Nickel-based alloys refer to a class of alloys that have high strength and a certain degree of oxidation and corrosion resistance at a high temperature of 650 to 1000 ℃. According to the main performance, it is further divided into nickel-based heat-resistant alloys, nickel-based corrosion resistant alloys, nickel-based wear-resistant alloys, nickel-based precision alloys and nickel-based shape memory alloys. According to the different substrates, superalloys are divided into: iron-based superalloys, nickel-based superalloys and cobalt-based superalloys. Among them, nickel-based superalloys are referred to as nickel-based alloys.

Corrosion resistant alloy

The main alloying elements are copper, chromium and molybdenum. It has good comprehensive performance and can resist various acid corrosion and stress corrosion. The earliest application (produced in the United States in 1905) is nickel-copper (Ni-Cu) alloy, also known as Monel (Monel alloy Ni 70 Cu30); in addition, there is nickel-chromium (Ni-Cr) alloy (nickel-based heat-resistant alloy) , The heat-resistant corrosion-resistant alloy in the corrosion-resistant alloy), nickel-molybdenum (Ni-Mo) alloy (mainly refers to Hastelloy B series), nickel-chromium-molybdenum (Ni-Cr-Mo) alloy (mainly refers to Hastelloy C Series) etc. At the same time, pure nickel is also a typical representative of nickel-based corrosion-resistant alloys. These nickel-based corrosion-resistant alloys are mainly used in the manufacture of various corrosion-resistant environmental parts such as petroleum, chemical industry, and electric power.

Nickel-based corrosion resistant alloys mostly have austenitic structure. In the state of solid solution and aging treatment, there are still intermetallic phases and metal carbonitrides on the austenite matrix and grain boundaries of the alloy. The classification of various corrosion-resistant alloys and their characteristics are as follows:

The corrosion resistance of Ni-Cu alloy is better than that of nickel in reducing media, and the corrosion resistance of oxidizing media is better than that of copper. It is resistant to high temperature fluorine gas, hydrogen fluoride and hydrogen fluoride in the absence of oxygen and oxidants. The best material for acid (see metal corrosion).

Ni-Cr alloy is also a nickel-based heat-resistant alloy; it is mainly used under oxidizing medium conditions. It resists high temperature oxidation and corrosion by gases containing sulfur and vanadium, and its corrosion resistance increases with the increase of chromium content. This type of alloy also has better resistance to hydroxide (such as NaOH, KOH) corrosion and stress corrosion resistance.

Ni-Mo alloy is mainly used under the conditions of reducing media corrosion. It is the best alloy resistant to hydrochloric acid corrosion, but in the presence of oxygen and oxidants, the corrosion resistance will be significantly reduced.

Ni-Cr-Mo(W) alloy combines the properties of the above-mentioned Ni-Cr alloy and Ni-Mo alloy. Mainly used under the conditions of oxidation-reduction mixed media. This type of alloy has good corrosion resistance in high-temperature hydrogen fluoride, in hydrochloric acid and hydrofluoric acid solutions containing oxygen and oxidants, and in wet chlorine at room temperature.

Ni-Cr-Mo-Cu alloy has the ability to resist both nitric acid and sulfuric acid corrosion. It also has good corrosion resistance in some oxidation-reduction mixed acids.