B. T. Golesich, Kuchera Defense Systems, Windber, PA; T. Eden, The Pennsylvania State University, University Park, PA; M. Sharma, Bucknell University, Lewisburg, PA
The Cold Spray process is an emerging technology that is being evaluated as a method to apply corrosion resistant coatings. Unlike thermal spray processes such as flame, arc, and plasma where a high energy source is used to heat metal powders to a molten or semi-molten state for deposition, the Cold Spray process uses pressurized gas and unique nozzle designs to accelerate the particles to a critical velocity to achieve a solid state deposition. In this study, the Cold Spray process was used to apply corrosion resistant coatings to aluminum alloys used in the aerospace industry. These high-strength alloys have excellent strength-to-weight ratios. During use, these alloys are subjected to environmental conditions that can cause corrosion effects leading to a reduction in performance and an increase in lifecycle costs. Commercially pure aluminum powder was applied to Al-2024-T3 and Al-7090 powder was applied to Al-7075-T6. The corrosion resistance of these coatings was evaluated and compared to the corrosion resistance of the bare and anodized materials. Specific DC and AC electrochemical tests were chosen, that would identify the susceptibility of the coatings to pitting in chloride solutions. These tests included (1) corrosion potential, (2) linear polarization (3) potentiodynamic polarization and (4) electrochemical impedance spectroscopy (EIS) It was observed that each of the coatings provided corrosion protection to the bare substrate material. Each coating/substrate system had its maximum impedance at lowest frequency value higher than those of the bare substrate. Bode impedance and phase plots for the coatings showed that each of the coatings displayed purely capacitive behavior after 1 day up to 1 week with minimal or no decrease in maximum impedance at lowest frequency. The microstructures and hardness of the coatings were also evaluated. The results of these evaluations are presented.
Summary: Kuchera Defense Systems, under an Air Force SBIR contract, studied the effect of coating 2xxx and 7xxx series aluminum (Al) alloys utilizing two cold spray processes to develop a new corrosion protection system. Both High Pressure (HP) and Low Pressure (LP) cold spray approaches were used to apply Commercially Pure Al to 2024 Al substrates and the High Pressure System was used to apply 7090 Al to 7075 Al substrates. These coatings were tested against base (unprotected) and anodized alloys for corrosion responses. The mechanical properties of the coated samples were evaluated by the Pennsylvania State University’s Applied Research Laboratory (ARL/PSU) and the corrosion properties of the coated samples were evaluated by the Mechanical Engineering Department at Bucknell University. Also assisting with the program were the Army Research Laboratories (ARL/Army) and Lockheed Martin Advanced Development Programs (LM ADP).
