Design of Cold spray 6061 Aluminum Depositions for Fatigue Crack Initiation and Growth Resistance in Structural Components, Coatings, and Repairs

Cold spray materials present several advantages associated with the solid-state character of the deposition process. Improved processing conditions have led to significant static mechanical properties increases, making these materials candidates for structural components in both bulk and coating/repair formats provided that their dynamic behavior is well understood. Thus, this research effort performed systematic S-N fatigue and fatigue crack growth (FCG) studies of high-integrity cold spray 6061 aluminum depositions as free-standing parts and coatings, and compared the results with wrought 6061 aluminum. Conventional and ultrasonic fatigue were first conducted on as-fabricated, bulk depositions and are used to investigate the crack-initiating defect population and sensitivity to loading frequency. Complementary long FCG testing of bulk as-fabricated, annealed, and T6 conditions at varied stress ratios reveals the mechanisms of crack propagation and role of inter-particle diffusion bonding. Finally, small FCG tests were conducted on cold spray-coated substrates to investigate the integrity of depositions in repair applications, with emphasis on stability of the deposition-substrate interface to spallation. These results are compared with tensile and shear testing to make inferences about dynamic performance from static material properties, along with design maps that provide insight for design of structural components and coating/repair applications with cold spray technology.