Coated graphite articles useful in metallurgical processes and method for making same
First Claim
1. A coated graphite article contactable by molten metal and alloy systems in metallurgical procedures involving molten metal or alloys thereof reactive with carbon in the molten state at temperatures up to about 2000°
- C., comprising a graphite substrate and a multiple-layer coating on surface regions of the substrate exposed to the molten metal or alloys with said coating providing a barrier for inhibiting diffusion of carbon from the graphite substrate into the molten metal or alloy, said coating comprising a first coating increment supported on said surface regions of the graphite substrate with said first coating increment being of a thickness in the range of about 0.005-0.060 inch and substantially formed of a carbide-forming metal selected from the group consisting of molybdenum, tungsten, niobium, tantalum, hafnium, titanium, zirconium, and combinations thereof, a second coating increment supported on the first coating increment with said second coating increment being of a thickness in the range of about 0.005-0.025 inch and substantially formed of a carbide-forming metal selected from the group consisting of molybdenum, tungsten, niobium, tantalum, hafnium, titanium, zirconium, and combinations thereof and a refractory metal oxide selected from the group consisting of partially stabilized zirconia, yttria, alumina, and combinations thereof, and a third coating increment supported on the second coating increment with said third coating increment being of a thickness in the range of about 0.005-0.030 inch and substantially formed of refractory metal oxide selected from the group consisting of partially stabilized zirconia, yttria, alumina, and combinations thereof.
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Abstract
Graphite articles including crucibles and molds used in metallurgical processes involving the melting and the handling of molten metals and alloys that are reactive with carbon when in a molten state and at process temperatures up to about 2000° C. are provided with a multiple-layer coating for inhibiting carbon diffusion from the graphite into the molten metal or alloys. The coating is provided by a first coating increment of a carbide-forming metal on selected surfaces of the graphite, a second coating increment of a carbide forming metal and a refractory metal oxide, and a third coating increment of a refractory metal oxide. The second coating increment provides thermal shock absorbing characteristics to prevent delamination of the coating during temperature cycling. A wash coat of unstabilized zirconia or titanium nitride can be applied onto the third coating increment to facilitate release of melts from the coating.
39 Citations
12 Claims
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1. A coated graphite article contactable by molten metal and alloy systems in metallurgical procedures involving molten metal or alloys thereof reactive with carbon in the molten state at temperatures up to about 2000°
- C., comprising a graphite substrate and a multiple-layer coating on surface regions of the substrate exposed to the molten metal or alloys with said coating providing a barrier for inhibiting diffusion of carbon from the graphite substrate into the molten metal or alloy, said coating comprising a first coating increment supported on said surface regions of the graphite substrate with said first coating increment being of a thickness in the range of about 0.005-0.060 inch and substantially formed of a carbide-forming metal selected from the group consisting of molybdenum, tungsten, niobium, tantalum, hafnium, titanium, zirconium, and combinations thereof, a second coating increment supported on the first coating increment with said second coating increment being of a thickness in the range of about 0.005-0.025 inch and substantially formed of a carbide-forming metal selected from the group consisting of molybdenum, tungsten, niobium, tantalum, hafnium, titanium, zirconium, and combinations thereof and a refractory metal oxide selected from the group consisting of partially stabilized zirconia, yttria, alumina, and combinations thereof, and a third coating increment supported on the second coating increment with said third coating increment being of a thickness in the range of about 0.005-0.030 inch and substantially formed of refractory metal oxide selected from the group consisting of partially stabilized zirconia, yttria, alumina, and combinations thereof.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
Specification