Abstract
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 Gd and Vd distribute non-symmetrically, different from Gn and Vn. The Gd is lower while the Vd is higher in the region near the boundary of [1?00] and [01?0] dendrite zones. As a result, the Gd/Vd in this region is lower. The Gd/Vd 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 Gd/Vd 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.
NSTL
Elsevier