Investigation on Effect of Insulation Materials on High-temperature Stress-rupture Behavior of GH4698 Alloy

GH4698 alloy is a key structural material for Chinese aero engines, and high temperature stress-rupture test is an important means for evaluating the service reliability of engine components. The stress-rupture test of GH4698 alloy is taken as the research object to explore the effects of insulation materials adopted during the test. Two types of insulation materials, namely asbestos cord and ceramic cord, were used to bind thermocouples for carrying out stress-rupture tests. The tested specimens were analyzed by SEM, OM, DSC, and XRD to analyze their microstructure and properties. The results show that at 650 ℃, hydrolysis occurs in the specimens insulated with asbestos cord, which induces severe high-temperature oxidation of GH4698 alloy. A loose and porous oxide layer forms on the specimen surface, damaging its surface integrity.Meanwhile, the alloy exhibits decreased hardness, which leads to premature fracture of the specimen. In contrast, specimens insulated with ceramic cord develop an extremely thin and dense oxide layer at high temperature, which do not affect the stress-rupture test