An improved process for the formation of an aluminum oxide protective coating has been developed. Barriers created with this new, patented alpha-Al2O3 oxide coating process have wide applications for making many useful alloys, superalloys, and metallic compounds. Alpha-Al2O3 applied by conventional processes inherently cracks and spalls from the substrate surface. The major weakness of conventional aluminum oxide coatings is their susceptibility to cracking and spalling. The overall process of mixed-oxide formation on an alloy indirectly causes spalling during oxidation of the alloy in air or oxygen. Voids are formed which become segregation sites for sulfur. Accumulation of sulfur in such voids causes separation of the oxide from the alloy. The process is solved by the use of a process medium that allows only single alpha-Al2O3 oxide to form, preventing the formation of voids and eliminating segregation of sulfur to the interface region. This makes possible the creation of several different alloys and superalloys that all have their surfaces protected by a single oxide, alpha Al2O3.
Excellent Adhesion and Cohesion of the Alumina Coating
Stud pull tensile tests have determined that the cohesive strength of this alpha-Al2O3 coating and the adhesive strength of the alpha-Al2O3/substrate bond are each greater than 15,000 psi. These high strengths validate the fact that an ordered structure of the alpha-Al2O3 molecules has been achieved.
Diffusion Barrier to Oxygen and Hydrogen
This process is unique because the processed alpha-Al2O3 molecules are FULLY OXIDIZED molecules with ORDERED STRUCTURES. The alpha-Al2O3 oxide structure, once formed, serves as a nearly perfect diffusion barrier for oxygen and hydrogen.
The Secret to the Patented Process
To make this process function properly to form the extraordinary alpha-Al2O3 oxide coating, the substrate must begin as an alloy, superalloy, or metallic compound material that contains at least 2 weight percent of aluminum. It must also not contain elements like titanium that form oxides in the presence of aluminum, but can contain any number of elements that do not form oxides in the presence of aluminum.
Benefits of Using The Alumina Coating
• The ability for one special alpha-Al2O3 oxide to serve as a nearly perfect oxygen and hydrogen barrier.
• The ability for this special alpha-Al2O3 to create a stainless surface finish that is, at the same time, a good protector of the substrate against chemical attack over a very wide range of temperatures.
• The ability for one special alpha-Al2O3 oxide to protect the surface of an alloy better than any known mix of oxides and at the same time to produce an alloy that has superior cohesive strength and that will bond strongly to the substrate of alloys it is protecting.
Applications for the Alumina Coating
• Aircraft manufacturing
• Aircraft engine manufacturing
• Automobile manufacturing
• Farm machinery manufacturing
• Fuel cell development
• Hydrogen fuelled, fuel cell powered vehicles
• Stirling engines
• Products that use hydrogen and are concerned about hydrogen leakage from the product’s interconnecting lines
• Stainless steel products
• Food production hardware, exhaust systems, grills, cooking utensils, structural beams/hardware, sheet metal objects
• Products made from superalloys
• Products from alloys that must be protected from atmospheric oxygen at all operable temperatures
• Hydrogen lines or containers that must prevent the permeation leakage of hydrogen from these lines or containers
• Manufacture of any metal products that must be protected from oxidation over a wide range of temperatures
• Rolling contact bearings
• Production of superior alloys that have optimized mechanical properties