Stray grain formation associated with constitutional supercooling during plasma re-melting of Ni-based single crystal superalloy based on temperature field simulation and actual substrate orientation

The stray grains formation associated with constitutional supercooling during plasma re-melting of Ni-based single crystal superalloy is investigated based on the temperature field simulation and actual substrate orientation. The calculated melting pools and dendrite growth directions consist with the experimental results. The G_d and V_d distribute non-symmetrically, different from G_n and V_n. The G_d is lower while the V_d is higher in the region near the boundary of [1−00] and [01−0] dendrite zones. As a result, the G_d/V_d in this region is lower. The G_d/V_d evaluates the degree of constitutional supercooling and the threshold value 1.3 × 10⁷ K s/m² is obtained for the equiaxed stray grains formation. The equiaxed stray grains forming in the region with G_d/V_d lower than the threshold value are intimately associated with constitutional supercooling, while the stray grains generated in the region near the boundary of melting pool closest to the substrate are independent of that. The origin of stray grains outside these two regions is probably same as that in the region near the boundary of melting pool closest to the substrate. Meanwhile, the strip-shaped stray grains develop due to the active<100>direction close to the direction of maximum temperature gradient.