When working with high-performance materials in extreme environments such as aerospace, nuclear, and marine engineering, selecting the right alloy is crucial. Among the most commonly used superalloys are NIMONIC and Inconel. Although both superalloys are recognized for their high strength and resistance to heat and corrosion, they differ significantly in terms of composition, mechanical properties, and suitability for various applications. This article will compare NIMONIC 90 bars and Inconel 718 bars, two popular grades in their respective families.
This blog explains the key differences between NIMONIC and Inconel bars, focusing on their composition, properties, and applications, helping engineers and procurement specialists choose the right alloy for their needs.
Understanding Superalloys: NIMONIC vs. Inconel
Both NIMONIC and Inconel are nickel-based superalloys developed for high-temperature and high-stress applications. These materials are especially valued in environments where standard stainless steel would fail due to heat, oxidation, or extreme pressure.
However, the differences between these two lie in their exact chemical makeup, mechanical behavior, and intended applications. Let’s break this down further.
What Are NIMONIC 90 Bars?
NIMONIC 90 is a precipitation-hardenable superalloy primarily composed of nickel (around 57%), chromium (18-21%), and cobalt (15-21%). It also contains smaller amounts of titanium, aluminum, and iron.
Key Characteristics of NIMONIC 90 Bars:
- Excellent high-temperature strength: NIMONIC 90 Bars retain mechanical strength and structural integrity at temperatures up to 920°C (1688°F), making them ideal for extreme heat applications.
- Superior creep and oxidation resistance: They resist deformation under long-term stress and maintain stability in oxidizing environments at high temperatures.
- Good weldability and fabricability: NIMONIC 90 Bars can be welded and formed using conventional techniques, although care is needed for thicker sections.
- Precipitation hardenable for increased strength: The alloy can be heat-treated to enhance its strength through controlled precipitation of hardening phases.
- High fatigue resistance under thermal cycling conditions: NIMONIC 90 performs reliably under repeated heating and cooling, minimizing the risk of failure in cyclic load conditions.
These properties make NIMONIC 90 bars ideal for demanding high-temperature applications such as turbine blades, jet engine components, high-temperature bolts and fasteners, and nuclear reactor parts. Specifically designed for mechanical strength at elevated temperatures, NIMONIC 90 excels in environments where materials are subjected to prolonged stress, extreme heat, and oxidation, ensuring long-term performance and reliability in some of the most critical and harsh engineering conditions.
What Are Inconel 718 Bars?
Inconel 718 is another nickel-based superalloy but with a significantly different chemical structure. It consists of nickel (50-55%), chromium (17-21%), iron (balancing element), and notable additions of niobium, molybdenum, titanium, and aluminum.
Key Characteristics of Inconel 718 Bars:
- Exceptional tensile, fatigue, creep, and rupture strength:
Inconel 718 bars offer outstanding strength under tension, cyclic loading, and prolonged high-stress conditions, making them suitable for critical structural components. - High resistance to corrosion and oxidation:
They resist chemical attack and oxidation in harsh environments, including acidic, marine, and high-temperature conditions, ensuring durability over time. - Great performance in both cryogenic and high-temperature environments (up to 700°C or 1290°F):
Inconel 718 maintains its toughness and mechanical properties from sub-zero temperatures up to 700°C, making it versatile for a wide range of thermal conditions. - Excellent weldability compared to other superalloys:
Unlike many high-strength alloys, Inconel 718 can be welded easily without cracking or losing its mechanical integrity, even in thick or complex sections. - Age-hardenable for added strength:
The alloy can undergo a heat treatment process (precipitation hardening) to significantly increase its strength and resistance to deformation.
Because of their excellent combination of strength and corrosion resistance, Inconel 718 bars are commonly used in gas turbines and jet engines, cryogenic storage tanks, chemical processing equipment, aerospace and marine applications, and nuclear fuel element spacers. Inconel 718 is often preferred in corrosive environments where both high mechanical strength and resistance to pitting, crevice corrosion, and chloride stress cracking are critical for long-term reliability and performance.
NIMONIC 90 vs. Inconel 718 – A Side-by-Side Comparison
Primary Elements
- NIMONIC 90 Bars are primarily composed of Nickel (Ni), Chromium (Cr), Cobalt (Co), Titanium (Ti), and Aluminum (Al), giving them exceptional strength and oxidation resistance at high temperatures.
- Inconel 718 Bars contain Nickel (Ni), chromium (Cr), Iron (Fe), niobium (Nb), Molybdenum (Mo), titanium (Ti), and Aluminum (Al), which together provide excellent corrosion resistance and mechanical properties.
Maximum Temperature
- NIMONIC 90 Bars can maintain their strength and performance at temperatures up to approximately 920°C, making them ideal for high-temperature applications like gas turbines.
- Inconel 718 Bars retain high mechanical strength up to about 700°C, performing exceptionally well in both cryogenic and moderately high-temperature environments.
Corrosion Resistance
- NIMONIC 90 Bars offer good resistance to oxidation and corrosion, especially at elevated temperatures, but are not as corrosion-resistant in chemical environments.
- Inconel 718 Bars excel in resisting a wide range of corrosive environments, including those involving acids, seawater, and high-pressure conditions.
Creep Resistance
- NIMONIC 90 Bars demonstrate high resistance to creep, making them suitable for components that experience prolonged stress at elevated temperatures.
- Inconel 718 Bars show very high creep resistance, especially when age-hardened, allowing them to withstand extreme operational stresses over time.
Fabrication
- NIMONIC 90 Bars are generally fabricable, but can be challenging to machine or weld in thicker sections due to their hardening properties.
- Inconel 718 Bars are known for their excellent weldability and machinability, even in complex and thick-walled components.
Applications
- NIMONIC 90 Bars are commonly used in the manufacture of turbine blades, high-temperature fasteners, and jet engine parts, thanks to their thermal stability.
- Inconel 718 Bars are widely used in aerospace, marine, and chemical processing industries due to their superior corrosion resistance and mechanical strength.
Age Hardening
- NIMONIC 90 Bars undergo age hardening to enhance strength and resistance to mechanical fatigue under high thermal loads.
- Inconel 718 Bars are also age-hardenable and benefit from a unique slow-aging process that enhances their strength and fatigue resistance.
Fatigue Resistance
- NIMONIC 90 Bars exhibit high fatigue resistance, especially under thermal cycling, making them ideal for rotating and high-stress parts.
- Inconel 718 Bars offer exceptional fatigue resistance, even under fluctuating loads and temperatures, contributing to their reliability in demanding aerospace applications.
Choosing Between NIMONIC 90 and Inconel 718
The decision to use nimonic 90 bars or inconel 718 bars depends entirely on the application’s specific demands. Here are a few guidelines:
- Go with NIMONIC 90 if you need superior performance at temperatures above 800°C and where creep resistance under prolonged stress is vital. It’s well-suited for static parts like turbine blades and high-temperature fasteners.
- Choose Inconel 718 if the application requires excellent corrosion resistance, high strength, and weldability—especially in environments involving fluctuating temperatures or exposure to chemicals. It’s a go-to material for dynamic and complex components like aerospace engine parts.
Final Thoughts
While both NIMONIC and Inconel are powerhouse materials in the world of high-performance alloys, understanding the differences between them is essential to choosing the right one for your project. Nimonic 90 bars are optimized for high-temperature strength and creep resistance, while inconel 718 bars offer a broader spectrum of strength, corrosion resistance, and ease of fabrication.
Each alloy has its own niche, and selecting the right one will result in longer component life, better performance, and reduced maintenance costs in extreme conditions. Whether you’re designing for aerospace, power generation, or chemical processing, knowing the distinct characteristics of these superalloys helps ensure success in demanding engineering applications.
