A brief discussion on methods of improving corrosion resistance through metal alloying
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This post was last edited by Wang Wei2 on 2024-10-6 at 11:55. By adding alloying elements that promote passivation to the base metal, materials with excellent corrosion resistance can be obtained when the addition level reaches a certain proportion. When chromium is added to iron, and the chromium content reaches over 12%, it becomes stainless steel, which possesses high corrosion resistance in oxidizing environments due to the formation of a passivation film on its surface. Adding nickel to chromium steel can broaden the passivation range and also improve mechanical properties. Chromium-nickel stainless steel containing 18% chromium and 9% nickel is the most widely used corrosion-resistant alloy in industry and civil applications. For example, when 14% silicon is added to iron, high-silicon iron with excellent acid resistance is obtained; its surface is covered by a silica protective film that provides good resistance to hot sulfuric acid, nitric acid, mixed acids, and similar substances. When the nickel content in nickel-copper alloys is above 30–40%, copper-nickel alloys containing 10–30% nickel (Cupronickel) and alloys with 70% nickel and 30% copper (Monel) can be obtained. These alloys exhibit better corrosion resistance in certain environments compared to pure copper and pure nickel. A series of nickel alloys are well-known for their corrosion resistance; for example, nickel cast iron has excellent alkali resistance. Nickel-molybdenum-chromium alloy is one of the few alloys capable of withstanding high temperatures and non-oxidizing acids (such as hydrochloric acid). Nickel-aluminum-chromium-iron alloys can resist high-temperature oxidizing acids, hypochlorites, seawater, etc., and perform better than ordinary stainless steels. Adding trace amounts of cathodic noble metals with low overpotential to certain active metals can promote passivation. For example, stainless steel and titanium are active in sulfuric acid at certain concentrations and temperatures; by adding 0.1–0.15% palladium or platinum to the base metal, numerous microcathodes are formed on the surface of the alloy, which facilitates the operation of local corrosion cells. As a result, the anode current increases rapidly, and the passivation region is quickly reached, thereby enhancing the corrosion resistance of the alloy.
The corrosion resistance of a material can be significantly improved by adding alloying elements to the base metal that promote passivation. For example, adding more than 12% chromium to iron allows for the creation of stainless steel, which forms a surface passivation layer in oxidizing environments, granting it high corrosion resistance. For another example, adding 14% silicon to iron produces high-silicon iron, a material that can resist strong corrosive agents such as hot sulfuric acid and nitric acid. Furthermore, increasing the proportion of nickel in nickel-copper alloys can yield superior corrosion resistance. There are also some special nickel alloys, such as nickel-aluminum-chromium-iron alloys, which can be used in high-temperature oxidizing acids and seawater environments. Adding a small amount of precious metals such as palladium or platinum to some active metals can also effectively promote the passivation process, thereby enhancing the corrosion resistance of the alloy. These methods provide various options for improving the corrosion resistance of metal alloys. .