Research

4020 KiB

Open AccessArticle

Formation and Corrosion Behavior of Mechanically-Alloyed Cu–Zr–Ti Bulk Metallic Glasses

by Pee-Yew Lee, Yeh-Ming Cheng, Jyun-Yu Chen and Chia-Jung Hu

Metals 2017, 7(4), 148; https://doi.org/10.3390/met7040148 - 20 Apr 2017

Cited by 15 | Viewed by 4646

Cu₆₀Zr₃₀Ti₁₀ metallic glass powder was prepared by mechanically alloying a mixture of pure Cu, Zr, and Ti powders after 5 h of milling. Cu₆₀Zr₃₀Ti₁₀ bulk metallic glass (BMG) was synthesized by vacuum hot [...] Read more.

Cu₆₀Zr₃₀Ti₁₀ metallic glass powder was prepared by mechanically alloying a mixture of pure Cu, Zr, and Ti powders after 5 h of milling. Cu₆₀Zr₃₀Ti₁₀ bulk metallic glass (BMG) was synthesized by vacuum hot pressing the as-milled Cu₆₀Zr₃₀Ti₁₀ metallic glass powder at 746 K in the pressure range of 0.72–1.20 GPa, and the structure was analyzed through X-ray diffraction and transmission electron microscopy. The pressure could enhance the thermal stability, and prolong the existence, of the amorphous phase inside the Cu₆₀Zr₃₀Ti₁₀ powder. Furthermore, the corrosion behavior of the Cu-based BMG in four corrosive media was studied using a potentiodynamic method. The Cu₆₀Zr₃₀Ti₁₀ BMG exhibited a low corrosion rate and current density in 1 N solutions of H₂SO₄, NaOH, and HNO₃. X-ray photoelectron spectroscopy results revealed that the formation of Zr- and Ti-rich passive oxide layers provides a high corrosion resistance against 1 N H₂SO₄ and HNO₃ solutions, and the breakdown of the protective film by Cl⁻ attack was responsible for pitting corrosion in a 3 wt % NaCl solution. The formation of oxide films and the nucleation and growth of pitting were analyzed through microstructural investigations. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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7974 KiB

Open AccessFeature PaperArticle

A Study on the Aging Behavior of Al6061 Composites Reinforced with Y₂O₃ and TiC

by Chun-Liang Chen and Chen-Han Lin

Metals 2017, 7(1), 11; https://doi.org/10.3390/met7010011 - 04 Jan 2017

Cited by 14 | Viewed by 4741

Abstract

The reinforcement particles play important roles in determining microstructural development and properties of Al6061 composites. In the present work, the aging behavior of Al6061 reinforced with Y₂O₃ and TiC particles produced via mechanical alloying are investigated. The results indicate that [...] Read more.

The reinforcement particles play important roles in determining microstructural development and properties of Al6061 composites. In the present work, the aging behavior of Al6061 reinforced with Y₂O₃ and TiC particles produced via mechanical alloying are investigated. The results indicate that the peak-aged Al6061 alloy without reinforcement demonstrates the highest hardness, which corresponds to the formation of the Mg–Si precipitates. However, precipitation formation is not observed in the case of the Al6061 composites, which can be attributed to the fact that the Mg–Si clusters and GP zones are inhibited by the presence of the reinforcement particles. The solute elements segregate in the complex oxides or carbides and contribute to only a slight increase in hardness. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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5210 KiB

Open AccessArticle

Microstructures and Properties Evolution of Al-Cu-Mn Alloy with Addition of Vanadium

by Fansheng Meng, Zhi Wang, Yuliang Zhao, Datong Zhang and Weiwen Zhang

Metals 2017, 7(1), 10; https://doi.org/10.3390/met7010010 - 30 Dec 2016

Cited by 15 | Viewed by 5902

Abstract

The effect of the vanadium addition on the microstructure, the precipitation behavior, and the mechanical properties of the Al-5.0Cu-0.4Mn alloy has been studied. The as-cast Al-5.0Cu-0.4Mn alloy was produced by squeeze casting and the heat treatment was carried out following the standard T6 [...] Read more.

The effect of the vanadium addition on the microstructure, the precipitation behavior, and the mechanical properties of the Al-5.0Cu-0.4Mn alloy has been studied. The as-cast Al-5.0Cu-0.4Mn alloy was produced by squeeze casting and the heat treatment was carried out following the standard T6 treatment. It is shown that, with the addition of V, grain refinement of aluminum occurred. During heat treatment, the addition of V accelerates the precipitation kinetics of θ′ (Al₂Cu) phase along the grain boundaries, and promotes the growth rate of the θ′ in the α(Al) matrix. Meanwhile, the addition of V retards the precipitation of T (Al₂₀Cu₂Mn₃) phase. The tensile strength of the Al-5.0Cu-0.4Mn alloy increases with the increase of V content, which can be explained by combined effects of the solid solution strengthening and precipitate strengthening. However, excessively high V addition deteriorates the mechanical properties by forming brittle coarse intermetallic phases. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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3781 KiB

Open AccessArticle

Properties of Mechanically Alloyed W-Ti Materials with Dual Phase Particle Dispersion

by František Lukáč, Monika Vilémová, Barbara Nevrlá, Jakub Klečka, Tomáš Chráska and Orsolya Molnárová

Metals 2017, 7(1), 3; https://doi.org/10.3390/met7010003 - 26 Dec 2016

Cited by 9 | Viewed by 4670

Abstract

W alloys are currently widely studied materials for their potential application in future fusion reactors. In the presented study, we report on the preparation and properties of mechanically alloyed W-Ti powders compacted by pulsed electric current sintering. Four different powder compositions of W-(3%–7%)Ti [...] Read more.

W alloys are currently widely studied materials for their potential application in future fusion reactors. In the presented study, we report on the preparation and properties of mechanically alloyed W-Ti powders compacted by pulsed electric current sintering. Four different powder compositions of W-(3%–7%)Ti with Hf or HfC were prepared. The alloys’ structure contains only high-melting-point phases, namely the W-Ti matrix, complex carbide (Ti,W,Hf)C and HfO₂ particle dispersion; Ti in the form of a separate phase is not present. The bending strength of the alloys depends on the amount of Ti added. The addition of 3 wt. % Ti led to an increase whereas 7 wt. % Ti led to a major decrease in strength when compared to unalloyed tungsten sintered at similar conditions. The addition of Ti significantly lowered the room-temperature thermal conductivity of all prepared materials. However, unlike pure tungsten, the conductivity of the prepared alloys increased with the temperature. Thus, the thermal conductivity of the alloys at 1300 °C approached the value of the unalloyed tungsten. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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3404 KiB

Open AccessArticle

Wear Behavior of Mechanically Alloyed Ti-Based Bulk Metallic Glass Composites Containing Carbon Nanotubes

by Yung-Sheng Lin, Chih-Feng Hsu, Jyun-Yu Chen, Yeh-Ming Cheng and Pee-Yew Lee

Metals 2016, 6(11), 289; https://doi.org/10.3390/met6110289 - 21 Nov 2016

Cited by 7 | Viewed by 4280

Abstract

The present paper reports the preparation and wear behavior of mechanically alloyed Ti-based bulk metallic glass composites containing carbon nanotube (CNT) particles. The differential scanning calorimeter results show that the thermal stability of the amorphous matrix is affected by the presence of CNT [...] Read more.

The present paper reports the preparation and wear behavior of mechanically alloyed Ti-based bulk metallic glass composites containing carbon nanotube (CNT) particles. The differential scanning calorimeter results show that the thermal stability of the amorphous matrix is affected by the presence of CNT particles. Changes in glass transition temperature (T_g) and crystallization temperature (T_x) suggest that deviations in the chemical composition of the amorphous matrix occurred because of a partial dissolution of the CNT species into the amorphous phase. Although the hardness of CNT/Ti₅₀Cu₂₈Ni₁₅Sn₇ bulk metallic glass composites is increased with the addition of CNT particles, the wear resistance of such composites is not directly proportional to their hardness, and does not follow the standard wear law. A worn surface under a high applied load shows that the 12 vol. % CNT/Ti₅₀Cu₂₈Ni₁₅Sn₇ bulk metallic glass composite suffers severe wear compared with monolithic Ti₅₀Cu₂₈Ni₁₅Sn₇ bulk metallic glass. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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3432 KiB

Open AccessFeature PaperArticle

by Manja Krüger, Janett Schmelzer and Maria Helmecke

Metals 2016, 6(10), 241; https://doi.org/10.3390/met6100241 - 14 Oct 2016

Cited by 16 | Viewed by 4684

Abstract

V-Si-B and Mo-Si-B alloys are currently the focus of materials research due to their excellent high temperature capabilities. To optimize the mechanical alloying (MA) process for these materials, we compare microstructures, morphology and particles size as well as hardness evolution during the milling [...] Read more.

V-Si-B and Mo-Si-B alloys are currently the focus of materials research due to their excellent high temperature capabilities. To optimize the mechanical alloying (MA) process for these materials, we compare microstructures, morphology and particles size as well as hardness evolution during the milling process for the model alloys V-9Si-13B and Mo-9Si-8B. A variation of the rotational speed of the planetary ball mill and the type of grinding materials is therefore investigated. These modifications result in different impact energies during ball-powder-wall collisions, which are quantitatively described in this comparative study. Processing with tungsten carbide vials and balls provides slightly improved impact energies compared to vials and balls made of steel. However, contamination of the mechanically alloyed powders with flaked particles of tungsten carbide is unavoidable. In the case of using steel grinding materials, Fe contaminations are also detectable, which are solved in the V and Mo solid solution phases, respectively. Typical mechanisms that occur during the MA process such as fracturing and comminution are analyzed using the comminution rate K_P. In both alloys, the welding processes are more pronounced compared to the fracturing processes. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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3890 KiB

Open AccessArticle

Study on the Thermal Conductivity Characteristics of Graphene Prepared by the Planetary Ball Mill

by Gwi-Nam Kim, Ji-Hye Kim, Bo-Sung Kim, Hyo-Min Jeong and Sun-Chul Huh

Metals 2016, 6(10), 234; https://doi.org/10.3390/met6100234 - 29 Sep 2016

Cited by 9 | Viewed by 4407

Abstract

This study was designed to examine the physical disintegration of graphene (GN), an excellent heat conductor, by using the planetary ball mill, a simple and convenient means to produce particles arbitrarily. The conditions for the disintegration of GN were distinguished by the rotation [...] Read more.

This study was designed to examine the physical disintegration of graphene (GN), an excellent heat conductor, by using the planetary ball mill, a simple and convenient means to produce particles arbitrarily. The conditions for the disintegration of GN were distinguished by the rotation of the planetary ball mill (200 rpm, 400 rpm, and 600 rpm) and by the duration of its operation (30 min, 60 min, and 90 min), respectively. From the results, we saw that, when experimental conditions are 200 rpm with 60 min, the particle size was the smallest (at 328 nm) and the results of thermal conductivity were the highest. In the absorbance results, GN was well dispersed because the value of its absorbance is high. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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3660 KiB

Open AccessFeature PaperArticle

Strong and Stable Nanocomposites Prepared by High-Pressure Torsion of Cu-Coated Fe Powders

by Timo Müller, Andrea Bachmaier, Erich Neubauer, Michael Kitzmantel and Reinhard Pippan

Metals 2016, 6(10), 228; https://doi.org/10.3390/met6100228 - 22 Sep 2016

Cited by 2 | Viewed by 4345

Abstract

Segregation and chemical inhomogeneity are well-known problems in powder metallurgy and are also an issue for new applications of powder mixtures, for example as starting materials for severe plastic deformation. In this study, Cu-coated Fe powder was prepared via immersion deposition, inductively hot-pressed [...] Read more.

Segregation and chemical inhomogeneity are well-known problems in powder metallurgy and are also an issue for new applications of powder mixtures, for example as starting materials for severe plastic deformation. In this study, Cu-coated Fe powder was prepared via immersion deposition, inductively hot-pressed and subsequently deformed using high-pressure torsion. The homogeneity of the pressed material was found to be much better than that of powder mixtures that were prepared for comparison. During severe plastic deformation, higher hardness was observed for the coated powder as compared to powder mixtures even after low strains. In the saturation state, the coated powder was found to result in a hardness of about 600 HV, which is significantly harder than for the powder mixtures. This is attributed to the greater amount of impurities introduced by the coating process. It is shown that coated powders are promising starting materials for severe plastic deformation in order to reduce the amount of strain necessary to reach the saturation state and to obtain high strength and more homogeneous mechanical alloying. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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4092 KiB

Open AccessArticle

Influence of Milling Atmosphere on the Controlled Formation of Ultrafine Dispersoids in Al-Based MMCs

by Eduardo S. Caballero, Jesús Cintas, Francisco G. Cuevas, Juan Manuel Montes and Fátima Ternero

Metals 2016, 6(9), 224; https://doi.org/10.3390/met6090224 - 12 Sep 2016

Cited by 6 | Viewed by 3925

Abstract

Properties of compacts made from aluminium powder, milled under different atmospheres, were evaluated. The duration of all the milling processes was 10 h, although different atmospheres were tested: vacuum, confined ammonia, and vacuum combined with a short-time ammonia gas flow (5 min). Milled [...] Read more.

Properties of compacts made from aluminium powder, milled under different atmospheres, were evaluated. The duration of all the milling processes was 10 h, although different atmospheres were tested: vacuum, confined ammonia, and vacuum combined with a short-time ammonia gas flow (5 min). Milled powders were consolidated by cold uniaxial pressing and vacuum sintering. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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2863 KiB

Open AccessArticle

Microstructure, Hardness Evolution, and Thermal Stability Mechanism of Mechanical Alloyed Cu-Nb Alloy during Heat Treatment

by Ruoshan Lei, Mingpu Wang, Shiqing Xu, Huanping Wang and Guangrun Chen

Metals 2016, 6(9), 194; https://doi.org/10.3390/met6090194 - 26 Aug 2016

Cited by 10 | Viewed by 4895

Abstract

The microstructure, hardness evolution, and thermal stability of mechanically alloyed (MA-ed) nanocrystalline Cu–10 wt %Nb solid solution during heat treatment were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) observations, and microhardness measurement. It is [...] Read more.

The microstructure, hardness evolution, and thermal stability of mechanically alloyed (MA-ed) nanocrystalline Cu–10 wt %Nb solid solution during heat treatment were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) observations, and microhardness measurement. It is found that the pronounced precipitation of Nb from the Cu-Nb supersaturated solid solution occurs at temperatures up to 700 °C, and the annealed alloy shows a bi-nanostructure with Nb nanoparticles dispersed in the nanocrystalline Cu matrix. The bi-nanostructure remains stable with Cu crystalline grain size below 100 nm and Nb particle size around 10 nm even after annealing at 900 °C for 3 h. The microhardness of the annealed sample shows a small increase after annealing at 400 °C, and then it shows a slow decreasing trend with further increasing temperatures. With the help of the kinetics analyses, it is found that the coarsening of the stable Nb nanoparticles is controlled by volume diffusion. The enhanced stability of the nanocrystalline Cu microstructure is mainly attributed to the solute drag and precipitate pinning effects. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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1330 KiB

Open AccessCommunication

Mechanical Alloying Synthesis of Co₉S₈ Particles as Materials for Supercapacitors

by Bo Li, Yuxia Hu, Jiajia Li, Maocheng Liu, Lingbin Kong, Yumei Hu and Long Kang

Metals 2016, 6(6), 142; https://doi.org/10.3390/met6060142 - 16 Jun 2016

Cited by 26 | Viewed by 5317

Abstract

Cobalt sulfide (Co₉S₈) particles are compounded as the electrode materials of supercapacitors by a mechanical alloying method. They show excellent properties including good cycling stability and high specific capacitance. A supercapacitor is assembled using Co₉S₈ as [...] Read more.

Cobalt sulfide (Co₉S₈) particles are compounded as the electrode materials of supercapacitors by a mechanical alloying method. They show excellent properties including good cycling stability and high specific capacitance. A supercapacitor is assembled using Co₉S₈ as the anode and activated carbon (AC) as the cathode. It gains a maximum specific capacitance of 55 F·g⁻¹ at a current density of 0.5 A·g⁻¹, and also an energy density of 15 Wh·kg⁻¹. Those results show that the novel and facile synthetic route may be able to offer a new way to synthesize alloy compounds with excellent supercapacitive properties. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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