Showing papers on "Titanium published in 1984"

Adhesion and Durability of Metal/Polymer Bonds

Abstract: A review is presented of those factors responsible for promoting the integrity and longterm durability of metal-polymer bonds used in the fabrication of aircraft and aerospace structures. Using a multidisciplinary approach and a variety of surface analytical techniques such as extended resolution scanning electron microscopy (XSEM), X-ray photo-electron spectroscopy (XPS), ellipsometry, and a new technique called surface behaviour diagrams (SBD), investigators at the author's laboratories have evolved several important concepts. First, it has been determined that the initial integrity of metal-polymer bonds depends critically upon the morphology of the surface oxide on the metal. For aluminium and titanium, the metals studied, it is demonstrated that certain etching or anodization pretreatment processes produce oxide films on the metal surfaces which, because of their porosity and microscopic roughness, mechanically interlock with the polymer forming much stronger bonds than if the surface were smooth. Second, the long-term durability of metal-polymer bonds is shown to depend strongly on the environmental stability (or lack of stability) of the same oxide which is responsible for good initial bond strength. For aluminium moisture intrusion at the bond line causes the oxide to convert to an hydroxide with an accompanying change in morphology and bond strength. For titanium the oxides appear to be much more stable than those on aluminium but under severe environmental conditions the oxide undergoes a polymorphic transformation which may lead to bond degradation. Third, it is observed that significant improvements in durability of adhesive bonds to aluminium can be achieved using an extremely simple treatment in which monolayer films of certain organic acids are applied to the adherend oxide to protect it against the effects of moisture.

SiC filament/titanium matrix composites regarded as model composites

Abstract: It is generally accepted that silicon carbide CVD-filaments are more suitable than the related boron filaments for reinforcing titanium alloys at medium temperatures Silicon carbide has a higher refractoriness and chemical inertia than boron Moreover, the SiC CVD-filaments retain a much higher fraction of their room temperature mechanical performances up to about 800 to 1000° C and could be produced in the future at a lower price Despite the fact that SiC seems to be less reactive than boron towards most metals, it nevertheless reacts with titanium and its alloys at rather low temperatures (700 to 800° C) Furthermore, silicon carbide when deposited from a gas phase (eg methyl chlorosilane and hydrogen mixtures) often contains small amounts of more reactive species such as elemental silicon or carbon In the same manner, coatings containing elemental carbon have been applied to SiC CVD-filaments in order to reduce their sensitivity to surface abrasion effects Therefore, SiC filament-titanium matrix composites must be regarded as non-equilibrium systems when they are heated at medium or high temperatures The occurrence of chemical interactions between SiC and titanium in the solid state, controlled by diffusion, has already been established either from experiments performed on diffusion couples with a plane interface [1, 2] or on fibrous composite samples [3–12] However, the nature of the phases and the growth mechanism of the filament-matrix (FM) reaction zone remains a subject of controversy The aim of the present contribution is to analyse, for various well characterized SiC-based CVD-filaments (stoichiometric SiC, SiC with a pyrocarbon coating, SiC with a SiC + C coating) and titanium matrices (unalloyed titanium or Ti-6Al-4V): (a) the FM interaction zone composition, (b) its kinetics of growth in the 700 to 1100° C temperature range, and (c) the growth mechanism The filaments which have been used here have been carefully analysed previously on a chemical, microstructural and mechanical point of view in Part 1 In the same manner, the results of the present study on FM chemical interaction will be later correlated with those of different mechanical characterizations [13, 14]

Oxide morphology and adhesive bonding on titanium surfaces

Abstract: Titanium metal was subjected to two surface treatments (alkaline peroxide etch and chromic acid anodization) and resulting oxide morphology examined by high-resolution scanning electron microscopy in a Jeol 100-CX STEM. The effects of treatment time in alkaline peroxide upon oxide morphology were followed and parallel mechanical measurements made on the strengths of adhesive bonds between the metal and an epoxy resin. These strengths were measured after a standard environmental exposure, namely 120 h in water at 80° C. As time-of-treatment increases, a micro-porous oxide layer is developed and adhesive strength rises to a maximum. Prolonged treatment with alkaline peroxide produces a drastic fall in adhesive strength accompanied by gross etching of the metal surface without changes in the oxide morphology. The loss of adhesive durability in this case is therefore attributable to surface chemistry effects rather than morphological changes.

The influence of the valence state of titanium in MgCl2-supported titanium catalysts on olefin polymerization

Abstract: The relationships between the valence state of titanium in MgCl2-supported titanium catalysts and polymerization performances for ethylene and propylene were studied. When the titanium species of the supported titanium catalyst 1 was preliminarily reduced by treating it with AlEt3, the resulting catalyst system 2 had lost the activity for propylene polymerization completely. The catalyst activity for ethylene polymerization was found to be reduced to 20% of that of the original catalyst 1. In the AlEt3-pretreated catalyst 2 no Ti4+ is found and 80% of the total titanium is present as Ti2+. The catalyst system 2 plus AlEt3, however, does exhibit activity towards ethylene-propylene copolymerization, propylene insertion being possible if the end of the growing polymer chain is an ethylene unit. The titanium in the AlEt3-reduced catalyst 2 could be oxidized again by treatment with various agents. The oxidized catalysts 3, in conjunction with freshly added AlEt3 as cocatalyst, are active for propylene polymerization and show increased activity for ethylene polymerization in relation to the extent of oxidation.

Hermetic electrical feedthrough assembly

Abstract: A hermetic feedthrough consisting of a niobium electrical lead-in wire surrounded by an alumina insulator which is carried by a niobium ferrule, the feedthrough being particularly adapted for being welded to the titanium container of an implantable medical device. The niobium and alumina parts are joined together by means of a pure gold braze, the surfaces of the alumina being first metallized with a layer of niobium, titanium or niobium/titanium and an optional overlying layer of gold.

High-Temperature Titanium Alloys—A Review

Abstract: This paper discusses the development of high-temperature titanium alloys for use in gas turbine engines, airframes, and other applications. The high strength-to-density ratio of titanium makes it a very attractive design choice in energy-efficient high thrust-to-weight engines. Consideration is given to both alloy chemistry effects and the role of microstructure in determining mechanical properties. Future developments in alloy modifications and coating advances should result in increased use of titanium in demanding high-temperature applications.

Crystal structures of two titanium tartrate asymmetric epoxidation catalysts

Abstract: Etude structurale des composes Ti 2 (OPr i ) 4 [(O-CHCONHCH 2 Ph) 2 ] 2 et Ti 2 (OEt) 2 (O−NPh−C(O)Ph) 2 [(O−CH−CO 2 −Et) 2 ] 2

Titanium silicide formation: Effect of oxygen distribution in the metal film

Abstract: The oxygen behavior and its influence on Ti silicide formation is systematically studied in the TiO2/Si and Ti/TiO2/Si systems using Rutherford backscattering, nuclear reaction analysis, and x‐rays diffraction techniques. After annealing in vacuum ( p<5×10−7 Torr), no reaction was observed up to 900 °C in the TiO2/Si system, whereas in the Ti/TiO2/Si system, metallic titanium reacts with the TiO2 film above 400 °C and at 600 °C a uniform oxygen solid solution is formed. The silicide formation starts at 650 °C and up to 750 °C the only phase formed is Ti5Si3. We found that this phase is kinetically favored as long as the Ti is being supplied by the unreacted film. The growth rate kinetics was found to have parabolic behavior and was therefore controlled by Si volume diffusion. Above 750 °C, TiSi2 forms very rapidly, its growth being nucleation controlled. During the growth of the silicide layer, a diffusion of oxgen toward the surface region was observed. When the oxygen concentration in the surface layer exceeded the solubility limit, Ti oxide precipitated and the silicide growth nearly stopped, even if some silicon reached the surface. At a temperature higher than 850 °C, a marked oxygen loss takes place, most probably via SiO sublimation. The sublimation process is favored by the presence of Si in the surface region and prevents the formation of a stable SiO2 diffusion barrier at the TiSi2/TiOx interface.

Fatigue properties of carbon- and porous-coated Ti-6Al-4V alloy.

Abstract: A porous metal coating applied to a solid substrate implant has been shown, in vivo, to offer advantages over current polymethylmethacrylate cement fixation in orthopedic devices. These advantages may be lost, however, in devices requiring a sintering heat treatment to apply the coating since these treatments may have a detrimental effect on the substrate material mechanical properties. In addition, more biocompatible interface coating materials have come of interest with recent literature reports of metal ion release. These coatings may be of particular use in porous-coated systems since the surface area of implant in contact with the surrounding tissues is greatly increased. This study investigated the effects that both a porous Ti- 6Al -4V alloy coating and a ULTI carbon coating have on the fatigue properties of a Ti- 6Al -4V alloy substrate system. The fatigue properties of uncoated as-received, uncoated sinter heat treated and notched Ti- 6Al -4V material were also investigated. The results of this study revealed endurance limits for Ti- 6Al -4V alloy tested with a rotating beam system of 617 MN/m2 (uncoated as-received), 624 MN/m2 ( ULTI carbon-coated), 377 MN/m2 ( sinter heat treated), 220 MN/m2 (notched) and 138 MN/m2 (porous-coated). No effects on fatigue properties were observed when testing the material in saline compared with air. The slight increase in fatigue strength for the carbon-coated material is thought to be due to the increase in surface hardness resulting from the formation of titanium carbides on the surface. The low-endurance limit of the porous-coated material is due to both the transition from the as-received equiaxed microstructure to a lamellar microstructure upon sintering and to the notch effect created by the porous coating.

Method for heat treating cast titanium articles to improve their mechanical properties

Abstract: Cast titanium alloys and a method of heat treating the alloys in order to obtain fatigue and mechanical properties comparable to wrought titanium is disclosed. The heat treatment is practiced by solution heat treating a cast titanium article above its beta transus, rapidly cooling, stabilizing at a temperature within the alloy's alpha/beta phase range, and finally aging the article to achieve the desired properties.

Electrode for medical applications

Abstract: In order to expand the availability of effective and usable electrodes for medical applications, an electrode is proposed which is comprised of an electrically conductive carrier material and of a porous layer in its active region which is composed of a carbide, nitride or carbonitride of one of the metals titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum or tungsten.

Auger Electron Spectroscopic Analysis of Hydroxylapatite Coatings on Titanium

Abstract: Investigating the bioreactive behavior of hydroxylapatite [Ca10(PO4)6 (OH)2] coatings on titanium requires an exact knowledge of structure and composition of the coating. Auger electron spectroscopic analyses were performed in addition to other microstructural analyses. Studies of the outer surface and of the interface between hydroxylapatite and titanium showed that the energy and the signal sensitivity of the Auger phosphorus peak depend on the chemical environment. Argonion bombardment was found to affect the spectrum of the low-energy P peaks.

Hydride formation rates of titanium-based b.c.c. solid solution alloys☆

Abstract: Titanium has an h.c.p. structure at room temperature and reacts with hydrogen at an appreciable rate only at elevated temperatures. However, the metal undergoes an allotropic transformation to a b.c.c. structure at 882.5 °C. The b.c.c. phase can be stabilized by suitable alloying with niobium, molybdenum, vanadium etc. so that the b.c.c. phase is retained at room temperature. Rapid reactions at room temperature of these b.c.c. solid solution phases with hydrogen have been observed when small amounts of a third element are added. Suitable additions are those elements which have radii 5% or more smaller than that of titanium.

Composition dependence of defect properties in electron-irradiated Fe-Cr-Ni solid solutions

Abstract: Austenitic Fe-16 wt.% Cr-20-45 wt.% Ni alloys have been studied by electrical resistivity measurements during 21K electron irradiation and during subsequent anneals. The Frenkel-pair resistivity and the activation enthalpy for interstitial and vacancy migration have been evaluated in the 16-45 alloy. An increase in nickel concentration results in a strongly increased interstitial mobility, a slightly reduced vacancy mobility and a smaller vacancy formation enthalpy. Self-interstitials interact strongly with silicon atoms and weakly with titanium atoms. Vacancy mobility is more affected by titanium than by silicon.

Corrosion Behavior and Use of Titanium and Its Alloys

Abstract: This review discusses the corrosion behavior of titanium and certain titanium alloys in a wide range of applications including aerospace, chemical, electrochemical, pollution control, power plants, and natural environments. Conditions in which the metal performs well, and also poorly, are discussed along with the various forms of damage observed. These forms include uniform, crevice, pitting, galvanic, erosion and stress corrosion, and hydrogen embrittlement. Means for avoiding damage and extending usage are also reviewed along with the advantages of inhibitors, anodic passivation, and special alloying.

Electrophotographic imaging member and process comprising sputtering titanium on substrate

Abstract: An electrophotographic imaging member comprising a substrate, a ground plane layer comprising a titanium metal layer contiguous to the substrate, a charge blocking layer contiguous to the titanium layer, a charge generating binder layer and a charge transport layer. This photoreceptor may be prepared by providing a substrate in a vacuum zone, sputtering a layer of titanium metal on the substrate in the absence of oxygen to deposit a titanium metal layer, applying a charge blocking layer, applying a charge generating binder layer and applying a charge charge transport layer. If desired, an adhesive layer may be interposed between the charge blocking layer and the photoconductive insulating layer.

Light induced chemical vapor deposition of conductive titanium silicide films

Abstract: Conductive titanium silicide-containing films and composites comprising substrates and the film are produced by light induced chemical vapor deposition. The process eliminates the need to anneal the silicide film in order to produce a conductive film and overcomes the problem of substrate damage associated with high temperature deposition processes. The process comprises the steps of: exposing gas phase reactants comprising a titanium halide and a silicon containing compound to high intensity light; exposing a preheated substrate to the exposed gases to cause a conductive titanium silicide film to be formed thereon; and, maintaining the substrate, throughout the process, at a temperature below that temperature which would induce a thermal reaction between the gas phase reactants. The films and composites produced by the process are particularly suited for use in VLSI and VVLSI production.

Method for refining microstructures of cast titanium articles

Abstract: The microstructure of titanium alloy castings is improved by a process which comprises beta-solution heat treating the cast article at or near the beta-transus temperature of the alloy, cooling the article to room temperature at a rate in excess of air cooling and aging the article at a temperature about 0.8 to 0.9 of the beta-transus.

Boron nitride containing titanium nitride, method of producing the same and composite ceramics produced therefrom

Abstract: Boron nitride containing titanium nitride in an amount of 0.05 to 10 wt.% which is produced at a relatively low temperature, utilizing a chemical vapor deposition technique. In the deposition process, boron, titanium and nitrogen source gases are introduced into an evacuated reactor together with a carrier and/or diluent gas and contacted with a heated substrate previously mounted in the reactor, whereby boron nitride with titanium nitride is deposited onto the substrate. The deposit thus obtained has a high density, a significantly improved heat-shielding ability, a high degree of anisotropy with respect to thermal diffusivity and a high chemical stability. By using such anisotropic boron nitride with BN ceramics, very useful BN type composite ceramics can be produced.

Analysis of titanium diffused planar optical waveguides in lithium niobate

Abstract: Characteristics of titanium indiffused waveguides in lithium niobate have been investigated. The effects of diffusion time, temperature, and ambient atmosphere on mode structure, surface refractive index, and profile, waveguide depth, surface morphology, and composition are described. Similarities and discrepancies between these and any previously published results are discussed and mechanisms for new features proposed. The necessity for fabrication in an oxygen atmosphere at elevated temperatures is demonstrated, and directions for further investigation indicated.