High temperature oxidation behavior of DD406 SX superalloy film cooling holes with different laser drilling processes

Abstract

Turbine blades of long-life civil aircraft and gas turbines are affected by high temperature oxidation during service, which greatly reduces the surface strength under complex working conditions and significantly shortens the service life. Therefore, oxidation resistance is one of the most specific properties that must be considered in the application of turbine blades. The influence of the different drilling processes for cooling holes on the oxidation behavior of Ni-based SX (single-crystal) superalloy at 980℃ and 1100 ℃ was investigated. The difference in the oxidation mechanism of the cooling holes under different drilling processes provided a basis for the establishment of the blade life model under service conditions. The results indicate that the film cooling holes processed by millisecond laser exhibit poor oxidation performance, and all oxidation kinetic curves basically obey the parabolic or linear law. In the initial oxidation stage of the millisecond laser specimen, the oxidation reaction is primarily determined by the growth pattern of outer NiO. Subsequently, a three-layer oxide layer（(Ni, Co)O-Spinel phase layer-α-Al2O3） gradually formed around the hole. There are relatively micro-holes under the internal α-Al2O3 layer and the γ'-free zone, which makes the oxide layer easy to exfoliate. Discontinuous α-Al2O3 is rapidly formed in the initial oxidation stage of the picosecond laser specimen, and then connected to each other to form the dense α-Al2O3 layer.

Keywords

• dd406 single-crystal superalloy
• turbine blade film cooling holes
• laser drilling
• oxidation kinetic
• oxidation mechanism