Method of making sintered aluminium nickel alloys

Details Method of making sintered aluminium nickel alloys Method of making sintered aluminium nickel alloys

1990-06-19

1991-01-15

Lechert, Jr., Stephen J.

Powder metallurgy processes

Powder metallurgy processes with heating or sintering

Metal and nonmetal in final product

719 23, 719 30, 719 12, 719 13, 419 17, B22F 100

Patent

active

049852000

DESCRIPTION:

BRIEF SUMMARY
This invention relates to sintered aluminium nickel alloys, and in particular to such alloys containing ceramic materials.
An industrial requirement exists for aluminium alloys which have high temperature strength and stability coupled with good wear resistance. The problem of satisfying both requirements in a single material presents considerable difficulty.
Conventional aluminium alloys containing copper or magnesium exhibit age hardening, and although these alloys have good mechanical properties at relatively low temperatures, unfortunately they have low wear resistance. Furthermore, at temperatures in excess of 180.degree. C. these alloys overage, resulting in deterioration of strength.
For the production of pistons, cylinder liners, or for other applications where a combination of high temperature strength and wear resistance is required, aluminium based casting alloys containing high levels of silicon, together with some copper and other ingredients are currently used. However, the use of silicon has the adverse effect of lowering the melting point of the alloy by about 90.degree. C., and, depending upon the other additions, this may be as much as 125.degree. C. below that of pure aluminium. This reduces the high temperature strength and increases the tendency to heat cracking.
In U.K. Patent No. 1331145 there is disclosed a sintered aluminium alloy composition comprising 5 to 10% of iron, nickel or chromium together with 0.5 to 5% of silicon carbide. These alloys are said to exhibit good high temperature strength and wear resistance. However, the processing route required to realise these advantages in practice has been reported elsewhere as complex, and to require cold pressing, warm repressing, and subsequent hot forging to final shape.
The problems inherent in the production of sintered aluminium alloys including iron, nickel or chromium arise from the fact that an intense exothermic reaction occurs during the sintering process. In the course of the reaction the aluminium melts, and there is an abrupt expansion of the sintering mass, and local weaknesses occur in the resultant alloy. The problems are well documented for the case of iron/aluminium, (with a preponderance of iron), in, for example, articles "Powder Metallurgy of Iron-Aluminium" by J. S. Sheasby in Volume 15 No. 4, 1979, pages 301-305 of The International Journal of Powder Metallurgy and Powder Technology, and "Sintering Behaviour of Iron-Alloy Powder Mixes" by D. J. Lee and R. M. German in Volume 21 No. 1, 1985, pages 9-20 of the same Journal.
Aluminium alloys having compositions similar to those of UK-A-13811145, but produced by processes other than Powder Metallurgy (sintering being a Powder Metallurgy process) are described in many publications. For example U.K. Patent Application No. 2088409A and U.S. Pat. No. 4,347,076 describe the production of alloys by the rapid cooling (typically 10.sup.5 degrees C. per second) of molten mixtures. This is a method requiring complicated and expensive equipment. U.K. Patent No. 1498357 describes electrical conductors made by a method involving extrusion, and U.K. Patent No. 868769 describes an alloy produced by compression and extrusion "to produce a shearing effect" of a mixture. U.K. Patent No. 846,530 also describes an alloy produced by hot-working, it being a requirement of the claimed alloy that "the iron-containing constituent in the hot-worked article (is) present in the form of finely divided uniformly distributed insoluble particles having a maximum thickness of 0.4 micron". U.K. Patent No. 516474 describes a method of producing an abrasive article containing "abrasive grains, for example, diamonds, and a sintered bond consisting entirely of aluminium or an aluminium base alloy". The method claimed involves the formation of a powdered mixture of abrasive, aluminium and a metal, pressurising to deform the metal particles, and then sintering.
The present Applicant's Patent GB No. 2179369B describes a method of producing a sintered aluminium alloy having good high temperature strength,

REFERENCES:
patent: 3893844 (1975-07-01), Nadkami
patent: 4077816 (1978-03-01), Nadkami
patent: 4274873 (1981-06-01), Nadkami

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