摘要
采用2种不同平台尺寸的模型试样,对镍基单晶高温合金定向凝固过程中的杂晶形成倾向性进行量化研究,对不同合金的杂晶形成倾向性及杂晶在平台内的形成机制进行探索.结果表明,平台长度越长、高度越小时,杂晶越容易在平台内形核并长大;在第一、二、三代镍基单晶高温合金SRR99,DD5和DD90中,第一代合金的杂晶形成倾向性最弱,第二代次之,第三代最强;凝固时平台尖角处的过冷度大于平台内部的过冷度,且随着平台长度增加和平台高度减小,平台尖角处的过冷度增大,当平台尖角处的过冷度达到临界形核过冷度时,杂晶在平台尖角处形核并快速长大进入平台内部.
Ni-based single crystal （SC） superalloys are preferential materials for manufacturing blades and vanes of gas turbines, due to their superior mechanical properties resulting from the absence of grain boundaries. However, as the component geometry becomes more complex and the content of refractory elements increases gradually, the forming frequency of stray grains increases significantly leading to the component rejection during directional solidification （DS） of Ni-based SC superalloys. This becomes now one of the major problems encountered during DS and single crystal growth. In the interest of saving the actual manufacturing cost, therefore, the alloys with weak tendency of stray grain formation should be first applied. However, there are still no effective method to quantitatively evaluate the stray grain formation ability of a certain Ni based SC superalloy. Thus, it is quite necessary to design a new method to do so. In this study, the two model samples with different platform geometries are first designed to investigate quantitatively the tendency of stray grain formation, used to summarize the ability of stray grain formation of different alloys and reveal the mechanism of stray grain formation within platforms. The first model sample with the same platform height but length increasing by degrees along the solidification direction, is used to quantitatively characterize the stray grain formation tendency of different superalloys by using its platform length of stray formation occurring first in time. The second model sample with the same platform length but height decreasing by degrees along the solidification direction, is used to quantitatively characterize this tendency by using the platform height of stray formation occurring first in time. The experimental results show that it is easier for stray grains to nucleate and length increasing or platform height reducing. grow within the platform region with either platform The stray grain formation within outside platform isprior to that within inside platform. This tendencies for the first, second and third generation SC superalloys, however, are different： the first is the weakest, following by tile second, and the third is tile strongest. Furthermore, the formation of stray grains is dominated by undercooling. The melt undereooling at platform edges is larger than within platform insides and increases gradually with either platform length lengthening or platform height reducing. When the undercooling at platform edges exceeds the critical nucleation undercooling, the stray grain would be able to nucleate and overgrow quickly into the platform insides.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第10期1229-1236,共8页
Acta Metallurgica Sinica
基金
国家自然科学基金项目U1037601和50931004
国家重点基础研究发展计划项目2010CB631206
中国科学院"百人计划"项目资助~~
关键词
镍基高温合金
定向凝固
杂晶
过冷度
Ni-based superalloy, directional solidification, stray grain, undercooling
