Hard Coating for High Temperature Applications

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Preparation and properties of Cr-C-P hard coatings annealed at high temperature for high temperature applications
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Inventors
Professor Christopher Schuh
Department of Materials Science and Engineering, MIT
External Link (schuh.mit.edu)
Marcelo Gines
Department of Materials Science and Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Preparation and properties of Cr-C-P hard coatings annealed at high temperature for high temperature applications

US Patent 7,910,231
Publications
Strategy to Improve the High-Temperature Mechanical Properties of Cr-Alloy Coatings
Metallurgical and Materials Transactions A, (2007) 38: 1367

Applications

This technology can be used to improve mechanical properties (hardness, toughness, wear resistance, lubricity) as barriers against corrosion of metals or metal alloys. Important developments in hard coating will lead to a better manufacturing  process that creates longer-lasting tools. 

Problem Addressed

When metallic or metallic alloy coatings are submitted to work at high application temperatures - above 200 degrees Celsius - some of them retain or enhance the initial properties, but most of them soften appreciably, particularly those that are nanostructured. For this reason, such coatings are often limited to low-temperature applications. Additionally, current technologies based on hexavalent chromium are detrimental to the environment. When carbon is incorporated in the electrochemistry bath, the alloying improves mechanical properties as temperature rises. 

Technology

The invention improves on Cr-C plating derived from a trivalent bath through the addition of phosphorous to the coating. Phosphorous is incorporated into the coating when hypophosphite-based baths are employed, but may also be introduced by addition of hypophosphite in organic baths, or by electroless deposition. The improved coating has hardness greater than 900 kgf/mm2 in advantageous conditions, and may similarly have hardness greater than 1000 kgf/mm2 at a temperature greater than 6500C. The coating can be deposited electrolytically or in the form of vapor. The coating should be exposed to a sufficient temperature to produce body centered cubic chromium, and annealed for at least five minutes. Upon thermal treatments, chromium nanocrystallization as well as precipitation of carbides and phosphides occurs, and the mechanical properties of the coating are improved.

Advantages

  • The Cr-C coating hardens considerably upon heating
  • Fewer health and environmental concerns