Effect of solution treatment on gamma-prime recovery in a creep-damaged directionally solidified Ni superalloy

The effect of different solution conditions on the gamma' phase of a creep-damaged DZ411 superalloy during a process combining hot isostatic pressing (HIP) and re-heat rejuvenation was investigated. The analysis results showed that proper solution temperature and time are necessary for dissolving coarsened and rafted gamma' precipitates, allowing the optimum reprecipitation of the gamma' precipitates during the following aging, avoiding incipient melting. It was also found that a higher solution temperature results in a smaller size and lower volume fraction of the gamma' precipitates. A two-hour solution treatment is enough to complete the dissolving of the remnant primary gamma' precipitates and produce unimodal spheroidal secondary gamma' precipitates. High cooling rates after the solution treatment give rise to finer and more secondary gamma' precipitates. The complete re-heat rejuvenation procedure including a full solution and two-step aging can produce duplex-sized gamma' precipitates including coarse cubic gamma' precipitates and fine spherical gamma' precipitates, endowing the superalloy with excellent high-temperature creep properties. It was verified that the gamma' precipitate morphology and creep properties of the creep-damaged DZ411 superalloy can be restored with a simple re-heat rejuvenation process.