Electrodeposited nickel?manganese: an alloy for microsystem applications

Abstract

A process has been developed, using LIGA fabrication techniques, for the electrodeposition of a high strength, heat resistant Ni–Mn alloy to meet the requirements of a mechanical microsystem component. The electrolyte bath chemistry consists of Ni sulfamate to which a small amount of manganese chloride is added. The Mn content for the electrodeposited alloys of interest is generally equal to or less than about 1 wt%. It is shown that its co-deposition with Ni is insensitive to feature aspect ratio and therefore not limited by mass transport effects, permitting uniform alloy deposition. While plating of this alloy at a constant current density yields a high strength deposit, it also results in a highly stressed film that makes the fabrication of thick section deposits problematic.To counter this, a pulsed deposition scheme is employed to fabricate a nanostructured film consisting of alternating nm-thick regions of low stress, relatively soft Ni, and high strength, and highly stressed, NiMn alloy. This moderates the high plating stress of the NiMn alloy and enables the deposition of thick deposits. Yield strengths of over 800 MPa are achievable in the pulse-plated material, with good as-plated ductility (∼6%). The material loses only about 15% of its original strength after a one hour, 600 °C anneal, and no embrittlement is observed since no sulfur-bearing additives are employed. To the contrary, ductility measured as strain to failure is improved.