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Title:: The influence of carbon contents on the microstructure and tensile preperties of a Ni-base single crystal superalloy

Author(s):: Tao Yan; Li Yongmei; Tan Zihao; Cao Liang; Wang Xinguang; 1.School of Mechanical Engineering，Liaoning Petrochemical University，Fushun 113001，China 2. Chinese Academy of Science，Institute of Metal and Research，Shenyang 110006，China

Keywords:: Ni-based single-crystalsuperalloy; turbine blades; tensile strength; carbides; directional solidification

摘要:: 研究了C元素對一種低成本第二代鎳基單晶高溫合金微觀組織與拉伸變形行為的影響。結果表明，隨C含量增加，鑄態合金枝晶間的共晶組織逐漸消失，MC型碳化物含量升高，而經標準熱處理后，不同C含量合金的γ+γ′兩相組織無明顯變化。當拉伸溫度為800℃和1100℃時，C含量增加均導致合金的拉伸強度與塑性降低。合金在拉伸變形中析出的顆粒狀M6C型碳化物與γ′相為共格析出關系，有助于阻礙超位錯切割γ′相，然而枝晶間富集Ta、W元素的MC型碳化物將消耗大量難熔元素，進而削弱基體固溶強化效果，導致合金拉伸強度降低；枝晶間骨架狀MC型碳化物促進800℃拉伸時合金沿碳化物的解理斷裂以及加速1100℃拉伸時顯微裂紋萌生與宏觀裂紋擴展則是合金塑性降低的主要原因。

Abstract:: The effect of carbon content on the microstructure and tensile properties, as well as the deformation behavior of a low-cost second-generation Ni-based single-crystal superalloy, was investigated. The results showed that the area fraction of eutectic microstructure in the interdendritic region decreased with the increase in carbon content, while the content of MC-type carbides increased correspondingly. After standard heat treatment, there was no significant difference in γ + γ′ microstructure for alloys with different carbon contents. For tensile properties, the increase of carbon content led to a decrease in tensile strength and plasticity at both 800 °C and 1100 °C. The granular M6C-type carbides coherently precipitation from the γ′ phase during the tensile deformation, which helps to hinder superdislocation cutting into the γ′ phase, but the Ta- and W-rich MC carbides located in the dendrites will consume a large number of refractory elements, which substantially weaken the solid solution strengthening effect of γ matrix, resulting in a reduction of tensile strength. The interdendritic skeleton-like MC carbides will promote the cleavage fracture along the carbides, and accelerate the micro-crack initiation and macro-crack extension, which are considered as the main reason for the decrease in the alloy’s plasticity at 800℃and 1100℃ respectively.