Most nickel-based corrosion resistant alloys have austenite structure. In the state of solution and aging treatment, there are intermetallic phases and metal carbonitrides on the austenite matrix and grain boundary of the alloy. Various corrosion-resistant alloys are classified according to their compositions, and their characteristics are as follows:
The corrosion resistance of nickel-copper alloy is better than that of nickel in reducing medium and better than that of copper in oxidizing medium. In the absence of oxygen and oxidant, it is the best material to resist high temperature fluorine gas, hydrogen fluoride and hydrofluoric acid (see metal corrosion).
Nickel-chromium alloy is also a nickel-based heat-resistant alloy; It is mainly used under the condition of oxidizing medium. It is resistant to high temperature oxidation and corrosion of sulfur and vanadium gases, and its corrosion resistance increases with the increase of chromium content. This alloy also has good resistance to hydroxide (such as NaOH and KOH) corrosion and stress corrosion.
Nickel-molybdenum alloy is mainly used under the condition of reducing medium corrosion. It is the alloy with the best corrosion resistance to hydrochloric acid, but in the presence of oxygen and oxidant, the corrosion resistance will obviously decrease.
Nickel-chromium-molybdenum (tungsten) alloy has the properties of the above nickel-chromium alloy and nickel-molybdenum alloy. It is mainly used under the condition of redox mixed medium. This alloy has good corrosion resistance in high temperature hydrogen fluoride gas, hydrochloric acid and hydrofluoric acid solution containing oxygen and oxidant and wet chlorine at room temperature.
Nickel-chromium-molybdenum-copper alloy has both nitric acid corrosion resistance and sulfuric acid corrosion resistance, and also has good corrosion resistance in some redox mixed acids.