Electrochemical deposition of Ag–Sn alloys onto copper and titanium plates

In this paper, we report a detailed study of the thermal properties of a peritectic Ag–Sn alloy electrochemically deposited onto copper and titanium plates in order to produce soldered contact structures. A comparative analysis of Ag and Sn codeposition and layer-by-layer deposition processes is presented.     

In situ formation of titanium carbide in titanium powder compacts by gas–solid reaction

Porous titanium compacts of fine and coarse sponge titanium powders were reacted with methane gas to produce Ti–TiC in situ composites. The kinetics of titanium carbide formation during the reaction were studied in relation to powder size, reaction temperature and time, and methane flow rate. The titanium carbide was initially formed as a layer around each titanium powder and the rate of formation was found to be diffusion-controlled. Titanium hydride was also formed during the reaction but was easily removed by post-vacuum annealing. A significant reduction of chlorine content in the compact also resulted during the processing. High temperature vacuum sintering could densify the reacted compacts to over 95% theoretical density and, at the same time, alter the layered titanium carbide phase into rounded particles. It was possible to produce fully dense titanium base composites containing up to 30 vol% by the present gas–solid reaction-based processing.     

In vivo evaluation of titanium implants coated with bioactive glass by pulsed laser deposition

During the past years, different techniques, like chemical treatment, plasma spraying, sputtering, enamelling or sol–gel; and materials, like metals, hydroxylapatite, calcium phosphates, among others, have been applied in different combinations to improve the performance of prostheses. Among the techniques, Pulsed Laser Deposition (PLD) is very promising to produce coatings of bioactive glass on any metal alloy used as implant. In this work the biocompatibility of PLD coatings deposited on titanium substrates was examined by implantation in vivo. Different coating compositions were checked to find the most bioactive that was then applied on titanium and implanted into paravertebral muscle of rabbit.     

Phase evolution and reaction mechanism during reduction–nitridation process of titanium dioxide with ammonia

Titanium nitride powders were synthesized from titanium dioxide at 1173–1373 K in ammonia atmosphere. The reduction–nitridation products with various fractions obtained at various temperatures were analyzed by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The reaction sequence from TiO₂ to TiN in ammonia atmosphere was changed by increasing the reaction temperature. The reaction sequence at 1173 K was found as TiO₂ → TiN_1?xO_x → TiN. When the reaction temperature was above 1273 K, the reaction sequence changed to as follows: TiO₂ → Ti₉O₁₇ → TiN_1?xO_x → TiN. Ti₃O₅ was not found as an intermediate phase on account of its instability in NH₃ atmosphere. The morphology of the synthesized TiN is closely related to that of the raw materials.     

Mechanical synthesis of nanostructured titanium–nickel alloys

The methods of mechanically assisted synthesis and mechanical alloying are used to obtain nanostructured TiNi shape-memory alloys. A stoichiometric mixture of Ti and Ni powders was subjected to intense mechanical treatment in a planetary ball mill. It was shown that after 30 h milling, the synthesis of the product with a mean particle size of 20–30 nm proceeded at 550 °C. XRD data show mainly the presence of TiNi, Ti₂Ni and TiNi₃ phases. Prolongation of the milling process up to 40 h leads to direct synthesis of a product with a similar phase composition. SEM and TEM analyses are used to study morphological changes of reagent and product particles in the course of mechanical treatment and after the synthesis of products. The mechanochemical synthesis routes are compared with the traditional method of thermal synthesis. The advantages of the mechanochemical methods of synthesis of nanostructured products and obtaining Ti–Ni powders with a high sinterability are also discussed. It was shown that after cold pressing and sintering at 800 °C, compacts containing even distributed pores with a mean size of 1 μm were obtained. TiNi bodies with similar structural peculiarities are suitable for the purposes of implantology.     

Precipitation behavior of Ag–Pd–In dental alloys

Age-hardening characteristics and precipitation behavior of Ag–25%Pd–3%In–1%Zn–0.5%Ir alloy were investigated in detail by means of hardness testing, X-ray diffraction, electron microscopy and resistivity measurement. The solution treating could be accomplished at 980 °C and the aging in the temperature range from 950 to 850 °C occurred by continuous precipitation. The aging in the temperature range from 850 to 450 °C occurred first, forming GP-zones with a hardness increase and then in overaging stage by forming discontinuous precipitation, which consisted of lamellae of solute (Pd, In, Zn) depleted Ag-rich phase and (Pd,Ag)₃(In,Zn) intermetallic phase. The hardness increased very fast to its peak in 10 min during aging at temperatures between 450 and 550 °C.     

Electrophoretic deposition of carbon nanotubes–hydroxyapatite nanocomposites on titanium substrate

Carbon nanotubes–hydroxyapatite (CNTs–HA) composites were synthesized, using an in situ chemical method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). HA particles were uniformly absorbed on the CNTs, with strong interfacial bonding. The CNTs–HA composites behaved like single composites when deposited on a titanium substrate by electrophoretic deposition (EPD). EPD was carried out at 10, 20 and 40 V, for 0.5 to 8 min at each voltage. Coating efficiency and weight increased with increasing deposition time, while the slope of the curves decreased, indicating a decrease in deposition rate. The CNTs–HA coating morphology was analyzed with scanning electron microscopy (SEM). The results revealed that decreasing the voltage used for deposition coatings could reduce cracking frequency. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed that the deposition coatings protected the titanium substrate from corroding in simulated body fluid (SBF). In addition, in vitro cellular responses to the CNTs–HA coatings were assessed to investigate the proliferation and morphology of osteoblast cell line.     

Cold-walled,in-situ sulfurization of Cu–In alloys

This article reports cold-walled, in-situ sulfurization of Cu₁₁In₉ for the formation of CuInS₂. The deposition of the precursor Cu–In layered films, the thermal annealing of the layered films, and the subsequent sulfurization of the annealed films were all performed in chamber without breaking the vacuum. The sulfurization was conducted at various pressures and temperatures under a 10% H₂S/Ar mixture. Conversion of the Cu₁₁In₉ phase to the desired CuInS₂ phase was achieved in 1 h at 146.7 Pa and 550 °C or at 1000 Pa and 450 °C. The CuInS₂ films obtained show low resistivity of the order of 10^? 1 Ω-cm and absorbance > 90%. A CuInS₂ film with a rougher surface exhibits a higher absorption coefficient.     

In situ X-ray analysis of mechanism of nonlinear super elastic behavior of Ti–Nb–Ta–Zr system beta-type titanium alloy for biomedical applications

Ti–XNb–10Ta–5Zr (mass %) alloys based on nominal compositions of Ti–35Nb–10Ta–5Zr, Ti–30Nb–10Ta–5Zr, and Ti–25Nb–10Ta–5Zr were fabricated through powder metallurgy and forging and swaging processes for biomedical applications. The tensile deformation mechanisms of the Ti–25Nb–10Ta–5Zr, Ti–30Nb–10Ta–5Zr, and Ti–35Nb–10Ta–5Zr alloys were investigated in situ by X-ray diffraction analysis under several loading conditions.Under the loading conditions, the X-ray diffraction peaks of all the specimens shifted to higher angles than those obtained under the unloading conditions. For the Ti–30Nb–10Ta–5Zr alloy, the elastic deformation is considered to progress continuously in a different crystal direction although after the elastic strain reaches elastic limit in the crystal direction where the elastic limit is the smallest, slip deformation occurs in that crystal direction. The elastic modulus of this alloy appears to decrease in terms of strain over the proportional limit. Thus, the elastic deformation behavior of the Ti–30Nb–10Ta–5Zr alloy does not obey Hooke's law.     

Preparation of Li–Al–O films by laser chemical vapor deposition

Li–Al–O films were prepared on AlN substrates by laser chemical vapor deposition at deposition temperatures (T_dep) of 800–1300 K and molar ratios of Li to Al precursors (R_Li/Al) of 0.1–12. Single-phase α-LiAl₅O₈ films having faceted grains with pyramidal and polygonal shapes were obtained at T_dep = 1107–1280 K and R_Li/Al = 0.1–2.9. Single-phase γ-LiAlO₂ films having pyramidal grains were prepared at T_dep = 984–1238 K and R_Li/Al = 0.9–10.6. Under the conditions of T_dep = 923 K and R_Li/Al = 11.4, single-phase β-Li₅AlO₄ films with a fluffy morphology were deposited. The highest deposition rate of Li–Al–O films was 98 μm h⁻¹ with a mixture of γ-LiAlO₂ and β-Li₅AlO₄ at T_dep = 944 K.     

In situ study on growth behavior of Cu6Sn5 during solidification with an applied DC in RE-doped Sn–Cu solder alloys

The growth behavior of Cu₆Sn₅ intermetallic compounds in rare earth (RE)-doped Sn–Cu solder alloys with an applied direct current (DC) has been in situ investigated using synchrotron radiation imaging technology. The morphological evolutions of Cu₆Sn₅ with various shapes of I-like, Y-like and bird-like are directly observed. After doping RE, the number of I-like and bird-like Cu₆Sn₅ is decreased, but the number of Y-like Cu₆Sn₅ is increased. The morphologies of Cu₆Sn₅ are more uniform and the mean lengths of Cu₆Sn₅ of different shapes are reduced in RE-doped alloys compared with that in RE-free alloys, which is attributed to the adsorption effect of RE. The growth orientation of Y-like Cu₆Sn₅ is changed after La is doped. Additionally, with an applied DC, the nucleation rate of Cu₆Sn₅ is increased and the growth rate is markedly enhanced resulting in the refinement of Cu₆Sn₅. Furthermore, the mechanisms of refinement caused by RE and DC are specifically discussed.     

Preparation of Ba–Ti–O films by laser chemical vapor deposition

Ba–Ti–O films were prepared on Pt-coated Si substrate by laser chemical vapor deposition, and their orientations and microstructures were compared. Ba₂TiO₄, BaTiO₃, BaTi₂O₅, Ba₄Ti₁₃O₃₀ and BaTi₄O₉ single-phase films were prepared at Ti to Ba molar ratio from 0.41 to 3.49. The α′-Ba₂TiO₄ film showed (0 1 0) and (0 9 1) co-orientation with elongated, truncated columnar grains. The BaTiO₃ film was composed of triangular and hexagonal grains with slight (1 1 1) orientation. The BaTi₂O₅ film had (0 1 0) orientation and faceted columnar grains. The Ba₄Ti₁₃O₄₀ film showed (1 0 0) and (0 1 2) co-orientation with shellfish-like grains. The BaTi₄O₉ film showed (0 1 0) orientation with slightly rounded faceted columnar grains. The deposition rates of Ba–Ti–O films ranged from 30 to 144 μm h⁻¹.     

Specific heats of commercial titanium alloys at 50–1100°C

Specific-heat measurements are reported for nine titanium alloys with and + structures; the temperature of the transition has been revised by DTA. A generalized approximating formula for the specific heat has been derived for the temperature range in which the structural state is stable, which contains a dimensionless parameter that includes the temperature of the transformation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 4, pp. 593–598, April, 1980.     

Effect of molybdenum on microstructure and wear properties of Fe–Ti–Mo–C laser clad coatings

Abstract

The AISI?1045 steel surface was alloyed with preplaced ferrotitanium (Fe–Ti), ferromolybdenum (Fe–Mo) and graphite powders using a 5 kW CO₂ laser. In situ carbide reinforced Fe based surface composite coating was fabricated. The results showed that (Ti,Mo)C particles with flower-like and cubic shapes were formed during laser cladding process. The growth morphology of the reinforcing (Ti,Mo)C carbide has typically faceted features, indicating that the lateral growth mechanism is still the predominant growth mode under rapid solidification conditions. Increasing the amount of Fe–Mo in the reactants led to a decrease in carbide size and an increase in volume fraction of carbide but increased the crack sensitivity of the coating. The multiple carbides of (Ti,Mo)C created a higher microhardness and excellent wear resistance than TiC alone under dry sliding wear test condition.     

Initial oxidation of Fe–Cr alloys: in situ STM and ex situ SEM observation

Abstract

In order to understand the initial oxidation of Fe–Cr alloys a single crystal of Fe–15Cr (100) was oxidized at 440°C under controlled oxygen partial pressure in a UHV system and the surface morphology was observed using in situ STM (basic pressure 1×10^?10 mbar); in addition, polycrystalline Fe&15Cr was oxidized at 400°C in an IR-furnace in atmospheric air and the morphology was observed using ex situ SEM. The chemistry of the surface oxide layers was studied by XPS.

Preparation of the single crystal in the UHV system did not lead to segregation of Cr to the surface during heating. In situ STM investigation showed that oxidation of Fe–Cr commenced by nucleation of Cr oxide on the surface, due to selective oxidation of Cr. When the Cr at the surface and at the interface was completely consumed by nucleation of Cr oxide, Fe oxidized and covered the initial Cr oxide nuclei, resulting in an Fe oxide layer on the surface. Ex situ experiments showed that initial oxidation of the mechanically prepared polycrystalline alloy depended on the defect distribution in the surface. It started with formation of whisker-type Fe oxides along defects and proceeded with spherical-type nucleation and growth of Fe oxide. In both experiments, the final product on the surface was Fe₂O₃.     

Formation of core–shell network structural titanium–nitrogen alloys with different nitrogen contents

High-dense titanium alloys with a 3D network core–shell structure of different N contents were synthesized successfully by means of spark plasma sintering of the nitrided titanium particles. The microstructure investigation shows that the core–shell structure with an obvious boundary within a grain is constructed in light of different solid solution levels of nitrogen in grain boundary and grain inner. The mechanical behaviors have been experimentally assessed through compressive testing. The compacts exhibit a much enhanced strength while retaining a reasonable ductility, which can be attributed to their novel core–shell structure. With an increasing N content as well as shell thickness, the strength increases and the ductility decreases, in accordance with the morphology observations.     

In situ boron carbide–titanium diboride composites prepared by mechanical milling and subsequent Spark Plasma Sintering

Boron carbide–titanium diboride composites were synthesized and consolidated by Spark Plasma Sintering (SPS) of mechanically milled elemental powder mixtures. The phase and microstructure evolution of the composites during sintering in the 1,200–1,700 °C temperature range was studied. With increasing sintering temperature, the phase formation of the samples was completed well before full density was achieved. The distribution of titanium diboride in the sintered samples was significantly improved with increasing milling time of the Ti–B–C powder mixtures. A bulk composite material of nearly full density, fine uniform microstructure, and increased fracture toughness was obtained by SPS at 1,700 °C. The grain size of boron carbide and titanium diboride in this material was 5–7 and 1–2 μm, respectively.     

In vitro degradation behavior and cytocompatibility of Mg–Zn–Zr alloys

Zinc and zirconium were selected as the alloying elements in biodegradable magnesium alloys, considering their strengthening effect and good biocompatibility. The degradation rate, hydrogen evolution, ion release, surface layer and in vitro cytotoxicity of two Mg–Zn–Zr alloys, i.e. ZK30 and ZK60, and a WE-type alloy (Mg–Y–RE–Zr) were investigated by means of long-term static immersion testing in Hank’s solution, non-static immersion testing in Hank’s solution and cell-material interaction analysis. It was found that, among these three magnesium alloys, ZK30 had the lowest degradation rate and the least hydrogen evolution. A magnesium calcium phosphate layer was formed on the surface of ZK30 sample during non-static immersion and its degradation caused minute changes in the ion concentrations and pH value of Hank’s solution. In addition, the ZK30 alloy showed insignificant cytotoxicity against bone marrow stromal cells as compared with biocompatible hydroxyapatite (HA) and the WE-type alloy. After prolonged incubation for 7 days, a stimulatory effect on cell proliferation was observed. The results of the present study suggested that ZK30 could be a promising material for biodegradable orthopedic implants and worth further investigation to evaluate its in vitro and in vivo degradation behavior.     

Gas-particle flow of cohesive aluminium powders during laser metal deposition – Experimental and numerical investigation

This paper investigates particle dynamics both inside and outside a Laser Metal Deposition nozzle of a Directed Energy Deposition processing head, i.e. a Laser Metal Deposition (LMD) nozzle, by way of high-speed imaging and particle tracking as well as through computer simulations that account for particle collision and van der Waals forces. It is shown that the particle accumulation phenomena observed experimentally with cohesive aluminium powders can be qualitatively reproduced numerically. It is also demonstrated that such computer simulations can yield the correct order of magnitude for particle velocities, which is rarely reported in the literature and usually unknown for any given LMD system. This work thus paves the way towards more accurate simulations of gas-particle flows in LMD nozzles, especially with cohesive powders.