Aluminum Coatings Applied by the Cold Spray Process for the Repair of Marine Grade Aluminum Sponsor: Dr. Airan Perez, ONR 333 Primary Investigator: Ben Bouffard, NSWCCD Code 614 Distribution A – Approved for Public Release

Outline Project Purpose Sensitization Powder Down-Selection Al-Al2O3 Coating Analysis Mechanical Properties of Coating Summary

Project Purpose AA5456 in fleet is prone to sensitization and cracking Talks with NAVSEA and TWH’s reveal that ships often crack, but immediate permanent repair is not possible Need temporary solution that will ‘keep the water out’ until next scheduled availability Currently use composite patch, which is not ideal: Needs to be implemented by highly skilled workforce Experiences adhesion problems in extreme UV environments Fire spread issues Cold Spray has well documented success in the DOD for dimensional repair of aluminum and magnesium components This project aims to repair cracks through material

Sensitization AA5xxx is supersaturated with Mg At temperatures above 65ºC Mg migrates out of solution and forms beta phase (Al2Mg3) along grain boundaries Beta phase is anodic to substrate, can lead to IGSCC

Powder Down-Selection Initially 3 powders procured for testing: Commercially pure Al Aluminum-Alumina mixture AA5456 Low pressure cold spray system being used has maximum temperature of 400 ˚C and pressure of 175 psi. Commercially pure Al and AA5456 have not deposited well with these parameters Aluminum-Alumina coating deposits extremely well-will be focus of this presentation

Al-Al2O3 Coating Analysis

Sensitized vs Unsensitized Substrate Pressure: 150 psi Temperature: 400 ˚C Standoff Distance: 25 mm Gun Transverse Speed: 30 mm/sec Gas Feed Rate: 30 % of max Thickness: 0.056 inches Al-Al2O3 Coating Al2O3 Particle Both interfaces show: Large Al2O3 particles within coating and embedded into substrate Coating particles result in a large deformation front (~20 um) within the substrate. Unsensitized Substrate Al-Al2O3 Coating Both coatings show: CP-Al particles seem to deform around Al2O3 particles Even distribution of Al and Al2O3 Low porosity observed within coating Al2O3 Particle Sensitized Substrate

EDS Results Majority of coating is comprised of aluminum & oxygen Substrate Al, O, Ti Coating Majority of coating is comprised of aluminum & oxygen Argon is present (used to atomize powder) Titanium is present in coating -Separate EDS analysis showed titanium present in original powder

Hardness sensitized unsensitized Sprayed Material Base Material

EBSD Analysis Alumina shows little deformation or change in general powder morphology Trend of large grains in center of particle and smaller grains along outside of particle Smaller interparticle boundaries are created during the severe strain localization resultant of spray process, which suggests this results in localized dynamic recrystallization CP-Al Particles Al2O3 Particle Kang, K.; Wang, J; Bae, G; Ha, S; Lee, C. Interfacial bonding and microstructural evolution of Al in kinetic spraying. Journal of materials Science 47 (2012)4649-4659. CP-Al Particles Al2O3 Particle

TEM of Single Particle Splat Image taken using selected area aperture to highlight dislocations Triple point intersection of grains Many dislocations visible, expect to see larger dislocation density along edge of particle

Potentiodynamic Curves High Epitt Potential Large Passivation Region Large difference in OCP Shows need for further galvanic study

Salt Fog Testing 1500 hours of B117 salt fog testing complete on Al-Al2O3 and AA5456 coatings AA5456 is showing pitting in coating, no damage around scribe Al-Al2O3 shows no pitting or corrosion in coating and no damage around scribe Al-Al2O3 Coating over unsensitized Al Al-Al2O3 Coating over Sensitized Al AA5456 Coating over Sensitized Al Representative original photos of select B117 panels

Salt Fog Testing Scribe panels show overall corrosion resistance, but in practice cold spray repair will be small area compared to substrate Made mock crack repair plates to test in ASTM B117 Use 0.25” and 0.5” width mock crack repairs in 4”x6” plates 11/16/2018

Salt Fog Testing Initial 50 hour 350 hour Al2O3 Coating Al2O3-AA5456 Couple U-50-A-half-1 for fill, S-50-A-H-1 for just cold spray 11/16/2018

Salt Fog Testing Minor pitting in Cold Spray material initiated at 350 hours (Pit diameter of about 10 microns) Pit density of cold spray is more severe than that observed in AA5xxx Pitting in 5xxx coalesces as intergranular corrosion begins No accelerated pitting in Cold Spray due to couple with AA5456 600 hour 950 hour Al2O3 Coating Al2O3-AA5456 Couple 11/16/2018

Al-Al2O3 Mechanical Properties 11/16/2018

Al2O3 Adhesion Properties ASTM C633 Adhesion CPAl-Al2O3 Specimen Avg Adhesion Value (ksi) Std Dev Majority of Failure Modes Sensitized Handheld 8.06 0.98 Adhesive Sensitized Robot 7.89 2.28 Unsensitized Handheld 7.83 n/a Unsensitized Robot 4.60 3.24 Coating 11/16/2018

Tensile Tests-All Cold Spray Tensile specimens machined out of bulk build Initial gauge diameters ~0.25 in Specimens tested in both transverse and longitudinal directions Transverse Longitudinal 11/16/2018

Tensile Tests-All Cold Spray Specimen Test Direction Average UTS (ksi) st dev Transverse 10.37 1.28 Longitudinal 7.21 1.45 Specimens tested in transverse spray direction show higher UTS than those tested in longitudinal direction Speed of robot important to consider, specimens tested with traversing gun speed of 20 mm/s showed UTS half the value of specimens tested with gun speed of 10 mm/s Important consideration for handheld gun application 11/16/2018

Fractography of Tensile Specimens-All Cold Spray Combination of intergranular and transgranular cracking Primarily cleavage fracture, representative of brittle failure No preferential fracture at alumina particles No failures at interpass regions Cleavage Alumina Flake point 11/16/2018

Tensile Tests– Cold Spray Repair Repaired different mock crack widths varying from 0.1” to 0.5” Crack widths similar to nozzle width could not be filled due to jet stream of process building over cavity (Takana 2010) 11/16/2018

Tensile Tests– Cold Spray Repair Fracture consists of both transgranular and intergranular cracking No preferential fracture at root or AA5456-Al2O3 coating interface Fracture cohesive through cold spray repair 11/16/2018

Summary Successful deposition of Al-Al2O3 using low pressure and air to deposit onto sensitized and unsensitized AA5456 Metallurgical analysis of Al-Al2O3 shows dense coating with low porosity and oxide formation, and similar deposition and interface between coating and sensitized and non-sensitized samples. Samples show an increased hardness at the interface and severe particle deformation within the coating Satisfactorily high (~8-10 ksi) adhesion and UTS values Tensile fracture surfaces show combination of intergranular and transgranular fracture representative of brittle failure

Acknowledgements Dr. Airan Perez Dr. Jennifer Wolk Caroline Scheck NISE 219 Funding under Dr. Jack Templeton Fred Lancaster Joseph Christophersen Wesley Monillas

Back Up Slides File: NAVAIR Brief