This blog will discuss a brief comparison between low- to high-temperature-deposition methods of surface-modification treatments in relation to thermal-diffusion treatments (Fig. 1). The low- to high-temperature-deposition methods of surface treatments include:

  • Electrodeposition
  • Thermal spraying (melted material sprayed onto a substrate steel)
  • Painting (powder coating)
  • Chemical treatments
  • Electroplating

Electrodeposition can be defined as an electro-metallic e-coating such as electro-painting. This method utilizes a paint powder and a depositing powder (at low temperature) by making use of an electric-charge system with the workpiece as the cathode and the paint powder the anode. Electrical current is used to deposit paint on the surface. It is similar (in principle) to electroplating.

Electroplating is a procedure that deposits a protective coating using a warm to hot liquid solution of the solute anode material onto a cathodic component that is immersed in the solute liquid for deposition. Electroplating is usually used to cover a less-expensive metal with a more-expensive metal or to cover a corrosive metal with a less-corrosive metal.

The major problem with electroplating is that parts are generally in a toxic liquid solution that requires good pre-cleaning of the component (cathode). The liquid-metal-carrying agent and the effluent necessitate extreme care in terms of personal operator safety.

A metallic anode is generally manufactured of the coating metal – a single metallic element (e.g., chromium, nickel, cadmium, copper) – to be deposited onto the cathodic components. Plating is performed to:

  • Improve wear resistance
  • Resist corrosion
  • Improve physical properties such as torsional strength, tensile strength and impact strength
  • Protect against indentation

Some alloys can be electro deposited, however, notably brass and solder. Plated "alloys" are not true alloys (i.e., solid solutions) but rather discrete tiny crystals of the metals being plated. In the case of plated solder, it is sometimes deemed necessary to have a "true alloy," and the plated solder is melted to allow the tin and lead to combine to form a true alloy. The true alloy is more corrosion resistant than the “as-plated” alloy.