Design of Cold Spray Aluminum Alloys for Structural Components, Coatings, and Repairs: Fatigue Mechanisms, Novel Interfacial Evaluations, and Methods for Material/Part Qualification

Sample, Christopher

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Design of Cold Spray Aluminum Alloys for Structural Components, Coatings, and Repairs: Fatigue Mechanisms, Novel Interfacial Evaluations, and Methods for Material/Part Qualification

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Cold spray technology offers a solid-state fabrication technique that is suitable for both bulk 3D components and coatings/repairs with enhanced corrosion, fatigue, fatigue crack growth (FCG), and fracture resistance. Successful implementation of the technology in high-integrity structural applications requires a comprehensive understanding of processing-structure-performance relationships, specifically the role of feedstock powder, processing parameters, and post-processing conditions on microstructural mechanisms of fatigue and coating-substrate interface behavior. Helium-processed Al-6061 cold spray materials have been investigated both as bulk depositions (as-sprayed and annealed) and coated specimens (as-sprayed on similar wrought Al 6061 and dissimilar cast Mg-AZ91E-T6 heat treated substrates). Microstructures, tensile and interfacial properties, and fatigue crack initiation and propagation responses were systematically evaluated and compared with those of equivalent conventional materials. Long and small FCG tests were conducted on bulk specimens at various stress ratios to establish microstructural mechanisms at different crack growth stages, which are related to powder particle boundaries and grain/subgrain orientations. The interfacial behavior of the cold spray coatings on substrates was examined using controlled FCG studies through the interface, novel interface strength testing methods, electron backscatter diffraction (EBSD) characterization, and fractographic observations. Complementary fatigue studies up to the gigacycle regime have also been conducted on bulk and coated cold spray materials and their conventionally fabricated counterparts to understand surface condition, residual stress, microstructure, and strain rate effects on crack initiation and early growth. The integrated knowledge and data emerging from this research are used to develop fatigue design tools and provide recommendations for optimization, qualification, and implementation of cold spray materials in safety-critical components, coatings, and repair applications.

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