Effect of preweld conditions on the strain ageing cracking susceptibility of IN939 superalloys heat affected zone

Abstract

The evolutionary behavior of precipitated phases is a key determinant of strain aging cracking sensitivity in superalloys. In multi-component superalloys, these behaviors are influenced by pre-weld conditions and heat input. The strain aging cracking (SAC) sensitivity of the heat affected zone (HAZ) of IN-939 superalloy with various pre-weld heat treatment conditions was studied. The SAC sensitivity of the IN-939 superalloy samples was evaluated through the strain-to-fracture test (STF) by monitoring the ductility and fracture time during the test. The SAC sensitivity influencing factors including microstructure evolution, phase precipitation behavior of IN-939 superalloys were analyzed by electron probe micro analyzer (EPMA)、in-situ and exit-situ TEM test. The results showed that the SAC sensitivity of overaged IN-939 superalloys is smaller than that of the solid-solution condition showing larger ductility and longer fracture time during the STF test. The fast precipitation of γ′ phase in the IN-939 superalloy HAZ during the STF test is responsible for the large SAC sensitivity of the solid-solution condition. The SAC sensitivity temperature range is well consistent with the fast precipitation temperature of γ′ phase.