Extended Life Coatings for Electrochemical Machining Tools

Electrochemical Machining (ECM) is a non-traditional process finding extensive use in aerospace and automotive industries that uses a tool (cathode) in an electrolyte medium to produce highly smooth, complex surfaces via electrolytic dissolution of the metal part (anode) being machined. Although the cathode is not in contact with the part and ECM is touted as no wear, it is plagued by stray current corrosion that significantly degrades the quality of machined metal and needs urgent attention. Developing a dense, pinhole free, dielectric, insulating coating for the cathode tool that mitigates stray corrosion and extends the life of the expensive, time consuming effort associated with design and manufacture of tools has a significant payoff. TA&T proposes to demonstrate the unique advantages of corrosion resistant, dielectric, insulating Physical Vapor Deposition (PVD) magnetron sputtered multilayer coatings that will ultimately enable unprecedented too life and exceptional ECM machining performance. Thin sputtered alternating multilayers have the advantages of producing dense, pinhole free, lower residual stress and reduced thermal conductivity properties compared to single layer coatings. The multilayer coatings will be deposited on 17-4 PH stainless steel coupons. X-Ray Diffraction analysis (XRD), Scanning Electron Microscope (SEM) and Energy-Dispersive X-ray spectroscopy (EDS) will be used to characterize the compositions and microstructures of the sputtered coatings to achieve the desired coating deposition parameters and coating properties. The electrochemical resistance of the multilayer coatings will initially be screened in potentiostatic voltage-current tests. A second set of tests will evaluate the performance of the coatings and their sub-layers under extreme ECM conditions of pH, abrasion, hydrogen evolution, and mechanical stress. Approved for Public Release | 22-MDA-11215 (27 Jul 22)