On the Deformation of Dendrites During Directional Solidification of a Nickel-Based Superalloy

Abstract

Synchrotron X-ray imaging has been used to examine in situ the deformation of dendrites that takes place during the solidification of a nickel-based superalloy. By combining absorption and diffraction contrast imaging, deformation events could be classified by their localization and permanence. In particular, a deformation mechanism arising from thermal contraction in a temperature gradient was elucidated through digital image correlation. It was concluded that this mechanism may explain the small misorientations typically observed in single crystal castings.

Impact of solute flow during directional solidification of a Ni-based alloy: In-situ and real-time X-radiography

“…Tandjaoui et al [34] combined synchrotron radiography and diffraction topography to study faceted silicon growth. First observations of dendrite growth and dendrite arm bending were reported in a Ni-based CMSX-4 superalloy by Aveson et al [35,36]. It is worth noting that the dendritic pattern in Ni, Co and Fe-based alloys was recently observed by Azeem et al by synchrotron tomography [37].…”

“…This large distance induced phase contrast in the images [45], especially at the edges between the solid and the liquid regions. Phase contrast was used to facilitate the visualization of the microstructure, since previous investigations have shown that a low absorption contrast is expected for this alloy [35,36].…”

Heterogeneity of the Dendrite Array Created in the Root of Cored SX Turbine Blades during Initial Stage of Crystallization

“…The growth of the dendrite is often limited and changed by the mould walls, resulting in the bending of the dendrites [ 10 , 12 , 27 , 28 , 29 ]. The bending is observed in the areas localized near the mould surface or in the areas where the step change geometry of cast occurs, for example in the root near the continuer-root connection.…”

2D single crystal Bragg-dip mapping by time-of-flight energy-resolved neutron imaging on IMAT@ISIS

“…However, the manufacture of single crystals of high quality and of practical size is no trivial task. All single crystals used in aerospace applications share the phenomenon of mosaicity 5 , whereby individual crystalline regions within the as-cast microstructure are slightly misorientated in respect to one another. Typically, the range of bulk (001) crystallographic plane misorientation in respect to the loading direction is between 0°–15°, with above 9° being especially detrimental to the mechanical properties 6 .…”

“…Axial misorientations are undesirable, as they increase cyclic stresses during thermal cycling and degrade the high temperature performance of the material 7 . The origin of single crystal mosaicity is thought to be related to plastic deformation during solidification 4 , 5 . However, owing to the difficulties in experimental observation, the mechanism behind mosaicity is poorly understood 8 .…”