Cu-Ti Phase Research Articles

Electromigration-enhanced Kirkendall effect of Cu/Ti direct diffusion welding by sparking plasma sintering

Electromigration-enhanced Kirkendall effect is firstly observed in Cu/Ti diffusion welding by sparking plasma sintering. Microstructural evolution and mechanical properties of Cu/Ti joints were systematically investigated to clarify the electromigration-enhanced Kirkendall effect on the mechanism of diffusion joining. Four types of Cu-Ti intermetallic compounds were formed at the interface of bonded joint: CuTi2, CuTi, Cu3Ti2, and β-Cu4Ti. At welding temperature less than 833 K, Cu atomic diffusion was enhanced by current, leading to large Kirkendall Voids along the Cu matrix near intermetallic, resulting in low joint strength. However, as the welding temperature increased to 833 K, a continuous CuTi2 Kirkendall plane was formed in the β-Cu4Ti compound layer, and the growth of the brittle CuTi phase was impeded. A notable observation of this study is that the temperature range for manufacturing high-strength Cu/Ti joints diffusion welding by SPS was determined to be 813–863 K, which is much wider than that reported in the literature. The maximum average shear strength of the joints welded at 833 K was 103.1 MPa, which is twice as large as the value commonly reported. This difference is attributed to the suppression of the brittle CuTi phase by the electromigration-enhanced Kirkendall effect.

Formation mechanism and microstructure evolution of Cu/Ti diffusion bonding interface and its influence on joint properties

Diffusion bonding was applied to join copper and titanium in this paper. The effect of process parameters on the interface microstructure and mechanical properties of the Cu/Ti joint were studied. The micro morphology and phase composition of Cu/Ti interface were analyzed. The microhardness, shear strength and the residual stress distribution of the joint were systematically evaluated. And then the microstructure evolution, the growth mechanism and the failure mechanism of the joint were revealed. Four intermetallic compounds CuTi2, CuTi, Cu4Ti3 and Cu4Ti were formed on the interface area. The formation trend was calculated as CuTi2 > CuTi > Cu4Ti3 > Cu4Ti. The maximum nano-hardness and Young's modulus reached to up 8.9 GPa and 171.2 GPa, respectively, which for the Cu4Ti3 phase at interface. The maximum shear strength was found to be 198 MPa for the joint at 830 °C for 30 min with 15 MPa. The fracture of the Cu/Ti joint mainly occurred in the CuTi and Cu4Ti3 phase. The residual stress mainly concentrated in CuTi2 and CuTi phases, which caused a large stress concentration during the uneven heating or cooling process.

Microstructure and Shear Strength of Brazing High Entropy TiZrHfNbMo Alloy and Si3N4 Ceramics Joints

The effects of different brazing processes on the interfacial microstructure and shear strength of TiZrHfNbMo high-entropy alloy (HEAS) and Si3N4 ceramic brazed joints were studied. There is no obvious defect in a brazed TiZrHfNbMo HEAS/AgCuTi/Si3N4 ceramic joint, and the two materials have good metallurgical bonding. The typical interface microstructure is Si3N4/Ti5Si3/Ag solid solution +Cu (s,s)+ CuTi/Cu2Ti/Cu4Ti + TiCu(Hf,Zr)NbMo/TiZrHfNbMo HEAs. With the increase of brazing temperature, the dispersed CuTi phase agglomerates in the brazed joint, and acts as the nucleate of the Cu-based solid solution. The thickness of the reaction layer increases with the increase of phases in the reaction layer on both sides of the joint. When the brazing temperature is 800 °C, 820 °C, 840 °C and 860 °C, the shear strength of the brazed joint is 30 MPa, 72 MPa, 86 MPa and 21 MPa, respectively. The formation of CuTi and Ti5Si3 intermetallic compounds increases the thickness of the reaction layer, and improves the strength of the joint. However, excessive CuTi and Ti5Si3 intermetallic compounds lead to a significant decrease in joint strength. The grain coarsening of the joint can also affect the strength of the joint.

Phase 3 adaptive trial design options in treatment of complicated urinary tract infection.

New antimicrobial drugs for treatment of complicated urinary tract infection (cUTI) are generally assessed in randomized, double-blind, noninferiority clinical trials. Robust historical data for the active comparator inform on treatment effect estimation, yet typically do not substitute for the active comparator data in the proposed trial. We report design options for a phase 3 trial of cUTI using a Bayesian hierarchical model and historical data from 2 well-executed phase 3 registrational trials of doripenem. The methodology is directly applicable to other phase 3 noninferiority settings. In addition to the research design application, we provide a novel methodology for assessing the robustness of type I error control. The model borrows heavily from the prior data when the current active comparator parameter estimate approximated the historical estimate. In contrast, the model had restricted borrowing when the 2 estimates were very different. The alternative trial design, with or without the inclusion of futility stopping criteria, provides a framework for future cUTI phase 3 trials.

Influence of post-weld heat treatment on microstructure and adhesion of Ti/Cu composite

ABSTRACTIt is well known that brittle interfacial intermetallics are typically present in laminated composites and degrade their mechanical performance. To investigate the relationship between intermetallics and mechanical properties, Ti/Cu-laminated composite plates prepared by explosive welding were studied with different heat treatments. A transition layer containing four zones of intermetallic phases, Cu4Ti, Cu4Ti3, CuTi, and CuTi2, was found at the interface between Ti and Cu after explosive welding. The intermetallics became thicker as the temperature of the heat treatment increased, especially for the CuTi phase. The sample treated at 473 K exhibited the highest bonding strength of 199.7 MPa, which was attributed to the elimination of residual stress during the welding and the diffusion of copper to improve interfacial bonding.

Microstructure and mechanical properties of porous Si3N4/Invar joints brazed with Ag-Cu-Ti+Mo/Cu/Ag-Cu multi-layered composite filler

Abstract Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was successfully designed to braze porous Si 3 N 4 and Invar alloy. To further reduce the CTE mismatch between the porous Si 3 N 4 and brazing filler, Mo particles were introduced into Ag-Cu-Ti. The effects of the Mo addition on the microstructure and mechanical properties of the brazed joints were studied. The results showed that, the addition of Mo particles into Ag-Cu-Ti lowered the CTE mismatch and improved the joint strength to a certain degree. However, an excessive content was harmful. The Mo particles could absorb Ti at high temperature, causing Ti shortage in the reaction with the ceramic. When cooling down, the absorbed Ti was released. The released Ti could react with Cu to generate Cu-Ti phase. So, additional Ti was adopted in the brazing filler as a supplement. When the Ti content was 5 wt%, the reaction layer on the ceramic interface was too thin to transfer enough load. However, when it reached 15 wt%, the Cu interlayer dissolved completely and Fe-Ti and Ni-Ti phases appeared. The maximum joint shear strength (83 MPa) was obtained with 10 wt% Ti and 5 vol% Mo, which had exceeded 90% of the porous Si 3 N 4 and was 56% higher than the joint brazed without Mo particles.

Modification of the Ti40Cu36Zr10Pd14 BMG Crystallization Mechanism with Heating Rates 10-140 K/min

The article presents investigations of Ti40Cu36Zr10Pd14 bulk metallic glass crystallization process heated with the rates of 10, 60, 100 and 140 K/min. High heating rates experiments were performed in a new type of differential scanning calorimeter equipped with a fast responding thermal sensor. Phase composition and microstructure were studied with x-ray diffraction and transmission electron microscopy. The observed crystallization proceeded in two separate steps. Applied high rates of heating/cooling resulted in the crystallization of only one CuTi phase, replacing typical multi-phase crystallization. The microstructure after crystallization was polycrystalline with some amount of amorphous phase retained. Kinetic parameters were determined with the use of the Kissinger and Friedman iso-conversional analysis and Matusita–Sakka iso-kinetic model. The kinetic analysis supplies results concerning autocatalytically activated mechanism of primary crystallization with decreasing activation energy and small density of quenched-in nuclei, in good agreement with previous structural investigations. The mechanism of secondary crystallization required dense nuclei site, increasing activation energy and large nucleation frequency. The amorphous phase of Ti40Cu36Zr10Pd14 BMG revealed high thermal stability against crystallization. Application of high heating rates in DSC experiments might be useful for the determination of mechanism and kinetic parameters in investigations of metallic glasses crystallization, giving reasonable results.

Microstructure formation and evolution mechanism of Cu-Ti coating during dual-magnetron sputtering and thermo plasma nitriding

Dual magnetron sputtering and thermo plasma nitriding were performed to fabricate Cu-Ti-N coating on the surface of Cu substrate, and the microstructure formation and evolution mechanism were investigated. The results showed that the composition of the Cu-Ti coating could be tuned to be around Cu:Ti = 1:1.2 by the appropriate choice of sputtering power for the dual targets, and only amorphous Cu-Ti phases formed. During the thermo plasma nitriding process, crystalline CuTi and Cu3Ti occurred. Moreover, a nitride layer of about 0.3 μm containing nanocrystalline TiN formed on the surface, and the multi-phase coating developed to be about 4 μm, which could provide better support for the nitrided layer.

First-principles investigation of structural, mechanical and electronic properties for Cu–Ti intermetallics

To design a high-performance Cu–Ti intermetallic coating, first-principles calculation is conducted to systematically investigate the phase stability, mechanical and electronic properties of the Cu–Ti binary intermetallics. The phase stability and mechanical properties are studied by calculating the formation enthalpy and independent elastic constants, respectively. The calculated formation enthalpy indicates that β-Cu4Ti, CuTi and CuTi2 are stable phases at 0K, while α-Cu4Ti, Cu3Ti, Cu3Ti2, and Cu4Ti3 are metastable phases. In addition, the mechanical properties of Cu–Ti intermetallics present a positive correlation with their formation enthalpy. The electronic structures of the Cu–Ti intermetallics are evaluated by analyzing the bonds character to reveal the bonding characteristics, which is crucial to the phase stability and mechanical properties. Among the Cu–Ti intermetallics studied, CuTi phase exhibits the highest stability, hardness and a higher brittleness among all Cu–Ti intermetallics, while other Cu–Ti intermetallics show good toughness. Based on the calculated results, a high strength Cu–Ti intermetallic coating consisting of hard CuTi particles on a ductile Cu4Ti3 matrix is proposed.

Effects of Ti and Be addition on microstructure and mechanical properties of Mg58.5Cu30.5Y11 bulk metallic glass

Based on the Mg58.5Cu30.5Y11 alloy, 10% Ti, 10% Be and 10% Ti70Be30 (mole fraction) were respectively added to the alloy and samples with a diameter of 3 mm were fabricated by conventional Cu-mold casting method. The phase constituent, thermal stability and microstructure of the alloys were investigated by using X-ray diffraction, differential scanning calorimetry and scanning electron microscopy, respectively. The effects of alloying elements Ti and Be on the microstructure and mechanical properties of Mg58.5Cu30.5Y11 alloy were discussed. The results show that CuTi phase is distributed in (Mg0.585Cu0.305Y0.11)90Ti10 and (Mg0.585Cu0.305Y0.11)90(Ti0.7Be0.3)10 alloys, while CuYBe glassy phase containing CuY crystals is embedded in the matrix of (Mg0.585Cu0.305Y0.11)90Be10 alloy. Under uniaxial compressive loading, the largest compressive fracture strengths for (Mg0.585Cu0.305Y0.11)90Ti10, (Mg0.585Cu0.305Y0.11)90Be10 and (Mg0.585Cu0.305Y0.11)90(Ti0.7Be0.3)10 alloys are 797.6, 952.6 and 1007.8 MPa, respectively, and the strengths are increased by about 17%, 40% and 48% compared with Mg58.5Cu30.5Y11 alloy. The strength reliability for the three alloys is much improved according to the strength distribution region of 10 samples of each alloy.

Ti–Cu–Zr–Fe–Nb ultrafine structure-dendrite composites with good mechanical properties and biocompatibility

Ti–Cu–Zr–Fe–Nb ultrafine structure-dendrite composites were designed by inducing Nb and more Ti to a Ti–Cu–Zr–Fe glass-forming alloy composition and prepared by copper mold casting. The composite alloys consist of β-Ti dendrites and ultrafine-structured CuTi2 and CuTi phases as well as a trace amount of glassy phase. The volume fraction of β-Ti dendrites increases with the increase in content of Nb which acted as the β-Ti phase stabilizer in the alloys. The composites exhibit high compressive yield strength exceeding 1200MPa, maximum strength around 1800MPa and low Young's modulus around 48GPa. The plasticity of the alloys is strongly influenced by the volume fraction and morphology of the dendritic β-Ti phase, and the compressive plastic strain was enlarged from 5.9% for the 4at% Nb alloy to 9.2% for the 8at% Nb alloy. The preliminary cell culture experiment indicated good biocompatibility of the composite alloys free from highly toxic elements Ni and Be. These Ti-based composite alloys are promising to have potential structural and biomedical applications due to the combination of good mechanical properties and biocompatibility.

Development of Nano-Structure Cu-Ti Alloys by Mechanical Alloying Process

Cu-Ti system with a terminal solution in the Cu-rich portion of equilibrium Cu-Ti phase diagram with a decreasing trend with temperature shows a potential to develop age hardenable alloys with suitable strength and thermal and electrical conductivities. In the present study, the mechanical alloy process has been employed to increase solubility of Ti in Cu matrix to make age hardenable Cu alloys. Cu-Ti powder mixtures with different rations of 1 and 6 wt% of Ti were milled in planetary ball mill for different milling times of 4, 12, 48, 96 and 192 hours. The milled powder mixtures were investigated and characterised by X-ray diffraction (XRD) technique. The results show increasing in lattice parameter of Cu, which indicates that Ti atoms are dissolved in the Cu matrix. Cu crystal sizes showed decreasing trend which were more obvious in the mixture with higher Ti contents. The final crystal sizes were in the range of 17-23 nm after 192 hours of milling.

Property of Cu-Zr-Ti Ternary Alloys

The influence of Zr on the property of Cu(50+x)Zr(40-x)Ti10 (0≤x≤30 at.%) alloys were investigated. The results show that the maximum size for the glass formation in this Cu-Zr-Ti system is less than 8 mm. The hardness increases with decreasing of the Zr content, then decreases when the Zr content exceeds 10~15 at.% due to the obvious alteration of the type of the crystalline phases and the microstructure. With decreasing of the Zr content, the transformation sequence of the main Cu-Zr phase is Cu10Zr7→Cu5Zr→Cu51Zr14; the transformation sequence of Cu-Ti phase is Cu4Ti3→CuTi→CuTi3. In addition, the atom ratio of Cu60Zr30Ti10 alloys is coherent with that of their corresponding crystalline phase, resulting in its better glass forming ability.

Nanocrystallization of gas atomized Cu47Ti33Zr11Ni8Si1 metallic glass

Cu47Ti33Zr11Ni8Si1 metallic glass powder was prepared by gas atomization. Decomposition in the amorphous alloy and primary crystallization has been studied by differential scanning calorimetry (DSC), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The glassy powder exhibits a broad DSC exotherm prior to bulk crystallization. Controlled annealing experiments reveal that this exotherm corresponds to a combination of structural relaxation and nanocrystallization. A uniform featureless amorphous contrast is observed in the TEM prior to the detection of nanocrystals of 4–6 nm in size. High-resolution TEM studies indicate that this nanocrystalline phase has a close crystallographic relationship with the γ–CuTi phase having a tetragonal structure. The product of the main crystallization event is also nanocrystalline, hexagonal Cu51Zr14, having dimensions of 20 nm. However, there is no evidence for possible amorphous phase separation prior to the nanocrystallization events.

Al-Cu-Ni-Ti (Aluminum-Copper-Nickel-Titanium)

An update of the Al-Ti phase diagram appears in this issue. For Al-Cu, Al-Ni, Cu-Ni, Cu-Ti, and Ni-Ti phase diagrams, see [Massalski2]. The binary phases NiAl and NiTi have the CsCl-type B2 structure. Compilations of data on the Al-Cu-Ni, Al-Cu-Ti, Al-NiTi, and Cu-Ni-Ti ternary systems are given in [1995Vil]. In the Al-Ni-Ti ternary system, the Heusler-type L21 phase Ni2AlTi is present along the NiAl-NiTi join.

Effect of the phase transition of Ti silicide on the thermal stability of Si‐interface in the Cu/CuTi2/Ti/Si contact system

AbstractIn an attempt to realize a stable Cu metallization in Si‐LSI, a Cu/CuTi2/Ti/Si contact system was prepared and its thermal stability was studied. As a result, although the phase transition from the intermediate CuTi2 phase to the CuTi phase was observed with increasing annealing temperature in the contact system, the interface between the metallization layers (Cu and CuTi) and Si in the system suppressed the excess diffusion of Si at temperatures up to 570°C. the reason is that the Ti silicide formed at the Si interface acts as an Si diffusion barrier until its chemical state transforms into TiSi2, which is the final phase of Ti silicide. However, the contact system failed due to a direct chemical reaction between Ti and/or Cu in CuTi and Si which diffused into the upper layer through TiSi2 when Ti silicide at Ti/Si interface formed TiSi2 at 600°C. Then the contact system resulted in the phase‐separated bilayer structure of silicide. It was revealed from these results with the thermal stability of this contact system is related closely to the phase transition of the Ti silicide layer at the Si interface with increasing annealing temperature.

Ｃｕ‐Ｔｉ‐Ｂ粉末のメカニカルアロイング過程に及ぼすボロン添加量の影響

Mechanical alloying teratment of mixtures of elemental copper, titanium and boron powders containing various amounts of boron was carried out by using high energy ball mill. For comparisons, the treatment of mixture of alloy powder prepared from Cu-8mass%Ti cast and the boron powder was also carried out. Influence of boron content on the formation of boride titanium during the mechanical alloying and subsequent heat treatment was examined. In the powder prepared from the mixture of elemental powders, a-solid solution and nonequilibrium Cu-Ti phase are formed during the mechanical alloying. When the powder was heat-treated at 1173K, the noncruilibrium phase disappears, and equilibrium Cu3Ti phase and ultrafine spherical boride titanium particles are formed. Ti3B4 and TiB2 particles are formed in the case of mixture with low contents of boron, but only TiB2 is formed from the mixture with high boron contents. The nonequilibrium Cu-Ti phase is also formed by the mechanical alloying in the powder prepared from the Cu-Ti cast, but the quantity of that phase is less than that of the powder prepared from the mixture of elemental powders.

Ｔｉ‐４３ａｔ％Ｃｕ非晶質粉末とアルミニウム粉末の機械的合金化

Mechanical alloying teratment of mixtures of elemental copper, titanium and boron powders containing various amounts of boron was carried out by using high energy ball mill. For comparisons, the treatment of mixture of alloy powder prepared from Cu-8mass%Ti cast and the boron powder was also carried out. Influence of boron content on the formation of boride titanium during the mechanical alloying and subsequent heat treatment was examined. In the powder prepared from the mixture of elemental powders, a-solid solution and nonequilibrium Cu-Ti phase are formed during the mechanical alloying. When the powder was heat-treated at 1173K, the noncruilibrium phase disappears, and equilibrium Cu3Ti phase and ultrafine spherical boride titanium particles are formed. Ti3B4 and TiB2 particles are formed in the case of mixture with low contents of boron, but only TiB2 is formed from the mixture with high boron contents. The nonequilibrium Cu-Ti phase is also formed by the mechanical alloying in the powder prepared from the Cu-Ti cast, but the quantity of that phase is less than that of the powder prepared from the mixture of elemental powders.

Metastable Structures in Quenched Cr-Ti and Electron Irradiated Cu-Ti Alloys

ABSTRACTElectron diffraction and imaging are used to characterize and contrast the structures and microstructures of a metastable Cr-Ti phase formed after quenching and a metastable Cu-Ti phase formed during electron irradiation. In both phases, marked structural anisotropies are found which have characteristics common to both of these bcc-based materials. It has been reported in the literature that this quenched-in metastable Cr-Ti phase undergoes a spontaneous structural relaxation into the amorphous state during sub-eutectoid temperature anneals [1]. Despite the similarity of the present experiments to those reported in the literature, an amorphization transformation was not observed. It is argued that the amorphization of this material requires the stabilization of the amorphous phase by an impurity.

Hydrogen-induced phase separation in amorphous Cu0.5Ti0.5 alloys. II. Thermal evolution.

The thermal evolution of ${\mathrm{Cu}}_{0.5}$${\mathrm{Ti}}_{0.5}$ amorphous hydrides has been studied by both calorimetry and neutron-diffraction experiments for different hydrogen contents. At high hydrogen contents, real-time neutron experiments performed during heating at a constant rate show that long-range crystallization into copper and titanium hydride takes place at a well-defined temperature, as confirmed by the exothermic peak in calorimetry. The onset of desorption of hydrogen at high temperature leads to the formation of metastable Cu-rich and then stable \ensuremath{\gamma}-CuTi phases. At smaller hydrogen contents, the evolution is much more gradual. Cu and ${\mathrm{TiH}}_{\mathrm{x}}$ diffraction lines progressively appear in the diffraction pattern. In the meantime the small-angle maximum shifts towards the origin. Crystallization into \ensuremath{\gamma}-CuTi proceeds in two stages. In the first one, unusual variation of the lattice parameters is observed, whereas the size of the crystallites is constant. The second one coincides with the decomposition of titanium hydride upon desorption of hydrogen. Such variations are compared to those extracted from small-angle neutron scattering experiments.