Molybdenum Sheet Research Articles

Preparation of a large-scale molybdenum single-crystal sheet by means of secondary recrystallization

Secondary recrystallization was used to produce a large-scale molybdenum single-crystal sheet. It was found that the presence of dispersed second phases such as calcium and magnesium oxides plays an important role in the grain growth of the rolled molybdenum, initially restraining normal grain growth and hence substantially promoting abnormal grain growth at higher temperatures. The secondary recrystallization temperature was dependent on the amount of the second phase present. Consequently a large-scale single-crystal sheet (2 mm × 40 mm × 180 mm) can easily be produced from a hot-rolled molybdenum sheet doped with CaO and MgO.

Embrittlement of sintered molybdenum predoped with carbon in high temperature oxygen-contaminated helium

Changes in the tensile properties of sintered molybdenum sheets predoped with carbon which were exposed to impure helium for 100 h at 1000 °C were examined at low temperatures. Scanning electron microscopy was employed to determine the fracture modes of these specimens. Grain boundary segregations were measured using Auger electron spectroscopy. The following results were obtained. 1. (1) The ductility of the materials was substantially reduced after exposure to oxygen-contaminated helium. Concurrent oxygen contamination and decarburization are responsible for grain boundary weakening, particularly near the specimen surfaces. 2. (2) The addition of carbon before exposure was shown to reduce the embrittlement of the materials.

Structure and hardness of explosively consolidated molybdenum

The structure of explosively consolidated molybdenum powder was observed to consist of inhomogeneous mixtures of both very fine grains and coarser grains, ranging from 1 to 25 μm in diameter. Both the fine and the coarse grains contain subgrain structures characterized by grain boundary misorientations averaging 6°; the average subgrain size ranges from 0.1 to 1 μm. The hardness of the explosively consolidated molybdenum powder, about 380 HV 10, is similar to that observed for shock-loaded molybdenum sheet, but the microstructures of the two materials differ. The hardness of the explosively consolidated powder and its change as a function of 1 h annealing temperature were observed to be considerably different from the hardness levels and changes in hardness observed for unsintered molybdenum extrusions and conventionally processed P/M molybdenum bars.

Microstructures in Explosively Consolidated Molybdenum Powder: A Tem Study

Dynamic compaction of metal and alloy powders has been recognized as a technique capable of producing consolidated materials possessing unique mechanical properties. In the present work molybdenum powder has been consolidated by explosives to produce a residual hardness which exceeds that of conventionally processed molybdenum bars by 55 percent, and unsintered molybdenum powder extrusions by 45 percent. This high hardness has been observed only in shock-loaded molybdenum sheet. A comparison of the microstructures in explosively consolidated molybdenum powder and shockloaded molybdenum sheet materials shows a very clear distinction between them. This is illustrated in Fig. 1(a) and (b). Figure 1(a) shows the asconsolidated molybdenum powder material to be characterized by fine subgrains having an average boundary misorientation of 6°. Dark patches of dislocation tangles also occupy many of the subgrains.

モリブデンに対するビーム振動を用いた電子ビーム溶接法の適用

The purpose of this study is to investigate the effects of macrostructure change of the weld joint on the ductility of electron-beam-welded molybdenum sheet. The material used was electron-beam-melted molybdenum. Beam oscillation was applied in order to change the unfavourable structure of the joint, particularly even flat and straight interfaces at the center of the weld metal or at the bond of weld. The ductility of the weldment was determined by tensile tests at -70°C and 20°C. Fracture mode and location of crack initiation and propagation were examined by a scanning electron microscopy.The results were summarized as follows:1) Fracture strength at -70°C of the weldment was increased by using beam oscillation.2) Strength and elongation at 20°C of the weldment were also increased by using beam oscillation. 3) Origin of fracture was located to be mainly at the grain boundaries on the bead surface at -70°C, whilst crack was initiated mainly from the grain boundaries in bulk at 20°C.4) Crack was propagated only along the center of the weld metal or the bond of weld without beam oscillation. On the other hand, the crack was propagated not only along these weak interfaces but also through other areas with beam oscillation.

Effect of carbon on the ductilisation of electron-beam welds in molybdenum

The ductility of unwelded and electron-beam welded molybdenum sheet has been evaluated by means of notch-bend testing at temperatures ranging from − 190 to 260°C. The effect of carbon additions on the ductile-brittle transition temperature and fracture behaviour of molybdenum has also been determined. The results indicate that carbon is very effective in lowering the ductile-brittle transition temperature of welded and unwelded specimens. It has been demonstrated that a balance exists between the ductilising effect of carbon and the embrittling effect of oxygen segregating to grain boundaries. For most effective ductilisation, an optimum amount of carbon is required to offset the embrittling effect of oxygen. It has been shown that the brittle fracture mode changes from intergranular to transgranular cleavage when optimum ductilisation is achieved. The decrease in the transition temperature has been explained in terms of the enhancement of the grain boundary crack nucleation stress with additions of carbon.

Improvement of ductility of molybdenum sheet by forming a surface layer containing boron

Improvement of ductility of molybdenum sheet by forming a surface layer containing boron

Chemical vapour deposition of scandium metal

An open-tube chemical vapour deposition technique was devised for the growth of scandium metal from its oxide as a starting material. Chlorination of the oxide with carbon tetrachloride vapour at 640 °C was followed by reaction in the vapour phase at about 860 °C between separate streams of scandium chloride and sodium carried by purified argon. The resulting single crystals of scandium grown on the end of the molybdenum tube carrying the sodium stream were typically in the forms of needles, up to 3.5 mm in length with a growth direction along the a axis, and of codepositing smaller plates and dendrites. Polycrystalline coatings and island-like crystallites were deposited on the molybdenum sheet surrounding the parallel streams of reactants, often together with small polyhedrons and hollow prisms.

Low-temperature ductility of an electron-beam-welded molybdenum sheet predoped with a small amount of carbon

The mechanical properties of unwelded and electron-beam-welded sintered molybdenum sheets, in which carbon was doped or not, were examined by means of a tensile test at temperatures from −100 to 80°C. Scanning electron microscopy was applied to determine the fracture mode of the specimen and to observe the distribution of precipitates over grain boundaries. The results indicated that a small amount of pre-doped carbon was effective on the improvement in the low-temperature ductility of the welded specimen as well as that of the unwelded one. Such effects are reasonably explained in terms of the enhancement of the crack propagation stress in the fused zone of the weldment.

Shock-induced cracks in molybdenum sheet

Intergranular cracks occurred in shock-loaded molybdenum for specimens of grain size 17 μm and larger; for smaller grain size specimens (<17 μm) there was almost no crack initiation except in very thin specimens with shock loading of high pressure and long pulse duration. Cracks were not nucleated by twin barriers, and grain-boundary ledges appear to be responsible for initiating and propagating the cracks. The crack density was observed to decrease with increasing grain size for both constant peak pressure and pulse duration. In addition, crack density, as measured by the crack length intersecting the unit area of surface, generally increased with increasing shock pressure at constant pulse duration and with increasing pulse duration, at constant shock pressure.

Bestimmung von stickstoff in refraktärmetallen—I molybdän und wolfram

This is a report on round-robin tests concerning the determination of nitrogen traces in molybdenum and tungsten, which were carried out by the refractory metals group of the chemistry section of the Gesellschaft Deutscher Metallhütten- und Bergleute. The following methods were used: classical and modified Kieldahl methods (in particular, a newly developed micro-Kjeldahl method), inert-gas fusion, vacuum fusion and ultrahigh-vacuum diffusion extraction. As the nitrogen values obtained by the first round-robin test exhibited considerable scatter, possible shortcomings of the various Kjeldahl methods, as well as the quantitative nitrogen recovery by the extraction methods, were carefully examined. The second round-robin test then gave the following results: the nitrogen content of the investigated molybdenum sheet was 2 ppm, the content of the tungsten sheet 0.5 ppm. Classical Kjeldahl methods are not applicable to the determination of nitrogen contents below 10 ppm. Frequently, detection limits of Kjeldahl methods range considerably above 10 ppm, mainly because of contamination by reagents and/or the laboratory atmosphere. The micro-Kjeldahl method and the hot-extraction and fusion-extraction methods are capable of determining nitrogen contents down to 1 ppm at best. The only method available for nitrogen determinations in metals at sub-ppm levels is by ultrahigh-vacuum diffusion extraction. The good agreement between the nitrogen values obtained for molybdenum by the micro-Kjeldahl method and by the various extraction methods is the most reliable proof of the quantitative nitrogen recovery by the extraction methods.

Direct observations of vacancies and vacancy-type defects in molybdenum following uniaxial shock-wave compression

Molybdenum sheet and small diameter wire samples were simultaneously shock-loaded to pressures of 150 and 250 kbar at a constant shock-pulse duration of 2 μsec. Thin foils and emission end-forms prepared from annealed as well as the shock-loaded samples were simultaneously examined by transmission electron and field-ion microscopy respectively. Dislocation loop densities were observed to increase from an annealed value of 5 × 10 9−4 × 10 14 cm −3 and 7 × 10 14 cm −3 at 150 and 250 kbar, respectively, and the corresponding average loop diameters were measured to be 57, 104 and 152 Å, respectively. A full determination of the relevant diffraction conditions and Burgers vectors of the loops in the electron microscope showed that 75% of the loops at 150 kbar and 80% of the loops at 250 kbar were vacancy type. By comparison, direct observations of vacancies and small vacancy aggregates in the field-ion microscope by systematic field-evaporation of atom layers showed a vacancy concentration of 1.2% in the annealed wires as compared with 2.2 and 6.0% vacancies in the 150 and 250 kbar shock-loaded wire samples respectively. Since the corresponding increase in dislocation density was determined to be 1.0 × 10 10−1.2 × 10 10 cm −2 between 150 and 250 kbar for a concomitant increase in average residual microhardness from 514 to 770 kg/mm 2 in the same pressure range, it is shown that shock induced vacancies contribute significantly to residual shock hardening.

Growth and Structure of Polycrystalline Indium Phosphide Layers on Molybdenum Sheets

Pinholeless polycrystalline indium phosphide layers were grown on molybdenum sheets at temperatures lower than 600°C using indium and phosphorus trichloride as the source materials. The low activation energy of the deposition rates and weak dependence of the rates on the partial pressure of indium monochloride suggest that surface processes play an important role in the growth of polycrystalline films. It was ascertained by an x‐ray diffraction measurement that the {110} and {331} orientations become noticeable with increasing thickness at higher temperatures, whereas the <111> orientation is dominant at lower growth temperatures. The development of the <110> orientation produces films with a columnar structure, which could be explained by the dependence of the growth rate on the crystallographic orientation.

Abstract: Electron beam deposition of alumina to rf modulated steel substrates

Radiofrequency modulation has been applied in an ion plating process for an insulator material. Alumina was evaporated from a 270° bent electron beam source. Heat dissipation at the substrate surface with respect to deposition rate and rf power input was measured by a calorimetric method. Films deposited at various conditions of substrate temperature and rf power were assessed. The effect of rf modulation was observed on appearance of films formed at low temperatures (220°C) and on fractured sections at high temperatures (410°C). For films formed at 280°, 360°, and 410°C on either steel or molybdenum sheets, no differences in pin hole, adhesion, and film composition can be detected due to the effect of rf modulation.

Effect of stress concentration on the mechanical properties of molybdenum sheet with protective coatings

1. Under conditions of brief static loading molybdenum sheet of grade MCh-II was found to be almost insensitive to stress concentrations (for the selected types of concentrators). 2. The presence of a diffusion protective coating leads to a considerable decrease in the ductility of the material over the whole investigated range of temperatures and to a decrease in its strength at temperatures below the coating deposition temperature. 3. It was established that the strength of specimens with protective coatings in the presence of stress concentrators is higher than the strength of smooth specimens with the same coatings.

モリブデンの脆性におよぼす予歪の効果について

The effect of prestraining by tension on the brittleness of electron beam melted pure molybdenum was studied and the following conclusions were obtained:(1) The brittleness of the recrystallized pure molybdenum sheets can be improved considerablly below room temperature by prestraining about 5∼10% in the ductile range. The effect of prestraining increases with the amount of prestrain and changes with the temperature at which prestrain was given.(2) The prestrained specimens containing many edge dislocations show better ductility at low temperature than the prestrained specimens containing many screw dislocations.(3) Strain ageing due to interstitial impurities is negligible below 300°C.(4) As an important mechanisum, free dislocations and some Frank-Read sources introduced by the prestraining release the stress concentration when the prestrained specimens were tensile-tested at lower temperature, and the brittleness can be improved.(5) Ageing at 500°C after prestraining at 300°C decreases the ductility of prestrained specimens at low temperature. This is due to the dislocation locking caused by the interstitial impurities.

Properties of molybdenum sheet with a two-phase structure after annealing

1. We investigated the effect of annealing 1 h at 400–1400°C on the mechanical properties of transverse and longitudinal samples and on the microstructure of molybdenum alloy sheet (alloyed with carbon and titanium). 2. The formation of second phase in molybdenum and selection of the optimal heat treatment conditions make it possible to obtain a high plasticity. 3. The optimal heat treatment to increase the plasticity of the material investigated is annealing at 1100°C for 1 h, which corresponds to the initial recrystallization temperature of the sheet investigated. 4. The formation of carbide phase in molybdenum prevents the development of recrystallization processes.

Untersuchungen über die verträglichkeit von uranmononitrid mit molybdän, wolfram und thoriumoxid bei hohen temperaturen

After annealing uranium mononitride and UN-Momixtures on molybdenum supports above 2000 °C under a vacuum of 10 −2-10 −5 torr, a molybdenum content of about 0.23 wt % in UN along with an increase of the UN lattice parameter observed at room temperature was observed. Though the appearance of substoichiometric uranium mononitride seems, in principle, to be possible, the cooling rate may not be sufficient to freeze in this condition. The decomposition of UN initiated at high temperatures under vacuum results in a γ-U-Mo-phase which can be detected by metallographic and X-ray methods; by microprobe analysis about 21–22 wt % of Mo and 78 wt % of U were detected. Moreover, the microanalytical studies showed up appreciable amounts of nitrogen (about 1 wt %). On the molybdenum sheet supports, UO 2-crystals orientated in [111] direction can be detected subsequent to annealing at 2400 °C under N 2 and X-ray diffraction also revealed a UN 2−x-phase with a lattice constant a 0 = 5.344 A ̊ . The X-ray studies with annealed UN-tungsten specimens up to 2400 °C do not give indications on possible reactions or solubilities. Changes in the lattice parameters could not be observed. After annealing of UN-ThO 2-mixtures carried out on tungsten-sheet- and ThO 2 supports no remarkable change in the UN lattice parameter is detected up to 2400 °C under 500 torr of nitrogen. After annealing on molybdenum supports a slight change Δa 0 = 0.005 A ̊ is measured following annealings at 1750 °C and 2000 °C under vacuum. However, the UO 2 impurities form a solid solution together with thorium oxide, as can be observed by the variation of the lattice constants. The upper temperature limits of satisfactory compatibility strongly depend on the annealing atmosphere. In the case of UN-Mo under 10 −5 torr of N 2 it is at 1550 °C and rises to about 2300 °C under 300 torr of N 2. Slightly higher temperatures are applicable to UN-W.

Réalisation et propriétés des photopiles solaires en couches minces de tellurure de cuivre et tellurure de cadmium

2014 We have made thin film solar cells by depositing cadmium telluride on molybdenum sheet by vapor reaction of the components. The p layer is obtained by vacuum evaporation of copper telluride and the p contact is made by an evaporated gold grid. We have measured the parameters of these cells. For a solar energy of 50 mW/cm2 the short circuit current is 7 mA/cm2, the open voltage is 400 to 500 mV and the efficiency 3 %. REVUE DE PHYSIQUE APPLIQUEE TOME 1, SEPTEMBRE 1966, PAGE

The effects of sintering on the microstructure and properties of sprayed molybdenum

Post-sintering treatments in hydrogen were applied to free-standing molybdenum shapes fabricated by the oxy-acetylene and arc-plasma flame-spray processes. Hydrogen sintering at 1350°C and 1450°C for periods of 9–48 h yielded substantial improvements in the tensile strength, modulus of elasticity, density and purity of the sprayed deposits. The low impact energy observed in as-sprayed material was retained in the sintered products. Shrinkage was found to be anisotropic and weight loss equivalent to reduction in MoO 2 content. The sprayed molybdenum was converted from a columnar structure to one typical of recrystallized molybdenum sheet.