Mo Plates Research Articles

The effect of strong magnetic field treatment on microstructure and room temperature compressive properties of NiAl–Cr(Mo)–Hf eutectic alloy

The Ni–33Al–28Cr–6Mo–0.2Hf (at.%) eutectic alloy was treated in a 10 T strong magnetic field at 1073 K, 1173 K and 1273 K for 1 h, respectively. Microstructure examination reveals that after the strong magnetic field treatment, Heusler particles (Ni 2AlHf) along eutectic cell boundaries distribute more uniformly, and moreover most Heusler particles have changed into Hf solid solution. In addition, after strong magnetic field treatment at 1173 K and 1273 K, the original eutectic cellular morphology is changed greatly; Cr(Mo) plates become spheroidizing and trend to align to the direction of strong magnetic field. The compression tests show that room temperature compressive ductility of the alloys with strong magnetic field treatment improves significantly, compared with the heat-treated alloy. The fracture characteristics change from debonding into transgranular cleavage, which indicates that the cohesion of grain boundaries get significant improvement.

Effect of the method of production of an Ni3Al/Mo layered composite material on its structure and properties

A stack of alternating 25 100-μ-thick Ni3Al plates and 28 200-μm-thick Mo plates is subjected to hot isostatic pressing (HIP) at a temperature T = 1200°C and a pressure P = 150 MPa for τ = 2.5 h followed by hot rolling at 1050–950°C to a thickness of 2.3 mm. The stack is then subjected to cold rolling (CR) to a thickness of 0.5 mm without intermediate annealing, subsequent annealing during HIP at T = 1200°C, P = 150 MPa, and τ = 2.5 h, and CR to a thickness of 0.22 mm. Upon CR at a strain e changing from 80.8 to 95.8%, the following specific structure forms in the longitudinal direction: molybdenum layers acquire a wavelike structure, can contact with each other, form “cells,” and retain almost the same thickness, and Ni3Al alloy layers are rejected between the molybdenum layers to form a regular structure made of alternating thickenings and thinnings across the rolling direction. Annealing during HIP and subsequent CR to e = 98.2% lead to the formation of zones with a broken alternation of layers in the longitudinal and transverse directions, which is related to different strain resistances of the (more refractory) molybdenum and Ni3Al layers at 20°C. The adhesion between the layers is good, and no intermediate phases form at the interface. The ultimate bending strength of the 2.3-mm-thick workpiece at 20°C is 1000 ± 100 MPa, and the prepared material has a plasticity margin.

Regular hexagonal MoS2 microflakes grown from MoO3 precursor

Regular hexagonal MoS2 microflakes with high yield were grown from MoO3 precursor by a sulfurization process using S powders as sulfuration reducer. The precursors, long and smooth MoO3 microbelts, were synthesized through a direct oxidation reaction of Mo plates in air. X-ray powder diffraction and scanning electron microscopy revealed that the sulfurized products were hexagonal MoS2 with regular hexagonal flake-like morphology. The results of transmission electron microscopy examinations demonstrated that the microflakes were single crystalline MoS2. Elemental analysis by EDAX and XPS showed that the microflakes consist of Mo and S with the atomic ratio near to 0.5. Factors influencing the formation of the product were systematically studied.

Microstructure and mechanical behavior of NiAl-based alloy prepared by powder metallurgical route

Rapidly solidified NiAl–28Cr–6Mo–B–Dy prealloyed powder doped with Nb powder was consolidated by hot pressing under 1250 °C for 30 min at 30 MPa. The consolidated material exhibited a different microstructure from the original powder, i.e. the NiAl and Cr(Mo) plates in the eutectic cell tend to break down into short platelets or even particles during hot pressing process. The mechanical behaviors at room temperature and at high temperature of consolidated sample from powder alloy were evaluated by three-point bending technique, tensile test and compressive test. The results showed that the hot pressing alloy possessed a reasonable combination of room temperature ductility and toughness, and elevated temperature strength.

Hydrothermal synthesis and characterization of ZSM-5 coatings on a molybdenum support and scale-up for application in micro reactors

A procedure has been developed to grow ZSM-5 crystals in situ on a molybdenum (Mo) support. The high heat conductivity (138 W/mK) and high mechanical stability at elevated temperatures of the Mo support allow the application of ZSM-5 coatings in micro reactors for high temperature processes involving large heat effects. The effect of the synthesis mixture composition on ZSM-5 coverage and on the uniformity of the ZSM-5 coatings was investigated on plates of 10 × 10 mm 2. Ratios of H 2O/Si = 50, Si/Al = 25, and TPA/Al = 2.0 were found to be optimal for the formation of uniform coatings of 6 g/m 2 at a temperature of 150 °C and a synthesis time of 48 h. Scaling up of the synthesis procedure on 72 Mo plates of 40 × 9.8 × 0.1 mm 3 resulted in a uniform coverage of 14.8 ± 0.4 g/m 2. The low deviation per individual plate (<3%) indicates the uniformity of the synthesis conditions in the scale-up procedure.

Joining of SiC fibre reinforced borosilicate glass matrix composites to molybdenum by metal and silicate brazing

The brazing of SiC fibre reinforced borosilicate glass matrix composites with Mo plates has been investigated. Molybdenum was chosen as the metallic partner under consideration of system requirements, e.g. thermomechanical stability at temperatures of interest (500–750∘C), and physical properties, e.g. coefficient of thermal expansion close to that of the glass matrix composite. Two brazing filler materials were investigated: a glass braze (Schott G018-174) and an active filler metal (Incusil ABA, brazing temperature = 740∘C). When using the glass braze the surface of the metal had to be roughened to ensure a bond of significant strength. Vacuum brazing with the active filler metal resulted in joints with high strength, which allows to fully utilise the mechanical competence of the glass matrix composite when the joint configuration is adapted to the relevant loading conditions. A novel design of a tool for hot glassware handling, made of glass matrix composite/Mo joints, is presented.

Synthesis of molybdenum borides and molybdenum silicides in molten salts and their oxidation behavior in an air–water mixture

The formation of various coatings in molybdenum–boron and molybdenum–silicon systems was investigated. Boronizing and siliciding treatments were conducted in molten salts under inert gas atmosphere in the 850–1050 °C temperature range for 7 h. The presence of boride (e.g. Mo 2B, MoB, Mo 2B 5) and silicide (MoSi 2, Mo 5Si 3) phases, formed on the surface of Mo plates, was confirmed by X-ray diffraction analysis. The distribution of elements was determined by means of wavelength dispersive spectroscopy (WDS) spectra of the surface and line-scan analyses from surface to interior. Depending on the process type (diffusional or electrochemical) and temperature, the thickness of the protective layers formed on the substrate ranged from 6 to 40 μm. The oxidation resistance of obtained phases was investigated in an air–water mixture in the temperature range of 500–700 °C for a period up to 400 h. An improved oxidation behavior of coated plates in comparison with that of pure molybdenum was observed.

Effect of directionally solidified microstructures on the room-temperature fracture-toughness properties of Ni-33(at. pct)Al-33Cr-1Mo and Ni-33(at. pct)Al-31Cr-3Mo eutectic alloys grown at different solidification rates

Directionally solidified (DS) Ni-33(at. pct)Al-33Cr-1Mo and Ni-33(at. pct)Al-31Cr-3Mo eutectic alloys were grown at different rates varying from 7.6 to 508 mm h−1. The microstructures consisted of eutectic colonies with parallel lamellar NiAl/(Cr,Mo) plates for solidification rates at and below 12.7 mm h−1. Cellular eutectic microstructures were observed at higher solidification rates, where the plates exhibited a radial pattern. Room-temperature fracture-toughness tests were conducted using a modified ASTM E-399 technique. The average fracture-toughness values for specimens with planar eutectic and cellular microstructures were about 12 to 15 and 17 MPa\(\sqrt m \), respectively, for both alloys. However, the Ni-33(at. pct)Al-33Cr-1Mo specimens grown at and above 254 mm h−1 exhibited fracture toughness values of about 8 MPa\(\sqrt m \) due to the presence of short (Cr,Mo) plates. The fracture toughness values for the Ni-33(at. pct)Al-31Cr-3Mo alloy were also correlated with quantitative microstructural data in an attempt to identify the relevant elements of the microstructure determining resistance to fracture. A phenomenological fracture model is presented in an attempt to rationalize the present observations.

Microstructural characterization of Si cones fabricated by Ar +-sputtering Si/Mo targets

Ar + sputtering of Si wafers surrounded by Mo plates induced the formation of uniform cones over a large area on the Si surface. Scanning electron microscopic study showed that the cones were formed on the entire surface of the Si wafer. The uniform cones were 0.4–0.7 μm in diameter and 5–6 μm high. They were further characterized by means of cross-sectional transmission electron microscopy, and micro-diffraction. It was found that the cone contained a pure Si regime and a Mo-rich regime. In the binary Mo–Si zone, we identified three distinct areas vertically: (1) domains of Mo-induced Si ordered structures; (2) a small volume of a new Mo 3Si 2 structural variant, intergrown with the Si ordered structure; and (3) a small amount of pure Mo nanoparticles covering the surface of the cones. The formation of the large and uniform cones may provide a new surface configuration for potential applications in surface science and technology.

Microstructural characterization of a directionally-solidified Ni–33 (at.%) Al–31Cr–3Mo eutectic alloy as a function of withdrawal rate

The Ni–33 (at.%)Al–31Cr–3Mo eutectic alloy was directionally-solidified (DS) at different rates, V I, varying between 2.5 to 508 mm h −1. Detailed qualitative and quantitative metallographic and chemical analyses were conducted on the directionally-solidified rods. The microstructures consisted of eutectic colonies with parallel lamellar NiAl/(Cr,Mo) plates for solidification rates at and below 12.7 mm h −1. Cellular eutectic microstructures were observed at higher solidification rates, where the plates exhibited a radial pattern. The microstructures were demonstrated to be fairly uniform throughout a 100 mm length of the DS zone by quantitative metallography. The average cell size, d ̄ , decreased with increasing growth rate to a value of 125 μm at 508 mm h −1 according to the relation d ̄ (μm) ≈ 465 V I −0.22, where V I is in mm h −1. Both the average NiAl plate thickness, Δ ̄ NiAl , and the interlamellar spacing, λ ̄ , were observed to be constant for V I ⩽ 50.8 mm h −1 but decreased with increasing growth rate above this value as Δ ̄ NiAl (m)=61.2 V I −0.93 and λ ̄ (μm)=47.7 V I −0.64, respectively. The present results are detailed on a microstructural map.

Development of the filter wheel for calorimeters on board ASTRO-E

X-ray spectrometer (XRS) is the main instrument for the ASTRO-E, scheduled for launch in February 2000. In order to maintain its superior energy resolution (FWHM ∼12 eV), we control the incident flux for the XRS to be less than several c/s/pixel using various filters. The filter wheel (FW) is placed above the XRS dewar, carrying 5 different filters which are selected by a stepping motor. The installed filters are 2 low-energy cut filters made of thin Be plates and 3 neutral density filters which are Mo plates with about 1800 pinholes each. The filter properties are measured with X-ray beams at various energies. Reliability of the FW system has been established by extensive tests on the prototype model. The flight-model FW has been already assembled, and qualified through a number of tests. Simulations of the XRS combined with the X-ray telescope are performed to study the on-board performances of filters for various X-ray sources.

Release of hydrogen molecules from hydrogen-containing carbon film deposited on molybdenum

Molybdenum (Mo) plates covered with a hydrogen-containing carbon film, C(H)/Mo, were prepared as a model system to simulate carbon–metal mixed materials. The C(H)/Mo samples annealed at given temperatures and times in vacuum were analyzed by means of X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), thermal desorption spectroscopy (TDS) along with X-ray diffraction measurements (XRD). The XPS measurements revealed that the sample surface was covered with a carbon film containing hydrogen and a small amount of oxygen below 773 K. The Mo3d 5/2 peak appeared only after annealing at 873 K for 600 s, indicating that carbon atoms diffused to the bulk of Mo. The XRD measurements showed that Mo 2C formed in the surface layer after annealing at 1073 K for 600 s. In addition, it was observed with TDS that hydrogen molecules desorbed from the sample above 873 K. All of the above observations indicate that solid state chemical reactions take place at relatively low temperatures to cause Mo 2C formation and H 2 release in the subsurface layer or out of the C(H)/Mo system.

Structural and morphological studies of the growth of MoO3 scales during high-temperature oxidation of molybdenum

The oxidation of polycrystalline Mo plates and of Mo(100), Mo(110), and Mo(111) single-crystal plates in pure oxygen at 8 × 104 and 2.7 × 103 Pa, at 743–1023 K leads to the growth of orthorhombic MoO3 only, as shown by X-ray diffraction and SEM observations. The stable oxides MoO2 and Mo4O11 were not identified. At each side of the molybdenum plate, the oxide scale is a stacking of MoO3 crystals with their [100] axes oriented normal to the surface of the initial Mo plate. The MoO3 crystals are very thick in the [010] direction, compared with the well-known shape of the MoO3 crystals grown from the vapor phase. Two main factors determine the oriented growth of MoO3 crystals from Mo oxidation. A growth mechanism involving a structural rearrangement of the Mo atoms at the reactional interface and oxygen diffusion through the oxide is proposed.

Microstructure and mechanical properties of resistance sintered titanium : C.H. Lui, P.W. Kao, Scripta Metall Mater, Vol 24 No 12, 1990, 2279–2284

The formation of various coatings in molybdenum–boron and molybdenum–silicon systems was investigated. Boronizing and siliciding treatments were conducted in molten salts under inert gas atmosphere in the 850–1050 °C temperature range for 7 h. The presence of boride (e.g. Mo2B, MoB, Mo2B5) and silicide (MoSi2, Mo5Si3) phases, formed on the surface of Mo plates, was confirmed by X-ray diffraction analysis. The distribution of elements was determined by means of wavelength dispersive spectroscopy (WDS) spectra of the surface and line-scan analyses from surface to interior. Depending on the process type (diffusional or electrochemical) and temperature, the thickness of the protective layers formed on the substrate ranged from 6 to 40 μm. The oxidation resistance of obtained phases was investigated in an air–water mixture in the temperature range of 500–700 °C for a period up to 400 h. An improved oxidation behavior of coated plates in comparison with that of pure molybdenum was observed.

Performance of JT-60 divertor plates

Operational experiences on the performance and material behavior of the JT-60 divertor plates are presented. The outside X-point operation using TiC-coated Mo (TiC/Mo) plates was performed with absorbed power up to 20 MW and duration of 1 s without degradation of the plasma performance by sweeping the separatrix to control the surface temperature below the melting point. The use of graphite divertor plates extended the absorbed power up to 25 MW with duration of 4 s in the lower X-point operation. However, the graphite was eroded and redeposited on the divertor plates and the carbon content in the plasma was increased compared to the outer X-point operation with carbon tiles. A few lower graphite tiles were seriously damaged and radioactivated. Improvements in thermal shock resistance and erosion characteristics of the graphite are necessary. High heat concentration at tile edges and disruption-induced heat loads should be avoided in the future devices.

Morphology and Microstructure of TiN and Ti(N, C) Thin Layers

AbstractThin layers of TiN and Ti(N, C) solid solution were obtained by the CVD process, making use of the following gas mixtures: TiCl4–N2–H2 for TiN and TiCl4–CCl4–N2–H2 for Ti(N, C). The thin layers deposition processes were carried out in the temperature range from 900–1450 °C. As growth substrates were used polycrystalline Al2O3, graphite, W, Mo and Cu plates and also single crystal Al2O3 (leucosapphire), (111) Cu and (111) Si plates. The influence of certain technological factors on the morphology of the layers obtained was studied. TEM examinations were also made of the microstructure of the thin TiN layers and the Ti(N, C) solid solution layers deposited on polycrystalline and single crystal Cu plates. Factors responsible for the presence of a high density of dislocations in the tested films were ascertained.

Plastic deformation in B.C.C. alloys induced by hydrogen concentration gradients

Electrolytic charging of hydrogen into one side of polycrystalline b.c.c. Ti-30 Mo plates (where the composition is given in approximate weight per cent) is found to generate dislocations at which the hydrogen atoms are trapped during their diffusion across the metal thickness. The defect generation is a result of stresses arising from the hydrogen concentration gradient at the entry surface. The generation of dislocations occurs on initiating the charging and persists thereafter with emission of dislocations towards the far side of the plate. As a consequence, slip lines and subgrains are formed at the entry and far sides. Also a non-homogeneous dislocation distribution and a piling-up at the grain boundaries occur. The slip line density is found to increase with the charging.current density and time of charging. Prolonged charging causes spontaneous fracture and plastic bending in the absence of external forces. Similar phenomena have been detected also in tantalum and niobium.