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Formation mechanism of abnormally large grains in a polycrystalline nickel-based superalloy during heat treatment processing

DOI: 10.1016/j.actamat.2019.02.012 DOI Help

Authors: Xin Wang (Central South University, China) , Zaiwang Huang (Central South University, China) , Biao Cai (University of Manchester) , Ning Zhou , Oxana Magdysyuk (Diamond Light Source) , Yanfei Gao (University of Tennessee) , Shesh Srivatsa (Srivatsa Consulting LLC) , Liming Tan (Central South University, China) , Liang Jiang (Central South University, China)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Materialia

State: Published (Approved)
Published: February 2019

Abstract: Controlling the final grain size in a uniform and controlled manner in powder metallurgy nickel-based superalloys is important since many mechanical properties are closely related to it. However, it has been widely documented that powder metallurgy superalloys are prone to suffer from growth of abnormally large grains (ALGs) during supersolvus heat treatment, which is harmful to in-service mechanical performance. The underlying mechanisms behind the formation of ALGs are not yet fully understood. In this research, ALGs were intentionally created using spherical indentation applied to a polycrystalline nickel-based superalloy at room temperature, establishing a deformation gradient underneath the indentation impression, which was quantitatively determined using finite element modelling, electron backscatter diffraction (EBSD) and synchrotron diffraction. Subsequent supersolvus heat treatment leads to the formation of ALGs in a narrow strain range, which also coincides with the contour of residual plastic strain in a range of about 2% to 10%. The formation mechanisms can be attributed to: (1) nucleation sites available for recrystallization are limited, (2) gradient distribution of stored energy across grain boundary. The proposed mechanisms were validated by the phase-field simulation. This research provides a deeper insight in understanding the formation of ALGs in polycrystalline nickel-based superalloy components during heat treatment, when subsurface plastic deformation caused by (mis)handling before super-solvus heat treatment occurs.

Journal Keywords: Nickel-based superalloys; Abnormal grain growth; Local strain distribution; Dislocation density; Phase field modeling

Subject Areas: Materials, Engineering

Instruments: I12-JEEP: Joint Engineering, Environmental and Processing