Creep deformation micro-mechanisms of CM 247 DS LC Ni-base superalloy under relevant service condition

Abstract

In order to meet the 21st century challenges, the need to improve the high temperature load bearing capabilities or creep properties of nickel base superalloys is more important than ever. Thorough understandings of creep deformation micro-mechanisms are essential for improving high temperature performance of these alloys. Therefore, in the present study, creep deformation micro-mechanisms of CM 247 DS LC alloy used for fabricating turbine blades and vanes under relevant service conditions have been explored. The creep deformation behaviour at the investigated temperatures has been divided into three temperature regimes. In the lower temperature regime, a classical three stage creep curve is observed, i.e., primary creep followed by steady-state creep and then an accelerating creep stage leading to failure. While, in the intermediate temperature creep regime a relatively shorter secondary creep region is seen, in contrast, secondary creep stage is almost missing in the high temperature regime. Transmission electron microscopic (TEM) studies revealed that the deformation micro-mechanisms in the low temperature regime are dominated by γ′-precipitates shearing of anti phase boundary (APB) coupled dislocations pair. In the high temperature regime, the deformation is dominated by the extensive dislocation networks formation and severe γ′-rafting. In the intermediate temperature regime, the deformation micro-mechanisms are basically mixture of both low and high temperature deformation micro-mechanisms. The facts revealed by TEM observations were well supported by scanning electron based factographic and microstructural analysis.