Abstract

The specification discloses a process for forming a diffusion surface layer extending inwardly from an outer surface of a metal substrate or member to be treated, the process including in a first activation stage, providing an activation treatment furnace containing an inert particulate refractory material and a metal based material including metals and metal halides for forming said diffusion surface layer, the activation treatment furnace having a flow of an inert gas and a flow of an hydrogen halide gas introduced into the inert particulate refractory material and the metal based material in the activation treatment furnace for a first period of time to activate at least an outer surface region of said metal based material to form an activated metal based material; and in a subsequent diffusion stage, providing a diffusion treatment furnace and introducing said metal substrate into said diffusion treatment furnace, said metal substrate having been pretreated to form a diffusion zone extending inwardly from the outer surface of the metal substrate in which nitrogen has been diffused to form an inner diffusion zone and an outer compound or white layer formed, at least in part, by an iron nitride, an iron carbide or an iron carbonitride compound without an oxide layer on said outer surface of the metal substrate, treating the metal substrate in the diffusion treatment furnace, sealed against the ingress of atmospheric air and under an inert gas atmosphere, in the absence of hydrogen halide gas for at least a second period of time, in the presence of said activated metal based material, to form said diffusion surface layer on said metal substrate.

IPC Classes  ?

• C23C 16/442 - Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using fluidised bed processes
• C23C 8/24 - Nitriding
• C23C 12/02 - Diffusion in one step

Abstract

The specification discloses a method and apparatus enabling the formation of a diffusion surface layer on a surface of a metal substrate, typically a ferrous based metal substrate, wherein in a first stage (80) in a first fluidized bed furnace (10'), a diffusion zone (83) is formed extending inwardly from the surface (85) of the metal substrate (86) in which nitrogen has been diffused to form a nitride or carbo nitride inner zone and an outer white layer (84) that is substantially free of porosity, treating the substrate formed in the first stage (80) to prevent formation of or remove any surface oxide on the surface (85) of the substrate (86), and in a second stage (81) separate from the first stage (80), holding the thus treated substrate (86) in a fluidized bed furnace (10) operated under an inert atmosphere and fluidized by a flow of inert gas or gases, the substrate (86) in the fluidized bed furnace (10) being treated in the presence of a halide gas and a particulate metal or metal alloy.

IPC Classes  ?

• C23C 8/06 - Solid state diffusion of only non-metal elements into metallic material surfacesChemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
• C23C 16/32 - Carbides
• C23C 16/442 - Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using fluidised bed processes
• C23C 8/28 - Solid state diffusion of only non-metal elements into metallic material surfacesChemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in one step
• C23C 16/34 - Nitrides
• C23C 8/30 - Carbo-nitriding
• C23C 16/02 - Pretreatment of the material to be coated
• C23C 12/00 - Solid state diffusion of at least one non-metal element other than silicon and at least one metal element or silicon into metallic material surfaces
• C23C 16/36 - Carbo-nitrides
• F23C 6/00 - Combustion apparatus characterised by the combination of two or more combustion chambers
• F23C 10/00 - Apparatus in which combustion takes place in a fluidised bed of fuel or other particles