Effect of microstructural evolution and mechanical properties of Haynes 230 superalloy during long-term aging at 700 °C

Abstract

The effect of long-term isothermal aging of Haynes 230 super-alloy in an advanced ultra-supercritical (A-USC) power plant at 700 °C for up to 10,000 h on microstructural evolution and tensile behavior. And utilizing a combination of the scanning electron microscope (SEM), X-ray diffraction analysis (XRD), and transmission electron microscope (TEM). Although the grain size and grain boundary M23C6 carbides did not change significantly, the dissolution of intercrystallite primary M6C carbides and the precipitation of intracrystalline secondary lamellar M6C carbides were observed at 2000 h to 10,000 h. According to the SEM and TEM results, it is shown that the dissolution of primary M6C carbides makes the W, Mo, and Cr in the γ matrix increase, while the precipitation process of secondary M6C carbides is M+ 6 C→M6C. To reduce the interfacial energy of the γ matrix, secondary M6C carbides are precipitated in the crystal under long-term aging at 700 °C, with a gradual increase in time content. the best tensile and yield strengths at 750 °C occur after 4000 h of aging, with microscopic voids forming mainly around the granular M6C carbides in the crystal, but the solid solution strengthening effect of the matrix provides the strength. The worst strength and elongation occur after 10000 h aging, when the dissolution of granular M6C and secondary precipitation of M6C carbides are most abundant, interfacial cavity formation of granular M6C carbides and brittle fracture of M6C carbide particles, and the growth of non-co-grained secondary M6C carbides with the matrix allow more microscopic cavities to appear during high-temperature tension, reducing the strength of Haynes 230 and plasticity.