N251-011 TITLE: Extreme High Speed Laser Application (EHLA) for Titanium Cylinders Bores

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials;Sustainment

OBJECTIVE: Develop Extreme High Speed Laser Cladding technology for the inner bore of titanium cylinders.

DESCRIPTION: Internal bore diameters of hydraulic cylinders and dampers experience excessive wear in extreme conditions and require replacement at high cost. Current titanium coating applications introduce a high heat-affected zone into titanium housings causing, delamination, reduced fatigue life, distortion, and surface cracking. Coating technologies available today are limited to select processes as to not affect the base titanium material but the processes still ultimately result in early failure of the component due to heat-affected zone penetration. Additionally, coating blind bores is not common in industry. This is due to fixturing and tooling available as discussed in the third paragraph.

Coating the bore of the cylinder with a hard, wear-resistant, and corrosion-resistant coating is desirable to extend the life of the component. The Extreme High Speed Laser Application (EHLA) technology is unique in that it melts the powder before it hits the substrate, which causes a very little heat-affected zone, by orders of magnitude less than common coating applications. For comparison purposes, EHLA may create heat-affected zone of ~0.001 in.–0.003 in. (0.025–0.076 mm), whereas traditional laser clad creates a heat-affected zone of 0.03 in. (0.076 mm), or more. With EHLA, the coating is metallurgical bonded via the fusion process to the base layers, so it does not chip, peel, or delaminate.

The EHLA process has mainly been used for line-of-sight applications, but the technology has progressed, and non-line-of-sight (NLOS) equipment is now available for use within the past year. The benefit of NLOS is that it allows the coating to get into smaller diameter bores, radii, and difficult transition areas of a part. A German company named the Fraunhofer-Gesellschaft originally developed this technology. China has heavily invested in this technology. The Fraunhofer-Gesellschaft is currently the only company in the world that has vast experience in extreme high-speed laser application technology. They have used this technology to coat external components. Small Internal bore application has been developed within the last year, which can now be applied down to 3.5 in. (8.89 cm) diameters. Successfully coating titanium bores with this technology will help future programs and future Original Equipment Manufacturers (OEMs) be less averse to selecting titanium as an actuator or cylinder material. By choosing titanium they can adhere weight savings on the aircraft because they get the added benefit of this novel wear coating's performance. This technology is not restricted to titanium cylinders, but the process can be adapted to coat aluminum and steel cylinders easily and have the same beneficial results. EHLA is cost-effective due to few required pre/post processing treatments, high repeatability and precisely controllable, and it can easily be removed and reapplied without the need of building another asset.

PHASE I: Identify potential wear coatings and application for use on Titanium cylinder substrates with NLOS applications using EHLA technology. Determine a coating material that can be applied to beta-STOA Ti-6Al-4V (Current supplier: Consolidated Industries) that has a high-Rockwell Hardness C (HRC) rating and high-wear resistance with small ductility in order to prevent wear and internal debris. Identify methods to ensure the surface has adequate texture for oil retention and lubricity. Determine and define the correct laser head and powder feeding rate to properly apply the coating onto the titanium cylinder that keeps the temperature at or below 350 °F (176.66 °C) with as little heat-affected zone as possible. Provide evidence of feasibility for developing the coating process in Phase II. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Prototype the EHLA NLOS process for application of wear coatings for Titanium cylinder substrates with minimum bore inside diameter of 3.5 in. (8.89 cm) and minimum length of 12 in. (30.48 cm) based on Phase I results. Develop and implement the coating method to ensure surface has adequate texture for oil retention. Complete necessary testing to validate the integrity of the substrate and the coating: metallurgical analysis, bond testing, wear testing, corrosion testing, and fatigue. Provide a report that outlines the prototype process, equipment, methodology and testing completed to verify integrity. Develop a plan to mature the technology in Phase III.

PHASE III DUAL USE APPLICATIONS: Using the matured EHLA NLOS process, coat a full-scale 53K titanium damper housing and complete a full-scale 1700 hr endurance test to demonstrate that the EHLA process provides minimal wear and corrosion resistance. Once complete, this technology can begin to integrate into the 53K fleet and become a route for OEMs to design hydraulic cylinders out of titanium to provide weight savings.

OEMs and the private sector will benefit from this technology by having the capability to coat titanium cylinders instead of typically going with steel in order to provide weight savings. Along with the added benefit of reducing internal wear, higher quality adhesion to the cylinder housing, and superior oil retention for a sliding seal. EHLA is available for use in multiple cylinder applications including aluminum and steel.

REFERENCES:

1. Li, Z.; Sui, S.; Ma, X.; Tan, H.; Zhong, C.; Bi, G.; Clare, A. T.; Gasser, A. and Chen, J. "High deposition rate powder-and wire-based laser directed energy deposition of metallic materials: A review." International Journal of Machine Tools and Manufacture, 181, 103942, 2022. https://www.sciencedirect.com/science/article/pii/S0890695522000931

2. Zhou, L;, Ma, G.; Zhao, H.; Mou, H.; Xu, J.; Wang, W.; Xing, Z.; Li, Y;, Guo, W. and Wang, H. "Research status and prospect of extreme high-speed laser cladding technology." Optics & Laser Technology, 168, 109800, 2024. https://www.sciencedirect.com/science/article/pii/S003039922300693X

3. "Fine and fast metal printing meets industrial challenges in 3D." Photonics Spectra, May 2024. https://www.photonics.com/Articles/Fine_and_Fast_Metal_Printing_Meets_Industrial/a69854

4. The Fraunhofer-Gesellschaft. (n.d.). https://www.fraunhofer.de/en.html

KEYWORDS: Coatings; Titanium; Extreme High Speed Laser Cladding; Wear Resistant; Actuators; Dampers

TPOC 1: Jeremy Pilkerton
(301) 997-5652
Email: [email protected]

TPOC 2: Robert Taylor
(301) 342-621
Email: [email protected]

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