Vapor Deposition Corrosion Resistant Coatings
Vapor deposition corrosion resistant coatings can be an excellent source for corrosion protection. Especially for those applications requiring hard thin films.
Derivatives of ‘DLC’, also referred to as diamond-like coatings, as well as some of the carbide and nitride-based materials are very popular -- both for their general oxidation protection and chemical corrosion stability.
Additionally, these vapor deposition corrosion resistant materials can be combined, multi layered deposits for enhanced protection.
The key to success using vapor deposition corrosion resistant coatings will be both in their chemical compatibility with their environment and ability to form pin hole free structures. Pin holes, also known as ‘holidays’, are those microscopic voids in the coating that expose the bare metal. Failure to recognize the need for a corrosion resistant metal surface can present risks to coating performance. That is why it is essential you understand the nature of the corrosion, or aspects of the ‘corrosive environment’.
Ideally, the densest structures, with the least likelihood of microscopic voids, are those formed by Chemical Vapor Deposition (CVD). Keep in mind, though, especially in consideration of your base metal, process temperatures range typically between 1500 and 2200 degrees Fahrenheit. Which may make Physical Vapor Deposition (PVD), whose processing temperatures run between 750 and 900 degrees Fahrenheit, more desirable forms of vapor deposition corrosion resistant coatings.
Advancements now include even lower temperature processing through Plasma Enhanced (PECVD) or Plasma Assisted (PACVD) vapor deposition. In contrast, these coatings can be processed below 550 F, yet with excellent adherence, uniformity, and corrosion resistant properties.
When do you use vapor deposition corrosion resistant coatings? Advantages are most gained in dynamic environments, where parts are moving or abrasion is high. Where ‘micro hardness’ is key. For example, where other physical properties are sought concurrently, such as dry lubrication.
Greater demands for corrosion resistance from engineered products, higher standards of performance, are all driving the need for new combinatory materials. Many of these vapor deposition corrosion resistant coatings are non-objectionable with FDA and show growing acceptance in the medical industry. This includes non-implantable and implantable device.
Once the corrosive environment and mechanics are clearly understood, the proper design criteria for coating material and coating process can be met. Today, the most promising breakthroughs in vapor deposition coatings, and their evolutionary outlook, are in their combination and architectures. Ultimately, vapor deposition corrosion resistant coatings will offer us more choice in the most demanding mechanical and thermal environments.