Research progress on aerospace materials and anti ablation coatings: a review

India B R. Dr. Jalandal Ambedkar National Institute of Technology and the Indian Institute of Technology reviewed and reported on the research progress of aerospace materials and anti ablation coatings. The related paper was published in Optics&Laser Technology under the title "Progress in aerospace materials and ablation resistant coatings: A focused review".

a key:
1. A comprehensive overview of the latest developments in aerospace materials that are reshaping the aerospace industry.
2. Explored the increasingly serious threat posed by laser and other directed energy attacks to aircraft that people are increasingly concerned about.
3. The latest progress of anti laser ablation coatings in responding to laser attacks was highlighted.

The article also elaborates on the laser ablation mechanism of coatings under high-energy laser irradiation.
It has become particularly important to study the progress of aerospace materials and their performance under different load conditions and environments in pursuit of better performance, economy, safety, and environmental friendliness. The key highlights of contemporary research include breakthroughs in various materials, such as the high strength of carbon fiber reinforced polymer (CFRP) relative to weight, better corrosion resistance of aluminum and titanium based alloys, and good thermal stability of nickel based superalloys and ceramic matrix composites (CMC).

The article explains the significant progress made in the development of aircraft materials, but currently, the resistance to laser ablation is a huge problem facing the aerospace industry, as the threat of laser attacks is becoming increasingly severe.

This review provides a comprehensive overview of the latest developments in anti laser ablation coatings and their ablation mechanisms. The article integrates insights from interdisciplinary research work, providing valuable resources for researchers, engineers, and practitioners aimed at improving the durability and performance of materials under laser ablation.

Literature shows that compared to coatings based on Zr and Si, composite coatings based on Zr and Si have higher resistance to laser ablation, as they synergistically combine high thermal conductivity, excellent hardness, and better thermal shock resistance. Introducing TiO2 into composite coatings can promote the formation of reactive oxygen species, facilitate oxidation reactions, help repair defects within the coating, and thus enhance the self-healing ability of the coating. In addition, the back surface temperature of the double-layer coating is the lowest, which means that due to the increase in reflectivity, the absorption of laser energy by the substrate is minimal, thus causing the least damage to the substrate. The multi-layer zirconia based system (ZBS) coating with molybdenum as the bonding layer has excellent resistance to laser ablation. However, multi-layer coatings such as high reflective outer layers and heat-resistant inner layers with optimal thickness still need to be studied in improving their resistance to laser ablation.

Figure 1. Materials used in different aircraft.

Figure 2. SEM images of aluminum alloy ablation points at different energies (30 fs, N=10).

Figure 3. SEM images of the ablation site of aluminum alloy under different laser pulse numbers (30 fs, 0.63 Jcm-2).

Figure 4. Surface morphology of induced pits on aluminum targets after air mediated ablation. (a) Overall view; (b) Central ablation area; (c) Peripheral ablation area.

Figure 5. SEM images of YSZ coating after ablation - (a) 1 second and (b) 10 seconds.

Figure 6.10 SEM image and EDS analysis of ZBS coating - (a) Region 1, (b) Region 2, (c) Region 3.

Figure 7. Phase composition and morphology of ZrC coating on silicon carbide coated C/C composite material.

Figure 8. SEM image of ZrC composite coating synthesized by reaction.

Figure 9. SEM images of the surface of in-situ ZrC composite coating after ablation at 10 seconds (a, b) and 20 seconds (c, d) under different magnifications (central region of the sample).

Figure 10. Proposed laser ablation mechanism.

Figure 11. Incremental Method for US Navy Laser Weapons.

Figure 12. MLD system (maritime laser weapon system) of the United States Navy.

Figure 13. Conceptual rendering of a 500000 watt laser weapon designed by Lockheed Martin for the US Department of Defense's High Energy Laser Expansion Program (HELSI). This laser weapon will be tactically configured and support military platforms. Image from Lockheed Martin Corporation.

Figure 14. Airborne laser weapon system. Image from Lockheed Martin Corporation.

In the past century, the aviation industry has made significant progress, much of which can be attributed to continuous improvement and innovation in structure and engine materials. The foundation of modern aerospace engineering is composed of high-performance alloys and composite materials based on Al, Mg, Ti, and Ni. Undoubtedly, these materials have good performance in terms of specific strength, corrosion resistance, wear resistance, etc., but still cannot meet the requirements of laser ablation resistance. With the large-scale development of lasers and other directed energy weapons, protecting aircraft materials from laser damage is a matter of concern. In order to protect the substrate from laser damage, people are developing anti laser ablation coatings.

In the past century, the aviation industry has made significant progress, largely due to continuous improvement and innovation in structural and engine materials. The foundation of modern aerospace engineering is based on high-performance alloys and composite materials of Al, Mg, Ti, and Ni. Undoubtedly, these materials have better performance in terms of strength, corrosion resistance, and wear resistance, but still cannot meet the performance requirements for laser ablation resistance. With the large-scale development of lasers and other directed energy weapons, protecting aircraft materials from laser damage has become a concern for people. We are currently developing anti laser ablation coatings to protect the substrate material from laser damage. Based on public literature, the following conclusions have been drawn:

i. Coatings based on Zr and Si have been proven to be quite effective in protecting substrates from laser damage. Compared with coatings based on Zr and Si, composite coatings based on Zr and Si have better reflectivity and thermal stability, thus exhibiting better resistance to laser ablation.

Ii. Introducing TiO2 into composite coatings can enhance their self-healing ability. Therefore, ZrO2/TiO2 coatings have self-healing properties, while ZrO2/SiO2 has a greater protective effect. Titanium dioxide has good thermal stability and can maintain its structural integrity and performance even in harsh environments.

Iii. It was found that the back temperature of the double-layer coating is the lowest, which means that due to the increase in reflectivity, the degree of laser energy penetration through the substrate is the smallest, thus causing the least damage to the substrate.

Iv. Multilayer ZBS coatings and bonding layers have excellent resistance to laser ablation. The thermal stress distribution is small and continuous, resulting in fewer cracks, thus possessing excellent resistance to thermal damage.

However, in the past, the use of Ti/TiO2 seems to be very limited when studying the ablation behavior of anti laser damage coatings. In previous literature, there has not been sufficient discussion on how to control the texture of the substrate surface to improve the adhesion of coatings on aircraft materials, thereby achieving anti laser ablation applications. Multiple layers of coatings can be attempted, such as a highly reflective outer layer and a heat-resistant inner layer with optimal thickness, to improve reflectivity and thermal damage resistance, thereby more effectively reducing laser ablation.

In summary, the development of anti laser ablation coatings and advancements in aerospace engineering mark a significant step forward in ensuring the safety and security of aircraft, their crew, and passengers. The aerospace industry can greatly improve its ability to resist laser attacks and enhance the overall integrity of aviation systems through continuous research and application.

Source: Yangtze River Delta Laser Alliance