摘要
航空发动机涡轮叶片内部的复杂气膜冷却系统使得叶片叶身部位壁厚越来越薄,导致其显微组织和力学性能与传统模拟材料(如实心标准试棒)存在明显差异。本工作利用铸造成型的K465合金空心管材模拟空心叶片叶身的显微组织,对其进行900~1050℃、300~1000 h热暴露处理,并测试热暴露前后在975℃、225 MPa条件下的持久性能。利用OM、SEM、TEM和XRD观察和表征热暴露前后的显微组织,利用物理化学相分析的方法测量析出相的化学成分,研究热暴露过程中显微组织的演变规律及其对持久性能的影响。结果表明:在900~1050℃热暴露过程中,K465合金管材中主要发生γ’相的溶解和粗化连接、MC型碳化物的分解以及晶界γ’膜的宽化;随着热暴露温度的升高和时间的延长,γ’相、碳化物和晶界的退化程度逐渐加剧,导致合金的持久寿命逐步降低。与已有文献报道的900℃热暴露时标准试棒中μ相大量析出的现象不同,管材中并未析出μ相;1000和1050℃热暴露后,管材和棒材组织退化程度接近。900℃热暴露时,冷却速率导致的薄壁效应对K465合金的显微组织和持久性能影响显著;而1000和1050℃热暴露时,薄壁效应不明显。本工作的研究成果为等轴晶铸造高温合金涡轮叶片的生产和服役损伤评价提供了参考依据。
The designed service temperature of turbine blades is rising with the increasing thrust of aircraft engines.A film cooling system is one of the promising ways to improve the service temperature of turbine blades.However,such a complex film cooling system can reduce the thickness of the blade airfoil and lead to obvious local differences in microstructure;these differences are caused by solidification and mechanical resistance between the blade airfoil and alloys such as standard solid bars.In this study,a thin-walled tube manufactured by the casting process was used to simulate the microstructure of the hollow blade airfoil.The tube was thermally exposed at a temperature range of 900~1050℃for 300~1000 h,and the corresponding stress rupture properties under 975℃and 225 MPa(pressure)were examined.The microstructures were investigated using OM,SEM,TEM,and XRD,and the chemical compositions of the precipitates formed were measured through physicochemical phase analysis before and after the thermal exposure.Through this analysis,the relationship between microstructural degradation and stress rupture properties was revealed.The results indicated that dissolution and coarsening ofγ’precipitates,degeneration of MC carbides,and broadening of theγ’film along the grain boundaries occurred in the K465 alloy tube during thermal exposure between 900℃and 1050℃.With increasing exposure temperatures and prolonged thermal exposure time,the degree of degradation of theγ’precipitates,carbides,and grain boundaries gradually increased.This resulted in a gradual reduction in stress rupture lives.Unlike the phenomenon observed in our previous study in which a large amount ofμphase precipitated in the solid bar following thermal exposure at 900℃;in the present study,theμphase did not form in the tube.However,the degrees of microstructural degradation in the tube and bar were similar after the thermal exposure at 1000 and 1050℃.The stress rupture lives of the tube were significantly higher than those of the bar after the thermal exposure at 900℃,whereas their stress rupture lives were similar after the thermal exposure at 1000 and 1050℃.The thin-wall effect caused by the cooling rate on the microstructure and the corresponding stress rupture property of K465 alloy was obvious at 900℃,whereas it was negligible at 1000 and 1050℃.These results provided guidance for the manufacturing and evaluation of microstructural degradation of turbine blades made of conventionally cast polycrystalline superalloys.
作者
郭小童
郑为为
李龙飞
冯强
GUO Xiaotong;ZHENG Weiwei;LI Longfei;FENG Qiang(State Key Laboratory for Advanced Metals and Materials,University of Science and Technology Beijing,Beijing 100083,China;China Electronic Product Reliability and Environmental Testing Research Institute,Guangzhou 510610,China)
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2020年第12期1654-1666,共13页
Acta Metallurgica Sinica
基金
国家重点研发计划项目No.2016YFB0701403
国家自然科学基金项目Nos.51631008和91860201。
关键词
K465合金
涡轮叶片
薄壁效应
显微组织
持久性能
K465 alloy
turbine blade
thin-wall effect
microstructure
stress rupture property
