1.The trade - off driven by solid - solution strengthening elements
When these elements are added in an appropriate amount, they cause lattice distortion of the nickel matrix, which significantly improves the room - temperature and high - temperature hardness of the alloy, and enhances its wear resistance.
However, excessive addition of such elements will lead to uneven distribution of the matrix composition, reduce the uniformity of the passivation film formed on the alloy surface, and even induce the precipitation of brittle intermetallic phases or carbides at grain boundaries. These microstructural changes will destroy the integrity of the passive film, increase the risk of pitting corrosion and intergranular corrosion, and thus reduce the overall corrosion resistance of the alloy in harsh environments (such as acidic, chloride - containing media).
During aging, a large number of fine and dispersed strengthening phases (such as γ' - Ni₃(Al, Ti) phase) precipitate from the matrix, which can pin dislocations and significantly improve the hardness and strength of the alloy.
However, if the aging process is not properly controlled (e.g., over - aging), the strengthening phases will grow coarsely, and even combine with carbon to form chromium - poor zones at grain boundaries. The chromium - poor zones lose the ability to form a dense passivation film, which will sharply reduce the intergranular corrosion resistance of the alloy. In contrast, solution annealing treatment can dissolve the strengthening phases into the matrix, improve the uniformity of the alloy, enhance corrosion resistance, but the hardness of the alloy will decrease accordingly.
Reasonable element matching: While adding strengthening elements, increase the content of corrosion - resistant elements such as chromium (Cr) and molybdenum (Mo) appropriately. Chromium can promote the formation of a stable Cr₂O₃ passivation film, and molybdenum can improve the pitting corrosion resistance of the alloy, offsetting the negative impact of strengthening elements on corrosion resistance.
Precision heat treatment: Adopt a two - stage aging process to control the size, morphology, and distribution of the strengthening phases, ensuring that the alloy has high hardness while avoiding the formation of chromium - poor zones.
Surface modification technology: Use surface treatment methods such as nitriding and passivation. The nitriding layer can improve the surface hardness and wear resistance of the alloy, while the passivation treatment can optimize the surface passive film structure and enhance corrosion resistance, so that the surface and matrix of the alloy can obtain excellent comprehensive properties.
