Patent ID: 6071563
Filing Date: 2000-06-06
Classification: C23D

Abstract:
In an article having a metal alloy component containing chromium, a method of protecting the metal alloy component against metal embrittlement by carburization or sulfidation when the metal alloy component is exposed to carbon or sulfur at an elevated temperature, the method comprising providing a metal alloy component containing chromium, coating a surface of the metal alloy component with a dry, porous layer of a pulverized glass that is thermally crystallizable and that is capable of combining with chromium oxide, heating the coated metal alloy component in an atmosphere containing oxygen to cause a layer of chromium oxide to form at the interface between the coating and the metal alloy component, thermally softening the glass coating and combining the layer of chromium oxide at the coating-metal alloy interface with an inner portion of the thermally softoned glass adjacent thereto to form a vitreous layer that is tightly adherent to the metal alloy surface, that contains chromium oxide, and that resists crystallization, the outer portion of the thermally softened glass remaining essentially uncombined, and cooling the coated metal alloy component to a lower temperature at which the outer portion of the glass layer that is essentially chromium-free crystallizes, holding at that temperature for a sufficient time to crystallize the glass, and then cooling the metal alloy component with a bi-layer coating of glass and glass-ceramic.