Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Making composite or hollow article
Patent
1986-01-08
1987-04-21
Lechert, Jr., Stephen J.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Making composite or hollow article
75231, 75235, 75236, 75243, 264 60, 264 65, 264125, 419 10, 419 17, 419 19, 419 23, 419 36, 419 37, 419 39, 419 56, 428552, 428564, B22F 700
Patent
active
046595473
DESCRIPTION:
BRIEF SUMMARY
The object of the invention is to prepare components using a powder-metallurgic manufacturing technique and starting from metal powder and refractory ceramic powder with high requirements as to the binding between the components involved.
The powder-metallurgic manufacturing technique is characterized by production in long series of parts having high dimensional accuracy. The chain of manufactures starts by mixing a metallic powder, for example iron powder, optionally having added pulverulent alloying agents thereto with a lubricant to facilitate the subsequent compacting operation. In this operation the powder mixture is compacted to a moulding blank the shape of which closely or completely corresponds to the shape of the final part. The blank is heated and is then maintained at a temperature at which it by sintering obtains its final properties, such as strength, toughness etc.
Serial manufacture of dry-compacted refractory ceramics shows several similarities with the powder-metallurgic manufacturing technique. In iron powder based manufacture sintering normally takes place within the temperature range 1000.degree.-1300.degree. C. For more low-melting metals and alloys, such as for example aluminium and bronze, the sintering temperature usually lies between 500.degree.-900.degree. C. When manufacturing powder-compacted refractory ceramics the sintering, however, takes place within the temperature range 1400.degree.-1700.degree. C.
Refractory materials are in combination with metals, for example as heat shielding, of quite a great interest. The difficulty of adjoining the refractory material with the metal in a durable manner lies in the fact that the materials involved normally have different coefficients of expansion. Joining may then be accomplished using for example countersunk bolts which, however, when used under mechanical load i.a. can result in unsuitably high weight to obtain the necessary strength. It is also possible to perform joining using a glue, but then it is a requirement that heating cannot take place beyond the heat resistance of the glue. If inorganic glue, for example water-glass, is used in such cases when the ceramics is expected to be subjected to a relatively high temperature there is an obvious risk that different coefficients of expansion will cause failure of the ceramics. Moreover, the multitude of operational steps in this manufacture results in high costs. Other known methods are for example soldering on ceramics. This is a laborious method requiring high accuracy and at least seven different operational steps. Moreover, it is required that the grain size of the soldering powder shall be less than 1 micron.
According to the invention it has, however, been found that it is possible by powder-pressing and subsequent sintering to obtain in a simple manner suprisingly good binding between ceramics and metal. The simplicity consists i.a. in the fact that it has been found possible in one step to press together the ceramic powder and the metal powder (for example iron powder). The pressing can take place at such low pressures as about 0.5 ton/cm.sup.2, and high strength can be obtained also in the ceramic part at such low temperature as 800.degree. C.
There are two partly overlapping problems which the inventors have been obliged to solve. The dilatation curves for metals and ceramics usually differ strongly from each other. It has been found that the damaging effect of this can be eliminated by using as a binding phase between a ceramic layer and a metal layer one or several layers of a mixture of the components involved. The fraction of metal or ceramics to be present in the mixture as wholly dependant on the area of use and whether the mixture shall be bound to ceramics and/or metal. It is obvious that sintered bodies also can be manufactured in accordance with the invention in only one layer and where the amount of the components involved can be controlled by the area of use. At the temperature which can be endured by the metal part of the sintered body the refractory ceramic
REFERENCES:
patent: 3953177 (1976-04-01), Sedlatschek et al.
patent: 4102679 (1978-07-01), Arvela
patent: 4500364 (1985-02-01), Krutenat
patent: 4569692 (1986-02-01), Butt
patent: 4569693 (1986-02-01), Albrecht et al.
Svensson Lars-Erik
Thornblad Ove
Hoganas AB
Lechert Jr. Stephen J.
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