Influence of withdrawal rate on microstructures of blade shaped directionally solidified DZ125 superalloy

As a precipitation hardened unidirectionally solidified Ni-based superalloy, DZ125 has been widely applied as structure materials in advanced aeroengine for gas turbine blades and vanes. In present, the paper on the influence of solidification parameters on microstructures have been largely published, but unfortunately, few of them have focused on giving a direct comparison between directional solidification characteristics in liquid metal cooling (LMC) and high rate solidification (HRS). In this paper, the influences of processing parameters on microstructures of blade shaped castings prepared both by LMC and HRS technique were studied. The results show that the dendrite structure and γ' precipitate in castings prepared by the same method are refined with elevated withdrawal rate; in the same solidification conditions, the LMC castings have finer dendrite structure and γ' precipitate than HRS, the larger the disparity between primary dendrite arm spacings in LMC and HRS castings, the thicker wall thickness is or the higher the withdrawal rate is. It is found that higher temperature gradient in front of solid/liquid interface can be obtained by LMC, and its variation with elevated withdrawal rate, however, is smaller than that by HRS. The γ+γ' eutectic fraction is lower for LMC castings than HRS castings except for withdrawal rate of 70 μm/s, only at which more severe segregation than HRS's occurs. Chinese script type MC flakes between dendrites in HRS castings are larger at withdrawal rate of 110 μm/s.