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采用OM,SEM和TEM及其HAADF模式下的元素面扫描,研究了一种铸造镍基高温合金长期时效期间初生MC碳化物的分解反应过程、形式及机理.结果表明,在长期时效过程中,初生MC分解反应分为3个阶段:MC+g→M_6C+γ′,MC+γ→M_6C+M_(23)C_6+γ′和MC+γ→M_6C+M_(23)C_6+h.HAADF模式下对分解区域进行元素面扫描,浓度梯度显示初生MC分解实际上是元素在初生MC和g基体之间的互扩散交流过程,分解产物中的C主要来源于初生MC,Ni,Al和Cr来源于g基体,而Ti,W和Mo不仅源于g基体也源于初生MC.合金具有较高的Ti+Nb+Ta+Hf原子分数和(Ti+Nb+Ta+Hf)/Al原子比是初生MC分解过程中析出h相的必要条件,而其析出的数量与初生MC的分解程度有关,分解程度越高,析出数量越大.
The decomposition process, form and mechanism of primary MC carbides during the long-term aging of a foundry nickel-base superalloy were investigated by OM, SEM, TEM and HAADF mode scanning. The results show that during the long-term aging process, The primary MC decomposition reaction is divided into three stages: MC + g → M_6C + γ ’, MC + γ → M_6C + M_ (23) C_6 + γ’ and MC + γ → M_6C + M_ (23) C_6 + Under the element plane scanning, the concentration gradient shows that the primary MC decomposition is actually the intercommunication process of the elements between the primary MC and the matrix g. The C in the decomposition products mainly comes from the primary MC, Ni, Al and Cr sources In the g matrix, Ti, W and Mo are not only derived from the g matrix but also from the primary MC. The alloys have higher Ti + Nb + Ta + Hf atomic fractions and (Ti + Nb + Ta + Hf) Necessary conditions for precipitation of h phase during primary MC decomposition are related to the amount of primary MC decomposition. The higher the degree of decomposition, the greater the amount of precipitation.