OXIDATION PROPERTY AND FAILURE MECHANISM OF A SINGLE PHASE PtAl2 COATING

Pt-modified aluminide coating has attracted great attention due to its advantage of the integrated property in resisting both high temperature oxidation and hot corrosion. By the presence of Pt, the spallation trend of the grown oxide scale and the detrimental effect of S can be restrained at a very low level. Besides, Pt could promote α-Al2O3 formation and stabilize β-NiAl phase. Thus Pt-modified aluminide (Pt-Al) coating has been widely used in some crucial applications requiring reliability and extended service life. There are mainly PtAl2, β-(Ni, Pt) Al and γ/γ ′-NiPtAl phases existing inside Pt-Al coating. In this work, a single phase PtAl2 coating was prepared on a Ni-based K38G superalloy through pulse-electroplating of Pt and pack aluminization under stepped heating mode. At 1100 °C , the isothermal oxidation behavior of the single phase PtAl2 coating was evaluated by thermogravimetric analysis (TGA). Cyclic oxidation test of the PtAl2 coating was performed within a vertical muffle furnace at the same temperature. The results indicate that the singular PtAl2 coating possesses quite good isothermal oxidation resistance. However, its resistance against cyclic oxidation is very poor. The cyclic stress induced by repeated heating and cooling has caused visible detachment of PtAl2 coating layer, and the spallation of PtAl2 in further would lead to a premature failure of the whole coating system. Partial spallation of PtAl2 layer, including unde*国家自然科学基金项目51301184,国家重点基础研究发展计划项目2012CB625100和国家高技术研究发展计划项目2012AA03A512