Papers by Keyword: Molybdenum

Abstract: Characteristic features and thermal stability of the structure of molybdenum processed by high pressure torsion, equal-channel angular pressing or multy-step forging have been investigated using transmission electron microscopy, X-ray diffraction analysis and orientation imaging microscopy. The structural factors responsible for the strengthening and thermal stability of molybdenum processed have been obtained. It has been demonstrated that only high pressure torsion is an effective method to refine molybdenum structure (down to 0.2 µm). Recrystallization occurs during the others investigated processing disabling significant grain size reduction.

Abstract: With the aim to study the regularities of surface diffusion in coadsorbed layers, we investigated diffusion of lithium on the (112) surfaces of Mo and W precovered with submonolayers of dysprosium and strontium, which have substantially lower mobilities than lithium. Experiments were carried out using scanning contact-potential microscopy, and Li diffusion parameters were extracted from diffusional evolution of coverage profiles. Dy and Sr preadsorbed in amounts of ∼10–1 of a monolayer were found to reduce the diffusion rate of Li by orders of magnitude. The strong impact of coadsorbates with low mobility on Li diffusion can be caused by important role of collective mechanisms in surface diffusion, which entails pronounced pinning effects, as well as by the possibility of formation of surface alloys and surface vitrification.

Abstract: In this work we present a novel procedure, involving linear viscoelastic analysis, to discriminate the two possible contributions of the observed damping peak which appears around 840 K – 1050 K in mechanically deformed high purity single-crystalline molybdenum. An interesting feature of the procedure is that, for low damping samples, it can efficiently resolve experimental peaks that result from the superposition of different processes independently of the ratio between their relaxation strengths. This allows us to confirm that two different relaxation processes appear in molybdenum in the temperature range about 0.3 Tm, one around 840 K, and the other one near 1050 K. These can be related to diffusion and to a coupled mechanism involving creation and diffusion of vacancies, respectively.

Abstract: Molybdenum coatings are commonly used in the industry for protection against wear. With an aim to investigate the erosion properties of this coating, molybdenum coating was sprayed onto both AISI 1045 and nickel-based superalloy (GH3039) substrate by electro-thermal explosion ultra-high speed spraying process. Phase composition, microstructure and microhardness of the coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness tester, respectively. Erosion tests of the coating at different particle impingement angel and material sample temperature were performed on a GW/CS-MS type tester. The high erosion resistance of the coating can mainly be attributed to high hardness, low porosity and metallurgical bonding between the coating and the substrate.

Abstract: Molybdenum has many prominent properties, such as high melting point, good thermal properties, low erosion rate and so on, which make it promising candidate materials for plasma facing materials in the next fusion reactor. In the present work, molybdenum coatings were deposited onto the oxygen-free copper substrates by atmospheric plasma spraying. Different interlayers were introduced between the coatings and substrates. SEM, EDS and XRD were used to investigate the photographs and compositions of these coatings. The bonding strength of the coatings was tested to investigate the effect of interlayers on adhesion of the coatings at room temperature and it was found that the coating without interlayers showed the highest bonding strength. Water quenching method was used to evaluate the adhesion of the coatings under thermal cycling conditions and the results showed that the molybdenum coating with two interlayers possessed of the highest resistance of thermal cycling wrack.

Abstract: Interdiffusion coefficients of the refractory elements in Fe-W-Re and Fe-Cr-X (X=Mo, W) ternary alloys have been measured on the basis of the modified Boltzmann-Matano method for ternary system. Both the cross interdiffusion coefficients, Fe ReW ~D and Fe WRe ~D were negative in Fe-W-Re ternary alloys. This result indicates that attractive interaction exists between W and Re atoms in iron alloys [1]. This is consistent with our previous experimental results that Re suppresses W diffusion in Fe-15Cr alloy [1]. In addition, the value of cross interdiffusion coefficient Fe CrW ~D was positive in Fe-Cr-W diffusion system, whereas Fe MoCr ~D was negative in Fe-Cr-Mo diffusion system.

Abstract: The need of an effective control of residual metal content inside the silicon epitaxial wafers is revamping for CCD and CMOS applications, which are very sensitive to small amount of heavy metals. The paper will discuss the strengths and the challenges associated to the integrated use of well known electrical techniques when metals like iron and molybdenum are present in concentration lower than 1E11 cm^3.

Abstract: This paper investigates the impact of iron (Fe) and molybdenum (Mo) when they are introduced in the feedstock for mono- and multicrystalline Float-Zone (FZ) silicon (Si) growth. Neutron Activation Analysis shows that the segregation coefficient is in agreement with literature values. Lifetime maps on monocrystalline wafers show a uniform lifetime which decreases with the increase of contamination levels. Multicrystalline wafers show low lifetime areas, corresponding to grain boundaries and highly dislocated areas, which are independent from the contamination levels. Intra grain areas have a higher lifetime which changes with the contamination levels. The solar cells show a reduced diffusion length in multicrystalline uncontaminated cells compare to the monocrystalline uncontaminated. In multicrystalline cells the lowest level of Fe introduced (1012 atm/cm3) has hardly any influence, whereas in the Mo-contaminated cells the impact is visible from the lowest level (1011 atm/cm3). In monocrystalline cells the diffusion length is reduced already at the lowest contamination level of Fe.

Abstract: Aqueous corrosion behaviors of Fe3Al-based iron aluminides were investigated. From the result of cyclic anodic polarization tests conducted in 3.5 wt.% NaCl solution at 25, 48, 72 and 95°C, as the temperature increased, the resistance to pitting corrosion decreased significantly, especially over the range of 25~48°C. From the result of crevice corrosion tests, no crevice corrosion occurred on FAL-Mo in the lower chloride-containing solution (200 ppm Cl-), however, FAL-Mo did not perform as well as the 304L SS in the higher chloride-containing solution (3.5 wt.% NaCl). From the result of anodic polarization tests performed in sulfur-compound solutions, additions of Cr and Mo to the Fe3Al-based iron aluminides tend to improve the aqueous corrosion resistance. Aqueous corrosion behaviors with different Al content evaluated by cyclic anodic polarization test in the chloride-containing solution exhibited the more stable passive behavior and the higher pitting resistance as Al contents increased.

Abstract: Molybdenum has many prominent properties, such as high melting point, good thermal properties, and low erosion rate and so on, which make it promising candidate materials for plasma facing materials in the next fusion reactor. In this paper, Molybdenum coatings were deposited onto the oxygen-free copper substrates by atmospheric plasma spraying. The spraying parameters had been carefully selected. Different interlayers were induced between the substrate and the coating. SEM and XRD were used to investigate the photographs and compositions of these coatings. The micro-hardness and bonding strength were also tested. Thermal behaviors of the coatings were evaluated by thermal shock tests. The coatings with interlayers showed better resistance of thermal shock but lower bonding strength compared to coatings that without interlayers.