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  • Muhammad Zakky Nurrachman posted an update 7 years, 8 months ago

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    Ceramals for Gas Turbines
    * EARTHY substances combined with
    metals are the most promising alloys for
    use in the turbine engines of tomorrow’s
    airplanes.
    These new substances are called “cera-
    mals” and they are used in the blades on
    the shafts of gas turbine engines where ex-
    treme high temperatures are encountered.
    Much research into alloys and other ma-
    terials needed to withstand the high tem-
    peratures within the gas turbine engine has
    been under way during the past decade, and
    particularly since the advent of the jet-
    propelled airplane.
    A leading part in such work has been
    taken by the National Advisory Committee
    for Aeronautics. A review of NACA re-
    search on these ceramals has been issued by
    the Society of Automotive Engineers.
    The report is by G. Mervin Ault and G.
    C. Deutsch, both of the Lewis Flight Propul-
    sion Laboratory maintained by the NACA
    at Cleveland. It covers work done by them
    and others at this government institution
    whose primary concern is aircraft engines
    and fuels.
    The high-temperature metal alloys now
    used in the blades on the shafts of turbines
    in both turbo-jet and turbo-prop engines are
    operating close to their upper temperature
    limits. Materials to withstand higher heat
    are necessary.
    Ceramic blades show favorable strength
    at high temperatures, but they tend to frac-
    ture with sudden drastic temperature
    changes, a common occurrence in gas tur-
    bines. Ceramics also are brittle and difficult
    to handle without breakage.
    The ceramals which were carefully investi-
    gated by the NACA included boron carbide
    ceramic to which iron was added, and
    titanium carbide which was used separately
    with cobalt, tungsten and molybdenum. The
    boron ceramic is one of the strongest; the
    titanium ceramic is the most resistant to
    shock.
    The boron carbide-iron ceramal, 36%
    iron, has a strength consistently lower than
    that of pure boron carbide, but the rate of
    decrease in the ceramal’s strength with in-
    crease in temperature is very low. At 2,400
    degrees Fahrenheit, the ceramal lost only
    27% of its room-temperature strength.
    Titanium carbide ceramals containing
    cobalt were investigated extensively because
    cobalt was known to bond well with ce-
    mented-carbide tool compositions. Ceramals
    containing from 5% to 30% of the metal
    were used. The purpose of this was to de-
    termine the best mixture for the blading.
    In bending tests, cobalt-bearing ceramals
    had exceptional strength up to 2,000 degrees
    Fahrenheit, but negligible strength at 2,400
    degrees. The tungsten and molybdenum
    compositions, on the other hand, have only
    moderate strength at the lower temperatures
    but considerably surpassed the cobalt cera-
    mal at 2,400 degrees.
    A titanium carbide ceramal with 20%
    cobalt was found resistant to thermal shock.
    The cobalt-bearing bodies were found re-
    sistant to oxidation. From the tests, the
    scientists decided that the titanium carbide
    with 20% cobalt was the best to use in
    actual operation tests in an engine.
    Science News Letter, June 3. 1950