1.Intergranular Embrittlement Due to Carbide Precipitation
During long‑term service at 700–900°C, carbides (e.g., Cr₂₃C₆) may precipitate along grain boundaries. While this can improve creep strength, excessive grain boundary carbide formation can lead to:
Reduced grain boundary cohesion
Intergranular cracking
Decreased ductility
This is often observed as a reduction in impact toughness or elongation after extended exposure.
2.σ‑Phase Formation
Inconel 601 has a low tendency to form σ‑phase compared to some other nickel‑chromium alloys. However, very long exposure times (thousands of hours) at 700–850°C may promote limited σ‑phase precipitation, which is brittle and can cause:
Reduced ductility
Increased hardness
Intergranular fracture
The extent of σ‑phase formation depends on composition, heat treatment, and service temperature.
3.Oxidation‑Induced Embrittlement
Long‑term oxidation at temperatures above 900°C can lead to subsurface oxygen penetration and the formation of internal oxides. This can cause:
Localized embrittlement
Reduced fatigue crack growth resistance
Surface degradation
However, the dense Al₂O₃ layer formed by Inconel 601 generally provides good protection against severe oxidation embrittlement.
4.Thermal Aging Effects
Prolonged thermal aging can cause:
Grain growth
Coarsening of precipitates
Reduction in dislocation density
These changes may slightly reduce the alloy's toughness and fatigue resistance, but the effect is typically manageable within the design limits of most high‑temperature applications.
Summary
Long‑term embrittlement: Inconel 601 is relatively resistant to embrittlement, but extended service at 700–900°C can lead to grain boundary carbide precipitation, limited σ‑phase formation, and oxidation‑induced damage, which may reduce ductility and toughness.
