Coating processes – With pretreatment of the base – Fluxing
Patent
1983-12-14
1987-04-21
Smith, John D.
Coating processes
With pretreatment of the base
Fluxing
295275, 164 97, 427404, 4274432, 427190, 427202, 427203, B22D 1914
Patent
active
046595937
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with processes for making composite materials and more particularly, composite materials comprising a first fibrous component forming the frame of the composite material and a second component consisting of a light alloy acting as a matrix and in the liquid state wetting the first component after pre-treatment of said first component by a fluorine containing agent in order to obtain a composite material having all the qualities inherent to this type of material. Reinforcement of light alloys by fibers having high mechanical characteristics has not heretofore had a development comparable to that of plastic materials, mainly because of technical difficulties encountered during processing.
However, composites containing a metallic matrix have certain interesting specific characteristics: ability to use with heat, resistance to fatigue; lack of aging, stability relative to various media, high thermal and electrical conductivities, reproducibility of characteristics, etc.
Among these materials, composites having an aluminum matrix reinforced by fibers such as carbon based fibers (carbon, silicon carbide) are particularly interesting because on the one hand of their mechanical characteristics, availability, the ability to weave them and the relatively moderate prices of this type of fibers and on the other hand because of the low density, low melting point and the low cost of aluminum alloys. The development of this type of composite is actually considerably delayed by the fact that their simplest production process, liquid phase impregnation, is complicated by the poor wettability of these fibers by most aluminum alloys in the liquid state as well as by the occurrence of chemical reactions between the fiber and the matrix tending to lessen the reinforcing power of the fibers.
It is known, as a matter of fact, that graphite (as well as most of the other forms of carbon) is not spontaneously wet by liquid aluminum (and most of its usual alloys, mainly foundary alloys) at temperatures below 100.degree. C. As a result liquid aluminum cannot spread on a graphite surface or penetrate by capillary action within its pores, some of which are very small, in the strands of carbon, fibers or in multidirectional porous preform shapes made therefrom. At the temperatures where aluminum wets graphite (0>1000.degree. C.) there occurs a very rapid chemical reaction accompanied by precipitation of aluminum carbide and causing an irreversible mechanical damage to the fibers. It is to be noted also that graphite and aluminum react together but more slowly at much lower temperatures (beginning at 550.degree. C.), the formation of Al.sub.4 C.sub.3 leading to a poor adhesion between the fiber and the matrix (and therefore to a tendency to delaminate and to poor transverse properties) and to weakening of the matrix.
Silicon carbon based fibers, such as for example NICALON, commercialized by the Japanese company and formed of a mixture of silicon carbide, carbon, and silica, though they have a better chemical compatibility with metals than those of pure carbon, are also poorly wet by liquid aluminum and most of its usual alloys).
In an attempt to avoid these problems, a considerable research effort has been devoted to the making by liquid means of fibrous composites having an aluminum based matrix. It should be distinguished first between the case of fibers having a large diameter such as boron filaments (coated or uncoated) or silicon carbide whose diameter is generally comprised between one and two hundred microns and which are obtained by deposition in vapor phase on a filamentary substrate of tungsten or carbon. The preforms made with the aid of these products, which have of necessity a very simple shape owing to the rigidity of these filaments, are characterized by very large pores which readily allow penetration by liquid aluminum using if necessary a slight pressure (impregnation by liquid or even semi-liquid means). These filaments because of their morphology and their mechanical characteris
REFERENCES:
patent: 4157409 (1979-06-01), Levitt et al.
patent: 4158710 (1979-06-01), Gierek et al.
Naslain Roger
Pailler Rene
Quenisset Jean-Michel
Rocher Jean-Philippe
Messier Fonderie d'Arudy
Smith John D.
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