Durable Hydrophobic Surface Treatments for Enhanced Corrosion Protection

Durable Hydrophobic Surface Treatments for Enhanced Corrosion Protection of Landing Gear Rebecca Martin, Adam Goff, Bryan E. Koene, Jeier Yang, Zak Bear Luna Innovations Incorporated August 12 -15, 7 -10, 2017 August 2019 Do. D--Allied. Nations. Technical. Corrosion. Conference

Sol-gel Formulation Overview • Combination of hard ceramic component with flexible linkers produce high toughness for abrasion resistance and durability Tough, Ceramic • • Durability Abrasion resistance Flexible component • • Luna synthesized Flexibility, adhesion Hydrophobic Additive • Bound into coating • Durable 2

Key attributes of the hydrophobic hybrid coating Hydrophobicity and watershedding Corrosion protection Coating exhibits > 110° contact angle and <5° watershed angle. Dense network provides a high physical barrier to electrolytes that cause corrosion; insulating electronic barrier for galvanic corrosion Adhesion The coating has robust adhesion to glass, plastic (acrylic, polycarbonate), paint (polyurethane, latex, acrylic), and metallic (aluminum, steel, etc. ) substrates. Flexibility, abrasion Coating exhibits excellent flexibility via a tough crosslinked polymer matrix resistance and abrasion/wear resistance associated with the inclusion of hard nanoparticles. Thickness and Weight The coating is very thin (1 -5 µm) and lightweight Environmental Durability Coating shows excellent resistance to degradation from salt spray and UV exposure. Facile synthesis and ease of The coating is readily prepared from commercial precursors. It is applied in application a single coat using spray, flow or brush methods with minimal surface preparation. 3

Application to Landing Gear Motivation Landing gear are flight and safety critical items that are prone to corrosion when the surface is damaged by impact or wear, particularly at the interface of mated metals where water pools or is entrapped by threaded parts Our Innovation A thin, durable, hydrophobic watershedding coating provides extended service life through barrier protection and corrosion & impact/wear resistance - Watershedding properties (3 -5°) - Fluid resistance (jet fuel, oil, de-icing, Skydrol, etc. ) - Abrasion resistance (sand, gravel, FOD) - Corrosion resistance demonstrated with accelerated test methods - Environmental durability to salt spray and QUV 4

Sol-gel Solution and Applied Surface Treatment Performance Material Property Test Method ASTM D 1200 Pot life MIL-PRF-32239, 85285; Storage Stability Operational Conditions MIL-PRF-85285 Required Response Gentoo Sol-Gel Solution Characteristics TBD, 4 h minimum PASS; >8 h o 6 -12 months, 35 -115°F; 100, 77, 40 F @ 3 mo. ea. PASS 65 -90°C, 20 -80% RH; 40°F and above PASS; recommend >D 5° from dew point; 65 -80°F ideal application temp Physical Characteristics of Sol-gel Treatment Hydrophobicity Flexibility Measurement ASTM D 522 Low Temp Flexibility Cure (solvent resist. ) Heat Resistance Strippability ASTM D 522 ASTM D 5402 ASTM D 2244, D 522, MIL-PRF-32239 with Cee. Bee A-235 Abrasion Adhesion ASTM D 1044, D 2486 ASTM D 3359 Contact Angle 105 + 3°; Watershed 10 + 2° No cracking -51 o. C, no cracking No effect DE<1. 0, no cracking after 1 h at 121. 2°C Sol-gel removal Durability of Sol-gel Treatment HSS Joint Test Protocol, ASTM D 3359 Wet Tape Paint Adhesion FOD or Chip Resistance ASTM D 3170, corrosion evaluation TBD ASTM G 154 cycle 2 QUV-B, D 4329 Weather Resistance Water Resistance Chemical Resistance Outcome DT <5%, DH <3% per 150 cycles 5 B on 6 h cured or mechanically abraded, full cured paint 5 B at RT, 49°C at 96 h, and 65°C at 168 h PASS Identical or better than control 1000 h with Dgloss <20, DE < 1. 0 PASS – better than control Fluid Resistance of Sol-gel Treatment MIL-PRF-23377 K MIL-PRF-32239, HSS Joint Test Protocol PASS ¼” mandrel; cracking on 1/8” w/ paint but no cracking on Gentoo only PASS 1” mandrel (½”) PASS; No change CA/WS, gloss or DE PASS with Cee Bee A-235 stripper No effect, adhesion No/minimal effect & better than control PASS; skydrol, degreaser, deicing, 5 JP-8

Fluid Resistance Sol gel coating on MIL PRF 85285 Wet tape adhesion – 5 B rating • 23 o. C (186 h); 49 o. C (96 h), 65 o. C (168 h) Fluid Resistance/ Immersion - excellent • Lubricating oil • Hydraulic fluid • JP-8 121 o. C (24 h) 66 o. C (24 h) Ambient (168 h) Fluid Corrosion Resistance Test • -37. 8 o. C (168 h) • Deicing/ Anti-Icing fluid: SAE AMS 1424 • Degrease Compound: MIL-PRF-87937 Other fluids (48 h exposure) • Naptha, heptane, polyalphaolefin coolant, Navy plastic polish, airplane wash cleaner fluid, Alodine 1201 wash/rinse 6

ASTM G-154 Cycle 2 1000 h QUV Exposure 5 x Microscope Image, 1000 h QUV Control Sol-gel Test Area • MIL-PRF-85285 E Type I Class H white gloss urethane topcoat paint control • Sol-gel surface treatment over control paint • ASTM G-154 Cycle 2 • UVB-313 lamp with 0. 71 W/m 2 irradiance Sample Control Sol-gel UV Exposure (h) Initial 500 h 1000 h ΔE NA NA 0. 9 1. 2 0. 7 1. 0 Gloss 91. 6 88. 7 82. 7 87. 7 75. 2 82. 6 Contact Tilt Δ Gloss Angle (o) NA 85 15 NA 110 5 -8. 9 90 11 -1. 1 109 8 -16. 4 77 17 -6. 1 107 6 7

Galvanic Fastener Assembly after 1340 hr in B 117 Salt Fog 65 -75% reduction in weight loss with hydrophobic, sol-gel coating • 7075 Al coated panel, scribed • Cd SS fasteners Coating Configuration Surface Treatment 8

ASTM B 117: 4130 Steel Panels Impacted per ASTM D 3170 (Chipping Resistance) Surface Treatment Sol-gel improves protection of underlying substrate from salt fog exposure after FOD impact 9

ASTM B 117: Painted, LHE Zn. Ni 4130 Steel 10

Large Threaded Part Testing: Background • Bolts made out of 300 M steel • Nuts made out of 300 M steel or 7075 -T 6 aluminum (galvanic) • Clearance on threads for sol-gel application • MIL-PRF-85582 Class N epoxy primer and MIL-PRF 85285 E Type I Class H polyurethane white topcoat sprayed on all exterior surfaces • Note that no primer/topcoat is applied to the male or female threads. This configuration leaves the threaded and flat mated coupon half interfaces LHE Zn-Ni plated only. • Sol-gel then applied 1) along all outer faces over top of the polyurethane topcoat and 2) along the male/ female threaded surfaces. • This configuration enables comparison of how coupons with and without the sol-gel applied behave under accelerated cyclic corrosion conditions 11

5040 h ASTM B 117 Exposure of LHE Zn-Ni 300 M threaded parts As removed from testing 12

5040 h ASTM B 117 Exposure of LHE Zn-Ni 300 M threaded parts • Plastic media stripped bolts • Light grey LHE Zn-Ni; black/dark grey LHE Zn-Ni consumed/missing Plastic media stripped bolts 13

5040 h ASTM B 117 Exposure of LHE Zn-Ni 300 M threaded parts Plastic media stripped nuts 14

272 cycles GMW 14872 Exposure of LHE Zn-Ni 300 M threaded parts 1 cycle = 24 hr 272 cycles = 6528 hr As removed from testing 15

272 cycles GMW 14872 Exposure of LHE Zn-Ni 300 M threaded parts Plastic media stripped 16

272 cycles GMW 14872 Exposure of LHE Zn-Ni 300 M threaded parts Plastic media stripped 17

KSC Coastal Atmospheric Exposure & Evaluation of Threaded Part Assemblies • 24 samples installed on a rack configured to hold cylindrical samples on June 15, 2017 • 16 month outdoor exposure 18

16 months of Kennedy Space Center, Florida beachside exposure of LHE Zn-Ni 300 M threaded parts • Images “as removed from testing” show LHE Zn-Ni consumption on exposed threads (white product) • Plastic media stripped controls images have significant LHE Zn-Ni consumption along bolt threads (black) 19

16 months of Kennedy Space Center, Florida beachside exposure of LHE Zn-Ni 300 M threaded parts 20

16 months of Kennedy Space Center, Florida beachside exposure of LHE Zn-Ni 300 M threaded parts • Plastic media stripped bolts • Inner threads of control black/dark grey while sol-gel threads grey/unchanged 21

Gentoo. TM Transparent hydrophobic coating Commercialization Scale up process (2013) • Demonstrated excellent abrasion resistance Develop transparent • Pilot scale coating (5 hydrophobic coatings (2010) gallons); prototype F-16 • Watershedding properties canopies treated on polycarbonate / acrylic substrates Technology Transition (2015) Air Force Commercialization Readiness Program – (CRP) additional funding through F 16 program office to transition for full scale demonstration leading to flight testing ● • (2014) License technology to Ultra. Tech International for manufacturing, marketing, sales under trade name • (2016) Product launch of Gentoo. TM 22

Acknowledgements Luna BOOTH NUMBER #TBD Durable Hydrophobic Coatings for Corrosion Protection of Landing Gear U. S. Air Force Phase I SBIR; Contract # FA 8222 -14 -M-0014 Air Force Program Monitor – Michael Blommer, Hill AFB 23

Durable Hydrophobic Surface Treatments for Enhanced Corrosion Protection of Landing Gear Adam Goff Luna Innovations Incorporated goffa@lunainc. com Rebecca Martin Luna Innovations Incorporated martinr@lunainc. com August 12 -15, 7 -10, 2017 August 2019 Do. D--Allied. Nations. Technical. Corrosion. Conference