Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-01-23
2003-11-04
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S404000, C428S569000, C428S667000, C427S421100, C427S446000, C427S450000, C419S028000, C419S035000, C148S513000, C075S252000
Reexamination Certificate
active
06641917
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spray powder to be used for forming a sprayed coating on the surface of a component part and a method for producing such a spray powder. More particularly, the present invention relates to a spray powder to be used for surface modification of a metal part represented by e.g. a machine part of an excavator to be used for civil engineering works, i.e. for surface modification of a substrate which is required to have extremely high impact resistance, excellent wear resistance and excellent corrosion resistance and wear resistance even under a wet environment, and a method for producing such a spray powder.
2. Description of the Background
Metal parts of various industrial machines or general-purpose machines are required to have various properties such as impact resistance, corrosion resistance and wear resistance depending upon the respective purposes. However, in many cases, the metal materials (substrates) constituting such metal parts can not adequately satisfy the required properties by themselves, and it is often attempted to solve such problems by surface modification by forming a coating on the substrate surface.
A thermal spraying process is one of surface modification techniques which are practically used, as well as physical vapor deposition or chemical vapor deposition. The thermal spraying process has characteristics such that the size of a substrate to be treated is not limited, a uniform coating can be formed on a substrate having a large surface area, the speed of forming the coating is high, its applications on site is easy, and a thick coating can be formed relatively easily. Accordingly, in recent years, its application has been expanded to various industries, and it has become an extremely important surface modification technique.
In the same meaning as “thermal spraying”, a term such as “building up” or “spraying” may sometimes be used. Among these terms, there is no distinct difference in the definitions, and there is no particular distinction also among the powders used therefor. A powder for forming a sprayed coating may not necessarily be limited for thermal spraying. Namely, a powder for thermal spraying may be used for building up or spraying, and inversely, a powder for building up or spraying may be used for thermal spraying.
Accordingly, “spray powder” in the present invention may be one which is used for “building up” or “spraying”.
Tungsten carbide is a material which has extremely high hardness and is excellent in wear resistance, and it is used as mixed or complexed with a metal such as Ni, Cr or Co, or an alloy containing such a metal, as a binder, to form a ceramic/metal composite material, i.e. a cermet, which is widely used as a material for a spray powder. “Cermet” is a term coined by taking the first three letters of each of “Ceramics” and “Metal”. Specifically, it is one having hard ceramic particles bound by a metal matrix and is a composite material having high hardness and high toughness. In the field of tool materials, cermet means a material of TiC type or Ti(C,N) type, but in a broad sense, it includes composite materials comprising ceramics and metals, in general.
A cermet powder is usually prepared by a technique represented by e.g. an agglomeration-sintering method, a sintering-crushing method or a fusion-crushing method.
The method for preparation of a cermet powder by the agglomeration-sintering method is as follows.
Firstly, a dispersion of a binder (such as PVA: polyvinyl alcohol) in a solvent (water or a solvent such as an alcohol), is added to a fine powder of the starting material, followed by mixing to prepare a slurry. This slurry is formed into a spherical agglomerated powder by means of e.g. a spray drier. Then, this agglomerated powder is subjected to de-waxing and sintering to remove the organic binder from the agglomerated powder and for the purpose of imparting a proper mechanical strength to the agglomerated powder particles.
And, the powder after the sintering is crushed by means of a crusher such as a ball mill. By this crushing, individual agglomerated powder particles will be separated, whereby a spherical powder can be obtained. Then, classification is carried out for the purpose of obtaining a spray powder having a particle size distribution required depending upon the spraying conditions or the type of the spraying apparatus to be used. For the classification, not only a method by means of a sieve, but also classification by a gas stream and other method, as well as a combination thereof, are known.
The powder particles obtainable by this agglomeration-sintering method are spherical and have a relatively uniform particle size distribution, whereby they have good flowability, and they are porous, have a large specific surface area and are easily meltable, and thus they have a characteristic that the spraying efficiency is high. Thus, this method is suitable as a method for preparing the cermet powder.
Whereas, the method for preparing the cermet powder by the sintering-crushing method is as follows.
Firstly, a fine powder of the starting material is sintered, and the obtained sintered product is mechanically crushed and then classified to obtain a spray powder having a desired particle size distribution. Industrially, after mixing the starting material, a method such as press molding may be carried out for the purpose of obtaining a sintered product having higher denseness. Further, the technique and purpose of the classification are the same as in the above-mentioned agglomeration-sintering method. The powder obtainable by this sintering-crushing method is composed of dense and firm particles, which have angular or bulky shapes having edges specific to a crushed powder.
On the other hand, the method for preparing a cermet powder by the fusion-crushing method is as follows.
Firstly, the starting material is heated, melted and cooled, and then, the obtained solidified product (ingot) is mechanically crushed and classified. The melting is carried out for the purpose of obtaining a dense powder, and an arc furnace is used for an industrial purpose. Further, the crushing of the ingot may be carried out by a technique such as a drop hammer or hammering, whereby coarse crushing, intermediate crushing or fine crushing may be carried out. The method and purpose of the crushing are the same as in the above agglomeration-sintering method or the sintering-crushing method.
The powder obtainable by this fusion-crushing method is homogeneous and composed of particles which are more dense and firm than the powder obtainable by the sintering-crushing method. Further, the shape of particles is angular or bulky similar to the particle shape obtainable by the sintering-crushing method.
The cermet powder prepared by such an agglomeration-sintering method, a sintering-crushing method or a fusion-crushing method, may be used as it is, as a spray powder. However, for the purpose of forming a dense sprayed coating, a self-melting alloy powder may be added and mixed to the cermet powder to obtain a spray powder, which may be sprayed, followed by fusing treatment to form a coating.
On the other hand, as a spray powder for forming a sprayed coating having excellent corrosion resistance and wear resistance under a wet environment, a WC/CrC/Ni type spray powder prepared by mixing Ni or a Ni-base alloy as a binder to tungsten carbide or chromium carbide as a ceramic material, followed by an agglomeration-sintering method, is widely used in the industrial field.
However, with a sprayed coating formed by using this WC/CrC/Ni type spray powder, it has been pointed out that toughness and impact resistance are not so high. Specifically, this spray powder has been used as sprayed to a substrate which is susceptible to wearing especially in a wet environment, but has had a problem that upon receipt of a large impact, the sprayed coating tends to have cracking, or the coating tends to peel from the substrate. The useful life of the substrate will be extremel
Itsukaichi Tsuyoshi
Osawa Satoru
Fujimi Incorporated
Kiliman Leszek
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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