Creep Strength of Yttrium Doped 4^th Generation Ni-Base Single Crystal Superalloy

Abstract

  The effects of yttrium addition on high temperature properties of the 4^th generation nickel-base superalloy were studied. Nickel-base superalloys, which possess both creep strength and oxidation resistance, are being required to satisfy high efficiency and reliability of jet engines. 4^th generation superalloys contain platinum groups metals such as ruthenium. In order to satisfy creep strength and phase stability, however ruthenium worsens oxidation resistance. Yttrium doping was found to increase the oxidation resistance due to the improved adhesive strength of Al₂O₃ oxide, and the effects of yttrium doping on creep strength are established in this paper.
   Yttrium-added TMS-138 alloy (TMS-138Y) showed high creep strength of 4^th generation superalloys, however the creep strength was slightly worse than the alloy without yttrium in the high-temperature low-stress creep condition. Microstructural observations confirmed the increase of Topologically Close Packed (TCP) phases in TMS-138Y. This was due to the formation of a yttrium-containing compound, Al_0.06Ni_0.73Co_0.04Y_0.18 (at.), which made incoherent interfaces that allowed TCP phases to precipitate by heterogeneous nucleation.