Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Patent
1986-09-10
1988-06-21
Zimmerman, John J.
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
428552, 428564, 428565, 428632, 428654, 428937, 427 34, B32B 1516, B05D 110
Patent
active
047525355
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an aluminum-based article provided with a heat barrier coating, especially engine parts such as piston crown or cylinder head a method of producing it, and the use of such coatings on aluminum-based surfaces for the protection against the effect of high temperatures, especially heat shock, and against corrosion; and the use of a special bonding layer.
It is known that metal articles can be coated with a heat barrier making the article more resistant to high temperatures. For instance, it is known to coat e.g. an engine piston with ceramic materials. More particularly, it is known to coat aluminum-based (silumin) engine pistons with a heat barrier in the form of a sandwich coating comprising alternate layers of ceramic material, such as ZrO.sub.2, and cermet layers in which zirconium dioxide may be included. A known coating of this type comprises a Ni-Al bonding layer on the substrate, followed by a cermet layer (30% NiAl, 70% ceramics), a ceramic layer, and thereafter several cermet layers (70% NiAl, 30% ceramics) alternating with ceramic layers, the outer layer being ceramic.
Such a sandwich coating, having ZrO.sub.2 as ceramics, has been tested, by the present inventor among others, using a test generally accepted for such coatings. This "accelerated" test essentially consists in subjecting the coating to treatment cycles comprising heating and guenching, each cycle consisting in that the coating is exposed for fifteen seconds to a flame having a temperature of 1100.degree. C., whereupon the coating is water cooled for fifteen seconds, followed by drying with pressurized air.
It was found that said sandwich coating does not meet the usual requirements of heat resistance for coatings on aluminum alloy. Cracks/flakes arose, first in the cermet material, and then the ZrO.sub.2 top layer began to spall.
To my knowledge it has not till now been reported that ceramic coatings have been made to adhere durably on aluminum alloys, tested in the above mentioned generally accepted way.
For iron/steel substrates it is known to use a bonding layer of MCr AlY, wherein M=Ni, Co, Fe or NiCo. For Al-based substrates it is known, as mentioned above, to use a bonding layer of nickel aluminide, i.e. nickel is the main metal.
It was now found that heat barrier coatings including an outer top layer of stabilized or partially stabilized ZrO.sub.2 can advantageously be deposited on substrates of aluminum alloy, such as silumin, by means of a special bonding layer of aluminum alloy. Preferably a cermet layer is used between the bonding layer and the outer ZrO.sub.2 top layer.
Thus, the invention relates to an aluminium-based article having a heat and corrosion protective, heat shock resistant coating, especially engine parts such a piston head, cylinder head or cover, characterized in that it has a coating consisting of an aluminium-based bonding layer and an outer top layer of stabilized or partially stabilized zirconium dioxide, and optionally a cermet layer, comprising zirconium dioxide and an aluminum-based metal component, between the bonding layer and the outer zirconium dioxide top layer. The bonding layer preferably has a thickness in the range 0.1-0.6 mm, especially about 0.3 mm. The outer top layer of stabilized or partially stabilized zirconium dioxide perferably has a thickness in the range 0.5-2.5 mm, especially 1.0-1.5 mm.
A preferred embodiment of the article according to the invention resides in that the bonding layer is applied by thermal spraying of a rapidly solidified powder. The particle sizes of the powder preferably lie in the range 5 .mu.m-60 .mu.m, especially 10-40 .mu.m.
According to a further, preferred embodiment the bonding layer substantially consists of 60-80% by weight of Al and 40-20% by weight of Si. Thus, said powder preferably has this composition.
Another preferred embodiment resides in that the cermet layer is a layer substantially consisting of zirconium dioxide and an aluminum-based alloy, preferably an alloy of 60-80% by weight of Al and 40-20% by weight of Si, a
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Norsk Hydro a.s
Zimmerman John J.
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