Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Making composite or hollow article
Patent
1992-12-10
1994-11-29
Walsh, Donald P.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Making composite or hollow article
419 17, 419 32, 419 38, 419 45, 264 60, 264DIG36, B22F 316, B22F 100, C01B 3130, C04B 3564
Patent
active
053688120
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention concerns the production of carbide bodies. It also concerns the production of metallic composites in the form of a metal matrix with particles of a carbide dispersed within the matrix. More particularly, it concerns the synthesis of carbides, and the production of carbide bodies and composites consisting of a metal matrix with a dispersed phase of the metal carbide, using mechanical alloying techniques.
BACKGROUND
Metallic carbides are very hard materials. They are used as abrasives, as the cutting part of lathe tools, masonry drills and the like, and as additives which increase the strength and hardness of metals and alloys used as cutting tools.
The conventional preparation of carbide bodies involves the steps of of a metal or a mixture of metals, the carbide of which is to be formed, with graphite powder in stoichiometric quantities to produce the required carbide or carbides, and optionally including an additive in the powder mixture to act as a bonding agent (for example, a quantity of powdered colbalt may be added to facilitate the bonding of the powder particles, particularly if a mixture of metal carbides is to be produced); product; and bonding between the powder particles to be effected, to form the carbide body.
It has been suggested previously that carbides can be produced by mechanical alloying. For example, the production of carbides of transition metals and elements of groups IIIA and IVA of the periodic table, using a mechanical alloying technique, has been described in the specification of International patent application No PCT/FR89/00384 (World Intellectual Property Organisation publication No WO 90/01016). The examples given in that specification show that when a small quantity of a powder of an element of the specified group is milled with graphite powder for around 24 hours in an inert atmosphere (usually argon), a carbide of the element is produced. In general, the carbide produced is that which would be expected from a complete reaction of a stoichiometric mixture of the element and graphite, but in some instances (for example, when the element is niobium, molybdenum or vanadium), "new" carbides are formed. However, the carbides formed by this technique (which is also reported in the paper by P Matteazze, G Le Caer and E Bauer-Grosse entitled "Synthesis of Advanced Ceramics by High Energy Milling") are deduced to be present from the analysis of X-ray diffraction patterns of the product powders and there appears to have been no attempt to form dense ceramic bodies from the small volume samples of the product carbides that are shown to be present. Certainly there is no indication that it would be possible to form machine tools or the like from carbide powders produced by the mechanical alloying process.
DISCLOSURE OF THE PRESENT INVENTION
It is an object of the present invention to provide a new, relatively inexpensive, and reliable method of producing (a) metal carbides, and (b) composites of metal or metal alloys having dispersed therein a quantity of a metal carbide, using mechanical alloying techniques.
This objective is achieved by mechanical alloying of particulate metals in a ball mill or the like with graphite and preferably, but not necessarily, with the addition of a surfactant. The milling of the powder is continued until a nanostructural mixture is achieved. At this stage, the mixture comprises small regions (sometimes layers) of metal and carbon, each region (or layer) having a thickness of several nanometers. Between these regions or thin layers, there are some particles of the true carbide, having a diameter of about 1 nanometer. This nanostructural mixture of metal, carbon and true carbides (which are present in a small proportion by weight and volume) can then be compacted in dies or moulds to form a required shape, which is subsequently annealed at a higher temperature. During the annealing step, there is a solid state reaction (transformation or formation) which produces either carbides as a single phase structure (for example,
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Calka Andrzej
Ninham Barry W.
Australian National University
Chi Anthony R.
Walsh Donald P.
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