鑄造鎳基高溫合金中初生MC碳化物的退化過程和機(jī)理
發(fā)布人：上海艾荔艾合金股份有限公司www.shailiai.cn
更新時(shí)間：2016-01-25
采用OM, SEM和TEM及其HAADF模式下的元素面掃描, 研究了一種鑄造鎳基高溫合金長期時(shí)效期間初生MC碳化物的分解反應(yīng)過程、形式及機(jī)理．
鑄造鎳基高溫合金中初生MC碳化物的退化過程和機(jī)理DEGENERATION PROCESS AND MECHANISM OF PRIMARY MC?CARBIDES IN A CAST Ni-BASED SUPERALLOY采用OM, SEM和TEM及其HAADF模式下的元素面掃描, 研究了一種鑄造鎳基高溫合金長期時(shí)效期間初生MC碳化物的分解反應(yīng)過程、形式及機(jī)理．結(jié)果表明, 在長期時(shí)效過程中, 初生 MC 分解反應(yīng)分為 3 段: MC+γ→ M6C + γ′, MC+γ→M6C + M23C6+ γ′和 MC+ γ→M6C + M23C6+?η．HAADF 模式下對分解區(qū)域進(jìn)行元素面掃描, 濃度梯度顯示初生 MC 分解實(shí)際上是元素在初生 MC 和 γ 基體之間的互擴(kuò)散交流過程, 分解產(chǎn)物中的C 主要來源于初生 MC, Ni,Al 和 Cr 來源于 γ 基體, 而 Ti, W 和 Mo 不僅源于 γ 基體也源于初生 MC. 合金具有較高的 Ti+Nb+Ta+Hf 原子分?jǐn)?shù)和(Ti+Nb+Ta+Hf)/Al 原子比是初生 MC 分解過程中析出 η 相的必要條件, 而其析出的數(shù)量與初生 MC 的分解程度有關(guān), 分解程度越高, 析出數(shù)量越大.?
Primary MC carbide is one of the most important phases in cast Ni-based superalloys. During?long-term thermal exposure, the primary MC carbide is not stable and tends to degenerate, exhibiting various?degeneration reactions, such as MC+γ → M23C6+γ′ and MC+γ → M6C+η. It is widely known that the degeneration?of primary MC carbide has obvious influence on the microstructural evolutions of superalloys, including?coarsening of γ' phase, coarsening of grain boundaries and precipitation of topologically close-packed (TCP)?phase, and consequently the mechanical properties of alloys. Much research work has focused on the degeneration?mechanism of primary MC carbide during long-term thermal exposure, however, it is not very clear so far. In this?work, a cast Ni-based superalloy is fabricated and thermally exposed at 850 ℃ for 1000~10000 h in order to?study the degeneration mechanism of primary MC carbide. The degeneration of primaryMC carbide is observed?by OM, SEM and TEM. High-angle annular dark field (HAADF) mode of TEM is used to clearly observe the?degeneration of primary MC carbide and the element distribution in the degeneration areas. The results show that?the primary MC degeneration is an inter-diffusion process which occurs between the primary carbide and the γ?matrix. During the degeneration, C is released from the primary carbide, Ni, Al and Cr are provided by the γ?matrix, while Ti, W and Mo come from both primary MC and γ matrix. The precipitation of η phase is determined?by the atomic fraction of Ti+Nb+Ta+Hf and atomic ration of (Ti+Nb+Ta+Hf)/Al and its amount is affected by the?degeneration degree of primary MC carbide. The higher the degeneration degree, the largerthe tendency for the?precipitation of the η phase.?
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