Nickel is a versatile metal that is found in abundance in the earth’s crust and core.Nickel alloys are alloys with nickel as principal element. First discovered and isolated by Axel Fredrik Cronstedt, a Swedish chemist and mineralogist, nickel exhibits several desirable properties that render it useful in industrial applications. For one, nickel is highly ductile and is valuable as an alloying element to alter the properties of other metals. For example, grades of stainless steel can be created by the addition of nickel to produce alloys that offer corrosion resistance and high-temperature endurance, making them ideal for uses in chemical plants where exposure to caustic substances may be expected.
This article will focus on reviewing the different types of nickel alloys that are commonly available. The alloy definition in the case of nickel alloys is one in which nickel is the primary element (i.e. has the highest concentration of all the metals in the alloy).
Properties of Nickel
Nickel, whose chemical symbol is Ni, has a silvery-white appearance and is a primordial element, with a face-centered cubic crystalline structure. It is magnetic at room temperature and has a Curie temperature of 253oC (487oF). Table below summarizes some of the other key physical properties and characteristics of nickel.
| Characteristic | Value |
|---|---|
| Atomic number | 28 |
| Atomic weight | 58.69 |
| Melting point | 1453oC |
| Boiling Point | 2730oC |
| Recyclable/Recoverable | Yes |
| Density | 8.90 g/cm3 @ 25oC |
| Curie Temperature | 253oC |
| Sound transmissibility | 4,900 m/s @ room temperature |
| Coefficient of Thermal Expansion | 13.4 μm/(m-oK) |
| Coefficient of Thermal Conductivity | 90.9 W/(m-oK) |
| Electrical Resistivity | 69.3 nΩ-m @20oC |
| Young’s Modulus | 200 GPa |
| Bulk Modulus | 180 GPa |
| Shear modulus | 76 GPa |
| Poisson’s ratio | 0.31 |
| Mohs hardness | 4.0 |
| Vickers hardness | 638 MPa |
Common Types of Nickel Alloys
Nickel will alloy easily with most metals such as copper, chromium, iron, and molybdenum. The addition of nickel to other metals alters the properties of the resulting alloy and can be used to produce desired characteristics such as improved corrosion or oxidation resistance, increased high-temperature performance, or lower coefficients of thermal expansion, for example.
The sections below present information about each of these types of nickel alloys.
Nickel-Iron Alloys
Nickel-iron alloys function in applications where the desired property is a low rate of thermal expansion. Invar 36, also sold with trade names of Nilo 6 or Pernifer 6, exhibits a coefficient of thermal expansion that is about 1/10 that of carbon steel. This high degree of dimensional stability renders nickel-iron alloys useful in applications such as precision measurement equipment or thermostat rods. Other nickel-iron alloys with even greater concentrations of nickel are used in applications where soft magnetic properties are important, such as transformers, inductors, or memory storage devices.
Nickel-Copper Alloys
Nickel-copper alloys are very resistant to corrosion by salt water or seawater and thus find application in marine applications. As an example, Monel 400, also sold under the trade names Nickelvac 400 or Nicorros 400, can find application in marine piping systems, pump shafts, and seawater valves. This alloy as a minimum concentration of 63% nickel and 28-34% copper.
Nickel-Molybdenum Alloys
Nickel-molybdenum alloys offer high chemical resistance to strong acids and other reducers such as hydrochloric acid, hydrogen chloride, sulfuric acid, and phosphoric acid. The chemical makeup for an alloy of this type, such as Alloy B-2, has a concentration of molybdenum of 29-30% and a nickel concentration of between 66-74%. Applications include pumps and valves, gaskets, pressure vessels, heat exchangers, and piping products.
Nickel-Chromium Alloys
Nickel-chromium alloys are prized for their high corrosion resistance, high-temperature strength, and high electrical resistance. For example, the alloy NiCr 70/30, also designated as Ni70Cr30, Nikrothal 70, Resistohm 70, and X30H70 has a melting point of 1380oC and an electrical resistivity of 1.18 μΩ-m. Heating elements such as in toasters and other electrical resistance heaters make use of nickel-chromium alloys. When produced in wire form they are known as Nichrome wire.
Nickel-Chromium-Iron Alloys
Nickel-chromium-iron alloys combine these elements to produce alloys that resist oxidation and high-temperature corrosion. Alloy 800, sold under the trade names Incoloy 800, Ferro chronin 800, Nickelva 800, and Nicrofer 3220, is used in furnace components such as petrochemical furnace cracker tubes, and as a material for sheathing of electrical heating elements. These alloys generally are also valued for their optimum creep and rupture properties at high temperatures. The composition of these alloys is typically 30-35% Nickel, 19-23% Chromium and a minimum of 39.5% Iron. The high concentration of iron has led to the reclassification of these alloys as stainless steel.
Nickel-Chromium-Molybdenum Alloys
With similar applications to nickel-molybdenum alloys, nickel-chromium-molybdenum alloys also provide high corrosion resistance especially with regard to reducing acids such as hydrochloric acid and sulfuric acid. One of the best known of these alloys is Alloy C-276, also sold under the trade names Hastelloy C276, Nickelvac HC-276, Inconel 276, and Nicrofer 5716. This alloy is used in pollution control stack liners, ducts, and scrubbers, as well as in chemical processing components such as heat exchangers, evaporators, or reaction vessels. The composition of this alloy is primarily nickel with 15-17% molybdenum, 14.5-16.5% chromium, 4-7% Iron, 3-4.5% tungsten, and smaller concentrations of other elements such as manganese.
Nickel-Chromium-Cobalt Alloys
These alloys of nickel add chromium and molybdenum to add creep rupture strength to the alloy. Alloy 617 is an example, sold under the trade names Inconel 617 and Nicrofer 617, which has a composition of 20-24% chromium, 10-15% cobalt, and 8-10% molybdenum with a minimum nickel content of 44.5%. Applications for these alloys include industrial furnace components, gas turbines, catalyst grid supports to produce nitric acid, and fossil fuel production facilities.
Nickel-Titanium Alloys
Nickel-titanium alloys feature shape retention of shape memory properties. By forming a shape from this alloy at a higher temperature and them deforming it from that formed shape at a lower temperature, the alloy will remember the initial shape and reform to that shape once heated to this so-called transition temperature. By controlling the composition of the alloy, the transition temperature can be altered. These alloys have a super-elastic property that can be exploited to provide, among other uses, a shock absorber against earthquake damage to help protect stone buildings.
Nickel Alloy Form Factors
Suppliers of nickel alloys offer them in a variety of form factors which commonly include:
- Angles
- Balls
- Pipe
- Tubing
- Bars
- Billets
- Ingots
- Channels
- Coils
- Wire
- Rods
- Sheets
- Plate
- Strips
- Flanges
- Forgings
Common Nickel Alloy Trade Names
Below in Table are some of the more common trade names of the types of nickel alloys.
| Name | Alloy type |
|---|---|
| Nickel 200 | 99% + pure Nickel |
| Nickel 201 | 99% + pure Nickel |
| Monel 400 | ickel-Copper |
| Monel R405 | Nickel-Copper |
| Monel K500 | Nickel-Copper |
| Inconel 600 | Nickel-Chromium-Iron |
| Inconel 601 | Nickel-Chromium-Iron |
| Inconel 617 | Nickel-Chromium-Cobalt |
| Inconel 625 | Nickel-Chromium-Iron |
| Inconel 718 | Nickel-Chromium-Iron |
| Inconel X750 | Nickel-Chromium-Iron |
| Incoloy 800 | Nickel-Chromium-Iron |
| Incoloy 825 | Nickel-Chromium-Iron |
| Hastelloy C22 | Chromium-Molybdenum-Tungsten |
| Hastelloy C276 | Nickel-Chromium-Molybdenum |
| Hastelloy B2 | Nickel-Chromium-Molybdenum |
| Hastelloy X | Nickel-Chromium-Iron-Molybdenum |
| Vascomax C250 | Nickel-Cobalt-Molybdenum |
| Vascomax 300 | Nickel-Cobalt-Molybdenum |
| Vascomax C350 | Nickel-Cobalt-Steel |
| Rene 41 | Nickel-Chromium |
| Multimet N155 | Nickel-Chromium-Cobalt |
| Waspaloy 25™ | Nickel-Cobalt |
| Invar 36 | Nickel-Iron |
| Invar 42 | Nickel-Iron |
Applications of Nickel Alloys
Nickel and nickel alloys are used for a wide variety of applications, the majority of which involve corrosion resistance and/or heat resistance. Some of these include:
- Aircraft gas turbines
- Steam turbine power plants
- Medical applications
- Nuclear power systems
- Chemical and petrochemical industries
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