Carbide

About: Carbide is a research topic. Over the lifetime, 36331 publications have been published within this topic receiving 503586 citations.

Wettability and interfacial energies in SiC-liquid metal systems

Abstract: The sessile drop technique is used to measure the contact angles of molten Si, Sn, Cu and Ni in contact with mono- and polycrystalline α-SiC as well as CVD β-SiC in purified argon atmosphere and at various temperatures. The contact angle of silicon, near its melting point, is about 38° on a mono- as well as polycrystalline α-SiC substrate and about 41.5° on β-SiC. Tin does not wet the SiC. Using data from the available literature, the work of adhesion and the interfacial energy between SiC and Si or Sn were calculated. In the α-SiC-Sn system, both quantities are linearly dependent on temperature in the investigated temperature range 523–1073 K. The metals copper and nickel react with silicon carbide. The silicon content of the copper drop depends on the annealing temperature. The nickel drop after cooling forms the compound Ni3Si2. The interferometric measured groove angle of SiC (thermal etching) in vacuum at 2020 K gives a mean value of 157.6±5.8°.

Carbon nanotubes–Fe–alumina nanocomposites. Part I: influence of the Fe content on the synthesis of powders

Abstract: Oxides based on a-alumina and containing various amounts of Fe (2, 5, 10, 15 and 20 cat.%) were prepared by decomposition and calcination of the corresponding mixed-oxalates. Selective reduction of the oxides in a H2-CH4 atmosphere produces nanometric Fe particles which are active for the in-situ nucleation and growth of carbon nanotubes. These form bundles smaller than 100 nm in diameter and several tens of micrometers long. However, the carbon nanotubes-Fe-Al2O3 nanocomposite powders may also contain Fe carbide nanoparticles as well as undesirable thick, short carbon tubes and thick graphene layers covering the Fe/Fe carbide nanoparticles. The influence of the Fe content and the reduction temperature on the composition and micro/nanostructure of the nanocomposite powders have been investigated with the aim of improving both the quantity of nanotubes and the quality of carbon, i. e. a smaller average tube diameter and/or more carbon in tubular form. A higher quantity of carbon nanotubes is obtained using a-Al1.8Fe0.2O3 as starting compound, i. e. the maximum Fe concentration (10 cat.%) allowing to retain the monophase solid solution. A further increase in Fe content provokes a phase partitioning and the formation of a Fe2O3-rich phase which upon reduction produces too large Fe particles. The best carbon quality is obtained with only 5 cat.% Fe (a-Al1.9Fe0.1O3), probably because the surface Fe nanoparticles formed upon reduction are a bit smaller than those formed from a-Al1.8Fe0.2O3, thereby allowing the formation of carbon nanotubes of a smaller diameter. For a given Fe content (≤ 10 cat.%), increasing the reduction temperature favours the quantity of nanotubes because of a higher CH4 sursaturation level in the gas atmosphere, but also provokes a decrease in carbon quality.

Effect of carbides on the creep properties of a Ni-base superalloy M963

Abstract: Effect of carbides on the creep properties of a cast Ni-base superalloy M963 tested at 800 and 900 °C over a broad stress range has been investigated. Correlation between the carbides and creep properties of the alloy is enabled through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). During high temperature creep tests, the primary MC carbide decomposes sluggishly and a large amount of secondary carbides precipitate. The cubic and acicular M 6 C carbide precipitates at the dendritic core region. Extremely fine chromium-rich M 23 C 6 carbide precipitates preferentially at grain boundaries. The M 6 C and M 23 C 6 carbides are found to be beneficial to the creep properties of the alloy. At lower temperature (800 °C), the interface of MC carbide with matrix is one of the principal sites for crack initiation. At higher temperature (900 °C), the oxidation and the precipitation of μ phase are the main factors for significant loss in creep strength of the alloy.