Development of Directionally Solidified Eutectic Nickel Alloys for Use in Aircraft Gas Turbines at Metal Temperatures Exceeding 1000 C.
Final rept. Jan-Oct 76,
UNITED TECHNOLOGIES RESEARCH CENTER EAST HARTFORD CONN
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Investigations to develop an isotropically ductile high temperature eutectic by ternary modifications and quaternary or quinary additions to the monovariant eutectic gammagamma-alpha Ni3AlNi-Mo were performed. Extensive substitutions 7 wo of chromium, cobalt, iron and tantalum and more limited substitution of tungsten, rhenium, titanium, and carbon demonstrated the wide flexibility of alloying. Tantalum and rhenium additions improved the high temperature creep strength and tantalum additions combined with chromium i.e. Ni-32 wo Mo-5.5 wo Al-3 wo Cr-1 wo Ta yielded an alloy whose cyclic oxidation resistance at 1000 C compared favorably to the outstanding oxidataion resistant nickel-base superalloy, B-1900. Since the measured coefficient of thermal expansion of gammagamma-alpha alloys are below the CTEs of conventional coatings the requirement of a compatible lower expansion coating was indicated. The ultimate shear strengths of gammagamma-alpha alloys at intermediate temperatures 760-880 C were found to be equivalent to nickel base superalloys. However, the shear creep rupture properties at 760 C were below those of the more isotropic superalloys. The thermal fatigue resistance of gammagamma-alpha alloys was found to be dependent on aluminum content. Alloys containing 7.8 wo Al exhibited substantially greater resistance to cyclic thermal fatigue 400-1122 C under stress than both D.S. Mar M200 Hf and gammagamma-delta. Author
- Metallurgy and Metallography
- Jet and Gas Turbine Engines