Nickel
Nickel alloys can offer enhanced corrosion resistance, toughness, strength at high and low temperatures, and interesting magnetic, thermal and electronic properties compared with other metals. Due to their higher nickel content compared with stainless steels, they can be appreciably more expensive, but find uses in more demanding applications from gas turbines to chemical plants and oil & gas industry components.
Nickel-Copper Alloys – Monel®
Nickel – copper alloys such as Alloy 400 and Alloy K-500, also known as Monel K500, (Special Metals Corporation’s family of Nickel-Copper alloys is known as Monel®) are based predominantly on nickel and copper, with smaller additions of manganese and iron. They are used where a higher strength is required compared to pure nickel, and resist corrosion in a wide range of environments. They can be fabricated readily by hot and cold working, machining, and welding. Nickel-Copper alloys find wide application in oil refining and marine applications where long corrosion-free life is required. Due to the good thermal conductivity of the alloys, they are also frequently used for heat exchangers where sea water is one of the fluids concerned.
Nickel-Iron-Chromium Alloys – Incoloy®
Nickel-Iron-Chromium alloys such as Alloy 825, also known as Incoloy 825, (Special Metals Corporation’s family of Nickel-Iron-Chrome alloys is known as Incoloy® ) were developed to provide a more cost-effective solution for applications requiring high-temperature and corrosion resistance – achieved by lowering the nickel content. Selectively alloying with other elements can greatly improve their performance in certain environments. For instance, Alloy 825 also contains molybdenum and copper to improve resistance to strongly reducing environments, such as those containing sulphuric and phosphoric acids.
Nickel-Chromium Super Alloys – Inconel®
Nickel-Chromium super alloys such as Alloy 625, also known as Inconel 625, and Alloy 718, also known as Inconel 718, (Special Metals Corporation’s family of Nickel-Chromium alloys is known as Inconel®) are typically used in high-temperature applications. When heated, they form a thick and stable passivating oxide layer protecting the surface from further attacks. These alloys retain their strength over a wide temperature range, particularly at elevated temperatures where aluminium and steel would otherwise succumb to creep failure. Varying levels of high-temperature strength can be developed by solid solution strengthening or precipitation strengthening (with niobium additions).
