Tensile, creep behavior and microstructure evolution of an as-cast Ni-based K417G polycrystalline superalloy

The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature (600-900 degrees C) properties. Since used in as-cast state, the comprehensive understanding on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under different conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and gamma/gamma' eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 degrees C to 700 degrees C, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate temperature embrittlement. When the temperature rises to 900 degrees C, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different testing conditions. At 760 degrees C/645 MPa, the creep cracks initiate at MC carbides and gamma/gamma' eutectic structures, and propagate transgranularly. While at 900 degrees C/315 MPa and 950 degrees C/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 degrees C/645 MPa to 900 degrees C/315 MPa and 950 degrees C/235 MPa, the gamma' phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate. (C) 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.