Types of Superalloys

Introduction

Modern standards of production can be highly demanding. Engineers and designers are constantly pushed to meet industry requirements in performance, longevity, sustainability, and cost optimization. Industrial production is in a constant state of development. New design principles, production methods, and materials are crucial for innovation.

Some industries can be particularly demanding, such as the aerospace industry. Aerospace products endure extreme conditions during their life span. Conventional methods and materials are not enough to meet the industry’s standards: that’s why materials such as superalloys are used by aerospace engineers.

What Are Superalloys?

In essence, superalloys are materials with extreme performance statistics. Key attributes of a superalloy are high durability, extreme mechanical strength, thermal resilience, and longevity. The most crucial characteristic of a superalloy is its ability to operate under high fractions of its melting point. All of the properties mentioned make superalloys essential to the aerospace industry.

The original idea of developing materials suitable to operate under extreme conditions was originated from the desire to design aerocrafts that would take us higher and faster. The very development of superalloys is deeply intertwined with the swift expansion of the aerospace industry after the second world war.

Types of Superalloys

There are numerous variations of superalloys used in the aerospace industry. One of the most commonly used variations is titanium-based superalloys. Pure titanium has a relatively low density, high strength, and high corrosion resistance. In addition, titanium is the only element that burns with nitrogen. Titanium is as strong as steel but almost half as lighter. These properties alone make it an ideal material for the aerospace industry since the weight/strength ratio is critical to the industry. Titanium is mixed with other elements in specific ratios to further enhance its already great properties.

One of the most commonly used titanium-based alloys is the Ti-6Al-4V alloy. It contains aluminum and vanadium, in addition to titanium, and is mostly used in the cockpit frame, wing box, and fastener construction of commercial airplanes. This alloy displays a good balance of characteristics including strength, ductility, fracture toughness, high-temperature strength, creep characteristics, weldability, workability, and thermal processability. Ti-6Al-2Sn-4Zr-2Mo alloy is a heat-resistant alloy developed in the latter half of the 1960s. Its heat-resistant temperature is approximately 450˚C. This alloy is commonly used for compressor discs where 500˚C is the upper service temperature limit. Ti-5Al-2Sn-2Zr-4Cr-4Mo alloy, occasionally referred to as “Ti17” alloy, was developed in the USA during the 1970s as an alloy having high strength and excellent fracture toughness. Its heat-resistant temperature is approximately 350˚C. In commercial aircraft engines, the fan and shaft are built as one piece to reduce engine weight. Ti-10V-2Fe-3Al alloy has excellent hardenability, high strength, and high fatigue strength and it is mainly used for landing gear.

In addition to titanium-based alloys, ferrous alloys are another category of alloys which is commonly used in various industries, including the aerospace and military industry. In essence, ferrous alloys are alloys that are mostly consisted of Iron. Some of the most commonly used ferrous-based alloys are stainless steel, cast iron, and high-carbon steel. Ferrous alloys generally display a good balance of performance, including heat and corrosion resistance, durability, strength, and thermal resilience. Even though they do not display extreme performance like titanium-based superalloys or other superalloys, their ease of synthesis and price/performance ratio makes them invaluable.

Another crucial category of alloys for the aerospace and military industry is aluminum-based alloys. Weight to strength ratio of raw aluminum is already impressive on its own. The addition of alloying elements is copper, magnesium, manganese, silicon, tin, nickel, and zinc enhances those properties making aluminum alloys a perfect fit for military and aerospace applications. 7xxx series of aluminum alloys are the class mostly used in aerospace applications. The main alloying element of the 7xxx series is Zinc, making this class the strongest aluminum alloy. 7xxx series alloys display yield strength above 500 MPa. The most commonly encountered examples of 7xxx alloys are Al-Zn-Mg-Cu and Al-Li-Cu-Mg.

Final Words

Due to the high demands of modern-day industry standards, new materials and alloys are constantly being developed. Industries such as aerospace and military can be named as one of the most demanding industries. Implementation of superalloys and high-performing materials is essential when it comes to fulfilling industry standards. The rapid expansion of technology in metallurgy and production methods paints the picture of a brighter future built on better and cheaper materials.