Ru对含Re单晶高温合金组织和凝固特性的影响

IMR OpenIR

	Ru对含Re单晶高温合金组织和凝固特性的影响
	孙国才
学位类型	硕士
导师	孙晓峰 ; 周亦胄
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	单晶高温合金钌定向凝固凝固特性组织稳定性 Single Crystal Superalloy Ru Directional Solidification Solidification Characteristics Microstructural Stability
摘要	"本文采用光学显微镜（OM）、扫描电镜（SEM）、差热分析法（DTA）和电子探针（EPMA）等方法研究了Ru对含Re单晶高温合金的凝固组织、γ′相形态与长期时效过程中组织稳定性的影响。通过显微硬度和纳米压痕对三种Ru含量不同的合金进行了硬度测试。并对籽晶法生长单晶过程中杂晶产生的原因进行了详细分析。研究结果表明：以3mm/min的抽拉速率进行定向凝固获得的单晶样品，其铸态组织都是枝晶组织。随着Ru含量的增加，合金的液相线变化不大，固相线明显降低，初熔温度降低，实际凝固范围增大，凝固组织的一次枝晶间距减小，γ/γ′共晶含量增加。加入Ru后，合金的热处理变得困难，固溶效果变差。对于成分相同的合金，晶体学取向偏离<001>越大，硬度越大。在晶体学取向基本一致的情况下，显微硬度随Ru含量增加而提高。加入Ru后，γ′相的硬度有所提高，当Ru含量超过某一值后，硬度基本不再改变。对比Ru对显微硬度和γ′相硬度的影响，可以看出Ru同时强化合金γ和γ′相。在1100℃长期时效过程中，铸态样品中很容易析出TCP相，且枝晶间是TCP相优先形核的位置，Ru的加入明显抑制了铸态样品中TCP相的形核和长大。但是，这种抑制作用在热处理态样品中并没有体现出来，三种热处理态合金析出TCP相的数量和尺寸没有明显的区别。Cr元素应该是造成这种差异的主要原因。铸态样品枝晶间Cr含量少，Ru能够抑制TCP相的析出。固溶处理后，Cr均匀分布于合金中，与Ru交互作用，减弱了Ru的抑制作用。用籽晶法生长单晶时，籽晶的密度和浇注合金熔体的密度差对杂晶的产生有重要影响。当熔体密度小于籽晶密度时，籽晶回熔区内不产生杂晶；当熔体密度大于籽晶密度时，回熔区内产生大量杂晶。对流引起的局部成分过冷是导致杂晶形核的主要原因。采用高密度，高熔点的合金做籽晶，能够提高籽晶法生长单晶的成功率。"
其他摘要	"In this dissertation, single crystal superalloys with different contents of Ru addition (0, 1.5, 3.0wt.%) were employed to study the influence of Ru addition on a Re-bearing alloy. Optical microscopy (OM), scanning electron microscopy (SEM), differential thermal analysis (DTA) and electron probe microanalysis (EPMA) method were used to investigate the as-cast microstructure, structural evolution during heat treatment and long term aging. The hardness of three alloys was analyzed by micro-hardness and nano-indentation hardness test. The mechanism of stray grain formation in the seed technology was investigated. All the three alloys with different Ru content were directionally solidified at a withdrawal rate of 3mm/min and the microstructures of the alloys were dendritic structures. With the increase of Ru content, the primary dendrite arm spacing of the solidification structure decreased and the γ/γ′ eutectic content increased. Liquidus of alloys had little change, but the solidus reduced with the increase of Ru. The initial melting temperature was reduced and the actual solidification range enlarged. The alloys with Ru additions were difficult to homogenize by heat treatment. As the <001> orientation was deviated from the sample axis, the hardness became greater for a certain alloy. As the <001> orientations of three alloys were similar, the micro hardness increased with the increase of Ru content. The hardness of γ′ increased with the increase of Ru content. However, when the Ru content exceeded a certain value, the hardness of γ′ reached a peak and then kept the same. Ru suppressed the precipitation of TCP phases in the as-cast sample. TCP phase was easier to precipitate in the interdendritic than in the dendrite trunk. After heat treatment, such suppressing effect on the precipitation of TCP phases was reduced. Cr should be the main reason for this difference. When a seed with smaller density was used to control the orientation of an alloy charge with greater density, stray grains formed in the melt-back region of the seed. In contrast, stray grains in the melt-back region can be avoided as a seed with greater density was used to control the orientation of an alloy charge with smaller density. The local composition undercooling induced by melt convection was the reason causing stray grains and the formation of stray grains followed the mechanism of nucleation and growth. It is better to use the seed with high density and high melting point to aviod the stray grains."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64528
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	孙国才. Ru对含Re单晶高温合金组织和凝固特性的影响[D]. 北京. 中国科学院金属研究所,2012.