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Why are Nickel-Based Alloys Superalloys?

Nickel Alloys

Some materials in the metal family are known as supermaterials or superalloys. These materials typically feature advanced properties. For instance, they can maintain their physical properties at higher temperatures and under specific stress.

One of the best examples of superalloys in the material world is nickel-based superalloys. This alloy possesses exceptional characteristics that make it better than other materials and superalloys, such as iron and cobalt-based superalloys. Besides high-temperature resistance, these nickel alloys can also withstand high corrosion and harsh working conditions.

However, people often need clarification about why nickel-based alloys are called superalloys. The answer simply lies in the remarkable properties of nickel alloys. Still, this article will help you build clear concepts regarding this query.

So, without further ado, let’s dive into the post!

 

What are Nickel-Based Alloys?

As the name implies, nickel-based alloys mainly consist of nickel and some other alloys. They are famous for their high corrosion resistance and excellent high-temperature strength. Additionally, these alloys can endure fatigue, creep, and tensile strength. Due to the above-mentioned features, they are usually referred to as nickel-based superalloys.

Moreover, they are considered perfect for the turbine, heat exchanger, and aero-engine applications.

Source: Youtube

 

Production and Processing of Nickel-Based Superalloys

The production and processing of nickel superalloys usually depend upon their compositions. However, the composition relies on the used amount of material. Generally, two or up to ten alloying elements can be used to form nickel-based superalloys. These elements make almost half of the entire weight of the superalloy.

Normally, when nickel combines with solutes like aluminum or titanium, it results in the formation of an equilibrium microstructure comprising gamma-prime and gamma. This ensures the strength of the superalloy under the influence of elevated temperature.

Nickel superalloys can be manufactured in various ways, such as powder, cast, or wrought. These superalloys absorb material strength through precipitation strengthening or solid solution treatment. Chromium, molybdenum, cobalt, niobium, iron, tungsten, and tantalum are typically used to strengthen solid solutions.

 

What are the Characteristics of Nickel-Based Superalloys?

The following are some characteristics that fit both superalloys and nickel alloys. That’s why these alloys are considered superalloys. Let’s have a detailed look!

  • High Heat Resistance

Usually, metals are subjected to losing their strength when exposed to high temperatures. But, nickel superalloys have the power to endure high temperatures, which makes them currently the most widely used superalloys. The reason behind this is that nickel can maintain the same structure (face-centered cubic) from room temperature to ni melting temperature. The inherent thermal protection of superalloys preserves the material’s integrity.

Typically, resisting the high heat depends upon various nickel compositions mixed with nickel-based alloys. For example, Inconel 718 nickel alloy comprises 55% nickel, 6% iron, 21% chromium, and a small percentage of manganese, carbon, and copper. It provides exceptional endurance to high temperatures and protection against oxidation and corrosion. Besides, a nickel alloy Duranickel has more than 94% nickel content. It has excellent spring properties up to 316°C and becomes much more robust when thermally treated.

  • Exceptional Strength

The external load determines the strength of a material applied to it without any deformation of the material. Nickel-based superalloys can exhibit a tensile strength greater than 700 MPa and a yield strength of 275 MPa.  Most commonly, these alloys can exhibit high strength even at extreme temperatures ranging from 650 to 1000°C.

Surprisingly, some nickel-based superalloys show yield strength up to 1125 MPa, which is greater than the diamond’s strength. No doubt, such exceptional strength can only be expected from superalloys.

In the application of disc and turbine, the phase of this superalloy contains niobium or vanadium. By using this phase, the manufacturers can efficiently increase the strength of the material.

  • Corrosion-Resistance

In environments like marine or chemical, corrosion and oxidation comparatively occur fast and harm the metal machinery. Fortunately, nickel alloys have excellent resistance to a corrosive and complex acidic environment, which is again one of the superalloys’ outstanding features. To withstand corrosion in these environments, these alloys mainly contain up to ten types of alloying elements.

Furthermore, the nickel element itself has excellent resistance to caustic alkali corrosion and stress corrosion of Cl ions. However, the addition of passivation elements in nickel-based alloys forms solid solutions with a substrate phase which helps to enhance the materials’ corrosion potential and thermodynamic stability. For instance, you may add copper (Cu), chromium (Cr), and molybdenum (Mo) to increase the alloy’s endurance to corrosion.

  • Machinability

The engineers need to search for materials that may go easy while machining. In this regard, nickel-based alloys have better yield strength, shear stress, and resistance to high temperatures. As a result, they outweigh other metals in terms of weldability.

Some famous examples of nickel-based alloys available in the market are as follows:

  • Alloy for chemical industries: Inconel, Monel, and Incoloy.
  • For electrical resistance alloy: Incoloy alloy 800, Resistohm, and, Brightray.
  • Resistant to Harsh Working Environments

Nickel alloys can withstand severe working conditions such as aerospace gas chambers, acidic environments, nuclear energy’s structural components, petroleum, and marine industries. Moreover, they are not affected by water, warm air, and particular aqueous solutions due to their high chemical stability.

In short, superalloy manufacturing can effectively withstand high-pressure, high-temperature, and corrosive conditions.

 

Some commonly used Types of Nickel-Based Alloys

Types of Nickel-Based Alloys

Types

Definition Applications

Examples

Nickel-Iron Alloys

The mixture of nickel with some amount of iron gives nickel-iron alloy that exhibits very low thermal expansion in extreme conditions. ● Precision measurement equipment

● Thermostat rods

● Transformers

● Memory storage devices

● Inductors

● Invar 36

● Invar 42

Nickel-Copper Alloys

As nickel-copper alloy constitutes copper, they are highly corrosion-resistant materials, and the lack of magnetic properties makes them applicable for various applications. ● Marine applications

● Piping systems

● Seawater valves

● Pump shafts

● Monel 400

● Monel R405

● Monel K500

 

Nickel-Chromium Alloys

Nickel-chromium alloys are characterized by high-temperature strength, good electrical resistance, and excellent endurance to corrosion at all temperatures. ● Electrical resistance heaters

● Toasters

● Other heating elements

● Rene 41

● Ni70Cr30

Nickel-Titanium Alloys

Nickel-Titanium alloys are famous for their shape resistance quality. When deforming the original shape of the part, it will remember its initial shape and can be converted back into it whenever needed. ● Pressure vessels

● Piping products

● Pumps and valves

● Heat exchangers

● Valves

● Alloy B-2

Nickel-Molybdenum Alloys

The presence of molybdenum in nickel-molybdenum alloy ensures high chemical resistance to reducing acids, like, sulfuric acid, hydrochloric acid, and phosphoric acid. ● Shock absorbers in construction ● Nitinol

 

Applications of Nickel-based Superalloys

  • Aerospace

High Cr nickel-based alloys with good thermal corrosion resistance and stable structure are considered best for the manufacturing of ships and industrial gas turbines. Particularly, aircraft are complex machines that require many specifications under severe conditions. Aerospace engineers mainly depend upon nickel-based alloys to design parts that can face harsh environmental conditions. These alloys have the ability to withstand extreme weather conditions to ensure safe use.

Gas turbines are one of the best applications of the aerospace industry. A turbine is a fan that rotates and uses a power source to generate, like a wind turbine. Pressurized gas generates the necessary energy to spin the turbine.

  • Combustion chambers

Materials for combustion chambers have relatively low strength requirements. However, strength must be maintained up to operating temperatures of 1100 °C or higher. Furthermore, oxidation resistance, along with thermal fatigue and buckling resistance, is the most critical need.

To make fabrication more accessible, the material must also have good formability and weldability. That’s why nickel-based superalloys are the best choice for combustion chambers.

  • Turbine Blades

The turbine blade’s airfoil section experiences a temperature range of 650-980 °C and pressure of 138MPa. At 760 °C, the blade root attached to the disk experiences tensile stresses of 276 to 552 MPa outside of the hot gas path. This is why turbine materials must have enough ductility to withstand creep deformation. Hence, nickel-based alloys are used in manufacturing turbine blades as their mechanical properties can be maintained for an extended period.

  • Steam Turbines

Nickel-based superalloys are used to make steam turbine disks. Turbine disks need high creep and tensile strength for burst protection at hub operating temperatures. The operating temperatures of a steam turbine disc are up to 760 °C. This temperature only occurs on the outer rim near where the blade is attached. Besides, operating stresses caused by centrifugal loads are high at the rim. It becomes higher toward the center of these rotating components, exceeding 483MPa.

  • Nuclear Applications

High temperatures and high levels of corrosion characterize nuclear plant environments. Control rods, reactor cores, and other components are produced using nickel-based alloys. As a result, the nuclear industry can benefit significantly from this superalloy.

  • Engine Parts

Due to their excellent heat resistance, superalloys are ideal for heat-generating applications like heat exchangers. This is because superalloys are used in the manufacturing of engine parts. In addition, accessories for plane and aerospace equipment also use ni based superalloys.

 

Conclusion

Finally, you come up with a logical answer to your query, why are nickel-based alloys superalloys? The outstanding features and applications of superalloy make it a perfect superalloy. In a nutshell, you can use nickel-based superalloys where high temperature, corrosion, and strength resistance are required. Using these alloys as a manufacturing material for your products will indeed positively affect them.

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