Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1989-01-04
1990-10-23
Lechert, Jr., Stephen J.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
419 2, 419 38, B22F 900
Patent
active
049649094
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a heat-insulating component and a method of making same. The invention also relates to a method of lowering the thermal conductivity of a component obtained from an iron-base powder mixture by moulding and sintering.
Substantial efforts have been made over the years to develop ceramic materials which are suitable for use in internal combustion engines. Although these efforts have met with some success, the ceramic materials, by being relatively brittle, have however caused a number of problems reducing their usefulness. Also, difficulties in durably joining the ceramic material to metal are encountered since the materials used normally have different coefficients of heat expansion. Similarly, the ceramic materials are difficult or impossible to use if after-treatment is necessitated by shape or demands on tolerance.
The need of being able to prevent heat from being conducted out to the engine block of an internal combustion engine has increased with the demand for exhaust emission control, like the demand for an increase of the efficiency of a diesel engine, e.g. by controlling the thermal losses.
The object of the invention therefore is to develop a product having a low thermal conductivity, more specifically a coefficient of thermal conductivity below about 12 W/m.sup.o K, and most preferably below about 7 W/m.sup.o K, in combination with toughness, strength, machinability, freedom of choice in respect of manufacturing method, and a coefficient of heat expansion allowing joining the product to metal in a simple and durable manner. It has been found quite surprisingly that this is feasible starting from a metallic powder.
It is not to be expected that metals without the addition of oriented ceramic flakes may be used for heat-insulating purposes. From British patent specification GB-2,124,658 it is thus known to use 10-30% by weight of oriented ceramic flakes in a stainless alloy for manufacturing brake components with directional heat transmission.
By adding silicon and possibly manganese to a powder or to a melt for atomization, consisting of pure iron or iron-nickel, and thereafter manufacturing porous sintered bodies, it was however found that it was possible to adjust the heat-insulating properties to values equivalent to those obtained with zirconium oxide.
Silicon strongly affects the thermal conductivity and the amount of silicon should be between 2 and 10% by weight and preferably between 4 and 8% by weight. If the amount of silicon becomes excessive, the liquid phase also becomes excessive, entailing that the powder body will collapse upon sintering and the porosity will decrease dramatically.
The addition of manganese primarily affects the workability of the sintered body but also, to some extent, the thermal conductivity. It has been found that if manganese is to be added, the amount should be between 3 and 12% by weight and preferably between 5 and 10% by weight.
If there is a demand for high corrosion resistance, chromium may also be added. The amount of chromium must not exceed 25% by weight since with larger amounts, a compact will not hold together after compaction. A chromium amount of about 21% has been particularly suitable.
For increased strength of the sintered body, nickel may be added in an amount of up to 15% by weight.
Also other alloying materials, such as molybdenum and carbon, may be added without noticeably deteriorating the inventive effect.
Powder mixtures may be preferable, giving increased flexibility in the choice of alloying additives and are sometime necessary for achieving the required compressibility. For certain components and methods of manufacture, it has however been found more appropriate to use prealloyed atomized powder.
To sum up, the present invention requires no ceramic flakes or in any way oriented particles, but the excellent heat-insulating properties are achieved by producing thermal barriers by structural transition, primarily by means of silicon but also by means of manganese. This entails e.g. that the components acco
REFERENCES:
patent: 3980444 (1976-09-01), Reen
patent: 3993445 (1976-11-01), Reen
patent: 4494988 (1985-01-01), Schumacher et al.
Engstrom Ulf
Mustonen Olavi
Hoganas AB
Lechert Jr. Stephen J.
Nigohosian, Jr. Leon
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