High Performance Nanostructured Ni-Mn Alloy for Microsystem Applications

Abstract

A process has been developed for the electrodeposition of a high strength, heat resistant Ni-Mn alloy for high aspect ratio microstructures (HARMST). A conventional Ni sulfamate electrolyte is employed with the addition of a small amount of manganese chloride. The deposits are low stress (< ∼ 60 MPa tensile), enabling the deposition of thick section films required for HARMST. The Mn content for the alloys of interest is less than about 1 wt %, and its codeposition is insensitive to mass-transport effects, permitting uniform alloy deposition, regardless of feature aspect ratio. A pulsed deposition scheme is employed to fabricate a nanostructured film consisting of alternating nanometer thick regions of relatively pure Ni, and hard, Mn-rich Ni; this moderates the high stress of the NiMn alloy and enables the deposition of thick deposits. Yield strengths of over 800 MPa are achievable, with good as-plated ductility (∼6%). The material loses only about 15% of its original strength after a 1 h, 600°C anneal, and no embrittlement is observed since no S-bearing additives are employed.