Metal carbide-containing refractory materials

Details Metal carbide-containing refractory materials Metal carbide-containing refractory materials

1998-10-21

2000-01-11

Mai, Ngoclan

Powder metallurgy processes

Powder metallurgy processes with heating or sintering

Heat and pressure simultaneously to effect sintering

423439, 423440, 501 87, 501 88, 264500, 264 291, B22F 315

Patent

active

060132264

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the production of metal-containing refractory materials, to refractory materials obtainable thereby and to compositions (hereinafter "blanks") for use in said process.
Refractory materials are useful in products which require resistance to extreme conditions, especially heat. Examples of such products include vehicle components such as aircraft brakes, space vehicle heat shields, etc.
EP-A-0373761 discloses a process in which a thermoformable carbon-containing precursor composition having defined viscosity characteristics is formed into a blank to which isostatic pressure is applied using an appropriate gaseous medium. The blank, which may if desired additionally contain refractory filler or reinforcement material, e.g. in particulate or fibrous form, is then heated so as to permit flow but not pyrolysis of the precursor composition, whereby the blank becomes sealed so that the isostatic pressure is electively transferred to the whole blank. The blank is thereafter heated further under an isostatic pressure of at least 500 bar to pyrolyse the precursor composition. This hot isostatic pressing (HIP) process obviates the previously felt need hermetically to seal the blank in an impervious envelope (e.g. comprising mild steel or molten glass) capable of withstanding the processing temperature (e.g. up to 2000.degree. C. or more), while yielding pyrolysed products which surprisingly retain their original shapes, remaining substantially undistorted and non-blistered during the HIP process.
The present invention is based on the finding that metal carbide-containing refractory materials may be formed in a particularly efficient and economical manner by pyrolysis under appropriate fluid pressure of a carbon-containing precursor together with a reactive metal source. This process permits the production of a wide range of metal carbide monoliths and composites with appropriate refractory properties.
Thus according to one aspect of the present invention there is provided a process for producing a metal carbide-containing refractory material wherein a blank comprising a reactive metal source and a carbon-containing precursor is pyrolysed under fluid pressure.
A particular advantage of the process of the invention is that in general the blanks do not suffer undue change of shape during processing, any change in dimensions normally being isotropic. The blanks thus retain "near-net shape".
The fluid pressure used in the process is conveniently that of an inert gas applied directly to the surface of the blank, although the blank may if desired be encased in a hermetically sealed envelope throughout the process. Thus, the process can comprise hot isostatic pressing, and the following description particularly relates to such use of HIP. The term "inert ga" as used herein refers to a substance which is in gaseous form under the conditions of the process and which does not have a deleterious effect on the process or product. Thus, if the process is a carbothermic reduction process, the inert gas can be a gas which will facilitate that process.
It will be appreciated that metals useful in the reactive metal source are those which are able to form one or more carbides. Such metals include those which are themselves refractory, for example, metals whose melting point is 1300.degree. C. or higher. The metal may be, for example, a member of Group II (e.g. IIa), III (e.g. IIIb), IV, V (e.g. Va) or VI (e.g. VIb) of the Mendeleef Periodic Table of Elements (CAS version). Table 1 presents, by way of example, metals which are known to form carbides.


TABLE 1 ______________________________________ Group of the Melting Point Mendeleef Periodic Metal Symbol (.degree. C.) Table of Elements ______________________________________ Silicon Si 1420 IVb Titanium Ti 1850 IVa Hafnium Hf 2500 VIa Molybdenum Mo 2500 VIa Tantalum Ta 2900 Va Tungsten W 2900-3000 Va Zirconium Zr 2130 IVa Boron B 2300 IIIb Beryllium Be 1280 IIa ______________________

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patent: 5258337 (1993-11-01), Cameron et al.
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