Abstract
In the present work, we investigate the evolution of mosaicity during seeded Bridgman processing of technical Ni-based single crystal superalloys (SXs). For this purpose, we combine solidification experiments performed at different withdrawal rates between 45 and 720 mm/h with advanced optical microscopy and quantitative image analysis. The results obtained in the present work suggest that crystal mosaicity represents an inherent feature of SXs, which is related to elementary stochastic processes which govern dendritic solidification. In SXs, mosaicity is related to two factors: inherited mosaicity of the seed crystal and dendrite deformation. Individual SXs have unique mosaicity fingerprints. Most crystals differ in this respect, even when they were produced using identical processing conditions. Small differences in the orientation spread of the seed crystals and small stochastic orientation deviations continuously accumulate during dendritic solidification. Direct evidence for dendrite bending in a seeded Bridgman growth process is provided. It was observed that continuous or sudden bending affects the growth directions of dendrites. We provide evidence which shows that some dendrites continuously bend by 1.7° over a solidification distance of 25 mm.
Highlights
Single crystal Ni-based superalloys (SXs) are high-temperature materials which can withstand mechanical loads at temperatures above 1000 ◦ C
We investigate the evolution of crystal mosaicity in Ni-based superalloy single crystals during seeded
Crystal mosaicity represents an inherent feature of dendritic single crystal superalloy microstructures obtained: related to elementary stochastic processes which govern solidification
Summary
Single crystal Ni-based superalloys (SXs) are high-temperature materials which can withstand mechanical loads at temperatures above 1000 ◦ C. They are used to manufacture first stage blades in gas turbines for energy production and aero engines [1,2,3]. Creep research throughout the last few decades has shown that mechanical high-temperature properties strongly depend on microstructure [2,4,5,6,7]. It is well known that the production of high-quality. Careful control of solidification and heat treatment conditions is required to understand how dendritic and interdendritic regions form, and how the well-known γ/γ’ microstructure evolves [11,15,16,17,18,19,20]
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