Introduction
Inconel is a family of nickel-chromium alloys that has proven to be indispensable in various industries, especially those operating in extreme conditions. Its ability to maintain its structural integrity and mechanical properties under elevated temperatures and corrosive environments makes it a material of choice for critical applications. In this article, the main characteristics of this alloy are presented, with a focus on the Inconel 625 and Inconel 718 variants, and their applications in different industrial sectors.
What is Inconel and what are its main properties?
They are nickel alloys containing chromium, molybdenum, and other elements that improve their mechanical properties and corrosion resistance. Inconel alloys are known for their exceptional strength in high-temperature environments and their ability to resist oxidation and corrosion. These materials are essential in applications where durability and performance in adverse conditions are required.
Chemical composition
The chemical composition varies according to the specific alloy. For example, 625 is composed of approximately 58% nickel, 21-23% chromium, 8-10% molybdenum, and small amounts of iron, niobium, and tantalum. This combination gives it exceptional resistance to corrosion and oxidation, as well as remarkable thermal stability.
On the other hand, 718, another outstanding alloy, contains between 50-55% nickel, 17-21% chromium, 4.75-5.5% niobium, as well as molybdenum, aluminum, and titanium. The presence of niobium and titanium allows this specific material to be strengthened by heat treatment, improving its mechanical properties, especially in very high-temperature applications.
Mechanical properties
These properties are a determining aspect of its value in industrial applications. Inconel 625, for example, has high tensile strength, creep resistance, and excellent ductility, even in extremely corrosive environments, which characterizes it for applications in the chemical, marine, and power generation industries.
Inconel 718, in contrast, has a combination of high mechanical strength and creep resistance, making it useful in aerospace applications and in the gas turbine industry. At temperatures of 700 °C, it remains stable, making it an ideal choice for aircraft engine components and other high-temperature systems.
Why is Inconel ideal for high-temperature and corrosive environments?
Their resistance to corrosion and high temperatures is one of the main properties to be considered in critical applications, such as severe conditions that would destroy other materials. Below, we analyze the factors that make them a preferred choice in these environments.
Corrosion resistance: This superalloy shows outstanding resistance to various types of corrosion such as pitting, crevice, and intergranular corrosion. This is due to the formation of a passive layer of chromium oxides on the surface of the material, which acts as a protective barrier against corrosive agents. In marine environments, for example, Inconel 625 is widely used in salt water, as components of underwater structures and naval propulsion systems.
High-temperature behavior: At high temperatures, Inconel is mechanically resistant to oxidation and wear, which is why alloys such as Inconel 718 are used in aerospace applications at temperatures above 700 °C.
Applications in aggressive environments
Inconel alloys are especially valued in industries where materials are exposed to highly corrosive environments and extreme temperatures. The petrochemical industry, for example, uses it in sour gas processing systems, where resistance to corrosion and oxidation is critical to safety and operational efficiency.
Industrial applications
The versatility of this material is reflected in its use in a wide range of industries. Below, we explore some of the most common applications in different sectors.
Power generation: One of the most hazardous applications is power generation, especially in nuclear and thermal power plants. In these environments, materials must withstand high temperatures, pressure, and exposure to corrosive environments. In these environments, Inconel, due to its anti-corrosive properties and thermal stability, is used as a component in boilers, heat exchange systems, and piping exposed to aggressive fluids.
Aerospace industry: Inconel 718 is one of the most widely used alloys in the aerospace industry due to its ability to maintain its mechanical strength at extremely high temperatures. Critical components of aircraft engines, such as turbine disks, combustion chambers, and blades, are manufactured with this alloy and it is also used in the manufacture of parts for rockets and other propulsion systems, where temperatures can exceed 1000°C.
Marine industry: Due to its characteristics and high resistance to marine environments, it is very useful in seawater. The properties of Inconel alloys make it perfect for manufacturing shafts, valve components, propellers, quick disconnects for submarines, and auxiliary propulsion engines for submarines.
Oil and gas industry: It is used in different applications in this industry. Due to its high corrosion and temperature resistance, it is used in oil refining, liquefied natural gas production, offshore systems, flow lines for subsea walls, flare stacks, wellheads, pipe casing, and risers.
Chemical and petrochemical industry: In the chemical and petrochemical industry, it is valued for its resistance to corrosion in environments containing acids, salts, and other aggressive compounds. It is widely used in piping systems, valves, and pressure vessels, where corrosion resistance is indispensable.
Medical industry: Due to its biocompatibility, wear resistance, corrosion resistance, and low magnetic susceptibility of 625, it is used to produce medical devices such as cardiovascular implants, surgical tools, orthopedic implants, dental implants, and diagnostic equipment.
Automotive industry: It is used in the manufacture of high-performance engine components, turbochargers, and exhaust systems requiring corrosion resistance at high temperatures.
Comparison between Inconel 625 and Inconel 718
Although these two alloys are widely used in the industries, their properties, and chemical compositions make them suitable for different applications.
Inconel 625: It has high corrosion resistance in a wide variety of corrosive media. Its ductility and weldability are considered ideal for applications in the marine and chemical industry, where a combination of mechanical strength and corrosion resistance is required. In addition, its thermal stability allows its use in components exposed to extreme temperatures without significant loss of mechanical properties.
Inconel 718: It is preferred in applications where high mechanical strength and creep resistance at elevated temperatures are required. Its ability to be reinforced by heat treatment allows it to maintain its strength at temperatures above 700 °C, which is why it is widely used in applications in the aerospace and power generation industries.
Conclusion
Inconel, in its different alloys and forms, is widely used in numerous industries thanks to its thermal and anticorrosive properties, as well as its resistance to extreme temperature and corrosion conditions. This material has proven to be fundamental in applications that require high mechanical standards and long-term durability, from power generation to the aerospace industry. Its use has enabled these industries to operate safely and efficiently in the most aggressive environments.
References
- https://www.bhansalioverseas.com/blog/common-applications-of-inconel-625-sheets-in-medical-devices/#:~:text=Inconel%20625%20sheets%20are%20often,%2C%20surgical%20instruments%2C%20and%20prosthetics.
- https://www.hq-specialalloys.com/applications-of-alloy-inconel-718-wire-in-different-industries/
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