Protective layers by nickel plating

Ref-Nr: TDO0215

demonstrator of the X-38 Crew Rescue Vehicle

Technology abstract

DURNI-COAT® is a process for the functional coating of metals, where the properties of the protective layer range from chemical resistance, dimensional accuracy, optimum anti-friction properties, electrical conductivity to improved hardness.

Technology Description

DURNI-COAT® is a process for the functional coating of metals, where the properties of the protective layer range from chemical resistance, dimensional accuracy, optimum anti-friction properties, electrical conductivity to improved hardness. The coating process allows for the chemical deposition of a protective layer without resorting to any external power source. In this process the work piece is immersed into an aqueous solution with a defined content of nickel ions. During the process, these ions reduce to nickel metal. The chemical reactants and suppliers of the necessary electrons are the so-called Hypophosphite ions that are contained in the solution. They are transformed into so-called Orthophosphate by oxidation in the course of the reaction. As a result, a nickel-phosphorus alloy layer forms on the work piece’s surface. This layer effectively protects the work piece against wear and corrosion.
By varying of the electrolyte and process parameters, the protective layer’s properties may be customised to specific applications. The wear and corrosion resistance depends on the layer's phosphorous content. This content in turns varies depending on the electrolyte's composition as well as process conditions. Even the layer thickness affects the coating's resistance: Layers with a thickness in the range of 2 to 10 μm are resistant to mild corrosion loads, while those in the range of 5 to 10 μm are resistant to mild wear loads. A moderate degree of resistance requires layers with a thickness in the range of 10 to 25 μm, while severe and very severe loads require thickness values ranging from 25 to 50 μm and over 50 μm respectively (standard layer thicknesses according to DIN EN ISO 4527).
In addition, DURNI-COAT® ensures uniform layer formation true to the original contours with a narrow layer thickness tolerance of ± 3 μm. Therefore, such coating is an ideal solution for the plating of geometrically complex work pieces with sharp edges and ledges, accessible cavities or bores. Prior to the surface treatment, all parts that should not be covered by the protective layer have to be masked by means of masking lacquer or tape. Masked areas will not be coated during the dipping of the parts into the nickel-electrolyte. After the treatment the masking can easily be removed.
The chemically nickel-plated surface resisted the surface loading experienced in hypersonic wind tunnel tests very well. Fig.1 shows a typical wind tunnel model used in such test campaigns. Most industrially utilized metals may be coated by this procedure and applications in the non-space domain are manifold.

Innovations & Advantages

  • accurately maintaining the original contours and dimensional accuracy
  • high sliding ability
  • protection against corrosion, erosion und cavitation
  • connectivity and solderability
  • surface hardness and wear resistance
  • magnetic properties
  • conductivity of the surface

Current and Potential Domains of Application

  • General Mechanical and Plant Engineering
  • Energy and reactor technology
  • Hydraulics
  • Automotive
  • Mining
  • Pharmaceutical and medical tool building
  • Food and home appliance industry
  • Instrumentation and control technology