Structural studies on Ti–Cu alloy obtained by high-energy ball milling

ABSTRACT

Ti₅₀Cu₅₀ (at.-%) alloy has been produced from elemental Ti and Cu powders by high-energy ball milling in a planetary ball mill. Structural evolution of the alloy during milling and after subsequent heat treatment have been studied. It has been stated that high-energy ball milling of the investigated powder produces two nanocrystalline solid solutions: Cu(Ti) and Ti(Cu), both characterised by the fcc (Fm-3 m) structure. The transition of Ti structure from hcp (P63/mmc) to fcc (Fm-3 m) is observed during milling. Heat treatment of the milled powder leads to recrystallisation of Cu(Ti) and Ti(Cu) solid solutions.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Processing and microstructural characterisation of laminated Ti-intermetallic composites synthesised using Ti and Cu foils

Ti-intermetallic laminated composites were fabricated by reaction synthesis in vacuum using Ti and Cu foils. The copper layers were completely consumed due to the formation of intermetallic phases. The Ti–Cu reaction was studied by interrupting in steps the reaction process to observe the microstructural changes. Microstructural examinations using scanning electron microscopy (SEM) and X-ray microprobe analysis demonstrated that five intermetallic compounds: Ti₂Cu, TiCu, Ti₃Cu₄, Ti₂Cu₃, TiCu₄ were formed after heat treatment at 1173 K for 1.8 ks. Heat treatment for 18 ks resulted in a microstructure consisting of Ti and TiCu layers, but with a thick Ti₂Cu interphase layer. The TiCu layers give high hardness to the composite, while unreacted titanium provides the necessary high ductility.     

Synthesis of Cu–Zr–Al/Al2O3 amorphous nanocomposite by mechanical alloying

Two routes were used to produce Cu–Zr–Al/Al₂O₃ amorphous nanocomposite. First route included mechanical alloying of elemental powders mixture. In second route Cu₆₀Zr₄₀ alloy was synthesized by melting of Cu and Zr. Cu₆₀Zr₄₀ alloy was then ball milled with Al and CuO powder. It was not possible to obtain a fully amorphous structure via first route. The mechanical alloying of Cu₆₀Zr₄₀, Al and CuO powder mixture for 10 h led to the reaction of CuO with Al, forming Al₂O₃ particulate, and concurrent formation of Cu₆₂Zr₃₂Al₄ amorphous matrix. The thermodynamical investigations on the basis of extended Miedema’s model illustrated that there is a strong thermodynamic driving force for formation of amorphous phase in this system. Lack of amorphization in first route appeared to be related to the oxidation of free Zr during ball milling.     

Tribochemical equilibrium in mechanical alloying of metals

The structure of the product in mechanical alloying depends both on the elemental composition and the milling conditions. An increase of ball energy led to more pronounced crystallinity of the product. Mechanical alloying at small ball energy leads to the formation of amorphous alloys for Zr-Co and Cu-Ti systems. Demixing of Ti₃Cu₄ into crystalline TiCu and TiCu₄ and demixing of Zr₅₀Co₅₀ into Zr₃Co and ZrCo₂ was found. The results are explained on the basis of the concept of tribochemical equilibrium.     

Mechanical alloying and sintering of nanostructured TiO2 reinforced copper composite and its characterization

Mechanical alloying is a suitable method for producing copper based composites. Cu–TiO₂ composite was fabricated using high energy ball milling and conventional consolidation. Ball milling was performed at different milling durations (0–24 h) to investigate the effects of the milling time on the formation and properties of produced nanostructured Cu–TiO₂ composites. The amount of the TiO₂ in the final composition of the composite assumed to be 0, 1, 3, 5 and 7 wt%. The milled composite powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy to investigate the effects of the milling time on the formation of the composite and its properties. Also hardness, density and electrical conductivity of the sintered specimen were measured. High energy ball milling causes a high density of defects in the powders. Thus the Cu crystallite size decreases, generally to less than 50 nm. The maximum hardness value (105 HV) of the sintered compacts belongs to Cu–5 wt%TiO₂ which has been milled for 12 h.     

Deformation-induced reactions of ZnO and TiO2

Reactions of ZnO and TiO₂ (anatase and rutile) in different mole ratios induced by high-energy ball milling were studied by X-ray diffraction. It was found that three main reactions could involve during high-energy ball milling: (1) (4 ? X)ZnO + (2 + Y) TiO₂ (anatase or rutile) → Zn_4?X Ti_2+Y O₈; (2) ZnO + TiO₂ (rutile) → ZnTiO₃, and (3) TiO₂ (anatase) → TiO₂ (II) → TiO₂ (rutile). Cubic Zn_4?X Ti_2+Y O₈ nanocrystals with an average crystal size of about 15 nm can be prepared by high-energy ball milling, which could be an attractive process to fabricate material in industrial scale. No decomposition of ZnTiO₃ into Zn₂TiO₄ and rutile was detected during milling. Anatase shows higher reaction activity than rutile and favours the formation of Zn_4?X Ti_2+Y O₈ while rutile favours the formation of ZnTiO₃. During the anatase-to-rutile transformation a transient metastable phase, TiO₂ (II) which is a high-pressure phase of TiO₂, is detected.     

Mechanochemical synthesis and characterization of nanocrystalline 0.4Bi(Zn1/2Ti1/2)O3-0.6PbTiO3 powders

Perovskite 0.4Bi(Zn_1/2Ti_1/2)O₃-0.6PbTiO₃ (BZT-PT) powders were successfully synthesized from precursor oxides using a high-energy planetary ball milling. The phase development of the powders during milling was studied by means of X-ray diffraction and Raman scattering techniques. The microstructure of the powders was characterized using transmission electron microscopy, and the thermal behavior was studied as well. The results reveal that after 15 h of milling the formation of BZT-PT phase can be completed and submicron agglomerates of small crystallite sized ~ 12 nm are present in the powders. However, further prolonging the milling time to 25 h leads to the amorphization of the BZT-PT phase.     

Refining of copper powder by a novel micro-abrasive milling method conducted in the air

The pure copper powder was milled by conventional high-energy ball milling (CM) and micro-abrasive milling (MAM) methods in the air or vacuum. The refining behavior of copper powder milled using these different methods has been studied, and the morphologies, microstructures, compositions, and properties of the milled powders have been thoroughly investigated. The results show that, as compared to CM, the MAMed copper powder had a better refinement behavior and contained a smaller number of agglomerates. After milling in the air for 30 h by MAM, whole copper powder was converted into Cu₂₊₁O. In addition, under the synergistic effects of micro-abrasion and exposure to oxygen, the Cu₂₊₁O powder was soft-agglomerated and had a specific surface area of 15.1031 m²/g and an average size of 375.4 nm. During the dispersion process, Cu₂₊₁O was partly converted into CuO and the microstructural evolution characteristics were disclosed. The dispersed powder had an average particle size of 179.5 nm. The refining mechanism of the copper powder prepared by the micro-abrasive milling method was also discussed.     

On the oxygen reduction reaction catalyzed by Ti -Cu binary films in 0.5 M sulfuric acid solution

Ti-Cu binary films co-sputtered in vacuum are catalytically active for the oxygen reduction in 0.5 M H₂SO₄. The activity for the oxygen reduction reaction (ORR) increased with increasing the Cu-content in the Ti-Cu films and it reached to a maximum with the copper composition up to 90 at.%. The constant Tafel slope of ~ 190 mV/decade which is comparable to that obtained on pure Cu films indicates that the active sites for oxygen reduction is copper sites. Through investigation of Tafel polarization, the Ti-Cu films revealed a constant Tafel slope (i.e., 190 mV/decade) similar to that of ORR on the pure Cu film. This infers that the electrochemical reduction of oxygen is predominated on the Cu-sites in the film. In the cyclic voltammograms, the strong broad peak should have arisen from the oxidation of Cu to Cu⁺ and Cu²⁺ ions. This oxidation indicated that the Ti-Cu films are unstable and the Cu-component is susceptible to dissolution in 0.5 M H₂SO₄. This dissolution caused a loss of catalytic activity in the films. Preparing the Ti-Cu films enriched in Ti will stabilize these films to prevent the Cu-dissolution.     

Optimization of mechanical property,antibacterial property and corrosion resistance of Ti-Cu alloy for dental implant

Ti-Cu alloys with different Cu contents (3, 5 and 7 wt%) were fabricated and studied as novel antibacterial biomaterials for dental application. The Ti-Cu alloys were annealing treated at different temperatures (740 °C, 830 °C and 910 °C) in order to obtain three typical microstructures, α-Ti + Ti₂Cu, α-Ti + transformed β-Ti, and transformed β-Ti. Mechanical, antibacterial and biocorrosion properties of Ti-Cu alloys with different microstructures were well analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile test, electrochemical test and antibacterial test. The results indicated that the Ti-Cu alloys with microstructure of α-Ti + Ti₂Cu showed the best ductility compared with other Ti-Cu alloys with microstructures of α-Ti + transformed β-Ti and complete transformed β-Ti, and meanwhile, increase of the Cu content significantly contributed to the decreased ductility due to the increasing amount of Ti₂Cu, which brought both solid solution strengthening and precipitation strengthening. Finally, the Ti-5Cu alloy with microstructure of α-Ti + Ti₂Cu exhibited excellent ductility, antibacterial property and corrosion resistance, providing a great potential in clinical application for dental implants.     

Study on the formation mechanism of Y-Ti-O oxides during mechanical milling and annealing treatment

Y-Ti-O nano-scale oxides play important roles in ensuring the excellent performance of oxide dispersion strengthened (ODS) steels. In this study, a model powder system of Y₂O₃ and Ti was designed to investigate the formation and evolution mechanism of Y-Ti-O oxides. The morphology of powders tended to be stable after high energy ball milling for 240 min in Ar. X-ray diffraction (XRD) results suggested that there was no formation of new phase after mechanical milling. Thermo-gravimetric and differential thermal analysis (TG-DTA) was applied to analyze physical and chemical reactions of milled powders respectively in Ar and air. The corresponding annealing and XRD were performed to study the types and structures of oxides at different temperatures. It shows that oxygen concentration and temperature are the critical factors affecting the formation of oxides. Ti was evolved into Ti₆O, Ti₃O and TiO₂ in turn with temperature increasing. Then only TiO₂ was reacted with Y₂O₃ to form Y₂Ti₂O₇. The formation of Y₂Ti₂O₇ began at around 500 ℃ and was completed around 1004 ℃. A maximum formation rate occurred at about 779 ℃. High resolution transmission electron microscopy (HRTEM) suggested that the main phase in powders sintered at 1100 ℃ was identified as pyrochlore structure Y₂Ti₂O₇.     

在酸性条件下采用高能球磨法制备 Cu2O纳米粉末

采用行星球磨机在pH=2的稀盐酸溶液中对Cu粉进行球磨，球磨机简体和磨球材质均为纯Cu，球料比为20：1，球磨机转速为300r／min，通过X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）等对球磨产物进行了表征．XRD结果表明，球磨3h后，所加入的纯Cu粉末基本转化为Cu20粉末．球磨70h后得到纯的Cu20粉末，粉末粒度为50-100nm．并对Cu20纳米粉末的生成机制及球磨工艺参数对Cu20形成的影响进行了讨论．     

EXAFS investigation of iron local environment in metal-doped titania photocatalysts prepared by hydrothermal and high-energy ball milling routes

Iron local environment was investigated by EXAFS in Fe- and (Fe, Eu)-doped TiO₂ photocatalysts, prepared by hydrothermal and high-energy ball milling (HEBM) routes. In the case of the hydrothermal samples, the substitution of Ti⁴⁺ by Fe³⁺ ions was evidenced. For the samples prepared by HEBM, the iron environment corresponds to mixed metallic and oxidized (FeO, α-Fe₂O₃) configurations, without a clear evidence of iron incorporation into the TiO₂ lattice. This could be related to the catalyst contamination by iron microparticles detached from the balls during milling process.     

Visible light degradation of Orange II using xCuyOz/TiO2 heterojunctions

Cu₂O/TiO₂, Cu/Cu₂O/TiO₂ and Cu/Cu₂O/CuO/TiO₂ heterojunctions were prepared and studied for their potential application as photocatalysts able to induce high performance under visible light. Orange II was used as a representative dye molecule. The effect of the amount and composition of the photosensitizers toward the activation of TiO₂ was studied. In each case, the global mechanism of Inter Particle Electrons Injection (IPEI) was discussed. The highest photocatalytic activity was observed for the system Cu/Cu₂O/CuO (MB2 catalyst) under visible light (t_1/2 = 24 min, k = 159.7 × 10⁻³ min⁻¹) and for the heterojunction cascade Cu/Cu₂O/CuO/TiO₂ (MB2 (50%)/TiO₂) under UV–vis light (t_1/2 = 4 min, k = 1342 × 10⁻³ min⁻¹). In the last case, the high performance was attributed firstly to the electromotive forces developed under this configuration in which CuO energy bands mediate the electrons transfer from Cu₂O to TiO₂. The formation of monobloc sensitizers also accounts for the decrease of the probability of the charges lost. It was demonstrated that “Cu₂O/CuO” governs the capability of the heterojunction cascade and Cu does not play a significant role regardless of the heterojunction cascade efficiency. The electrical energy consumption per order of magnitude for photocatalytic degradation of Orange II was investigated for some representative catalytic systems. Visible/MB2 and UV/vis MB2 (50%)/TiO₂ exhibited respectively 0.340 and 0.05 kWh m⁻³ demonstrating the high efficiency of the systems.     

Synthesis of titanium carbide and TiC–SiO2 nanocomposite powder using rutile and Si by mechanically activated sintering

High-energy ball milling was applied with subsequent heat treatment for synthesizing nanoparticles of TiC powders by the carbothermic and carbosilisisothermic reduction of titanium oxide (rutile type). The milling procedure involved milling of TiO₂/C and TiO₂/Si/C powders at room temperature in an argon atmosphere. The progress of the mechanically induced solid state reaction was monitored using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that TiC nanoparticles were duly synthesized in the TiO₂/C system at 1700 °C in 60-h milled samples. In the non-milled samples, although heated at the same temperature, only a minor amount of a lower degree of titanium oxide (Ti₃O₅) was observed to form. Further, in other non-milled samples, but with Si initially present, despite heating to 1550 °C no TiC phase was detected. However, using Si as a reducing agent accompanied by graphite, after 60 h ball milling, only Si remained as a distinguishable crystalline phase. Further, heat treatment of activated powders by forming the interphase compounds (such as Ti₃Si₅ and Ti₅Si₃) remarkably decreased the synthesis temperature to 900 °C for the 60 h milled samples.     

Influence of Primary Milling on Structural and Electrical Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Ceramics Obtained by Sintering Process

In this article, the influence of primary mechanical milling of precursors on the microstructure and dielectric properties of Bi₄Ti₃O₁₂ ceramics was studied. Precursor material (mixture of Bi₂O₃ and TiO₂ powders) was ground by a high-energy attritorial mill for (1, 3, 5, and 10) h. Bi₄Ti₃O₁₂ ceramics were obtained by a solid-state reaction process, synthesized at an intermediate temperature (800 °C) and finally sintered at high temperature (1140 °C). Structure studies were performed by X-ray diffraction (XRD) and scanning electron microscopy techniques. XRD patterns were analyzed by the Rietveld method using the DBWS 9807a program. The thermal properties of the studied materials were measured using differential thermal analysis and thermal gravimetric techniques. These studies indicate that one-, three-, and five-hour primary high-energy ball milling followed by sintering is a promising technique for pure Bi₄Ti₃O₁₂ ferroic ceramics preparation. The investigation of Bi₄Ti₃O₁₂ shows that ceramics obtained from a precursor and milled for 5 h have the best dielectric properties.     

Brazing continuous carbon fiber reinforced Li2O–Al2O3–SiO2 ceramic matrix composites to Ti–6Al–4V alloy using Ag–Cu–Ti active filler metal

C_f/LAS composites and TC4 alloy were brazed successfully by vacuum brazing using Ag–Cu–Ti active filler metal. The interfacial microstructure was characterized by a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction. The effects of brazing temperature on the interfacial microstructure and joint properties were investigated in details. Various phases including TiC, TiSi₂, Ti₃Cu₄, Cu (s,s), Ag (s,s), TiCu and Ti₂Cu were formed in the brazed joints. Interfacial microstructure varies greatly with the increase of brazing temperature, while the amount of Ti₂Cu reduced, but no new phase is generated. The optimal shear strength of the joint is 26.4 MPa when brazed at 890 °C for 10 min. Shear test indicated that the fracture of the brazed joints went through the TiSi₂ + TiC layer close to the C_f/LAS composites interface.     

Synthesis of copper nanoparticles from refractory sulfides using a semi-industrial mechanochemical approach

The large-scale mechanochemical reduction of binary sulfides chalcocite (Cu₂S) and covellite (CuS) by elemental iron was investigated in this work. The reduction of Cu₂S was almost complete after 360 min of milling, whereas in the case of CuS, a significant amount of non-reacted elemental iron could still be identified after 480 min. Upon application of more effective laboratory-scale planetary ball milling, it was possible to reach almost complete reduction of CuS. Longer milling leads to the formation of ternary sulfides and oxidation product, namely cuprospinel CuFe₂O₄. The rate constant calculated from the magnetometry measurements using a diffusion model for Cu₂S and CuS reduction by iron in a large-scale mill is 0.056 min^−0.5 and 0.037 min^−0.5, respectively, whereas for the CuS reduction in a laboratory-scale mill, it is 0.1477 min⁻¹. The nanocrystalline character of the samples was confirmed by TEM and XRD, as the produced Cu exhibited sizes up to 16 nm in all cases. The process can be easily scaled up and thus copper can be obtained much easier from refractory minerals than in traditional metallurgical approaches.     

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi₂O₃ and TiO₂. Only Bi₄Ti₃O₁₂ phase was formed after 3 h of milling time. The excess of 3 wt% Bi₂O₃ added in the initial mixture before milling does not improve significantly the formation of Bi₄Ti₃O₁₂ phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time. The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi₄Ti₃O₁₂ did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi₄Ti₃O₁₂ crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis.     

Amorphous Ti–Cu–Ni–Al alloys prepared by mechanical alloying

Ti _x (CuNi)_90–x Al₁₀ (x = 50, 55, 60) amorphous powder alloys were synthesized by mechanical alloying technique. The evolution of amorphization during milling and subsequent heat treatment was investigated by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The fully amorphous powders were obtained in the Ti₅₀Cu₂₀Ni₂₀Al₁₀, Ti₅₅Cu_17.5Ni_17.5Al₁₀ and Ti₆₀Cu₁₅Ni₁₅Al₁₀ alloys after milling for 30, 20 and 15 h, respectively. Differential scanning calorimetry revealed that thermal stability increased with the increasing (CuNi) content: Ti₆₀Cu₁₅Ni₁₅Al₁₀, Ti₅₅Cu_17.5Ni_17.5Al₁₀ and Ti₅₀Cu₂₀Ni₂₀Al₁₀. Heating of the three amorphous alloys at 800 K for 10 min results in the formation of the NiTi, NiTi₂ and CuTi₂ intermetallic phases.