Effect of Cooling Rates on Solidification Microstructures and Tensile Property of a Novel Wrought Superalloy

Abstract

The effects of cooling rates on solidification behaviors, segregation characteristics and tensile property of GH4151 alloy were investigated using microstructure characterization and tensile test. Firstly, a relationship between the secondary dendrite arm spacing and cooling rate was determined and it was confirmed to be valid. Secondly, it can be found from microstructure observations that the morphology of (Nb, Ti)C carbides transits from blocky and script type to fine script type and spotty type, and the refined γ′ phase was observed due to decrease of segregation with increasing cooling rates. Thirdly, the solidification microstructures of the industrial-scale samples were analyzed. The morphology of η phase changes from indistinguishable shape, fine needle-like shape to large block-like shape with increasing ingot diameter. As a result, the mechanical properties of alloy decrease due to increase of brittle precipitations. The experimental results show that the precipitation behavior of GH4151 is affected by segregation degree of elements, and the segregation degree is determined by solute distribution process and solid back-diffusion process.

Keywords

GH4151 superalloy / solidification / segregation / cooling rate / tensile properties