Processing, microstructure and mechanical properties of W50Al50 bulk alloy obtained by mechanical alloying and hot-pressing

The Al50W50 alloy bulk bodies were fabricated by using mechanical alloying and hot-pressing in this work. The Al50W50 alloy had excellent thermal stability up to 1300 degreesC under vacuum and Its optimum microhardness, bending strength and compressive strength were 10.21 GPa, 570 MPa and 2.07 GPa, respectively.

Preparation of W-Al alloys by mechanical alloying

W1-xAlx (x=0-0.86) alloys were synthesized by mechanically alloying the pure metal powder mixtures at designated compositions by conventional high-energy ball milling. The W-Al alloys were stable under high pressure and high temperature. The alloys were lighter than W. The hardness and oxidation resistance of the alloys was greatly improved compared to both W and Al. (C) 2002 Elsevier Science B.V. All rights reserved.

EXTENDED SOLUBILITY AND SPIN-GLASS BEHAVIOR IN A AG-GD SOLID-SOLUTION PREPARED BY MECHANICAL ALLOYING

The effects of mechanical alloying on the solubility in a Ag-Gd solid solution have been investigated. The study shows that the solubility of Gd in Ag can be extended to about 5 at. % Gd by mechanical alloying from the equilibrium solubility of less than 0.95 at. % Gd. Ag85Gd15 prepared by mechanical alloying exhibits a spin-glass-type transition at similar to 5 K. A Curie-Weiss behavior at higher temperatures and x-ray patterns of the material indicate that Gd atoms are either dissolved in the Ag matrix or in the form of small clusters of diameters of a few nanometers;

Fabrication of Ti-Al coatings by mechanical alloying method

By means of the mechanical alloying (MA) method, Al and Ti + Al coatings were deposited on Ti alloy substrates. During the mechano-activation processing, the substrate surface was impacted by a large number of flying balls along with particles of powder. The repeated ball collisions with the substrate resulted in the deposition of powder on its surface. MA technique produced Ti + Al coating with a thickness of 200 µm and Al one with a thickness of 50 µm after 2 h milling at room temperature. The as-synthesized coatings showed structures with high apparent density and free of porosity. The surface morphology of the MA-coatings was very rough. Annealing treatment led to the leveling of this uneven morphology. Annealing at temperatures ranging between 600 °C and 1100 °C gave different aluminide phases on the samples. In the case of Al coating, Al3Ti and Ti3Al compound were observed upon heating up to 1100 °C. In the case of Ti + Al coating, Al3Ti, Al2Ti, TiAl and Ti3Al were formed on the surface.

Composition dependency of the glass forming ability (GFA) in Mg—Ni—Si system by mechanical alloying

The pure elemental powder mixtures with the compositions of Mg₆₅Ni_xSi₃₅−_x (x = 10, 20, 25, 33 at.%) were subject to high-energy ball mill, and the structures of the mixtures at different intervals of milling were characterised by X-ray diffraction (XRD). The compositional dependency of the glass forming ability (GFA) in Mg–Ni–Si system was evaluated based on the experimental results and the theoretical calculation. The compositional dependency of GFA in Mg–Ni–Si system can be understood well by comparing the enthalpies of the crystalline and amorphous phases based on the Miedema's theory for the formation enthalpy of alloys. Increasing the Ni/Mg ratio and/or decreasing Si content can improve the amorphous formability. The calculation results might be of great help in optimising the composition with high GFA in Mg–Ni–Si system.

Microstructure evolution of TI-SN-NB alloy prepared by mechanical alloying

In the present study, Ti-16Sn-4Nb alloy was prepared by mechanical alloying (MA). Optical microscopy, scanning electron microscopy combined with energy dispersive X-ray analysis (SEM-EDX), and X-ray diffraction analysis (XRD) were used to characterise the phase transformation and the microstructure evolution. Results indicated that ball milling to 8 h led to the formation of a supersaturated hcp α-Ti and partial amorphous phase due to the solid solution of Sn and Nb into Ti lattice. The microstructure of the bulk sintered Ti-16Sn-4Nb alloy samples made from the powders at shorter ball milling times, i.e. 20 min- 2 h, exhibited a primary α surrounded by a Widmanstätten structure (transformed β); while in the samples made from the powders at longer ball milling times, i.e. 5- 10 h, the alloy evolved to a microstructure with a disordered and fine β phase dispersed homogeneously within the α matrix. These results contribute to the understanding of the microstructure evolution in alloys of this type prepared by powder metallurgy.

Preparation of Mg55Ni35Si10 amorphous powders by mechanical alloying and consolidation by vacuum hot pressing

Amorphous 55Mg35NilOSi alloy powder has been synthesized by mechanical alloying technique using pure Mg, Ni and Si elemental powders. The transformation of the crystalline powders into an amorphous one has been investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. The new material produced has a higher thermal stability than reported results, which is beneficial to the fabrication of Mg-Ni-Si bulk amorphous components through powder metallurgy.

Effects of process control agent on the microstructure and mechanical properties of Ti-Sn-Nb alloy prepared by mechanical alloying

In the present study, the influence of process control agent (PCA) on the characteristics of powder and bulk sintered Ti-16Sn-4Nb (wt. %) alloy prepared by mechanical alloying has been investigated. The elemental Ti, Sn and Nb powders were mechanically alloyed in a planetary ball mill for a short period of time using two types of PCA, namely stearic acid (SA) and ethylene bis-stearamide (EBS). The powder morphology, microstructural evolution of the bulk sintered alloy, phase formation and hardness of the alloy have been studied as a function of PCA. Results indicated that the addition of PCA leads to a delay in aIloy formation and introduces contaminations (mainly carbon and oxygen) into the material. The microstructural observation of the bulk alloy revealed a homogeneous distribution of fine Nb-rich colonies (ß-phase) within the a-Ti matrix for small amount of PCA. The hardness values of samples exhibited a significant increase with increasing amount of PCA, reaching a value of ~ 600 BV.

Study on the role of stearic acid and ethylene-bis-stearamide on the mechanical alloying of a biomedical titanium based alloy

The present study examines the influence of different contents and types of process control agent (PCA), i.e., stearic acid (SA) and ethylene-bis-stearamide (EBS), on the microstructural evolution and characteristics of Ti-16Sn-4Nb (wt pct) alloy powders and bulk samples. The characterization of the powders and bulk samples was carried out by using chemical analysis, optical microscopy, scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS), and X-ray diffractometry. Results indicated that the powder recovered from the ball milling containers increased with increasing amounts of SA and EBS. Furthermore, adding more SA or EBS to the powder mixture resulted in a considerably smaller particle size, with a flaky-shaped morphology for the given ball milling time. Also, a slightly higher effectiveness was found for EBS when compared to SA. Meanwhile, the addition of both SA and EBS led to a delay in the alloy formation during mechanical alloying (MA) and caused contamination of the material with mainly carbon (C) and oxygen (O). An optimum amount of 1 wt pct PCA led to a good balance between cold welding and fracturing, and thus favored the formation of the titanium alloy. The microstructural observation of the bulk alloy showed a homogeneous distribution of fine Nb-rich ß-phase colonies within the α-Ti matrix with the addition of PCA less than 1 wt pct.

Thermal stability of the Al70Ni10Ti10Zr5Ta5 amorphous alloy powder fabricated by mechanical alloying

An Al₇₀Ni₁₀Ti₁₀Zr₅Ta₅ amorphous alloy powder was fabricated by mechanical alloying. The phase structure and characteristic temperatures of the alloy were determined by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The glass transition behavior and crystallization kinetics were analyzed using Lasocka and Kissinger functions. The results show that the alloy has a higher crystallization temperature, a higher effective activation energy of crystallization and a wider supercooled liquid region than the previously reported values, suggesting a high thermal stability and promising applications.

The addition of a surfactant at regular time intervals in the mechanical alloying process

The impact of regular additions of a surfactant (ethylene bis-stearamide; EBS) at different time intervals was investigated on the powder characteristics of a biomedical Ti-10Nb-3Mo alloy (wt.%). Ball milling was performed for 10 h on the elemental powders in four series of experiments at two rotation speeds (200 and 300 rpm). The addition of 2 wt.% total EBS at different time intervals during ball milling resulted in noticeable changes in particle size and morphology of the powders. The surfactant addition at shorter time intervals led to the formation of finer particles, a more homogenous powder distribution, a higher powder yield, and a lower contamination content in the final materials. Thermal analysis of the powders after ball milling suggested that differing decomposition rates of the surfactant were responsible for the measured powder particle changes and contamination contents. The results also indicated that the addition of surfactant during ball milling at 200 rpm caused a delay in the alloy formation, whereas ball milling at 300 rpm favored the formation of the titanium alloy.Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.

Properties and in vivo investigation of nanocrystalline hydroxyapatite obtained by mechanical alloying

Mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) using three different procedures. The milled HA was studied by X-ray diffraction, Infrared, Raman scattering spectroscopy and Scanning Electron Microscopy (SEM). We obtained HA with different degrees of crystallinity and time of milling. The grain size analysis through SEM and XRD shows particles with dimensions of 36.9, 14.3 and 35.5 nm (for (R1), (R2) and (R3), respectively) forming bigger units with dimensions given by 117.2, 110.8 and 154.4 nm (for (R1), (R2) and (R3), respectively). The Energy-Dispersive Spectroscopy (EDS) analysis showed that an atomic ratio of Ca/P= 1.67, 1.83 and 1.50 for reactions (R1), (R2) and (R3), respectively. These results suggest that the R1 nanocrystalline ceramic is closer to the expected value for the ratio Ca/P for hydroxyapatite, which is 513 congruent to 1.67. The bioactivity analysis shows that all the samples implanted into the rabbits can be considered biocompatible, since they had been considered not toxic, bad not caused inflammation and reject on the part of the organisms of the animals, during the period of implantation. The samples implanted in rabbits had presented new osseous tissue formation with the presence of osteoblasts cells. (C) 2004 Elsevier B.V. All rights reserved.