecting the magnetic behavior of the alloy is the accumulation of internal stresses. Second, for long milling times, magnetic anisotropy can be explained using three contributions: long-range magnetoelastic, averaged short-range magnetoelastic and averaged magnetocrystalline anisotropies.     

Preparation of W–Al–Mo ternary alloys by mechanical alloying

Single phase W_XAl₅₀Mo_50−X (X = 40, 30, 20 and 10) powders have been synthesized directly by mechanical alloying (MA). The structural evolutions during MA and subsequent as-milled powders by annealing at 1400 °C have been analyzed using X-ray diffraction (XRD). Different from the Mo₅₀Al₅₀ alloy, W₄₀Al₅₀Mo₁₀ and W₃₀Al₅₀Mo₂₀ alloys were stable at 1400 °C under vacuum. The results of high-pressure sintering indicated that the microhardnesses of two compositions, namely W₄₀Al₅₀Mo₁₀ and W₃₀Al₅₀Mo₂₀ alloys have higher values compared with W₅₀Al₅₀ alloy.     

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.     

On the general outline of physical properties of amorphous-nanocrystalline Fe-Cr-Mn-N alloy powders prepared by mechanical alloying under nitrogen

This paper reviews last findings about physical properties of Fe-Cr-Mn-N powders synthesized by mechanical alloying under nitrogen. Their thermal, magnetic, indentation, and grain growth behaviors and nitrogen distribution in their amorphous-nanocrystalline structure are regarded as a function of milling time. Particularly, the role of nitrogen in the aforementioned phenomena is reviewed in detail.     

Synthesis of amorphous Ti—Al alloys by mechanical alloying of elemental powders

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Phase formation during mechanical alloying and subsequent low-temperature heat treatment of Al–27.4at%Fe–28.7at%C powders

Phase formation during high energy ball milling of a ternary elemental powder mixture with a composition of Al–27.4at%Fe–28.7at%C and during low temperature heat treatment of the milled powder was studied. It was found that an amorphous phase formed during prolonged milling. During heating the shorter time milled powder, Al and Fe reacted first, forming the AlFe phase and then at a higher temperature, AlFe reacts with Fe and C, forming the AlFe₃C_0.5 phase. During heating the longer time milled powder which contains a substantial amount of amorphous phase, the amorphous phase partially crystallizes first, forming the AlFe and AlFe₃C_0.5 phases, and then AlFe reacts with the remaining amorphous phase, forming the AlFe₃C_0.5 phase. Overall, mechanical alloying of Al, Fe and C elemental phases enables formation of an amorphous phase, while low temperature heat treatment of mechanically milled powder facilitates formation of AlFe and AlFe₃C_0.5 phases.     

TEM study of TiN coatings fabricated by mechanical milling using vibration technique

A mechanical milling method was used for the deposition of TiN coatings. The principle of this method is that a substrate and powder were placed along with balls into the vibration chamber that was vibrated by a mechano-reactor. During mechanical milling process, the substrate surface was impacted by a large number of flying balls. The TiN particles trapped in between the balls and the substrate became cold welded to the surface. The repeated substrate-to-ball collisions forged TiN particles into a coating on the substrate surface. The process allowed the thick TiN coatings to be produced at room temperature in an ambient atmosphere. TEM study of the as-fabricated coatings was carried out. The coating formation depended on the size of the initial TiN particles. The 50-nm TiN nanoparticles were more easily cold welded than 1.5-μm microparticles. The nanoparticles had a tendency to consolidate and densify into the bulk material under the applied compressive loading. The TiN particles better consolidated and densified on the hard Ti surface than on the soft Al one.     

Development of nano-structure Cu-Zr alloys by the mechanical alloying process

Cu-Zr alloys have many applications in electrical and welding industries for their high strength and high electrical and thermal conductivities. These alloys are among age-hardenable alloys with capability of having nano-structure with high solute contents obtainable by the mechanical alloying process. In the present work, Cu-Zr alloys have been developed by the mechanical alloying process. Pure copper powders with different amounts of 1, 3 and 6 wt% of commercial pure zirconium powders were mixed. The powder mixtures were milled in a planetary ball mill for different milling times of 4, 12, 48 and 96 h. Ball mill velocity was 250 rpm and ball to powder weight ratio was 10:1. Ethanol was used as process control agent (PCA). The milling atmosphere was protected by argon gas to prevent the oxidation of powders. The milled powders were analysed by XRD technique and were also investigated by SEM observations. Lattice parameters, crystal sizes and internal strains were calculated using XRD data and Williamson-Hall equation. Results showed that the lattice parameter of copper increased with increasing milling time. The microstructure of milled powder particles became finer at longer milling time towards nano-scale structure. SEM observations showed that powder particles took plate-like shapes. Their average size increased initially and reached a maximum value then it decreased at longer milling times. Different zirconium contents had interesting effects on the behavior of powder mixtures during milling.     

Structure and phase transformations in Fe–Ni–Mn alloys nanostructured by mechanical alloying

Ternary Fe₈₆Ni_xMn_14−x alloys, where x = 0, 2, 4, 6, 8, 10, 12, 14, 16 at.%, were prepared by the mechanical alloying (MA) of elemental powders in a high-energy planetary ball mill. X-ray diffraction analysis and Mössbauer spectroscopy were used to investigate the structure and phase composition of samples. Thermo-magnetic measurements were used to study the phase transformation temperatures. The MA results in the formation of bcc α-Fe and fcc γ-Fe based solid solutions, the hcp phase was not observed after MA. As-milled alloys were annealed with further cooling to ambient or liquid nitrogen temperatures. A significant decrease in martensitic points for the MA alloys was observed that was attributed to the nanocrystalline structure formation.     

Synthesis process of Mg–Ti BCC alloys by means of ball milling

The synthesis process of Mg–Ti alloys with a BCC (body centered cubic) structure by means of ball milling was studied by X-ray diffraction and various microscopic techniques. The morphology and crystal structure of Mg–Ti alloys changed with increase of milling time. During ball milling of Mg and Ti powders in molar ratio of 1:1, firstly, plate-like particles stuck on the surface of the milling pot and balls. After these plate-like particles fell off from the surface of the milling pot and balls, spherical particles with the mean diameter of 1 mm, in which concentric layers of Mg and Ti were disposed, were formed. These spherical particles were crushed into spherical particles with the diameter of around 10 μm by introduction of cracks along the boundaries between Mg and Ti layers. Finally, the Mg₅₀Ti₅₀ BCC phase with the lattice parameter of a = 0.342(1) nm and the grain size of 3 nm was formed. During milling of Mg and Ti to synthesize the BCC alloy, Mg and Ti were deformed mainly by the basal plane slip and the twinning deformation, respectively. Ti acted as abrasives for Mg which had stuck on the surface of the milling pot and balls. The BCC phase was found after Mg dissolved in Ti.     

机械球磨时间对W-Nb合金氦辐照行为的影响

实验采用不同球磨时间制备W-Nb复合粉末,并通过放电等离子烧结方法制备W-Nb复合材料。所得的W-Nb复合材料用剂量为9.90×10₂₄ ions/m₂的氦离子束辐照11分钟,随后分别在900、1100和1300℃下热处理1小时。实验结果表明,球磨时间不同导致复合材料中钨铌固溶程度不同,进而造成了材料抗辐照损伤性能的差异。其中,球磨36小时的试样的固溶程度最低,其在辐照后表面损伤也最严重,表面出现了纳米绒毛状结构。此外,在同一个样品中,钨的不同的晶面取向也导致了不同的表面损伤形貌。通过对比不同热处理温度的试样,发现富铌区域的晶粒发生了明显的长大,但富钨区域的表面形貌几乎没有变化。这是由于铌的加入使得He在钨中的解吸峰右移。     

Electrochemical characteristics of an amorphous Mg0.9V0.1Ni alloy prepared by mechanical alloying

Electrochemical characteristics of an amorphous MgNi alloy with Mg partially substituted by V were investigated. A Mg_0.9V_0.1Ni alloy prepared by mechanical alloying (MA) exhibited much better cycle life than MgNi alloy. It was found that the partial substitution of Mg in MgNi with V could suppress the formation of Mg(OH)₂ on the alloy surface during the charge–discharge cycling in alkaline solution. This may have unveiled an important factor to improve cycle life of the Mg-based alloy for use in nickel–hydrogen batteries.     

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.     

Cobalt- and copper-substitution effects on thermal stabilities and hydriding properties of amorphous MgNi

Amorphous (a-)Mg(Ni_1−xT_x) with T=Co and Cu were formed by mechanical alloying in the composition range x=0–0.5. The crystallization temperatures increase/decrease by Co/Cu substitution, while the enthalpies of amorphous formation are little changed by substitution. On the other hand, the p–c isotherms indicate that the hydrogen-site energies become partially unstable with substitution. The relation between the enthalpy of amorphous alloy formation and subsequent hydride formation is discussed quantitatively on the basis of thermal analysis and the rule of reversed stability.     

Investigations of mechanically alloyed Ni–Zr–Ti–Si amorphous alloys with significant supercooled regions

This study examined the amorphization behavior of Ni₅₇Zr₂₀Ti_23−xSi_x (x=0, 1, 3) alloy powders synthesized by mechanical alloying technique. According to the results, after 5 h of milling, the mechanically alloyed powders were amorphous at compositions of Ni₅₇Zr₂₀Ti_23−xSi_x (x=0, 1, 3). The amorphization behavior of Ni₅₇Zr₂₀Ti₂₀Si₃ was examined in details. The conventional X-ray diffraction and synchrotron EXAFS results confirm that the fully amorphous powders formed after 5 h of milling. The thermal stability of the Ni₅₇Zr₂₀Ti_23−xSi_x amorphous powders was investigated by differential scanning calorimeter (DSC). As the results demonstrated, the amorphous powders were found to exhibit a large supercooled liquid region before crystallization. The supercooled liquid regions, defined by the difference between T_g and T_x, (i.e. ΔT=T_g−T_x), are 95 K, 66 K, and 88 K, for Ni₅₇Zr₂₀Ti₂₃, Ni₅₇Zr₂₀Ti₂₂Si₁, and Ni₅₇Zr₂₀Ti₂₀Si₃, respectively.     

Fabrication of high strength conductivity submicroncrystalline Cu-5 % Cr alloy by mechanical alloying

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Synthesis of HCP, FCC and BCC structure alloys in the Mg–Ti binary system by means of ball milling

Mg_xTi_100−x (35 ≤ x ≤ 80) alloys with hexagonal close packed (HCP), face centered cubic (FCC) and body centered cubic (BCC) structures were successfully synthesized by means of ball milling. Mg_xTi_100−x alloys with a BCC structure at x = 35 and 50 and with a HCP structure at x = 80 were synthesized by milling of Mg and Ti powder using stainless steel milling balls and pots. At x = 65, the BCC and HCP phases were synthesized. Mg_xTi_100−x alloys with a FCC structure were synthesized at x = 35 and 50 by milling using zirconia milling balls and pots. The FCC and HCP phases were synthesized at x = 65 and 80 using zirconia milling balls and pots. The crystal structure of Mg_xTi_100−x alloys synthesized by the ball milling method depended on the materials of milling balls and pots. That indicates that milling products are determined by the dynamic energy given by the milling setup. The lattice parameters of Mg_xTi_100−x in the HCP, FCC and BCC phases increased with increase of the Mg content, x.