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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1h后形成的氧化膜包含亚稳态和稳态Al_2O_3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q-Al_2O_3向稳态a-Al_2O_3转变,导致氧化膜中a-Al_2O_3与q-Al_2O_3呈区域层状分布,氧化1 h后Ni Pt Al涂层表面会形成约0.5 mm厚的q-Al_2O_3层。随着q-Al_2O_3的快速生长,NiPtAl中b-NiAl向g’-Ni_3Al转变,由于Pt在g’相比b相中溶解度小而发生偏析,从而导致在氧化膜a-Al_2O_3与q-Al_2O_3层界面处含有Pt颗粒。另外,初期Al_2O_3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q-Al_2O_3层的黏结性能,最终导致氧化层脱落。
The high-temperature oxidation of Pt-modified aluminides (NiPtAl) on the surface of CMSX-4 alloy was investigated by means of short-term high temperature oxidation. The microstructure of NiPtAl surface oxide film was investigated at 1150 ℃. The results show that the oxide film formed after oxidation for 1 h contains the metastable and steady Al 2 O 3 regions, while the oxide films are partially peeled off and the voids and Pt particles are observed inside the oxide film. The results show that the metastable q-Al_2O_3 phase changes to the steady-state a-Al_2O_3 during the initial oxidation of the coating, resulting in a layered distribution of a-Al_2O_3 and q_Al_2O_3 in the oxide film. After oxidation for 1 h The surface of the Ni Pt Al coating forms a layer of q-Al 2 O 3 about 0.5 mm thick. With the rapid growth of q-Al 2 O 3, b-NiAl in NiPtAl is transformed into g’-Ni_3Al. Due to the small solubility of Pt in g ’phase compared with that in b phase, the segregation occurs, resulting in the formation of a-Al_2O_3 and q-Al_2O_3 The interface contains Pt particles. In addition, the rapid growth of the initial Al 2 O 3 layer led to the formation of cavities in the oxide film. The defects such as internal stress and internal voids caused by the growth and phase transformation of the oxide film reduced the adhesion of the surface q-Al 2 O 3 layer and eventually led to the oxide layer falling off.