鎳基合金表面Pt改性鋁化物涂層的初期Al2O3微觀結(jié)構(gòu)分析

鎳基合金表面Pt改性鋁化物涂層的初期Al2O3微觀結(jié)構(gòu)分析Microstructure Analysis of Initial Alumina of Pt-modified Aluminide Coatings on Ni-base Alloy

對CMSX-4合金表面Pt改性鋁化物（NiPtAl）高溫涂層進(jìn)行了短期高溫氧化實(shí)驗(yàn)，研究了NiPtAl在1150 ℃形成表面氧化膜的微觀結(jié)構(gòu)。結(jié)果表明，氧化1 h后形成的氧化膜包含亞穩(wěn)態(tài)和穩(wěn)態(tài)Al2O3區(qū)域，同時部分區(qū)域發(fā)生氧化膜脫落，并在氧化膜內(nèi)部觀察到空洞和Pt顆粒。分析表明，在涂層初期氧化過程中，NiPtAl涂層表面亞穩(wěn)態(tài)θ–Al2O3向穩(wěn)態(tài)α–Al2O3轉(zhuǎn)變，導(dǎo)致氧化膜中α–Al2O3與θ–Al2O3呈區(qū)域?qū)訝罘植迹趸?h后NiPtAl涂層表面會形成約0.5 μm厚的θ–Al2O3層。隨著θ–Al2O3的快速生長，NiPtAl中β-NiAl向γ'-Ni3Al相轉(zhuǎn)變，由于Pt在γ'相比β相中溶解度小而發(fā)生偏析，從而導(dǎo)致在氧化膜α–Al2O3與θ–Al2O3層界面處含有Pt顆粒。另外，初期Al2O3層的快速生長導(dǎo)致氧化膜內(nèi)部形成空洞，氧化膜的生長和相變導(dǎo)致的內(nèi)應(yīng)力和內(nèi)部空洞等缺陷降低了表面θ–Al2O3層的黏結(jié)性能，最終導(dǎo)致氧化層脫落。

NiPtAl coatings are widely used as overlaying coatings besides bondcoats for thermal barrier coating (TBC) systems within high temperature environment. Oxidaiton behavior of NiPtAl coatings is mainly contribution for the failure of TBC systems or overlaying coatings. An initial oxide layer growth characteristics play a key role to extend lifetime of TBC system or overlaying coatings. In this work, the oxidation experiments of the Pt modified aluminide coating on CMSX-4 Ni-base alloy were carried out at 1150 ℃ for 1 h in 80%Ar+20%O2. The microstructures of oxide on the NiPtAl coatings are studied by using OM, SEM, TEM and Raman spectroscopy. The results indicated that the oxide layer on the NiPtAl coatings included stable and met-stable Al2O3 after 1 h oxidation, and part of spalled oxide layer as well as pores within the oxide layer. The 0.5 μm thickness whisker-like θ–Al2O3 could form on NiPtAl coating during the initially oxidation stage. At the initial oxidation stage θ–Al2O3 fastly grew which resulted β-NiAl to γ'-Ni3Al transformation. The Pt particles formed on the inter-surface between α–Al2O3 and θ–Al2O3 layer due to a less Pt solid solubility in γ'-Ni3Al compared to β-NiAl in the coating. Fast growth of initial Al2O3 could induce pores formation within the alumina layer. The pores and stress due to oxidation and phase transformation could decrease the alumina adherence, and at last resulted the oxide spallation.

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