Plating on some difficult-to-plate metals and alloys

Abstract

Electrodeposition of coatings on metals such as beryllium, beryllium-copper, Kovar, lead, magnesium, thorium, titanium, tungsten, uranium, zirconium, and their alloys can be problematic. This is due in most cases to a natural oxide surface film that readily reforms after being removed. The procedures we recommend for plating on these metals rely on replacing the oxide film with a displacement coating, or etching to allow mechanical keying between the substrate and plated deposit. The effectiveness of the procedures is demonstrated by interface bond strengths found in ring-shear and conical-head tensile tests.

Electrochemical Healing of Fractured Metals

“…These values are very low compared to 10× to 70× higher interfacial shear strength values measured via ring shear testing of nickel plated on a range of metallic alloys, which underwent multi-step processes that included chemical or electrochemical pre-treatment in acidic solutions, followed in some cases by plating in a low-pH nickel solution (e.g., Woods strike), before plating in a standard nickel sulfamate solution. [45,47,51] Our framework obviates the need for these multistep processes since it removes interfacial adhesion as the limiting factor of healing performance, replacing it instead with factors that can more easily be controlled such as exposed area and charge input.…”

“…See Supporting Information for the full derivation of Q, C, and T (Equations S17-S22). Improving the adhesion between the plated nickel and structural metal, as measured by the interfacial shear strength 𝜏 Ni-M , using proven chemical and electrochemical processes, [41,45,47] can decrease the energetic and financial costs of electrochemical healing. For a structural metal with A M = 2.0 mm 2 , required charge input decreases by 80% to 67.1 mAh due to a 5× improvement in 𝜏 Ni-M , by 90% to 33.5 mAh due to a 10× improvement, and by 95% to 16.8 mAh due to a 20× improvement.…”

“…Prior work on the electrochemical joining of metal parts achieved high adhesion of plated nickel to other metals, but required multi-step processes with acid pre-treatments and plating in different electrolyte chemistries, and did not present a model that predicted or provided understanding of how to achieve optimal mechanical properties of the joined parts. [45][46][47][48][49] Here, we propose a framework for electrochemical healing, based on an experimentally validated theoretical model that elucidates the geometric, electrochemical, and mechanical parameters needed for 100% recovery of tensile strength in fully fractured structural metals. This framework enables the full restoration of tensile strength in nickel, low-carbon steel, two "unweldable" aluminum alloys, and a difficult-to-weld 3D printed funicular shellular structure.…”

Ni-P coatings electroplating - A review, Part I: Pure Ni-P alloy

“…However, stainless steel for example can be problematic owing to the formation of a passive oxide layer which prevents Ni-P coating from sticking to its surface. Conventional way of addressing this issue is to apply on the substrate surface a Wood's or another nickel strike before Ni-P electroplating [99]. Being highly acidic it dissolves the oxide and concurrently forms a thin layer of nickel on the stainless steel surface.…”

Fabrication of Thorium and Thorium Dioxide

“…It is due to a thin naturally forming oxide surface film that is often difficult to remove and that reforms quickly when a cleaned surface is exposed to air or water. As a result, adherent electrodeposits are obtained only when either: 1) the oxide film is removed for sufficient time to permit an initial deposit; 2) the film is replaced with another that does not interfere with adhesion; 3) the film is incorporated into the deposit in a compatible manner; or 4) the surface is severely etched to allow mechanical keying between the substrate and deposit [56]. Successful procedures that rely on one or more of the above principles have been documented.…”