薄板试样定向凝固枝晶竞争生长

The competitive growth of dendrite arrays in the directional growth of a thin sample

摘要:

深入理解高温合金定向凝固杂晶演化具有重要的科学和工程意义,其中枝晶竞争生长是揭示晶界演化与淘汰的关键环节。定向凝固双晶竞争生长的实验研究证实了传统尖端过冷度理论的局限性,定量相场模拟的研究获得了大量统计规律,促进了人们对定向凝固双晶竞争生长的理解。本文在薄板状试样的定向凝固过程中,同时获得了大量的不同取向的枝晶竞争生长,通过拼接金相显微组织同时获得多个晶界的取向演化规律。在多次实验的基础上最终获得实验统计结果,与相场模拟结果基本一致。后续采用商业软件ProCAST的CAFE计算晶粒定向竞争生长晶界演化,统计结果发现与实验结果存在偏差。本次实验研究检验了薄板状试样枝晶竞争生长的统计规律,对认识高温合金定向凝固过程中晶界取向的演化具有重要的意义。

Abstract:

The high performance blade has been the widely applied to increase the efficiency of the aircraft engine, and its fabrication has been well developed. However, the appearance of misoriented grains always decrease of production yield. Competitive growth of dendrite arrays with different orientation in directional solidification is an important phenomenon for the fabrication of single crystal blade. The question has caught attention for many years. The tip undercooling has been the only criterion for the elimination of unrefereed dendritic grains for a long time and is implanted in commercial software ProCAST to simulate the grain growth. However, the experimental bicrystal growth in directional solidification identified the drawback of the tip undercooling criterion. Quantitative phase field simulations showed more details of the bicrystal competitive growth. The grain boundary evolution has been one of the key indicators for competitive growth. The previous tip undercooling criterion could not predict the grain boundary evolution. The huge phase field simulations reveal the statistic evolution rule of the grain boundary direction. In this paper, we proposed a sheet sample with multiple bycrystals configurations. The microstructures were observed in a stitching picture. The competitive growth and the grain boundary selection of dozens of biocrystals have been summarized within several samples. The statistical results agree with the phase field simulation. However, the CAFE simulation results from the ProCAST can not predict the grain boundary evolution. The method proposed here can be applied to investigate the competitive growth with a high throughput way. The results are helpful to understand the unoriented grains in fabrication of single crystal blade.