Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-10-21
2002-06-11
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S307300, C428S313900, C428S131000, C419S006000, C419S008000, C419S027000, C419S038000, C419S063000
Reexamination Certificate
active
06403210
ABSTRACT:
This invention relates to a method for manufacturing a composite material, in particular a ceramics or the like containing composite material, as well as to a composite material.
The use of ceramics in applications where conventionally metals were used has recently increased markedly. Reasons for this are, for instance, various clearly improved material properties, such as wear-resistance, hardness, corrosion-resistance, modulus of elasticity, dimensional stability, chemical resistance and heat-resistance. One of the important disadvantages of the use of ceramic materials, however, is that they are relatively brittle. Further, their resistance to thermal shocks is poor. Moreover, good ceramic composites are relatively expensive. As a consequence, the possible areas of application of ceramic composites are limited.
In order to avoid these disadvantages, a number of proposals have been made for the manufacture of such composites with improved properties.
European patent application 0,378,500 describes a method for manufacturing a metal-infiltrated composite material which comprises reaction products of the metal with boron and/or carbon. To that end, from a boron door material and a carbon donor material, a self-supporting intermediate of a relatively high porosity is formed, whereby bonds between the material particles are effected, for instance during sintering of the intermediate. Thereafter the intermediate is contacted with a molten parent metal, in a manner and for a time suitable to obtain a reactive infiltration. The space existing between the mutually bonded particles is thereby filled with the metal and the whole is maintained at a suitable temperature for a suitable time, in such a manner that at least chemical bonds are formed between boron and metal, carbon and metal and boron, and/or carbon and metal. As a result of the reactive infiltration, a composite material is formed with mutually bonded particles with residual metal between them.
In this method, bonds between the different particles are effected, partly prior to the infiltration. As a result, a base product with a relatively high density and relatively coarse particles is formed, whereby the product does not acquire a completely open porous network. Any closed porosity present in the product is not removed and therefore not filled with metal during the infiltration. The particles are not entirely surrounded by the metal, so that no fully continuous matrix is obtained in which the particles are embedded. Moreover, the properties of the starting materials change considerably as a result of the chemical reactions.
U.S. Pat. No. 4,879,262 describes a method for manufacturing composites and in particular boron-containing composites, using combustion synthesis of boride compounds and composites. To that end, a suitable mixture of at least a first, B
4
C rich component and a second, B
4
C/TiB
2
rich component is composed and heated such that a maximum inclusion of the relatively light B
4
C into the relatively heavy B
4
C/TiB
2
is obtained, whereafter a self-sustaining combustion is effected in the mixture, such that a densification of the matrix arises as a result of the chemical reaction. The densification is not maximal, so that a porous structure is left. Thereafter the porous composite obtained is infiltrated with liquid metal, for instance aluminum. As a result, a composite of a relatively high density is formed. It is noted that in this way other composites can also be obtained, provided a self-sustaining combustion front can be generated therein.
This method can only be used with specific combinations of starting materials, while moreover heating prior to the combustion is required in order to obtain a good densification. Further, a relatively coarse division of the particles is obtained, while the particles will frequently be in mutual abutment. Any porosity present, which may or may not have arisen during the reaction, is not prevented, reduced or removed in this known method. No completely open porous network is formed, so that the particles cannot be completely surrounded by the metal. Moreover, as a result of chemical reactions that occur, the properties of the starting materials change.
European patent application 0,207,371 describes a method for manufacturing composites, in which powders are dynamically densified to a very high relative density. The shock induced by an explosive and/or strike plate in this method should be so high that exothermic sintering of the powders occurs. Chemical bonds and possibly plastic bonds between the powder particles are thereby formed, so that a closed network is obtained of, for instance, metals, oxides and the like, and a substantially full density.
In this method a very strong shock should be induced, in such a manner that the starting powders enter into an exothermic chemical reaction. As a result, the composition, and hence the chemical and mechanical properties, of the mixture changes. Moreover, a continuous network of ceramic particles fixedly bonded to each other is obtained, which particles are therefore not embedded in another material which forms a continuous matrix. As a result, the material obtained does not have an optimum resistance to, for instance, thermal shocks and it is insufficiently tough. Moreover, only starting powders capable of entering into the desired exothermic reactions with each other can be used.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method of the type described in the opening paragraph hereof, in which a relatively brittle, powdered material, preferably ceramic particles, in the composite are substantially, at least practically completely embedded in a matrix of a second material which through infiltration is introduced into a product formed by the relatively brittle material, with a completely open porous network. To that end, the method according to the invention is characterized by the steps of:
dynamically densifying an amount of granular or powdered relatively brittle material or a mixture of one or more of such materials;
whereby
the material or mixture of materials is densified in such a manner that a continuous porous product is obtained;
and infiltrating this with a second material,
whereby
after infiltration the brittle material particles are embedded in a continuous network of the second material.
In this description “dynamic densification”, also referred to “explosive compaction” or “shock densification”, is understood to mean: densifying a material using shock waves. For a review, reference is made to R. Prümmer, Ber. Dt. Keram. Ges.50, pp. 75-81, (1973).
By dynamically densifying the brittle material in accordance with the invention, a relatively highly dense product which has a fully open porous structure is obtained. That is to say, the particles are densely stacked without forming any fixed bonds between them. Thereafter, through infiltration, the porous network can be filled with a second material, for instance liquid metal or like material. Preferably, capillary infiltration is used. Owing to the product formed having an open porous continuous network, the particles can be entirely circumfused with metal. Thus a continuous matrix of the second material is obtained, in which the brittle particles are completely embedded, as a result of which the desired properties are obtained.
In a preferred embodiment, the method according to the invention is characterized in that the brittle material is predensified prior to the dynamic densification. Such predensification can occur in different ways, for instance by pressing the starting powders by using vibration techniques, by sludge densification and the like, or by combinations of different techniques. In some cases, pouring the brittle material into a die may already provide for a suitable predensification.
During the dynamic densification, in particular the pressure and the pulse duration that occur in the predensified product supply too little energy for bonds to form between the individual powder particles. On the other hand, a high powder
Carton Erik Peter
Maas Amanda Margaretha
Stuivinga Marianne Euphemia Corry
Copenheaver Blaine
Nederlandse Organisatie voor toegepast-natuurwetenschappelijk On
Norris McLaughlin & Marcus P.A.
Vo Nai
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