Low-temperature brazing of titanium by the application of a Zr–Ti–Ni–Cu–Bebulk metallic glass (BMG) alloy as a filler

Titanium (Ti) was successfully brazed at low temperatures below 800 °C by employing a Zr_41.2Ti_13.8Ni_10.0Cu_12.5Be_22.5 (at.%) bulk metallic glass (BMG) alloy as a filler. Through the use of this alloy filler, the detrimental segregation of Zr–Cu–Ni filler elements was completely eliminated by heating to well below 800 °C, so the resultant joint was quite homogeneous with a coarse acicular structure. The disappearance of the Zr–Cu–Ni segregated region was rate-controlled by the diffusion of the filler elements in the Ti base metal. Remarkably, the mechanical property and corrosion resistance of the homogeneous joint brazed at 800 °C for 10 min were mostly comparable to those of bulk Ti.     

Formation and thermal stability of new Zr–Cu-based bulk glassy alloys with unusual glass-forming ability

The simultaneous addition of Al and Ag to Zr–Cu binary alloys increased in the stabilization of supercooled liquid, the reduced glass transition temperature and γ value, leading to greatly enhance the glass-forming ability (GFA). The Zr–Cu–Ag–Al glassy alloy samples with diameters above 15 mm were obtained in the wide composition range of 42–50 at% Zr, 32–42 at% Cu, 5–10 at% Ag, and 5–12 at% Al. The best GFA was obtained for Zr₄₈Cu₃₆Ag₈Al₈ alloy, and the glassy samples with diameters up to 25 mm were fabricated by an injection copper mold casting. The Zr₄₈Cu₃₆Ag₈Al₈ glassy alloy exhibited high tensile and compressive fracture strength of over 1800 MPa.     

Hydrogenation of Zr–Cu–Al–Ni–Pd metallic glasses by electrochemical means

Amorphous materials of Zr–Cu–Ni–Al systems have shown attractive electrochemical hydrogen absorption properties. A comparison between Zr₆₀Cu₁₅Al₁₀Ni₁₀Pd₅ and Zr₆₅Cu_17.5Al_7.5Ni₁₀ reveals that the palladium (Pd) increases the hydrogen absorption capacity. Charging melt-spun Zr₆₀Cu₁₅Al₁₀Ni₁₀Pd₅ ribbons electrochemically to different hydrogen-to-metal (H/M) ratios and following the effusion of hydrogen by thermal desorption analysis (TDA) reveals hydrogen desorption from interstitial sites of high energy levels at temperatures below 630 K. Zirconium hydrides are formed above 630 K. At higher temperatures partial desorption of hydrogen occurs. The thermal stability observed with differential scanning calorimetry (DSC) of the amorphous phase has been significantly deteriorated by hydrogen absorption. After hydrogenation, the crystallization behaviour shows suppression of the characteristic quasicrystalline phase and depends on the hydrogen content. Therefore, at low hydrogen concentrations H/M = 0.3, Cu and/or Cu-rich phases are primarily formed while at high hydrogen concentrations H/M ≥ 0.9 Zr-hydride phase(s) are mainly formed.     

Microstructure identification of devitrified Cu–Ti–Zr–Ni bulk amorphous alloy

The microstructures of devitrified Cu–Ti–Zr–Ni bulk amorphous alloy were identified by X-ray diffractometry (XRD) and transmission electron microscope (TEM). XRD and TEM examinations show that the deep eutectic structures of the tested alloy consist of CuTi₂–Cu₁₀Zr₇, Cu₃Ti–CuZr, Cu₃Ti–Cu₁₀Zr₇–CuZr low-order eutectics. Moreover, short-range ordering clusters in the melt with configuration similar to that of Cu₁₀Zr₇ compound may contribute to the glass forming ability of bulk amorphous Cu–Ti–Zr–Ni alloy.     

In situ composite formation in the Ni–(Cu)–Ti–Zr–Si system

In situ composites were synthesized by arc melting Ni–(Cu)–Ti–Zr–Si alloys. The X-ray diffraction patterns of rapidly cooled cast strips show a primary Ni(Ti, Zr) B2 structure superimposed on the diffuse scattering maxima from the amorphous phase. Compression test results show that the composite starts to yield at 1200 MPa and fractures at 1900 MPa.     

Property improvement of copper films with zirconium additive for ULSI interconnects

Thermal stability of Cu–Zr/Zr–Si/Si connect system was evaluated by a standard four-point probe (FPP) method, X-ray diffraction (XRD) and Auger electron spectroscopy (AES) analyses. And the Cu/Zr–Si/Si connect system was used as control experiment. XRD spectra for the Cu–Zr/Zr–Si/Si and Cu/Zr–Si/Si stacked films after annealing showed that the Cu–Zr/Zr–Si/Si specimen was stable up to 650 °C. However, the peaks of Cu silicide (Cu₃Si) appeared for Cu/Zr–Si/Si specimen after annealing at 650 °C. The formation of high resistivity Cu₃Si corresponding to the drastic increase in sheet resistance of copper film. The results observed by AES were consistent with those obtained from XRD measurements and demonstrated that Cu–Zr/Zr–Si/Si system had more thermal stability than that of the Cu/Zr–Si/Si system. The thermal stability of Cu–Zr/Zr–Si/Si specimen was obviously improved when Zr was introduced into Cu film.     

Amorphous and nanocrystalline sputtered Mg–Cu thin films

Binary Mg–Cu amorphous alloys were first fabricated in 1980s via liquid quenching. In this study, the Mg_1−xCu_x (x varying from 38 at.% to 82 at.%) partially amorphous thin films are prepared via co-sputtering. Upon thermal annealing, the Mg₂Cu or MgCu₂ nanocrystalline phases are induced in the Mg-rich or Cu-rich thin films, respectively. Due to the presence of fine nanocrystalline Mg₂Cu or MgCu₂ particles in the Mg–Cu amorphous matrix, the as-sputtered thin films show satisfactory Young's modulus 100 GPa and hardness 4 GPa.     

Formation and properties of the Zr75−xAlxNi10Cu10Ti5 bulk metallic glasses

Zr-based bulk metallic glasses (BMGs) exhibit interesting mechanical properties since they combine high fracture stress, elastic strain (up to 2%), significant fracture toughness and good corrosion resistance. Quaternary systems with general composition Zr–Ni–Cu–Ti show wide composition ranges in which BMG can be obtained. The addition of the another element to the quaternary alloys often increases the glass forming ability (GFA). The aim of this work was to study the influence of aluminium content on the GFA and on the mechanical properties of the Zr–Ni–Cu–Ti alloys. Multicomponent Zr_75−xAl_xNi₁₀Cu₁₀Ti₅ (x = 15, 20 at%) alloys were produced by melt spinning method obtaining ribbons, and by casting technique into a copper mould, manufacturing rod shape samples with maximum diameter of 2 mm. Supercooled liquid region depends on chemical composition and exceeds 45 °C. Vickers microhardness of studied alloys is comparable to the highest ones for other Zr-based BMG.     

Similar and dissimilar friction welding of Zr–Cu–Al bulk glassy alloys

The friction welding of three kinds of Zr–Cu–Al bulk glassy alloys (BGAs) which show eutectic or hypoeutectic compositions to similar and dissimilar BGAs and crystalline metals has been tried. The shape and volume of the protrusion formed at the weld interface were investigated. In order to characterize the friction welded interface, micrographic observation and X-ray diffraction analysis on the weld cross-section were carried out. A successful joining of Zr–Cu–Al bulk glassy alloys to similar and dissimilar BGAs was achieved without occurrence of crystallizations at the weld interface through the precise control of friction conditions. In addition, the joining of Zr₅₀Cu₄₀Al₁₀ BGA to crystalline alloys was tried, but it was only successful for specific material combinations. The residual strength after welding of dissimilar BGAs was evaluated by the four-point bending test.     

Constitution of the high-Al region of Al–Cu–Rh

Phase equilibria between 540 and 1010 °C were studied in Al–Cu–Rh alloys containing more than 50 at.% Al. Congruent equiatomic AlRh dissolves more than 40 at.% Cu and extends up to 58 at.% Al at the high-Cu part of its compositional range. High-temperature cubic C-Al₅Rh₂ (C-phase) dissolves up to 13 at.% Cu, “Al₃Rh” (₆-phase) up to 15 at.% Cu and Al₉Rh₂ up to 1.5 at.% Cu. The solubility of the third element in other binary Al–Rh and Al–Cu phases is below 0.5 at.%. Close to the high-Cu limit of the C-phase region the fcc C₂-phase structurally related to the C-phase is formed. Stable decagonal phase (D₁-phase) is formed below 1005 °C in a compositional range extending from Al₆₅Cu₁₆Rh₁₉ to Al₆₂Cu₂₃Rh₁₅, which shifts to higher Cu concentrations with decreasing temperature. An additional ternary phase forming around the Al₇₀Cu₂₀Rh₁₀ composition below 660 °C was revealed. Partial 1010, 990, 900, 800, 700, 600 and 540 °C isothermal sections were determined.     

Phase equilibria in the Ni–Cr–Ti system at 850°C

The isothermal cross-section through the ternary phase diagram Ni–Cr–Ti at 850°C was constructed by means of diffusion couples and equilibrated alloys. No ternary phases exist in the system at this temperature. The topology of the isotherm is largely determined by the presence of the TiCr₂-Laves phases which are in equilibrium with the binary Ti–Ni intermetallics. About 10 at.% of Ni can be dissolved in the hexagonal β-TiCr₂ at 850°C, and the solubility of nickel in cubic α-TiCr₂ is approximately 4 at.%. A small amount of nickel or chromium increases the stability of the b.c.c. β-Ti structure. At this temperature the β-Ti(Ni)-based solid solution can dissolve up to 18 at.% of Cr.     

Electrochemical properties and surface analysis of Cu–Zr–Ag–Al–Nb bulk metallic glasses

The electrochemical properties and surface characteristics of Cu–Zr–Ag–Al–Nb bulk metallic glasses (BMGs) were investigated. The alloys exhibit excellent corrosion resistance after immersion in 1N H₂SO₄ and 1N NaOH. The corrosion rates of the alloys in chloride-ion-containing solutions significantly decrease by alloying with Nb element. The formation of Zr- and Nb-enriched surface films could be responsible for the high corrosion resistance.     

Determination of phase equilibria in the Co-rich Co–Al–W ternary system with a diffusion-couple technique

Phase equilibria in the Co-rich Co–Al–W ternary system were determined with a unique diffusion-couple technique in which Co–27Al and Co–15W binary alloys (at. %) were first coupled for interdiffusion and then heat-treated for precipitation. After a diffusion process at 1300 °C for 20 h, concentration gradients of Al and W were formed in the γ-Co(A1) matrix in the vicinity of the coupled interface. After a heat treatment at 900 °C for 500 h the γ′-Co₃(Al,W)(L1₂) phase was formed with a coarsened shape in contact with the γ, CoAl(B2) and Co₃W(D0₁₉) phases. Additionally, it appeared with a submicron cuboidal shape within the γ matrix. After 2000 h, however, the coarsened γ′ phase became infrequent and the three phases of γ, CoAl and Co₃W came into frequent contact with each other. These results clearly demonstrate that the γ′ phase is metastable and the three phases of γ, CoAl and Co₃W are thermodynamically in equilibrium at 900 °C in the Co–Al–W ternary system.     

Structure and optical properties of nanocrystalline NiO thin film synthesized by sol–gel spin-coating method

NiO thin film was prepared by sol–gel spin-coating method. This thin film annealed at T = 600 °C. The structure of NiO thin film was investigated by means of X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). The optical properties of the deposited film were characterized from the analysis of the experimentally recorded transmittance and reflectance data in the spectral wavelength range of 300–800 nm. The values of some important parameters of the studied films are determined, such as refractive index (n), extinction coefficient (k), optical absorption coefficient (α) and band energy gap (E_g). According to the analysis of dispersion curves, it has been found that the dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters and high-frequency dielectric constant were determined. In such work, from the transmission spectra, the dielectric constant (_∞), the third-order optical nonlinear susceptibility χ⁽³⁾, volume energy loss function (VELF) and surface energy loss function (SELF) were determined.     

Coarsening of second phase in a two-phase Zr–2.5Nb: On the role of phase boundaries

Deformed two-phase Zr–2.5Nb was subjected to 700 °C annealing and associated coarsening. After primary recrystallization, the second-phase body-centered cubic β was well dispersed on the grain boundaries of hexagonal α matrix. Prolonged annealing led to the presence of the β, mainly at the α tri-junctions. The two-phase coarsening was associated with clear trends of widening in the second-phase size distribution and changes in phase boundary nature. The former is contrary to what is expected. Changes in phase boundary nature were through increased concentration of 45°[0 0 1] phase boundaries—good-fit interfaces, present in larger β particles, which were estimated to have higher three-dimensional lattice coincidence and hence lower energy. Simple analytical modeling, assuming dissolution-controlled particle coarsening and a lower interfacial energy of the phase interface with the 45°[0 0 1], was shown to explain these experimental observations.     

In situ impedance spectroscopy study of the electrochemical corrosion of Ti and Ti–6Al–4V in simulated body fluid at 25 °C and 37 °C

The corrosion resistance of Ti and Ti–6Al–4V was investigated through electrochemical impedance spectroscopy, EIS, potentiodynamic polarisation curves and UV–Vis spectrophotometry. The tests were done in Hank solution at 25 °C and 37 °C. The EIS measurements were done at the open circuit potential at specific immersion times. An increase of the resistance as a function of the immersion time was observed, for Ti (at 25 °C and 37 °C), and for Ti–6Al–4V (at 25 °C), which was interpreted as the formation and growth of a passive film on the metallic surfaces.     

Experimental determination and thermodynamic assessment of the phase diagram in the Co–Zr system

The phase diagram in the Co–Zr system was determined using the electron probe microanalyzer (EPMA), differential thermal analysis (DTA) and X-ray diffraction (XRD) technique. The experimental results indicate that (1) the solubility region of the Co₂Zr phase is from 25 to 34 at.% Zr; (2) the CoZr₃ phase exists and the temperature of the peritectoid reaction (CoZr₂ + (βZr) ↔ CoZr₃) is about 981 °C; (3) the solubilities of Zr in the (αCo) phase and Co in the (βZr) phase are about 0.15 and 2.5 at.%, respectively. A thermodynamic assessment of the Co–Zr binary system was carried out by the CALPHAD (calculation of phase diagrams) method. The Gibbs free energies of the solution phases (liquid, fcc, bcc and hcp) were described by the subregular solution model, and those of the intermetallic compounds (Co₁₁Zr₂, Co₂₃Zr₆, Co₂Zr, CoZr, CoZr₂ and CoZr₃) were described by the sublattice model. A proper set of the thermodynamic parameters has been derived for describing the Gibbs free energies of each phase in the Co–Zr system. An agreement between the calculated results and experimental data is obtained.     

Synthesis of ultrafine (Ti, W, Mo, V)(C, N)–Ni composite powders by low-energy milling and subsequent carbothermal reduction–nitridation reaction

Ultrafine (Ti, W, Mo, V)(C, N)–Ni composite powders with globular-like particles of 50–300 nm were synthesized at static nitrogen pressure from oxides by a simple and cost-effective route which combines traditional low-energy milling plus carbothermal reduction–nitridation (CRN) techniques. Reaction path of the (Ti, W, Mo, V)(C, N)–Ni system was discussed by X-ray diffraction (XRD) and thermogravimetry–differential scanning calorimetry (TG–DSC), and microstructure of the milled powders and final products was studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results show that CRN reaction has been enhanced by nano-TiO₂ and nano-carbon powders. Thus, the preparation of (Ti, 15W, 5Mo, 0.2V)(C, N)–20Ni is at only 1300 °C for 1 h. During synthesizing reaction, Ni solid solution phase forms at about 700 °C and reduction–carbonization of WO₂ and MoO₂ occurs below 900 °C. The reactions of TiO₂ → Ti₃O₅, Ti₃O₅ → Ti(C, O) and Ti(C, O) → Ti(C, N) take place at about 930 °C, 1203 °C and 1244 °C, respectively.     

Investigations of mechanically alloyed Ni–Zr–Ti–Si amorphous alloys with significant supercooled regions

This study examined the amorphization behavior of Ni₅₇Zr₂₀Ti_23−xSi_x (x=0, 1, 3) alloy powders synthesized by mechanical alloying technique. According to the results, after 5 h of milling, the mechanically alloyed powders were amorphous at compositions of Ni₅₇Zr₂₀Ti_23−xSi_x (x=0, 1, 3). The amorphization behavior of Ni₅₇Zr₂₀Ti₂₀Si₃ was examined in details. The conventional X-ray diffraction and synchrotron EXAFS results confirm that the fully amorphous powders formed after 5 h of milling. The thermal stability of the Ni₅₇Zr₂₀Ti_23−xSi_x amorphous powders was investigated by differential scanning calorimeter (DSC). As the results demonstrated, the amorphous powders were found to exhibit a large supercooled liquid region before crystallization. The supercooled liquid regions, defined by the difference between T_g and T_x, (i.e. ΔT=T_g−T_x), are 95 K, 66 K, and 88 K, for Ni₅₇Zr₂₀Ti₂₃, Ni₅₇Zr₂₀Ti₂₂Si₁, and Ni₅₇Zr₂₀Ti₂₀Si₃, respectively.