On the Origin of Mosaicity in Directionally Solidified Ni-Base Superalloys
34 Pages Posted: 27 May 2021 Publication Status: Accepted
Understanding the formation of secondary grains within single crystal alloys is of central importance to the aerospace industry, where components are directionally solidified in an axial thermal gradient. Post-mortem advanced microscopy characterisation techniques are employed to deduce the dendrite tip kinetics from transverse sections of a single crystal turbine blade orthogonal to the growth direction. As a result, it has been possible to highlight the role of isotherm curvature in inducing lateral macro-segregation parallel to a growing solidification front. Using crystallographic data from time-of-flight energy-resolved neutron imaging and novel Bragg-dip post processing, it is established that lateral macro-segregation induces mosaicity within single crystals, where fastest growing dendrites demonstrate greater deviation of <001> from the growth axis. Further, dendrites are found to grow in rows defined by the  and  crystallographic directions. In light of these findings, the origins of mosaicity are discussed.
Keywords: Directional solidification; Dendrite growth; Mosaicity; Time-of-flight energy-resolved neutron imaging; Crystal orientation
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