QuestionWhat can you tell us about nickel-based alloys?
AnswerNickel alloys are those that commonly contain at least 50% nickel. Examples of the major nickel-alloy families include:
- Nickel 200
- Nickel-copper (e.g., Monel 400 & Monel 500)
- Nickel-chromium (e.g., Inconel 600 & X-750)
- Nickel-chromium – molybdenum (e.g., Hastalloy C-276 and Inconel 625)
Commercial nickel and nickel alloys are available in a wide range of wrought grades and a more limited number of cast grades. Many trade names apply to nickel alloys such as Monel, Hastalloy, Inconel and Incoloy to name a few. Casting alloys are identified by ACI (Alloy Casting Institute) and ASTM designations. Casting alloys contain additional elements such as silicon and manganese to improve fluidity and pressure tightness.
Pure Nickels and Extra-High-Percentage Nickel Alloys
Nickel 200 and 201 are wrought-alloy examples of this class containing 99.5% Ni. The cast grade, designated CZ-100, is recommended for use at temperatures above 315°C (600°F) because its lower carbon content prevents graphitization and subsequent ductility loss. These alloys are particularly well suited for food-contact applications.
Duranickel 301 is a precipitation-hardened 94% nickel alloy that has excellent spring properties to 315°C (600°F). During thermal treatment, Ni3AlTi particles precipitate throughout the matrix, enhancing alloy strength. Corrosion resistance is similar to that of commercially pure wrought nickel.
Binary Nickel Alloys
The primary wrought alloys in this category are the Ni-Cu grades known as Monel alloy 400 (Ni-31.S% Cu) and K-500 (Ni-29.S% Cu), which also contain small amounts of Al, Fe and Ti. The Ni-Cu alloys differ from Nickel 200 and 201 in that their strength and hardness are enhanced by age hardening. Although the Ni-Cu alloys share many of the corrosion characteristics of commercially pure nickel, their resistance to sulfuric and hydrofluoric acids as well as brine is better. Handling of waters, including seawater and brackish water, is a major application. Monel alloys 400 and K-500 are immune to chloride-ion stress-corrosion cracking, which is often considered in their selection.
Other binary nickel families include Ni-Mo and Ni-Si types. Hastalloy B-2 (Ni-28% Mo), for example, offers excellent resistance to hydrochloric acid, aluminum-chloride catalysts and other strongly reducing chemicals. It also has excellent high-temperature strength in inert atmospheres and vacuum.
Cast Ni-Cu alloys include both low- and high-silicon grades. Grades A and E (1.5% Si) are commonly used in conjunction with wrought nickel-copper in pumps, valves and fittings. A higher silicon grade – QQ-N-288, Grade B (3.5% Si) – is used for rotating parts and wear rings because it combines corrosion resistance with high strength and wear resistance. Grade D (4.0% Si) offers exceptional galling resistance.
Two other binary cast alloys are ACI N-12M-1 and N-12M-2. These Ni-Mo alloys are commonly used for handling hydrochloric acid in all concentrations at temperatures up to the boiling point. These alloys are produced commercially under the trade names Hastalloy alloy B and Chlorimet 2.