Structure Refinement by a Liquid Metal Cooling Solidification Process for Single-Crystal Nickel-Base Superalloys
Structure Refinement by a Liquid Metal Cooling Solidification Process for Single-Crystal Nickel-Base Superalloys
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DOI：
10.1007/s11661-011-0920-8
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发表时间：
2012-03-01
影响因子：
2.8
通讯作者：
Pollock, T. M.
中科院分区：
文献类型：
--
作者：
Brundidge, C. L.;Vandrasek, D.;Pollock, T. M.
为了评价一种新型高热梯度凝固工艺的优点，在一定冷却速率范围内对镍基高温合金单晶进行了定向凝固。采用液态金属强化冷却工艺对圆柱形棒材进行了凝固实验。这种高梯度铸造工艺的结构细化程度，微观结构的变化，和孔隙率分布进行了评估。使用锡基液态金属冷却（LMC）技术以8.4和21.2 mm/min之间的速率和使用常规布里奇曼工艺以3.4 mm/min的速率固化1.6 cm直径的圆柱形棒。LMC过程产生了平均一次枝晶臂间距（PDAS）和二次枝晶臂间距（SDAS）的值低至164和25 μ m，分别为酒吧的几何形状评价细化的微观结构。一个最佳的中间撤回速度为12.7毫米/分钟产生高达50和60%的细化PDAS和SDAS，分别。进一步提高抽拉速度会产生更小的SDAS和孔径，但会产生不希望的晶界和过度的二次枝晶臂生长。Voronoi镶嵌法被用来检查的极端的枝晶臂间距相比，平均测量值，堆积的枝晶，和孔隙度的大小和位置与枝晶结构的相关性。一个简单的表达式预测的最大孔径。
Single crystals of a nickel-base superalloy were directionally solidified (DS) over a range of cooling rates to evaluate the benefits of a new high thermal gradient solidification process. Solidification experiments were conducted on cylindrical bars with a liquid-metal-enhanced cooling process. This higher gradient casting process was evaluated for the degree of structure refinement, microstructural variability, and porosity distributions. Cylindrical bars of 1.6-cm diameter were solidified at rates between 8.4 and 21.2 mm/min using a tin-based, liquid metal cooling (LMC) technique and at a rate of 3.4 mm/min with a conventional Bridgman process. The LMC process produced a refined microstructure with average primary dendrite arm spacing (PDAS) and secondary dendrite arm spacing (SDAS) values as low as 164 and 25 mu m, respectively, for the bar geometry evaluated. An optimum intermediate withdrawal velocity of 12.7 mm/min produced up to a 50 and 60 pct refinement in PDAS and SDAS, respectively. Further increases in withdrawal velocity produced smaller SDAS and pore sizes, but undesirable grain boundaries and excessive secondary dendrite arm growth. Voronoi tessellation methods were used to examine the extremes of the dendrite arm spacings in comparison to the average measurements, the packing of dendrites, and the correlation of porosity size and location with the dendrite structure. A simple expression for prediction of the maximum pore size is developed.