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.     

Amorphization and nanostructure synthesis in Al alloys

The recent innovations in metallic glasses have led to new alloy classes that may be vitrified and a re-examination of the commonly used criteria for glass formation and stability. In one case large, bulk volumes may be slowly cooled to the glassy state that signifies a nucleation-controlled synthesis. The other important case is represented by Al and Fe based marginal glass formers that have been synthesized under growth controlled kinetic conditions mainly by rapid solidification processes. With marginal glass forming alloys the termination of the amorphous state upon heating is often characterized by a primary crystallization reaction that yields a high number density in the range of 10²¹–10²² m⁻³ of Al nanocrystals (15–20 nm in diameter) dispersed within a residual amorphous matrix. At the same time the results from alternate synthesis strategies involving intense cold rolling reveal that the primary crystallization reaction can be bypassed during deformation alloying of elemental multilayers or enhanced during deformation bonding of amorphous ribbons. The kinetics analysis of the crystallization behavior provides insight into the origin of the dispersed nanocrystal and amorphous matrix microstructures, the important influence of heterogeneous catalysts and an effective assessment of the overall stability that are essential for microstructure control.     

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.     

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。     

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.     

Changes in the microstructure and hydrogen storage properties of Ti-Cr-V alloys by ball milling and heat treatment

Changes in the microstructure and hydrogen storage properties of Ti-Cr-V alloys were investigated after a combination of ball milling and heat treatment. Two different sets of balls and vials made of tungsten carbide (WC) and stainless steel (STS) were used for milling the samples. Ball milling using WC balls and vials induced WC contamination, and it caused compositional changes in the matrix during heat treatment. When STS balls and vials were used, meanwhile, no peak of the second phase caused by contamination was found in the X-ray diffraction (XRD) data. In the case of the sample that completed only the milling process, the crystallite size calculated from the XRD data, 20-30 nm, agreed well with the grain size obtained from transmission electron microscopy (TEM). On the other hand, for the sample that was heat treated after milling, the strain decreased from 0.74% to 0.18%, the crystallite size increased to 70-80 nm, and the grain size grew up to the level of hundreds of nanometers. The changes in microstructure induced by the ball milling and heat treatment influenced the hydrogen storage properties, such as plateau pressure, hysteresis, and phase transformation with hydrogen absorption. Thus, the relationship between the microstructure and hydrogen storage properties can be explained.     

Production and mechanical properties of aluminum alloys with dispersed nanoscale quasicrystalline and amorphous particles

By the dispersion of nanoscale quasicrystalline and amorphous particles in Al phase, new Al-based alloys with good mechanical properties were developed in a high Al concentration range of 93–95 at.% for Al−Cr−Ce−Co, Al−V−Fe, Al−Ti−M and Al−Fe−Cr−Ti alloy systems. The Vickers hardness of a melt-quenched (MQ) Al_84.6Cr_15.4 alloy with almost a single icosahedral quasicrystalline phase (QC) was 710. The addition of Ce and Co in the Al−Cr binary alloys was effective for the extension of the concentration range of the QC to a lower solute concentration range. The fracture strength (σ_f) increased to 1340 MPa for the MQ Al_94.5Cr₃Ce₁Co_1.5 alloy in which the particle size and volume fraction were approximately 40 nm and 70%, respectively. The σ_f of the MQ Al₉₄V₄Fe₂ alloy was 1390 MPa and the particle size and volume fraction were about 10 nm and 50%, respectively. Similarly, σ_f of the MQ Al₉₃Ti₄Fe₃ alloy was 1320 MPa and the particle size and volume fraction were about 11 nm and 30%, respectively. Power metallurgy (P/M) Al₉₃Fe₃Cr₂Fe₂ alloy with dispersed nanoscale QC exhibited ultimate tensile strength (σ_UTS) of 660 MPa, 0.2 % proof stress (σ_0.2) of 550 MPa, plastic elongation (ε_P) of 4.5%, Young's modulus (E) of 85 GPa, Vickers hardness (Hv) of 192 and specific strength (σ_UTS/ρ) of 2.20×10⁵ Nm/kg at room temperature and σ_UTS of 350 MPa, σ_0.2 of 330 MPa and ε_P of 1.5% at 573 K. The QC structure in the P/M Al₉₃Fe₃Cr₂Ti₂ alloy remained almost unchanged even after annealing for 720 ks at 573 K and good wear resistance against S50C steel was also maintained for the extruded alloy tested at sliding velocity of 0.5 to 2 m/sec. These mechanical properties are promising for the future extension of the new Al-based alloys to practical materials. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

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.     

Al-V合金预磨状态对Al-Fe-V-Si-Nd机械合金化过程中显微组织演化的影响

采用高能球磨法制备Al89.5Fe6 .4V0 .7Si2 .4Nd合金粉末 ,并用X射线衍射技术研究了球磨过程中的组成。发现经 60h高能球磨 ,合金粉末的微观组织由Al非晶和Al3V相组成 ;Al V合金的预磨状态影响Al89.5Fe6 .4 V0 .7Si2 .4Nd合金机械合金化过程中显微组织演化。     

High-speed milling of titanium alloys using binderless CBN tools

The performance of conventional tools is poor when used to machine titanium alloys. In this paper, a new tool material, which is binderless cubic boron nitride (BCBN), is used for high-speed milling of a widely used titanium alloy Ti–6Al–4V. The performance and the wear mechanism of the BCBN tool have been investigated when slot milling the titanium alloy in terms of cutting forces, tool life and wear mechanism. This type of tool manifests longer tool life at high cutting speeds. Observations based on the SEM and EDX suggest that adhesion of workpiece and attrition are the main wear mechanisms of the BCBN tool when used in high-speed milling of Ti–6Al–4V.     

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.     

Amorphization in the Al---C system by mechanical alloying

Mechanical alloying of a powder mixture of elemental Al and graphite has been performed in a high-energy ball mill. The structural evolution has been characterized by X-ray diffraction and transmission electron microscopy. The carbide Al₄C₃ is first formed as an intermediate product. Further milling leads to destabilization of Al₄C₃. It is proposed that destabilization of Al₄C₃ is induced by the accumulated defects and the high pressure due to collision of the balls. Balling milling of the elemental Al---C powder mixture finally results in a f.c.c. solid solution with a carbon content up to 23 at%. Whereas an amorphous phase is formed in the composition range of 28–50 at% C.     

Structural transition of Ni-Mn-Ga ferromagnetic shape memory alloy particles prepared by ball milling

The size, crystal structure and phase transformation of Ni49.8Mn28.sGa21.7 alloy particles prepared by planetary ball milling （PBM） and vibration ball milling （VBM） were investigated by SEM, XRD and DSC. The results show that the particles milled by PBM for 4 h exhibit irregular polyhedron, with the size distribution between 5 pm and 40 pm. These particles present disordered fct structure with no phase transformation behaviour. When annealed at 600℃ for 1 h, the crystal structure of the particles evolves from disordered fct to Heusler completely. The particles milled by VBM for 4 h exhibit flaky shape, with the size distribution from 3 μm to 30μm. The particles present disordered fcc structure with no phase transformation behaviour. However the crystal structure of these particles doesn＇t transform from disordered fcc to Heusler completely aider annealing at 600 ℃ for 1 h, for the severe lattice distortion induced in the VBM process is not eliminated entirely.     

Synthesis of FeS2 and FeS nanoparticles by high-energy mechanical milling and mechanochemical processing

High-energy mechanical milling of the FeS₂ pyrite led to the formation of sub-micron particles with nano-scaled grains. FeS₂ nanoparticles were obtained, when NaCl was used as the dispersion medium. FeS₂ pyrite and FeS troilite phases could be formed after high-energy mechanical milling. The formation of FeS₂ pyrite required a long milling time. The resultant powders consisted of nano-scaled particles. The use of the solid dispersion medium (NaCl) can promote dispersion of nanoparticles. This work has shown that iron sulfide nanoparticles can be synthesized by mechanochemcial process with a solid dispersion medium.     

Carbon nanocomposites synthesized by high-energy mechanical milling of graphite and magnesium for hydrogen storage

Nanocomposites obtained by mechanical milling of graphite and magnesium with organic additives (benzene, cyclohexene or cyclohexane) have been studied with the aim of preparing novel hydrogen storage materials. The organic additives were very important in the milling processes to determine the characteristics of the resulting carbon nanocomposites. The mechanical milling with high energy resulted in the generation of large amounts of dangling carbon bonds in graphite with simultaneous decomposition of graphite structure. Such dangling bonds of carbon acted as sites to take up hydrogen. It has been proved by temperature programmed desorption (TPD) and neutron diffraction measurements that the hydrogen taken up in the nanocomposites exists in at least two states; in the form of C–H bond formation in the graphite component and in the form of hydride in the magnesium component. The relative amounts of two types of hydrogen strongly depended upon differences in additives used (benzene, cyclohexene or cyclohexane). When C₆D₆ besides C₆H₆ was used as additive, the hydrogen taken up was discussed from the standpoint of isotope effects. Upon addition of titanium tetraisopropoxide, the features of hydrogen uptake by the nanocomposites changed completely.     

Estimation of thermal expansion properties of quasicrystalline alloys

By investigating the thermal expansion properties of three quasicrystalline alloys Al65Cu20Cr15 quenched,Al65Cu20Cr15 cast and Al65Cu20Fe15 cast particles reinforced A1 matrix composites from 25℃ to 500℃, the thermal expansion coefficients of three quasicrystalline alloys were theoretically estimated. The results show that the thermal expansion coefficients of the composites are much lower than that of pure A1, and the thermal expansion coefficients of the composites reinforced by Al-Cu-Cr quasicrystalline particles are lower than those of the composites reinforced by Al-Cu-Fe quasicrystalline particles. According to estimating, quasicrystalline alloys have negative thermal expansion coefficients, and the thermal expansion coefficients of Al-Cu-Cr quasicrystalline alloys are lower than those of Al-Cu-Fe quasicrystalline alloys. In the alloys, the more the qusicrystalline content, the lower the thermal expansion coefficient.     

Synthesis of nanocomposite hydrides for solid-state hydrogen storage by controlled mechanical milling techniques

The following composite hydride systems: NaBH₄–MgH₂, MgH₂–LiAlH₄, MgH₂–VH_0.81 and MgH₂–NaAlH₄, were synthesized in a wide range of compositions by controlled reactive/mechanical (ball) milling in a magneto-mill. In effect, composites having nanometric grain sizes of the constituent phases (nanocomposites) were produced. It is shown that the hydrogen desorption temperature of the composite constituent with the higher desorption temperature in the systems such as NaBH₄ + MgH₂, MgH₂ + VH_0.81 and MgH₂ + LiAlH₄ substantially decreases linearly with increasing volume fraction of the constituent having lower desorption temperature according to the well-known composite rule-of-mixtures (ROM). It is also shown that the ROM behavior can break down due to an ineffective milling of a composite. The composite system MgH₂ + NaAlH₄ does not obey the ROM behavior.     

Structures,properties and responses to heat treatment of deformation processed Cu-15% Cr composite powders prepared by mechanical milling

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H NMR study of hydrogen stored in activated carbon powder prepared by mechanical milling

A ¹H NMR study was carried out using hydrogenated activated carbon powder (AC) prepared by mechanical milling in a H₂ atmosphere. Chemical shifts in the hydrogenated milled AC were observed near 0 and 2 ppm. In addition, the peak near 0 ppm was separated into two peaks (α and β) by the deconvolution of the NMR spectra; −0.6 and 0.2 ppm. This indicates that hydrogenated milled AC has three hydrogen components with different molecular mobilities. Measurement of the spin-lattice relaxation time (T₁) revealed that the hydrogen near 0 and 2 ppm consisted of two components (Components 1 and 2) and one component (Component 3), respectively. However, the activation energies (E_a) of each hydrogen component could not be estimated because the plots of inverse temperature (1/T) versus the logarithm of T₁ (ln T₁) were scattered. We assumed that the components near 0 ppm (Component 1 and/or 2) were thermally unstable because the intensity of the chemical shift near 0 ppm decreased as the measurement temperature increased, and this might have an effect on T₁ measurements. The spin-spin relaxation time (T₂) indicated high and low molecular mobility at each chemical shift and several temperatures.     

Microstructures and transformation behavior of Ti-Ni-Cu shape memory alloy powders fabricated by ball milling method

Ti-Ni and Ti-Ni-Cu alloy powders have been fabricated by ball milling after which their microstructures and transformation behaviors were investigated by means of scanning electron microscopy, X-ray diffraction, energy dispersive X-ray analysis, transmission electron microscopy and differential scanning calorimetry. The powders of as-milled Ti-Ni-Cu alloys whose Cu-content is less than 5 at.% were mixtures of crystal and amorphous, whereas those alloy powders whose Cu-content is more than 10 at.% were crystalline. The B19’ martensite is formed in the Ti-Ni-Cu alloy powders whose Cu-content is less than 10 at.%, whereas the B19 and B19’ martensites coexist in those whose Cu-content is more than 10 at.%. The martensitic transformation range became wider with increasing rotating speed, and so endothermic and exothermic peaks obtained from differential scanning calorimetry were indiscernible.