定向鎳基高溫合金DZ466表面CoAl涂層氧化行為研究

定向鎳基高溫合金DZ466表面CoAl涂層氧化行為研究Oxidation and Microstructure Evolution of CoAl Coating onDirectionally Solidified Ni-Based Superalloys DZ466

采用低壓化學(xué)氣相沉積法(LP-CVD)在定向凝固鎳基高溫合金 DZ466 表面制備 CoAl 涂層，通過 900 ℃下約 5000 h 恒溫?zé)岜┞秾嶒灒芯苛?DZ466 合金及其表面 CoAl 涂層的高溫氧化行為和內(nèi)部組織演變。結(jié)果表明，由于 CoAl 涂層 Al 含量較高，促進(jìn)了表面 Al2O3 的形成，改善了 DZ466 合金 900 ℃抗氧化性能。揭示了熱暴露過程中 CoAl 涂層基體相及析出相的演變規(guī)律，涂層的基體相由 β-NiAl/CoAl 相逐漸轉(zhuǎn)化為γ?-Ni3Al 相，涂層與基體合金間的元素互擴(kuò)散促使基體相轉(zhuǎn)變優(yōu)先在靠近基體合金側(cè)進(jìn)行。熱暴露后，CoAl涂層中間層中析出 α-Cr 相，α-Cr 相傾向于在碳化物附近形核并依附于碳化物生長。涂層內(nèi)層中有針狀 TCP相(μ 相)析出，μ 相的整齊排列形態(tài)與 γ/γ?的立方化組織密切相關(guān)。涂層內(nèi)部組織演變存在遺傳效應(yīng)。

Aluminide coatings are widely employed to protect internal cooling channels of high grades blades and buckets in gas turbines have always been in severe conditions including high temperature oxidation and hotcorrosion. There is a major concern for the application of aluminide coatings that refer to the inter-diffusionbetween aluminide coating and superalloy substrate at high temperatures. Diffusion of Al from the coating to theunderlying substrate usually leads to depletion of Al in the coating, resulting in inferior oxidation resistance of thecoating. Accordingly, Ni declines to diffuse counter currently from the substrate into the coating, as well as otherrefractory elements, such as Cr, Mo and W etc.. The inter-diffusion between aluminide coating and superalloysubstrate results in degradation or various evolution behaviors of aluminide coatings, in other words, substratecomposition significantly affects the properties of aluminide coatings. CoAl coating was prepared on directionallysolidfied superalloy DZ466 by low presure chemical vapour deposition (LP-CVD). Oxidation behavior andmicrostructure evolution of CoAl coating was investigated during long term (about 5000 h) exposure at 900 ℃.Results suggested that, high concentration of aluminum did help to form Al2O3 on the surface of coating,improving oxidation resistance of DZ466 at 900 ℃. Evolution of matrix phase and precipitates in the CoAlcoating during exposure was displayed, β-NiAl/CoAl phase in the coating transformed gradually to be γ?-Ni3Alphase, higher transformation rate for the γ? phase closed to the substrate due to the diffusion between the coatingand the substrate superalloy. During exposure, α-Cr phase precipitated in the middle layer, which inclined to formclose to carbides and grow by consuming them. Needle like TCP phase (μ phase) grew in the inner layer thatarranged in order, which was due to the cubic microstructure of γ/γ?. Heredity-effect was in company with theprecipitates evolution.

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