Breakthrough new discoveries in 3D printed single crystal superalloys

China Xi'an Jiaotong University School of Materials uses advanced characterization technologies such as synchrotron microdiffraction and transmission electron microscopy to start from the microstructural evolution laws, customize a heat treatment system for 3D printed single crystal superalloys, and solve the problem of recrystallization after 3D printing of individual crystal leaves. A new mechanism for plastic deformation recovery of superalloys is proposed.

The blades of aero engines are made of expensive single-crystal nickel-based superalloys. Due to the harsh service environment, single-crystal leaves are susceptible to local damage, and the development of reliable blade repair technology is essential for aero-engine life extension and cost reduction. 3D printing shows its attractive application prospects in the field of repair / remanufacturing of single-crystal blades due to its "precise positioning and controlled additive" characteristics. However, due to the fast cooling speed of 3D printing, it is easy to cause a metastable microstructure with high residual stress and high dislocation density. This metastable structure is prone to recrystallization during standard heat treatment or service, leading to a decrease in the high-temperature mechanical properties of the material and a potential safety hazard. Therefore, it is urgent to develop a new process to meet the current problems of 3D printed single crystal superalloys: no recrystallization, low stress, low dislocation density, and morphology, density, and matrix of the γ ′ precipitation-enhanced phase. Superalloys are consistent.

The standard heat treatment system for superalloys generally consists of a reliable solution and aging. The practice has proved that this process can cause 3D printed superalloys to recrystallize. After systematic literature research and comprehensive analysis, the authors have proposed and confirmed that adding a "Recovery" step before the reliable solution can eliminate the recrystallization driving force. After the "recovery-solution-aging" treatment, the residual stress of the superalloy is removed along with the directional coarsening of the microstructure γ ′ phase, and the dislocation density can be reduced to about 5% before heat treatment. The precipitation strengthens γ ′ after aging. The stage reaches the same level as the as-cast substrate. Because the phenomenon found is similar to the Rafting effect of superalloys under high temperature creep conditions. It has a recovery effect, and it is named the "Rafting-enabled" fact. Recovery). This discovery breaks through the perception that the single crystal superalloy cannot recover, which provides a scientific basis for designing non-standard heat treatment systems for 3D printed superalloys. It shows that the new heat treatment system can fully meet 3D printing—the need for single crystal blade repair.

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