Encapsulated Wear Particles

Abstract

Incorporating hard particles in a matrix forming the surface of a member can significantly increase wear resistance. Practical use of diamond in industrial applications is limited as the carbon structure breaks down to graphite in air at temperatures over 700° C. When exposed to molten iron the diamond surface can also chemically react and dissolve into the iron. Metal compounds that coat the diamond can provide one or more protective layers that limit contact of the diamond surface with elements that will degrade its structure. Coating can also provide a wettable surface for the molten matrix during processing to improve retention of the particle in the matrix.

Description

FIELD OF THE INVENTION[0001]This invention relates to component wear surfaces with embedded wear particles to increase hardness and limit erosion of the surface.BACKGROUND OF THE INVENTION[0002]Industrial applications often put tools in cyclic contact with abrasive materials that remove the surface of the tool. Over the service life of the tool the abrasive materials wear away and erode the exposed tool surface until the tool has to be replaced. A harder surface for the tool can extend the service life of the tool by reducing the rate of wear during operation.[0003]Wear tools can be manufactured by casting, powder metallurgy infiltration or other techniques. Methods for modifying the hardness of tool materials include alloying, case hardening and heat treating. Incorporating wear resistant particles or materials into the body of the tool during forming of the part can also limit erosion during operation to provide increased service life.[0004]Material preparations and manufacturing ...

AI Technical Summary

Benefits of technology

[0006]Harder materials are more resistant to abrasion and erosion than softer materials. Many methods of hardening tools and tool surfaces are used to make them more erosion resistant. Material selection, alloying and heat treating provides the broadest hardness properties for the tool. Case hardening can provide additional hardness. Hard particles resistant to wear can also be incorporated into or on the surface of the tool to further limit erosion.

[0009]The present invention pertains to hard particles also called wear particles that are coated with a metal nitride layer or with metal carbide and metal nitride layers to enable inclusion in or exposure to molten metal and in particular to ferrous based alloys. The present invention enables hard particles (e.g., diamond particles) to be included in or on parts that are cast or produced by other manufacturing processes involving molten metal without undue degradation that would ordinarily prevent their use. This new use of such hard particles can provide a longer useful life for all kinds of products exposed to abrasive wear.

[0010]In one embodiment of the invention, a wear particle to be embedded in a ferrous matrix is a diamond particle coated with metal carbide. To protect the metal carbide layer from chemical degradation, a layer of metal nitride is deposited on the carbide layer.

[0011]In relation to alloys where the metal nitride coating does not have adequate wetting in relation to a molten ferrous matrix, the nitride layer can be formed as a sub-stoichiometric metal nitride or with an inner portion as a stoichiometric ratio of metal to nitrogen atoms that transitions to an outer sub-stoichiometric layer of metal nitride at the surface. The sub-stoichiometric metal nitride can better interact with the molten matrix so the particle is better retained in the solid matrix.

[0014]In another embodiment, a wear resistant surface is deposited on a metal substrate by an arc welding process using welding rod. The welding rod has a metal matrix, core or periphery that incorporates a binder, flux and / or encapsulated hard (e.g., diamond) particles. The encapsulated particle includes a primary layer of encapsulation and a secondary layer of encapsulation to limit degradation of the particle during processing. During welding the particles pass from the binder on the welding rod to the welding pool and are incorporated into or on the surface on solidification.

Problems solved by technology

Surfaces of wear tools and wear members that are in sliding or impacting contact with other materials are subject to erosion.

Ground engaging tools have very high rates of wear and must be replaced frequently.

Practical use of diamond in industrial applications is limited as the diamond structure can break down to graphite in air at temperatures over 700° C. When exposed to molten iron the diamond surface can also chemically react and dissolve into the iron.

Common practice has taught away from embedding multi-coated diamond in ferrous castings as coatings would not be able to protect the diamond from high casting temperatures and aggressive chemical attack.

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