Titanium vs. Inconel vs. Steel: Choosing the Right Aerospace Fastener Material
Thousands of bolts, rivets, screws, and pins are utilized across an aircraft, but different sections face vastly different physical demands. This means that engineers must be incredibly selective regarding fastener materials to balance their weight and the type of resilience they must present. Titanium, Inconel, and steel are among the most popular options, so this blog will cover their distinct properties and applications to help you make the appropriate choice for any repair.
Titanium
As every ounce of weight saved on an aircraft translates to increased fuel efficiency and payload capacity, titanium is prized for its exceptional strength-to-weight ratio. While its main benefit is being roughly 40% lighter than steel alloys, this metal also presents:
- Superior Corrosion Resistance: Titanium naturally forms a passive oxide film that protects it from the corrosive effects of saltwater, moisture, and various hydraulic fluids.
- Thermal Stability: With a lower coefficient of thermal expansion compared to most aerospace metals, titanium is much less prone to fatigue or loosening in joints where standard thermal cycling occurs.
- Superior Material Compatibility: Titanium is highly compatible with carbon-fiber-reinforced polymers (CFRP) without any major risk of galvanic corrosion, so fasteners made from this material are able to be integrated into composite structures without requiring extensive insulation layers, specialized coatings, or heavy sealants.
With these strengths, titanium fasteners are prevalent in airframe structures, wing skins, and engine components. However, this is only as long as they are not placed where temperatures are expected to exceed 600°F, since they begin to lose their structural properties and succumb to oxidation beyond this threshold. Furthermore, even though they are corrosion resistant in many conditions, embrittlement and cracking can occur if they are exposed to specific de-icing fluids or certain chlorides at high temperatures.
Inconel
Inconel refers to a variety of nickel-chromium superalloys, these materials having the unique ability to withstand the most demanding thermal environments where other metals would soften or oxidize. Although they are heavier than titanium, this is further made up for by their:
- Oxidation and Corrosion Resistance: Most Inconel grades naturally develop a thick oxide layer when heated, protecting the fastener from becoming brittle or failing as a result of high-pressure environments, chemicals, or volatile gases.
- Mechanical Strength: Broadly, the Inconel family is known to resist creep, which is the tendency of a solid material to deform permanently under persistent mechanical stresses. Inconel 718 is the most common grade for aerospace fastener materials for its high yield, tensile, and creep-rupture strength at temperatures up to 1,200°F.
Aside from their relatively heavy weight, the main issue of utilizing Inconel is caused by their manufacturing process. Inconel becomes harder and more brittle as it is deformed, mandating specialized tooling and costly production cycles to achieve the high-tolerance threads required for aerospace standards. Thanks to these drawbacks, Inconel fasteners are mostly reserved for the hot sections of an aircraft, such as turbine engines, exhaust manifolds, heat shields, and combustion chambers.
Steel
Despite the rise of more exotic alloys, steel is still widely employed for its:
- Versatility: The aerospace industry utilizes a broad spectrum of steel alloys to fit environmental demands. For example, 300-series stainless steels display excellent corrosion resistance, whereas A286 iron-base superalloys fit applications requiring high strength and oxidation resistance at elevated temperatures.
- High Strength: Generally, steel alloys offer excellent fatigue life and tend to deform slightly rather than fracture under sudden, extreme loads. Some high-strength alloy steels, such as 4130 or 4340, provide tensile and shear strengths exceeding titanium.
- Manufacturing and Cost Efficiency: Steel is much more affordable and easier to manufacture than other metals, making them perfect wherever the additional benefits offered by more options are not necessary.
Steel fasteners are favored for heavy-load applications like landing gear assemblies, engine mounts, and wing attachment points. While 300-series stainless steels provide the necessary corrosion resistance for moisture-prone areas, many other forms of alloy steel are very susceptible to atmospheric corrosion and hydrogen embrittlement and need plating to last.
Turn to Parts Circuit for the Aerospace Fasteners You Need
It might seem to be the priority to choose the aerospace fastener material that presents the best balance between strength and weight, but each of these options have distinct advantages and weaknesses in different areas that should be part of your decision making. Regardless of which type ends up suiting your requirements, you can source a wide array of high-quality aerospace fasteners on Parts Circuit.
As an ASAP Semiconductor owned and operated platform, we are backed by industry-leading certifications and complete supply chain transparency that guarantees everything we offer holds up to the rigorous standards of the aerospace industry. Moreover, we pride ourselves on creating a seamless experience where you can easily track down the exact items you need from our extensive inventory and request rapid, tailored quotes. We look forward to aiding with all your procurement needs, so learn more about our services by exploring our website and connecting with our experts!
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