The structural and electrical properties of Metglas and amorphous metal films

We prepared non-alloyed, alloyed and gas-doped metal films by vapour quenching under ultrahigh vacuum conditions in order to find non-crystalline phases. Of the metals investigated (titanium, zirconium, vanadium, niobium, chromium, molybdenum, nickel, platinum, cobalt, copper, tungsten and tantalum such as TaNi, TaCo, WN, TaAr and TaN exhibited a non-crystalline phase which we call metglas because of its structural similarity to bulk Metglas®. TaNi and TaN films exhibited in addition a non-crystalline structure which we call solid-amorphous. The criteria for the characterization of the metglas and solid-amorphous structure are given.     

Oxygen adsorption on the (110) face of tantalum,niobium, molybdenum and tungsten single crystals

Preliminary surface studies using work function techniques are reported for the (110) face of the refractory metals tantalum, niobium, molybdenum and tungsten, both in the clean state and during the introduction of pure oxygen gas at room temperature. The conclusions of Haas et al from LEED measurements on the same group are substantiated. The surface potential changes as a function of exposure for tantalum and niobium are very similar but quite different from molybdenum and tungsten which are also similar. The latter show a two phase adsorption, both of which are electronegative, the former an initial electronegative phase followed by a pressure dependent electropositive phase. Solution of oxygen into the bulk probably takes place for tantalum and niobium to give rise to the electropositive state. Differences in atomic size are small for all four metals and thus the observed groupings are probably a consequence of chemical effects and similarities existing between members of groups VB and VIB.     

Corrosion of bio implants

Chemical stability, mechanical behaviour and biocompatibility in body fluids and tissues are the basic requirements for successful application of implant materials in bone fractures and replacements. Corrosion is one of the major processes affecting the life and service of orthopaedic devices made of metals and alloys used as implants in the body. Among the metals and alloys known, stainless steels (SS), Co-Cr alloys and titanium and its alloys are the most widely used for the making of biodevices for extended life in human body. Incidences of failure of stainless steel implant devices reveal the occurrence of significant localised corroding viz., pitting and crevice corrosion. Titanium forms a stable TiO₂ film which can release titanium particles under wear into the body environment. To reduce corrosion and achieve better biocompatibility, bulk alloying of stainless steels with titanium and nitrogen, surface alloying by ion implantation of stainless steels and titanium and its alloys, and surface modification of stainless steel with bioceramic coatings are considered potential methods for improving the performance of orthopaedic devices. This review discusses these issues in depth and examines emerging directions.     

Lichtbogen- und Plasmaspritzen von Sondermetallen

Arc and plasma spraying of special materials with high oxygen affinity Within the framework of the research work dealt with in this paper, metallic coatings of titanium, tungsten, molybdenum, tantalum and zirconium were produced on steel base material by the spray-deposition process. — The affinity of the molten special metals to reactive gases (particularly oxygen) is high, therefore. The spraying operation was carried out in an inert gas chamber. The equipment used to produce these metallic coatings comprised a two-wire arc-gun designed by the authors and a commercially available plasma-gun adapted to suit the test conditions. — In the case of all the special metals sprayed in this way the principal mechanism effecting adhesion must be seen to reside in a metallurgical interaction between base und sprayed metal. — Observations are discussed concerning structural peculiarities and embrittlement effects depending on the kind of shielding gas employed.     

Substrate heating rates for planar and cylindrical-post magnetron sputtering sources

Substrate heating energies per atom deposited are reported for planar magnetron sputtering of aluminum, chromium, nickel, copper, molybdenum, indium, tantalum, tungsten and platinum in argon as well as for aluminum and chromium sputtered in O₂. Data are also reported for cylindrical magnetron sputtering of niobium, silver, tantalum, tungsten and Pb-Sn in argon as well as for molybdenum sputtered in neon, argon, krypton and xenon. The planar and cylindrical magnetron heating rates were comparable. The heating energies for argon sputtering ranged from 10–15 eV per deposited atom for the light metals to almost 100 eV atom^-1 for tantalum and tungsten. The implied reactive sputtering heating energies were about 500 eV molecule^-1 for Cr₂O₃ and 1150 eV molecule^-1 for Al₂O₃. Special experiments were conducted to examine the contributions to the substrate heating of plasma species and ion neutralization and reflection at the cathode. The data indicate that charged plasma species do not contribute significantly to the heating but that neutralized and reflected ions play a significant role in the planar as well as the cylindrical cases despite the differences in cathode geometry.     

Chemical vapor deposition of doped TiO2 thin films

Niobium-, tantalum- and fluorine-doped TiO₂ films were made by atmospheric pressure chemical vapor deposition from titanium alkoxides mixed with niobium ethoxide, tantalum ethoxide and t-butyl fluoride respectively. 4% H₂ in N₂ was used as the carrier gas and the deposition temperatures were in the range 400–600°C. The resistivities of the films increased dramatically with film thickness. For highly doped films 1 μm thick resistivities as low as 0.01 Ω cm were achieved.     

Hot-working and strengthening in metal carbide-graphite composites

A study of the hot-pressing of graphite-metal powder mixes up to 2700° C has been effected, concentrating on metals such as titanium, vanadium, niobium, tantalum and zirconium which form stable refractory carbides. In particular, it is shown that titanium/vanadium and graphite/electrographite powder compacts can be deformed plastically and even die-moulded rapidly above 2000° C in a one-stage process to form strong, shock-resistant composite artefacts consisting of a graphite matrix hardened by finely divided metal carbide. The compressive strength is increased by a factor of 10 over a typical electrographite. Densification and strengthening are induced at much lower temperatures than those required for pure carbons and graphite.     

The important role of titanium microalloying in refining austenite grain of heavy-duty H-beam steel during rough rolling produced by a new technology

A new technology of austenite grain refinement, fine austenite enhanced ferrite transformation, is proposed for heavy-duty hot-rolled H-beam steels in this work. Titanium microalloying is very important and necessary for the new technology. The effect of titanium on the prior austenite grain size of steels during simulated rough rolling was investigated. The results show that the prior austenite grain sizes of specimens with titanium and niobium elements are much finer than those of specimens with niobium but without titanium deformed at the same parameters. For the alloying composition of studied steels, titanium nitride particle maybe precipitated in specimens with titanium at above 1,200 °C, however, niobium carbide particles can't form in specimens without titanium at above 1,150 °C. The thermodynamically stable titanium nitride particles can impede the grain growth at high temperature for example furnace heating before rough rolling and bring the epitaxial growth of niobium carbide on pre-existing themselves which induces a large number of titanium nitride-niobium carbide composite precipitates. These fine precipitates can pin austenite grain boundaries effectively and ensure austenite grain refinement.     

Role of zirconium in microalloyed steels: a review

Recently there has been a renewed interest in the addition of zirconium to microalloyed steels. It has been used since the early 1920s, but has never been universally employed, as have niobium, titanium or vanadium. The functions of zirconium in steelmaking are associated with a strong chemical affinity, in decreasing order, for oxygen, nitrogen, sulphur and carbon. Historically, the main use of additions of zirconium to steel was for combination preferentially with sulphur, to avoid the formation of manganese sulphide, known to have a deleterious influence of the impact toughness of wrought and welded steel. Modern steelmaking techniques have also raised the possibility that zirconium additions can reduce the austenite grain size and increase dispersion strengthening, due to precipitation of zirconium carbonitrides, or in high nitrogen vanadium–zirconium steels, vanadium nitride. This review gathers information on the compounds of zirconium identified in steels together with crystallographic data and solubility equations. Also brief accounts of the role of sulphides and particles in general on austenite grain size control and toughness are included.     

Bilayer systems of tantalum or zirconium nitrides and molybdenum for optimized diamond deposition

Thermo chemical computing validates the stability of different nitrides against Co, Mo, and methane up to 1150 K, showing the highest chemical stability against carburization for ZrN and TaN under static conditions.Single zirconium and tantalum nitrides layers have been sputtered onto WC-Co substrates as diffusion barriers and buffer layers under specific reactive sputtering conditions. To improve the nuclei density of diamond during CVD processing, a thin Mo extra layer has been added (< 500 nm). In this study, two bilayer systems have been tested: TaN-Mo and ZrN-Mo. Nano crystalline diamond has been grown under negative biased substrates.After diamond deposition, a massive carburization of molybdenum and tantalum nitride is observable whereas zirconium nitride is not. Nevertheless, a small amount of cobalt has migrated through the ZrN layer. The better efficiency of the ZrN layer to prevent diffusion of the Co element, leads to expect an increased adhesion of diamond on ZrN-Mo bilayer coating. A TEM study is done to improve understanding of phenomena occurring at the interfaces during process.     

Quaternary Ti–20Nb–10Zr–5Ta alloy during immersion in simulated physiological solutions: formation of layers,dissolution and biocompatibility

Samples of the quaternary Ti–20Nb–10Zr–5Ta alloy were immersed in Hanks’ simulated physiological solution and in minimum essential medium (MEM) for 25 days. Samples of Ti metal served as controls. During immersion, the concentration of ions dissolved in MEM was measured by inductively coupled plasma mass spectrometry, while at the end of the experiment the composition of the surface layers was analyzed by X-ray photoelectron spectroscopy, and their morphology by scanning electron microscopy equipped for chemical analysis. The surface layer formed during immersion was comprised primarily of TiO₂ but contained oxides of alloying elements as well. The degree of oxidation differed for different metal cations; while titanium achieved the highest valency, tantalum remained as the metal or is oxidized to its sub-oxides. Calcium phosphate was formed in both solutions, while formation of organic-related species was observed only in MEM. Dissolution of titanium ions was similar for metal and alloy. Among alloying elements, zirconium dissolved in the largest quantity. The long-term effects of alloy implanted in the recipient’s body were investigated in MEM, using two types of human cells—an osteoblast-like cell line and immortalized pulmonary fibroblasts. The in vitro biocompatibility of the quaternary alloy was similar to that of titanium, since no detrimental effects on cell survival, induction of apoptosis, delay of growth, or change in alkaline phosphatase activity were observed on incubation in MEM.     

Analysis of interaction between reactants and substrate materials during the growth of tantalum coatings

We have analyzed interaction between reactants and substrate materials during the reduction of tantalum bromide with cadmium in the course of tantalum deposition on Cu, Fe, Mo, and Ni metallic substrates and the 25Kh3M3NBTsA, Ni₃Al, VKNA, and ZhS32 alloys. The results indicate that molybdenum and nickel substrates are the most stable to the reactants used in this study; copper and iron experience etching; and aluminum, chromium, and titanium are capable of competing with cadmium as a reducing agent. The presence of carbon in the substrate material leads to the formation of tantalum carbide in the metal–coating interfacial layer. In the absence of aluminum, oxygen impurities are likely to be removed as oxybromides. Optimal materials for the fabrication of reaction chambers for tantalum deposition are nickel-coated high-temperature steels.     

Hochschmelzende Metalle und ihre Legierungen

Refractory metals and alloys. The application of refractory metals such as niobium, tantalum, molybdenum, tungsten, chromium and rhenium at high temperatures is discussed on the basis of a compilation of their physical, chemical and technological properties. The present state of knowledge in this field indicates, that the high temperature strength needed can be obtained with some of the refractory alloys also at temperatures much higher than 1000°C. However, at present, the oxydation resistance has not yet been improved far enough to allow the use of these materials in air.     

Development of structural steels with re resistant microstructures

Abstract

This paper is concerned with the design and characterisation of fire resistant steels for building construction. Steel design considerations are discussed. Issues raised include controlling the grain size, properties of substitutional elements, and processing. New experimental fire resistant steels microalloyed with molybdenum and niobium, or tungsten, titanium, and boron have been made and their microstructures and tensile properties characterised. The steels possess satisfactory high temperature strength, owing partly to their relatively large grain sizes compared with conventional steels. The nature of equilibrium precipitation has been calculated using Thermo Calc. Optical microscopy, SEM, TEM, and differential scanning calorimetry have been used to determine the physical characteristics. The strengthening mechanisms observed on the experimental steels of this study could be attributed to secondary formation of fine precipitates, in line with previous observations.     

Development Of New Low-Alloy Steels For Rock Roller Drill Bits

We consider the influence of complex microalloying on the mechanical properties, wear resistance, and contact fatigue of steels used for rock roller drill bits. We established that the complex microalloying of new steels with niobium, titanium, and rare-earth metals increased the mechanical characteristics and abrasive wear resistance by 20% and the contact fatigue by 75%. The optimum ratio of carbide-stabilizing elements, namely, niobium and titanium, in the steel, which is additionally microalloyed with rare-earth metals, is determined. As an alternative to high-nickel steels, we developed new low-alloyed 20KhGN2MBTA and 20KhGNBTChA steels. Translated from Fizyko-Khimichna Mekhanika Materialiv. Vol. 36. No. 3, pp. 102–107. May-June. 2000.     

Determination of the True Temperature of Molybdenum and Luminous Flames from Generalized Wien’s Displacement and Stefan–Boltzmann’s Laws: Thermodynamics of Thermal Radiation

The true temperature of thermal radiation of molybdenum and luminous flames is defined from the temperature dependences of generalized Wien’s displacement and Stefan–Boltzmann’s laws. For determining the true temperature of molybdenum, experimental values of either the position of the maximum of the spectral emitted density or the total emitted density are needed. It is shown that the thermal radiation of molybdenum belongs to the same universality class as that of tantalum, tungsten, and zirconium and titanium carbides. The thermodynamic functions of thermal radiation of molybdenum and luminous flames are constructed.     

Thermal Diffusivity Measurements of Refractory Metals as Candidate Reference Materials by the Laser Flash Method

A working group for standardization has organized to establish the Japanese Industrial Standard (JIS) for thermal diffusivity measurements of metals in the temperature range of 300–1700 K by the laser flash method. As candidate reference materials with high purity, high-temperature stability, and easy-to-get on a commercial basis, tantalum, niobium, and molybdenum have been selected. Thermal diffusivity values of the specimens, cut out of these materials, have been measured independently by members of the working group. Comparisons of results have been performed for different high-temperature stabilities, repeatabilities, and manufacturers, as well as by different members. Comparisons show that the measured values agree within 10% for different specimens by different institutions, and no systematic differences have been observed for materials from different manufacturers. The measured results for molybdenum specimens agree well with the recommended values of thermophysical properties of matter from the TPRC data series, and the high-temperature stability is found to be the best. The results for tantalum and niobium, however, show significant differences with those of the TPRC data series in the high-temperature range, and some further study on the stability of these materials is needed for recommending these values. As a result, molybdenum can be recommended as a reference material for practical use of the laser flash method. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Reduction of titanium and other metal oxides using electrodeoxidation

Abstract

Many reactive and refractory metals are currently produced industrially by reducing their compounds, including oxides, using a more reactive metal. In some cases, where there is substantial oxygen solubility in the metal, the oxygen is first removed by carbochlorination followed by reduction. Titanium and zirconium are made by reduction of the volatile tetrachlorides by magnesium. The processes consist essentially of two reduction steps: reducing magnesium chloride to magnesium metal and then reduction of the metal compound; this makes the overall reduction process relatively expensive. Electrodeoxidation is very simple in that the oxide to be reduced is rendered cathodic in molten alkaline earth chloride. By applying a voltage below the decomposition potential of the salt, it has been found that ionisation of oxygen is the dominant cathode reaction, rather than alkaline earth metal deposition. In the laboratory, this technique has been applied to reduce a large number of metal oxides to the metals, including titanium, zirconium, chromium, niobium, tantalum, uranium and nickel. Furthermore, when mixed oxides are used as the cathode, alloys or intermetallic compounds of uniform composition are obtained. This may offer advantages over conventional technology for those alloys that are difficult to prepare at present, owing to differences in either density or vapour pressure.     

Influence of titanium and nitrogen on hot ductility of C–Mn–Nb–Al steels

Abstract

The influence of small additions of titanium on the hot ductility of C–Mn–Nb–Al steels has been examined. Titanium and nitrogen levels varied in the ranges 0·014–0·045 and 0·004–0·011 wt-%, respectively, so that a wide range of Ti/N ratios could be studied. The tensile specimens were cast and cooled at average cooling rates of 25, 100, and 200 K min^-1 to test temperatures in the range 1100–800°C and strained to failure at a strain rate of 2 × 10^-3 s^-1. It was found that ductility in the titanium containing niobium steels improved with a decrease in the cooling rate, an increase in the size of the titanium containing precipitates, and a decrease in the volume fraction of precipitates. Coarser particles could be obtained by increasing the Ti/N ratio above the stoichiometric ratio for TiN and by testing at higher temperatures. However, ductility was generally poor for these titanium containing steels and it was equally poor when niobium was either present or absent. For steels with ～0·005 wt-%N ductility was very poor at the stoichiometric Ti/N ratio of 3·4 : 1. Ductility was better at the higher Ti/N ratios but only two of the titanium containing niobium steels gave better ductility than the titanium free niobium containing steels and then only at temperatures below about 950–900°C. One of these steels had the lowest titanium addition (0·014 wt-%), thus limiting the volume fraction of fine Ti containing particles and the other had the highest Ti/N ratio of 8 : 1. However, even for these two steels ductility was worse than for the titanium free steels in the higher temperature range. The commercial implications of these results are discussed.     

Criteria for Selecting Substrates for Nb<Subscript>3</Subscript>Sn Electrodeposition

We studied the effect of substrate material on the microstructure and properties of Nb₃Sn coatings produced by electrochemical coreduction of Nb and Sn ions in the cathodic zone in molten salts. The results demonstrate that continuous superconducting Nb₃Sn coatings can be produced on molybdenum, tantalum, niobium, copper, nickel, Invar and the 60% Ni + 22% Mo + 12% Fe alloy. The coatings grown on molybdenum, tantalum, and niobium have the highest purity. To ensure good superconducting properties of electrodeposited coatings, preference should be given, all other factors being the same, to substrate materials with thermal expansion coefficients close to or smaller than that of Nb₃Sn.