对CMSX-4合金表面Pt改性铝化物(NiPtAl)高温涂层进行了短期高温氧化实验,研究了NiPtAl在1150 ℃形成表面氧化膜的微观结构。结果表明,氧化1 h后形成的氧化膜包含亚稳态和稳态Al₂O₃区域,同时部分区域发生氧化膜脱落,并在氧化膜内部观察到空洞和Pt颗粒。分析表明,在涂层初期氧化过程中,NiPtAl涂层表面亚稳态θ-Al₂O₃向稳态α-Al₂O₃转变,导致氧化膜中α-Al₂O₃与θ-Al₂O₃呈区域层状分布,氧化1 h后NiPtAl涂层表面会形成约0.5 μm厚的θ-Al₂O₃层。随着θ-Al₂O₃的快速生长,NiPtAl中β-NiAl向γ'-Ni₃Al转变,由于Pt在γ'相比β相中溶解度小而发生偏析,从而导致在氧化膜α-Al₂O₃与θ-Al₂O₃层界面处含有Pt颗粒。另外,初期Al₂O₃层的快速生长导致氧化膜内部形成空洞,氧化膜的生长和相变导致的内应力和内部空洞等缺陷降低了表面θ-Al₂O₃层的黏结性能,最终导致氧化层脱落。

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 in extending lifetime of TBC system or overlaying coatings. In this work, the oxidation experiments of the Pt modified aluminide coating on CMSX-4 Ni-based 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 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 result in the oxide spallation.