Mo Fibers Research Articles

Analysis of guided optical eigenmodes in magneto-optical fibers with applications to OAM mode selective couplers

Mode division multiplexing technology can regard each eigenmode in optical fibers as an independent channel to carry different data information, helpful for improving the transmission capacity of optical fiber communication systems. The spatial distribution, state of polarization and propagation constant of guided optical eigenmodes in the magneto-optical fiber are derived theoretically by the analysis of linear polarization and exact modes. The transverse distribution of the eigenmodes in the MO fiber can be constructed by those of exact modes in the conventional fiber. The effect of applied magnetic field on the eigenmodes and their effective refractive indices is studied. Simulation results show that, the eigenmodes in the MO fiber may be represented by the pseudo-modes of circular polarization () or the true modes of orbital angular momentum () when applied magnetic field is sufficiently large. The measurement method for weak magnetic field based on Stokes parameters is proposed. The magnetic tunability of OAM mode selective couplers is also analyzed.

Vitamin D Supplementation and Muscle Power, Strength and Physical Performance in Older Adults: A Randomized Controlled Trial

BackgroundLow 25-hydroxyvitamin D (25[OH]D) concentrations (<30 ng/mL [<50 nmol/L]) have been associated with muscle weakness and impaired physical performance in observational studies. However, the effect of vitamin D supplementation on changes in muscle strength and physical performance in randomized controlled trials has been mixed. ObjectivesTo determine the effect of daily vitamin D supplementation on leg power, strength, and physical performance in low-functioning older adults with 25(OH)D concentrations of 18 to <30 ng/mL. MethodsIn this double-blind, randomized controlled trial, 136 low-functioning [Short Physical Performance Battery (SPPB) scores ≤10] adults aged 65–89 y with 25(OH)D concentrations of 18 to <30 ng/mL were randomly assigned to 2000 IU/d vitamin D3 or placebo for 12 mo. Lower-extremity leg power (primary outcome), leg and grip strength, SPPB, timed up and go (TUG), postural sway, and gait velocity and spatiotemporal parameters (secondary outcomes) were assessed at baseline, 4 and 12 mo. A subset (n = 37) also underwent a muscle biopsy at baseline and 4 mo and muscle fiber composition and contractile properties were assessed. ResultsParticipants’ mean ± SD age and SPPB scores at baseline were 73.4 ± 6.3 y and 7.8 ± 1.8, respectively. Mean ± SD 25(OH)D concentrations at baseline and 12 mo were 19.4 ± 4.2 ng/mL and 28.6 ± 6.7 ng/mL in the vitamin D group and 19.9 ± 4.9 ng/mL and 20.2 ± 5.0 ng/mL in the placebo group for a mean ± SE difference of 9.1 ± 1.1 ng/mL (P < 0.0001). However, there were no differences in change in leg power, leg or grip strength, SPPB score, TUG, postural sway, or gait velocity and spatiotemporal parameters by intervention group over 12 mo or muscle fiber composition and contractile properties over 4 mo. ConclusionsIn low-functioning older adults with 25(OH)D concentrations of 18 to <30 ng/mL, randomization to 2000 IU/d vitamin D3 did not result in improvements in leg power, strength, or physical performance or muscle fiber composition and contractile properties.This trial was registered at clinicaltrials.gov as NCT02015611.

Molybdenum-fiber strengthened brazing of carbon/carbon composite and nickel-based superalloy

The robust and reliable joining of carbon/carbon (C/C) composites and metals has important application value in the aerospace field. However, the low interface bonding strength when joining the two dissimilar materials remains a persistent problem and leads to low joint strength. In this work, a novel interface strengthened brazing process has been developed for joining a C/C composite and a nickel-based superalloy (GH3044). Before joining, high-strength molybdenum (Mo) fibers are planted on the surface of the C/C composite, then the fiber-treated C/C composite is brazed to the GH3044 superalloy using a BNi-2 filler. The results show that a sound joint with robust Mo fibers crossing the interface between the C/C substrate and the brazing layer is obtained. Owing to the pinning effect of the Mo fibers, the joining interface area is increased and cracking is effectively prevented. As a result, the bonded joint exhibits excellent mechanical properties. The maximum shear strength of the joint was measured to be 60 MPa, which is 2.14-times that of the joint without fiber-planting. The maximum three-point bending strength of the joint was measured at 31 MPa, which is 2.58-times that of the joint without fiber-planting.

Mechanical Properties of Special-shaped Mo Fiber Reinforced Mineral-filled Polymer Composite

With superior vibration alleviation property, mineral-filled polymer composite (MFPC) has attracted more attention in the field of mechanical manufacturing. However, the application of MFPC is limited by its inferior mechanical strength. Straight-line and special-shaped Mo fibers were respectively added into MFPC to improve its mechanical properties in the paper. The influences of fiber shape and matrix performance on interface bonding property of fiber-matrix were studied systematically. And the effects of fiber shape and fiber content on compressive and flexural strength of MFPC were separately discussed. Finite element analysis was employed to further verify experimental results. Compared with straight-line fiber, both pulling ability and interfacial bonding strength of special-shaped Mo fiber are greatly improved when mass ratio r of resin and curing agent is identical. For the same fiber, interface bonding strength of r=4:1 is obviously greater than that of r=7:1. The maximum mechanical strength is achieved when mass fraction of fibers is 1.2 %. Mechanical properties of MFPC reinforced by special-shaped fibers are much better than those reinforced by straight-line fibers. By contrast, the reinforcing effect of M-shaped fibers is optimal, followed by N-shaped, U-shaped the third, and V-shaped the minimum, which consists with the results of finite element simulation.

Influences of Mo Fibers on Mechanical Properties of Resin Mineral Composites

The influences of new, scrap, and five modified Mo fibers on interface bonding strength of fiber-matrix and mechanical strength of RMC were studied. Typical specimens with different fibers and mass ratio of resin and hardener were prepared to verify the above assumptions. Theoretical analysis and experimental results prove that, compared with ordinary new Mo fibers, scrap Mo fibers can perform better in improving interface bonding strength and mechanical properties of RMC because many discharge pits randomly distribute on the surface of scrap fibers. For five modified Mo fibers, interface bonding strength and the reinforcing effect on RMC have been improved obviously. Wherein, comprehensive mechanical properties of RMC are optimal with the addition of M6 fibers which have undergone combined surface treatment including acidification, gasphase oxidation and coupling treatment. And interface bonding strength between M6 fiber and matrix is the maximum.

Novel ceramic matrix composites with tungsten and molybdenum fiber reinforcement

Ceramic matrix composites usually utilize carbon or ceramic fibers as reinforcements. However, such fibers often expose a low ductility during failure. In this work, we follow the idea of a reinforcement concept of a ceramic matrix reinforced by refractory metal fibers to reach pseudo ductile behavior during failure. Tungsten and molybdenum fibers were chosen as reinforcement in SiCN ceramic matrix composites manufactured by polymer infiltration and pyrolysis process. The composites were investigated with respect to microstructure, flexural- and tensile strength. The single fiber strengths for both tungsten and molybdenum were investigated and compared to the strength of the composites. Tensile strengths of 206 and 156 MPa as well as bending strengths of 427 and 312 MPa were achieved for W/SiCN and Mo/SiCN composites, respectively. The W fiber became brittle across the entire cross section, while the Mo fiber showed a superficial, brittle reaction zone but kept ductile on the inside.

Continuous Mo fiber reinforced Ti/Al3Ti metal-intermetallic laminated composites

In this work, continuous Mo fiber as a reinforcement was introduced into Ti/Al3Ti metal-intermetallic-laminated (MIL) composite via vacuum hot pressing (VHP). In order to avoid excessive consumption of Mo fibers reacting with Al, and also obtain an appropriate amount of Al3Ti, a Ti foil with the thickness of 0.1 mm as an expendable was inserted between the Al foil and Mo fibers. The microstructure characterization of the MIL composite was performed via X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the tensile mechanical properties were measured by employing an Instron-5500R load frame. Results indicated that after VHP, the inserted thin Ti foils were completely depleted and converted into the dominant phase Al3Ti, which existed in the intermetallic layer. Four Al–Mo intermetallic, Al8Mo3, Al4Mo, Al5Mo and Al12Mo were successively formed around Mo fiber. The sequence of these Al–Mo intermetallic can be well explained by the thermodynamics calculation combined with the kinetic factor. Tensile tests show that when the arrangement of the fibers is parallel to the tensile direction, the introduction of Mo fibers significantly improves the tensile strength and strain to failure of the composite fibers, which is obviously related to the excellent mechanical properties of the Mo fibers themselves and their good bonding with the matrix.

Mechanical Properties of Mo Fiber-reinforced Resin Mineral Composites with Different Mass Ratio of Resin and Hardener

Mo fibers were added to RMC with different mass ratios of resin and hardener to improve its mechanical properties. The influences of fiber surface state and hardener content on interface bonding strength and mechanical properties of RMC were studied, respectively. Furthermore, strain values of typical measuring points on samples of Mo fiber reinforced RMC (MFRRMC) under different loads were obtained by experiments and finite element analysis. The experimental results prove that scrap Mo fibers can improve interface bonding strength and mechanical properties of RMC better than new smooth Mo fibers because of the discharge pits randomly distributed on the surface of scrap fibers. With the decrease of hardener content, not only interface bonding strength between fiber and matrix, but also compression and flexural strength of MFRRMC increase firstly and then decrease. The properties are best while the mass ratio of resin and hardener reaches 4:1. It is indicated that finite element calculation data basically agree with experimental data by comparison of strain values on typical measuring points, which can provide an important intuitive reference for successive study on other mechanical properties of MFRRMC, validating the correctness of simulation method as well.

Interface Bonding Property Finite Element Simulation of Mo Fiber-Reinforced Polymer Concrete

Interface bonding property of Mo-fiber reinforced polymer concrete not only depends on its material properties of components but also on microstructure characteristics of fibers including surface state, fiber content, fiber shape, bonding state between fiber and matrix, and so on. Interface bonding mechanism was firstly analyzed in the paper, and finite element simulation was employed to study the influence of fiber surface state, fiber number, bonding state between fiber and resin on interface property respectively. Research results show that the addition of Mo fibers can effectively restrain deformation of matrix, and scrap Mo fibers used as tool electrode material in Wire Electrical Discharge Machining before can improve interface bonding strength better than new smooth Mo fibers. With the increase of fiber number, deformation of the composite is decreasing. When fiber number is identical, maximum deformation of new and scrap Mo fiber-reinforced matrix in complete bonding state is respectively decreased by 12.6% and 14.5% on average compared with in complete debonding state.

Characterization of dislocation structures and deformation mechanisms in as-grown and deformed directionally solidified NiAl–Mo composites

Directionally solidified (DS) NiAl–Mo eutectic composites were strained to plastic strain values ranging from 0% to 12% to investigate the origin of the previously observed stochastic versus deterministic mechanical behaviors of Mo-alloy micropillars in terms of the development of dislocation structures at different pre-strain levels. The DS composites consist of long, [100] single-crystal Mo-alloy fibers with approximately square cross-sections embedded in a [100] single-crystal NiAl matrix. Scanning transmission electron microscopy (STEM) and computational stress state analysis were conducted for the current study. STEM of the as-grown samples (without pre-straining) reveal no dislocations in the investigated Mo-alloy fibers. In the NiAl matrix, on the other hand, a〈100〉-type dislocations exist in two orthogonal orientations: along the [100] Mo fiber axis, and wrapped around the fiber axis. They presumably form to accommodate the different thermal contractions of the two phases during cool down after eutectic solidification. At intermediate pre-strain levels (4–8%), a/2〈111〉-type dislocations are present in the Mo-alloy fibers and the pre-existing dislocations in the NiAl matrix seem to be swept toward the interphase boundary. Some of the dislocations in the Mo-alloy fibers appear to be transformed from a〈100〉-type dislocations present in the NiAl matrix. Subsequently, the transformed dislocations in the fibers propagate through the NiAl matrix as a〈111〉 dislocations and aid in initiating additional slip bands in adjacent fibers. Thereafter, co-deformation presumably occurs by 〈111〉 slip in both phases. With a further increase in the pre-strain level (>10%), multiple a/2〈111〉-type dislocations are observed in many locations in the Mo-alloy fibers. Interactions between these systems upon subsequent deformation could lead to stable junctions and persistent dislocation sources. The transition from stochastic to deterministic, bulk-like behavior in sub-micron Mo-alloy pillars may therefore be related to an increasing number of multiple a〈111〉 dislocation systems within the Mo fibers with increasing pre-strain, considering that the bulk-like behavior is governed by the forest hardening of these junctions.

Microstructure and phase stress partition of Mo fiber reinforced CuZnAl composite

A Mo fiber reinforced CuZnAl composite was prepared by means of friction stir processing and wire drawing. Reinforcing effect of the Mo fiber and phase stress partition in the composite were investigated by means of in-situ synchrotron X-ray diffraction. The maximum elastic strain of the Mo fiber achieved was 1.8%, implying a component stress of 550MPa on the fibers. The Mo fibers, with a volume fraction of 10%, carried 80% of stress fraction during tensile deformation. The change of modulus caused by stress-induced martensitic transformation strain resulted in redistribution of the phase stress partition between Mo fibers and CuZnAl matrix.

Elevated temperature tensile properties and deformation of directionally solidified NiAl–Mo in-situ composites

Four composition NiAl–xMo (x=7.8, 9, 13 and 16at.%) alloys were directionally solidified by a liquid metal cooling technique at a growth rate of 6μm/s. Perfectly aligned fibrous microstructures were fabricated for all four alloys. Tensile properties at elevated temperature were performed. Damage evolution and fracture characteristics at elevated temperature were also investigated. The fracture behavior of the composites in all tensile tests exhibited a ductile behavior at 1000°C. The high temperature tensile strength was found to increase with the volume fraction of Mo rods. The fibers are expected to bear the greater part of the imposed load due to the strong interface of the constituent phases. The Mo fibers' solid solution strengthened by both Ni and Al also contributes to the strength of composite.

Mechanical properties of Mo fiber-reinforced resin mineral composites

Mo fiber-reinforced resin mineral composite (RMC) belongs to a multiphase material, whose mechanical strength depends on the property of components and microstructure characteristics of Mo fibers including surface state, fiber content, fiber shape, and so on. The reinforcing mechanism of Mo fiber is analyzed and the reinforcing effects of new and scrap fibers on RMC are studied, respectively, in the paper. Typical samples with different fiber parameters are prepared to validate the aforementioned assumptions. Experimental results and finite element simulation prove that scrap Mo fibers can improve the mechanical properties of RMC better than ordinary new Mo fibers because of the discharge pits randomly distributed on the surface of scrap fibers. The reinforcing effect is best while the fiber content is 1.2% of the total mass. If the length, diameter, and mass fraction of fibers are identical, special-shaped fibers such as U, V, N, W perform better obviously, and their maximum pulling load is much bigger than ordinary linear fibers.

Tensile creep of directionally solidified NiAl–9Mo in situ composites

Well-aligned Mo fiber-reinforced NiAl in situ composites were produced by specially controlled directional solidification. The creep behavior parallel to the growth direction was studied in static tensile tests at temperatures between 900°C and 1200°C. A steady-state creep rate of 10−6s−1 was measured at 1100°C under an initial applied tensile stress of 150MPa. Compared to binary NiAl and previously investigated NiAl–Mo eutectics with irregularly oriented Mo fibers, this value demonstrates a remarkably improved creep resistance in NiAl–Mo with well-aligned unidirectional Mo fibers. A high-resolution transmission electron microscope investigation of the NiAl/Mo interface revealed a clean semi-coherent boundary between NiAl and Mo, which enabled an effective load transfer from the NiAl matrix to the Mo fibers, and thus leads to the remarkably increased creep strength. The stress exponent, n, was found to be between 3.5 and 5, dependent on temperature. The activation energy for creep, Qc, was measured to be 291±19kJmol–1, which is close to the value for self-diffusion in binary NiAl. Transmission electron microscopy observations substantiated that creep occurred by dislocation climb in the NiAl matrix. The Mo fiber was found to behave in a quasi-rigid manner during creep. A creep model for fiber-reinforced metal matrix composites was applied for an in-depth understanding of the mechanical behavior of the individual components and their contribution to the creep strength of the composite.

Fabrication and properties of continuous unidirectional Mo fiber reinforced TiAl composites by slurry casting and vacuum hot pressing

Abstract TiAl matrix composites reinforced by continuous fibers are potential structural materials for application in aerospace industry. However, the complicated fabrication procedures and high cost limit their applications. In this paper, slurry casting was proposed to simplify the fabrication procedures, and metallic Mo fibers instead of brittle ceramic fibers were applied to improve the room temperature brittleness and high temperature strength of the TiAl matrix, due to molybdenum’s low price, good toughness and excellent high temperature mechanical properties. Firstly, slurries were prepared by mixing Ti and Al elemental powders with organic binder (polymethyl methacrylate) and solvent (acetone); and then a monolayer of preform was fabricated by coating a layer of aligned Mo fibers with a certain thickness of slurry; after reaching the expected number of layers the preform were cut and finally degassed and consolidated by vacuum hot pressing to produce composites. 20 vol.% Mo f /TiAl composites with Mo fibers distributing uniformly in the matrix without bending were obtained. The matrix and fibers are well bonded through a reaction zone which consists of a thin δ -(Mo, Ti) 3 Al inner layer and a thick β’ -(Mo, Al)Ti outer layer. The composite consolidated at 1100 °C exhibits a good balance of room temperature and high temperature (800 °C) strength, 721 MPa and 731 MPa, respectively. The Mo fibers’ plastic deformation, necking and debonding contribute to the toughening of the composites. And the composites are greatly strengthened at high temperature due to the good properties of Mo fibers.

Effect of fabrication parameters on the microstructure and mechanical properties of unidirectional Mo-fiber reinforced TiAl matrix composites

Effect of the fabrication parameters on the microstructure and mechanical properties of unidirectional Mo-fiber reinforced TiAl matrix composites was investigated. The composites were fabricated through the following two steps. The first is the preparation of the composite preforms by powder slurry casting; the second is degassing the preforms at 380°C for 0.5h, 1h and 2h and then hot pressing them at different temperatures between 1000°C and 1380°C for 0.5h, 1h and 2h. In all the synthesized composites, Mo fibers distribute homogeneously and the matrices consist of two phases, i.e. γ-TiAl and α2-Ti3Al. Two reaction layers, i.e. δ-(Mo,Ti)3Al inner layer and β‘-(Mo,Al)Ti outer layer, were formed between the Mo fibers and matrix. With the hot pressing temperature and time increasing, the two reaction layers become thicker by consuming the Mo fibers and the matrix becomes denser, which is harmful and beneficial to the strengthening of the composites, respectively. The composite fabricated by hot pressing at 1100°C for 1h has good balance between the fiber degradation and matrix densification, and its flexural strength in the direction parallel to the fibers is 735.5MPa at room temperature and 762.9MPa at 800°C; whereas the room temperature flexural strength in the direction perpendicular to the fibers is 249.3MPa and increases with the degassing time increasing. After bending test, a main macro-crack together with a large number of micro-ones was observed within the matrix of the fractured samples, and the fractured Mo fibers showed obvious necking and localized debonding with the inner reaction layer. All these can absorb a great amount of energy before fracture, and thus the composite is highly toughened.

Influence of fiber alignment on creep in directionally solidified NiAl–10Mo in-situ composites

A NiAl–Mo eutectic having a nominal composition of Ni–45Al–10Mo was directionally solidified in a floating-zone furnace at two different growth rates, 20 and 80 mm/h. At the slower growth rate, the Mo fibers in the composite are well-aligned with the growth direction, whereas at the higher growth rate cellular microstructures are observed. Creep testing at 900 °C showed that the minimum creep rate is much higher for cellular than for well-aligned structures. In the cellular case a “soft” cell boundary consisting primarily of binary NiAl surrounding “hard” eutectic cell interiors seems to facilitate cell boundary sliding and therefore results in low creep strength. A microstructure-based composite model is used to explain the effects of fiber alignment on creep resistance.

Synthesis and characterization of molybdenum‐modified polycarbosilane for SiC(Mo) ceramics

AbstractA novel molybdenum‐containing polycarbosilane, polymolybdenocarbosilane (PMoCS), for SiC(Mo) fiber has been synthesized from polysilacarbosilane (PSCS) and MoCl5 as raw materials. The synthesis conditions is investigated. Characterization performed on the as‐synthesized PMoCS includes Fourier Transformed Infrared Spectroscopy (FT IR), gel‐permeation chromatography (GPC), X‐ray photoelectron spectroscopy (XPS), 1H NMR, and 29Si NMR, respectively. The polymer‐to‐ceramic conversion is studied with thermogravimetric analysis (TGA) and X‐ray diffraction (XRD). Preliminary research on the melt spinnability of PMoCS is carried out. The results show that the synthesis reaction is temperature‐dependent. Mo exists mainly as SiMo bonds. The reaction mechanism is believed to involve HCl elimination between SiH and MoCl, and followed by the Kumada rearrangement. The ceramic yield of PMoCS, prepared with 10 wt % MoCl5, is approximately 78.5% at 1200°C in a N2 flow. The XRD results suggest that ceramics pyrolyzed in the range of 800–1000°C are all amorphous, while β‐SiC and β‐MoSi2 crystals are observed at 1200 and 1400°C, respectively. The conversion from β‐MoSi2 to α‐MoSi2 is almost completed at 1600°C. PMoCS is melt spinnable into flexible and uniform green fibers with the diameters about 13.4 μm to 12.2 μm. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Investigation into microstructure and mechanical properties of NiAl-Mo composites produced by directional solidification

Abstract Mo fiber reinforced NiAl in situ composites with a nominal composition Ni-43.8Al-9.5Mo (at.%) were produced by specially controlled directional solidification using a laboratory-scale Bridgman furnace equipped with a liquid metal cooling (LMC) device. The microstructure of as-produced composites was characterized by electron microscopy (SEM, TEM, HRTEM) and microanalysis (EDX, SAED). The strength and plasticity at elevated temperatures (700 °C, 1100 °C) were examined by tensile tests. The fracture toughness at room temperature (RT) was measured by four-point bending tests. For a constant temperature gradient (8.9 K/mm) it was found that the alignment and size/spacing of single crystalline Mo fibers were mainly controlled by the solidification rate. When the solidification rate decreased from 1.33 mm/min to 0.33 mm/min the Mo fibers arranged themselves gradually from an initially irregular distribution to an alignment parallel to the solidification direction. The strength at elevated temperatures and the fracture toughness at RT were dominated by the Mo fiber alignment: the yield strength of the composites increased from 273 MPa at 700 °C and 68 MPa at 1100 °C for a random Mo fiber arrangement to 811 MPa at 700 °C and 344 MPa at 1100 °C for well aligned Mo fibers. The fracture toughness at RT was also apparently improved from 8.7 MPa m0.5 to 14.5 MPa m0.5 upon Mo fiber alignment. The influence of Mo fiber alignment on the mechanical properties of as-produced NiAl-Mo composites will be discussed in terms of the active strengthening and toughening mechanisms.

Mechanical properties of NiAl-Mo composites produced by specially controlled directional solidification

ABSTRACTMo fiber reinforced NiAl in-situ composites with a nominal composition Ni-43.8Al-9.5Mo (at.%) were produced by specially controlled directional solidification (DS) using a laboratory-scale Bridgman furnace equipped with a liquid metal cooling (LMC) device. In these composites, single crystalline Mo fibers were precipitated out through eutectic reaction and aligned parallel to the growth direction of the ingot. Mechanical properties, i.e. the creep resistance at high temperatures (HT, between 900 °C and 1200 °C) and the fracture toughness at room temperature (RT) of in-situ NiAl-Mo composites, were characterized by tensile creep (along the growth direction) and flexure (four-point bending, vertical to the growth direction) tests, respectively. In the current study, a steady creep rate of 10-6s-1 at 1100 °C under an initial applied tensile stress of 150MPa was measured. The flexure tests sustained a fracture toughness of 14.5 MPa·m1/2at room temperature. Compared to binary NiAl and other NiAl alloys, these properties showed a remarkably improvement in creep resistance at HT and fracture toughness at RT that makes this composite a potential candidate material for structural application at the temperatures above 1000 °C. The mechanisms responsible for the improvement of the mechanical properties in NiAl-Mo in-situ composites were discussed based on the investigation results.