High Temperature Strength of Ir-based Refractory Superalloys

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  • Yamabe-Mitarai Yoko
    High Temperature Materials 21 Project, National Research Institute for Metals
  • Ro Yoshikazu
    High Temperature Materials 21 Project, National Research Institute for Metals
  • Nakazawa Shizuo
    High Temperature Materials 21 Project, National Research Institute for Metals
  • Harada Hiroshi
    High Temperature Materials 21 Project, National Research Institute for Metals

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Other Title
  • Ir基高融点超合金の高温強度
  • Irキ コウユウテン チョウゴウキン ノ コウオン キョウド

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Abstract

The purpose of this paper is to understand the high-strength and deformation mechanism of new-generation “refractory superalloys”. Refractory superalloys are defined as alloys that have an fcc and L12 two-phase coherent structure and yet considerably high melting points. This paper examines compressive strength up to 1800°C and creep behavior at 1500°C of Ir-V, -Ti, -Nb, -Ta, -Hf, and -Zr binary refractory superalloys. It is indicated that the precipitation-hardening effect depends on L12 precipitate morphology. Plate-like precipitates are more effective for precipitation hardening than cuboidal precipitates. Shearing of precipitates was observed in the alloy with plate-like precipitates using TEM. When plate-like precipitates form, a dislocation cannot bypass around a plate, thus being forced to shear a precipitate. However, high-coherency strain energy at the interface prevents the dislocation motion. Therefore, large precipitation hardening appeared in the alloy with plate-like precipitates. On the other hand, the creep resistance of the alloy with plate-like precipitates was smaller than that of the alloy with cuboidal precipitates because discontinuous coarsening occurs and the microstructure becomes coarse in the alloy with plate-like precipitates.

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