镍基高温合金定向凝固过程中的汇聚型双晶竞争生长
发布人：上海艾荔艾合金股份有限公司www.shailiai.cn
更新时间：2016-05-10
采用籽晶法控制晶体取向, 研究了不同抽拉速率下镍基高温合金汇聚型双晶的竞争生长.
镍基高温合金定向凝固过程中的汇聚型双晶竞争生长CONVERGING COMPETITIVE GROWTH IN BI-CRYSTAL OF Ni-BASED SUPERALLOY DURING DIRECTIONAL SOLIDIFICATION采用籽晶法控制晶体取向, 研究了不同抽拉速率下镍基高温合金汇聚型双晶的竞争生长. 结果表明, 低抽拉速率下, 非择优枝晶能够穿插进入择优枝晶间的液相通道, 抑制择优枝晶的生长, 使晶界向择优晶粒方向偏移. 高抽拉速率下, 非择优枝晶几乎全部被晶界择优枝晶阻挡, 晶界与择优枝晶干平行. 非择优枝晶进入择优枝晶间的液相通道使择优枝晶萎缩消失是非择优晶粒淘汰择优晶粒的主要因素, 并以此提出了抽拉速率对竞争生长的影响机制.
Ni-based single crystal superalloy has been widely used in turbine blades owing to its excellent high temperature mechanical behavior. In order to completely exhibitits high temperature mechanical properties, the seed method has been used to produce Ni-based single crystal components for [001] orientation paralleling to main force direction. Stray crystals, which unexpectedly nucleate in the melt-back region, will competitive grow with seed during directional solidification. It is important to profoundly understand the mechanism of competitive growth for finding ways to overgrow stray crystal during producing Ni-based single crystal components. However, within the published research there are conflicting views on the mechanism of competitive growth at converging case. Using seed technology, bi-crystal converging competitive growth was investigated with different pulling rates. A series of polishing and imaging quenching interface were done for the positional relationship of dendrites near grain boundary in 3D reference. It was found that solidification microstructures were different with different crystal orientations. Unfavorable orientated dendrite tilting to heat flux restrained favorable orientated dendrite aligning to heat flux mainly thought inserting into the favorable orientated dendrites channel, and this resulted in unfavorable orientated dendrite growth over growing favorable orientated dendrite at low pulling rate. However, at high pulling rate the unfavorable dendrites mainly blocked by grain boundary favorable dendrite and the grain boundary grew paralleling to favorable orientated dendrite core. Favorable orientated dendrite depressing and vanishing, owning to that unfavorable orientated dendrite inserting into favorable orientated dendrites channel result in adjusting primary dendrite spacing, is the main factor to favorable orientated grain overgrew by unfavorable orientated grain. According to above mechanism, effect of pulling rate on competitive growth at converging case was interpreted. This could broaden our understanding of competitive growth at converging case in 3D reference.
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