Enhancing Rotary Engine Performance with Hexagonal Boron Nitride Coatings

This Phase I effort aims to prove the technical feasibility of hexagonal boron nitride (hBN) as a protective coating to improve the efficiency, durability, and performance of Navy UAV rotary engine components operating in harsh marine environments. Rotary engines used in UAVs are exposed to high temperatures, corrosion, abrasive particulates, and thermal cyclingóall of which degrade core components including apex and side seals, shafts, springs, and rotors. These degradation mechanisms reduce sealing integrity and emulsify liquid lubricants, ultimately impairing power output, and efficiency losses.hBN is a two-dimensional ceramic coating with a rare combination of properties ideal for addressing the Navyís material and tribological challenges. It is synthesized on iron and nickel containing metal alloys and exhibits exceptionally low friction at temperatures exceeding rotary engine operating temperatures, making it well-suited for use as a solid lubricant in high-contact interfaces such as seal-to-housing sliding surfaces. hBN's abrasion resistance mitigates wear caused by salt, sand, and dust which are common threats in coastal environments. Additionally, hBN is chemically stable when exposed to fuel and salt conditions, offering robust protection against pitting, crevice, and galvanic corrosion. hBN also retains structural integrity at temperatures exceeding 850∞C, enabling them to withstand the thermal cycling inherent in start-stop rotary engine operation.hBN's high thermal conductivity promotes lateral heat spreading, helping prevent hot spots that cause localized fatigue and warping in lightweight alloys. Moreover, as an electrical insulator, hBN can mitigate galvanic coupling when dissimilar metals are present within the engine assembly.While hBNís protective characteristics are well-established at the laboratory scale, its historical limitation has been cost-effective, scalable synthesis. This project leverages technology developed at Oak Ridge National Lab (ORNL) which enables a scalable and cost effective CVD method. The process uses abundant cost-effective benign precursors in place of traditional cost prohibitive and hazardous precursors. It is also leverages gas injection that enables atmospheric pressure, which opens opportunities for commercial scalability and high volume manufacturing, which overcomes the limits of low pressure systems using sealed batch processes.