SRR99镍基单晶高温合金在落管微重力环境下的枝晶生长行为研究

Dendrite Growth of SRR99 Nickel-Base Single Crystal Superalloy under Microgravity Condition Formed by Long Drop Tube

利用50m长落管研究了SRR99镍基单晶高温合金在微重力与重力环境下的枝晶生长行为。采用金相显微镜观察了试样在微重力(微重力试样)和重力(重力试样)下凝固组织的差异,并利用图像分析软件测量了枝晶的一次臂和二次臂的长度及间距。结果表明,微重力试样在下落过程中从未熔部分外延生长的最大长度约为1.7mm,重力试样的最大长度为1.9mm。微重力试样的一次枝晶干粗大,平均间距约为80μm,而重力试样中存在较多的细小一次枝晶干,一次臂平均间距约为71μm。一次枝晶平均间距在微重力环境下增大20%。微重力试样的二次臂长度较长,且在20～160μm的整个长度范围内较均匀分布;重力试样二次臂长度较短,且集中分布在20～80μm区间内。微重力试样和重力试样的二次枝晶臂平均间距相同,均为17μm。

The dendrite growth of SRR99 nickel-base single crystal superalloy under microgravity and normal gravity environment was investigated by using 50 m long drop tube.The differences of solidification microstructures between the samples solidified under microgravity（μg sample） and normal gravity（1g sample） were observed using optical microscope（OM）.Furthermore,the lengths and spacings of the primary and secondary dendrite arms were measured with the aid of image analysis software.The results showed that,the maximum epitaxial growth distance from unmelted part for the μg sample was about 1.7 mm,while it was about 1.9 mm for the 1g sample.The primary dendrite trunks of the μg sample was coarse,and the average spacing between them was about 80 μm;while,there were a large number of fine primary dendrite arms in the 1g sample,and the average primary arm spacing was about 71 μm.The average primary arm spacing increased about 20% under microgravity.Moreover,in the μg sample the secondary dendrite arms were longer and scattered in the range of 20~160 μm,but in the 1g sample the secondary dendrite arms were shorter and mainly focused in the range of 20~80 μm.In addition,the average secondary arm spacings of the μg sample and the 1g sample were both 17 μm.