Influence of Secondary Dendrite Orientation on the Evolution of Misorientation in the Platform Region of Single Crystal Superalloy Turbine Blades

In the castings of Ni-base single crystal superalloys, misorientation defects are detrimental to mechanical performance at high temperatures. In this study, combined seeding-grain selection technique is used to study the effects of secondary dendrite orientation and withdrawal rate on dendrite growth and the associated evolution of misorientation in the platform region of single crystal superalloy turbine blades. It is observed that the rapid growth of dendrite arms near the platform edge induces a long secondary dendrite arm and the convergent boundary of dendrite arms (CBDA), and the misorientation angle along the CBDA monotonically increases. Furthermore, with the decrease in misorientation angle of the <001> SX orientation from the platform edge, the growth trace of dendrite arms required to cover CBDA increases, and the long secondary dendrite arm becomes more vulnerable to the contraction stress around platform edge, which leads to increased misorientation angle.