一方向凝固したNi基超耐熱合金のクリープ強度とγ'粒度の関係
1987 年 73 巻 2 号 p. 364-371
詳細
1987 年 73 巻 2 号 p. 364-371
Correlations of γ' size distributions with creep and creep rupture properties at 900°C under the stress of 30.0kgf/mm2 were investigated using materials three-step heat treated at various solution temperatures on a directionally solidified nickel-base superalloy CM247LC. Size distributions of extracted γ' particles were measured by means of photo-extinction and sedimentation. It became clear that creep rupture lives and minimum creep rates were dependent most preferably on the amount of eutectic γ'-γ' phase, and that, irrespective of solution temperatures and material conditions such as as-cast or heat-treated conditions, the minimum creep rates became higher and the creep rupture lives became lower highly correlatively as the volume fractions of γ' larger than 2 μm in eutectic γ'-γ' regions to the total amount of γ' became greater. According to observations of substructures formed during secondary creep region and secondary cracks formed during creep rupture tests, it was found that eutectic γ-γ' phase did not only contribute inefficiently to creep deformation resistance, but also accelerated crack propagation. This fact is considered to explain possibly the role of eutectic γ-γ' phase in creep properties mentioned above.
