極微小SPクリープ試験片を用いた一方向凝固Ni基超合金のクリープ寿命評価

抄録

Creep damage in structural components under elevated temperatures leads to a severe failure and / or fracture. In order to prevent these accidents and to improve the integrity of components, more reliable methodologies have been required. Small Punch (SP) creep test has been proposed as a semi destructive testing method which employs small disc specimen. Polycrystalline materials were mainly examined in the SP creep test so far, and there are few reports where the anisotropic material was employed. A series of the SP creep test were conducted at 720oC using very small disc specimens of a Ni-base directionally solidified (DS) superalloy; Inconel 713C. The disc-type SP creep specimen has 5 mm in diameter and 0.25 mm in thick, and was cut out along longitudinal (LD) and transverse (TD) directions of the DS ingot. Experimental test results show that the creep rupture lives cut along the TD are one and a half times or twice as long as those cut out from the LD due to the hardness of breakage across the directionally crystalline. It was also found that the rupture life of the specimen of the TD depends on Dendrite Arm Spacing, i.e., finer the DAS is, longer the rupture lives are. Then, the SP creep test should be performed attentively checking the DAS if the anisotropic material is employed.