Steel plays a crucial role in various applications within modern aircraft and aerospace systems. Different grades of steel are utilized for structural components, leveraging their high strength, toughness, stiffness, and corrosion resistance.
Image Credit: Andrei Armiagov/ShutterStock.com
As a result of these favorable properties, essential components like landing gears, engine mounts, bolts, and fuselage components have been commonly manufactured using steel.
In response to the rigorous requirements of contemporary aircraft, ongoing research aims to enhance steel characteristics and devise new processes that substantially boost its durability and resilience to environmental factors, contributing to improved overall aircraft performance.
Advances in Martensitic Steels for Aerospace Structural Applications
Ultra-high strength steels (UHSS) are high-strength steels with a yield strength surpassing 1380 MPa. They find common applications in critical components, such as aero-engine bearings and landing gear, due to their exceptional strength, toughness, and fatigue properties.
In the structural design of aerospace products, prioritizing lightweight design is a fundamental concept. Despite the prevalence of high-specific strength materials like aluminum alloy, titanium alloy, and composites, the use of steel in aircraft structures has diminished.
Nevertheless, UHSS remains the preferred material for aero-engine main bearings and landing gear. Achieving UHSS with ultimate tensile strength exceeding 2 GPa in a singular case is readily achievable.
Controlling the size, quantity, and location of nano-scale particle formation is crucial for enhancing the strength and toughness of structural steel. Researchers published an article in the Journal of Materials Research and Technology specifying a novel strengthening method for aerospace steels.
The latest method involves combining low lattice misfit Nano-particles with the creation of a martensite matrix containing many dislocations. This approach uses the synergistic effects of NiAl nano-particles and high-density dislocations to strengthen the material.
Utilizing a nano-scale co-precipitation strengthening method with NiAl is a potential approach for enhancing toughness. By advancing the strength grade, this method can synergistically combine various types of nano-particles, surpassing the performance achieved by strengthening steel with a single type of nano-particle.
Developing new Ultra-High Strength Steels (UHSS) requires careful consideration of composition design, preparation processes, and service performance. The aim is not only to address the limitations of conventional UHSS but also to thoroughly explore and utilize innovative strengthening and toughening mechanisms to optimize the balance between strength and toughness.
Development of an Armor for Aerospace-Grade Steels
Hexagonal boron nitride (hBN) is a key 2D material known for its flat layered structure, chemical inertness, and significant thermal stability. These characteristics make it versatile for various applications. In addition to its role as a substrate, hBN serves as an insulating material and an excellent protective layer, preventing corrosion and providing resistance against high-temperature oxidation.
Researchers in Advanced Materials Interfaces reported a chemical vapor deposition process for the uniform growth of hBN on extensive surfaces of diverse alloys and steels, irrespective of their intricate shapes.
In contrast to prior reports of limited protection by hBN against corrosion and oxidation, the study demonstrates the effective safeguarding of steels against 10 % hydrochloric acid (HCl) and resistance to oxidation at 850 °C in the presence of air. A substantial decrease in the friction coefficient of the steels coated with hBN is also showcased.
The team highlighted the effectiveness of hBN films, directly synthesized on steels, in protecting against corrosion and high-temperature oxidation. They also demonstrated improved tribological properties.
The armor for steel provided enhanced protection to the parts for up to 10 days. This protective coating will significantly improve the durability of several aerospace components, especially those present in the combustion chambers of modern engines.
An Introduction to Passively Precipitated Hardening Steel
For steel components utilized in aircraft, a specialized chemical treatment called passivation is applied. This significantly enhances corrosion resistance. Manufacturers employ various types of Precipitation Hardening stainless steels in different parts of aircraft.
Custom450 is chosen for turbine blade production, AM350 is applied in shafts, rotors, and turbine blades, while 15-5PH and 17-4PH are preferred for structural components such as flaps. These materials and treatments are crucial for ensuring the durability and reliability of aerospace components exposed to demanding operational conditions.
An article published in Metals investigated the electrochemical behavior of passivated 15-5PH, 17-4PH, Custom450, and AM350 stainless steels using citric and nitric acid baths. Passivation was conducted for varying durations at different temperatures.
The evaluation was performed in sodium chloride (NaCl) and sulfuric acid (H2SO4) solutions using potentiodynamic polarization curves (PPC) as per the ASTM G5-13 standard.
In H2SO4, a secondary passivation was observed, while in NaCl, there was a pseudo-passivation with an unstable passivation film. Current densities in NaCl ranged from 10-4 to 10-5 mA/cm2, whereas those in H2SO4 were around 10-2 to 10-3 mA/cm2.
Citric acid demonstrated passivation effectiveness, with corrosion resistance comparable to nitric acid in some cases. Recent research has highlighted that citric acid can easily be used for passivation techniques, as it results in less environmental degradation and does not release toxins.
High-Performance Bamboo Steel: A New Material for Aerospace Parts
Researchers all over the world are trying to minimize the emissions and environmental effects of the aerospace sector. The use of natural materials will significantly reduce greenhouse gas emissions.
To develop an alternative to conventional steel, researchers have introduced an efficient top-down approach to transform natural bamboo into "bamboo steel." This method is outlined in an article published in ACS Applied Materials and Interfaces.
The fabrication involved removing lignin and hemicellulose, freeze-drying, epoxy infiltration, and densification with in situ solidification. The resulting bamboo steel is a super-strong composite material with impressive specific tensile strength (302 MPa g-1 cm3), surpassing conventional high-specific-strength steel (227 MPa g-1 cm3).
Bamboo steel exhibited high tensile strength (407.6 MPa), record flexural strength (513.8 MPa), and substantial toughness (14.08 MJ/m3). This approach, using naturally abundant bamboo, holds promise for developing sustainable aerospace and civil engineering materials specialized for structural parts.
More from AZoM: Mechanical Materials Testing Used in Aerospace Applications
References and Further Reading
Li, J., et al. (2023). Progress on improving strength-toughness of ultra-high strength martensitic steels for aerospace applications: a review. Journal of Materials Research and Technology. doi.org/10.1016/j.jmrt.2022.12.177.
Vlassiouk, I., et al. (2024). Armor for Steel: Facile Synthesis of Hexagonal Boron Nitride Films on Various Substrates. Advanced Materials Interfaces. doi.org/10.1002/admi.202300704.
Villegas-Tovar J., et al. (2023). Electrochemical Corrosion Behavior of Passivated Precipitation Hardening Stainless Steels for Aerospace Applications. Metals. doi.org/10.3390/met13050835.
Wang, Y., et al. (2020). High-performance bamboo steel derived from natural bamboo. ACS applied materials & interfaces. doi.org/10.1021/acsami.0c18239.
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.