DZ22B高温合金相变过程及凝固组织转变研究

Phase Transformation Process and Solidification Microstructure Transition of DZ22B Superalloy

采用差示扫描量热仪对DZ22B高温合金凝固过程及相变行为进行描述,对比分析了不同冷速影响下合金二次枝晶间距、碳化物的转变行为。随冷速提高,组织显著细化,二次枝晶间距由冷速5 K/min时125μm持续下降到80 K/min时37μm。枝晶组织的细化可以减弱凝固后期残余液相中溶质偏析,碳化物形貌由连续网状向不连续条块状发生转变。大冷速条件下枝晶间流动管道的变窄及凝固时间的缩短共同抑制Hf元素的趋肤效应,有利于富Hf碳化物相形成。

Solidification process and phase transformation behavior of DZ22 B superalloys were analyzed by differential scanning calorimetry methods. After comparison of solidification microstructure with different cooling rates, the transition regularity of secondary dendrite spacing and carbidesphase were explored. Obvious dendrite refinement occurred with the increase of cooling rate, and the average secondary dendrite spacing decreased from125 μm at the cooling rate of 5 K/min to 37 μm at the cooling rate of 80 K/min. The refinement of dendrite morphology was advantageous for the reduction of solute micro-segregation at later solidification stage, which generated the morphology change of carbides from continuous net shape to dispersive strips or blocks. Moreover,the skin effect of Hf element can be suppressed for higher cooling rate because of the thinner flowing channel and shorter solidification period, which can facilitate the formation of Hf-rich carbides.