極微小SPクリープ試験片による小型タービンホイールのクリープ強度評価および微視組織との関係

抄録

Superior creep strength has been required in turbine wheels employed under high temperatures. Since they are produced using investment casting method, mechanical properties sometimes depend on each portion of turbine wheel due to the complex shape. Although conventional SP creep tests adopt 10mm in diameter and 0.5mm in thickness are employed to examine local properties at high temperatures, other new testing methods are required because these turbine wheels are small and have thinner thickness of blades. Employing very small, half-size of the conventional SP creep test specimen, a series of creep tests for three turbine blades of Inconel 713C were conducted where the test temperature and the applied load were fixed at 720°C and 150N. Microstructural observation shows equiaxed at tip and columnar grains at root of the blades. SP creep rupture lives of specimens sampled from the root are generally longer than those from the tip. SEM observations reveal that creep cracks developed along the grain boundary. Specimens from the root have longer columnar grains, and creep crack mainly developed along the boundary of columnar grains. Creep rupture lives depend on dendrite arm spacing; the smaller D.A.S., the longer rupture lives.