Patent Application
20070284073
The present invention provides a method of making a composite casting wherein a reinforcement insert is disposed in a metallic matrix to provide reinforcement of the matrix. For purposes of illustration and not limitation,
Before each reinforcement insert 14 is positioned in a respective mold cavity 12, it is coated with a protective ceramic coating 16 that preferably is substantially non-reactive with the molten metallic material to be cast about the insert 14 in the mold cavity 12 to form the solidified metallic matrix. The ceramic coating material preferably is chosen to be substantially non-reactive with the particular molten metallic material to be cast into the mold cavities 12 in that at least some of the thickness of the ceramic coating remains after the molten metallic material has been cast and solidified about the reinforcement insert. The ceramic coating 16 thus is chosen according to the molten metallic material to be cast in the mold 10. The ceramic coating can applied to the insert by vapor deposition (e.g. chemical vapor deposition, electron beam physical vapor deposition, physical vapor deposition, etc.), by plasma or flame (e.g. HVOF) spraying, or by applying a ceramic slurry to the insert and drying the slurry. The ceramic coating can be applied to any appropriate thickness on the reinforcement insert. For purposes of illustration and not limitation, the thickness of the ceramic coating can be from about 0.1 or less mil and up to about 5 mils.
Coating of the reinforcement insert 14 with the ceramic coating 16 pursuant to the invention is especially useful, although not limited to, making composite castings that are made by casting a reactive molten metal or alloy in the mold 10.
For purposes of illustration, titanium and its alloys form reactive molten melts that can react with the reinforcement insert 14 if it is not coated to generate casting porosity and to degrade the reinforcement insert. Illustrative titanium alloys include, but are not limited to, Ti-6Al-4V, Ti-5Al-5Mo-5V-3Cr, and Ti-6Al-2Sn-4Zr-2Mo where the numeral represents weight percent of the particular element (e.g. Ti-6Al-4V includes 6 weight % Al and 4 weight % V, balance Ti). In casting titanium alloys, a slight oxygen enriched layer may be formed on the outer surface of the alloy casting but the ceramic coating on the reinforcement insert 14 is substantially non-reactive with the alloy.
When the molten metallic material comprises reactive molten titanium or molten titanium alloy, the reinforcement insert 14 can comprise silicon carbide (e.g. SiC), boron carbide (e.g. B4C), silicon nitride (e.g. Si3N4), or an intermetallic compound, such as TiAl, coated with a ceramic coating 16 preferably comprising erbium oxide or yttrium oxide. The reinforcement insert 14 itself may comprise a titanium matrix composite (TCM) having SiC and/or SiN fibers residing in a titanium matrix as described in U.S. Pat. No. 5,981,083, which is incorporated herein by reference. The erbium oxide or yttrium oxide coating 16 can be applied to the reinforcement insert 14 preferably by chemical vapor deposition, electron beam physical vapor deposition, physical vapor deposition and other vapor deposition processes, although other coating methods can be employed.
After the reinforcement insert 14 is coated with the ceramic coating 16, each insert 14 is positioned in a respective mold cavity 12 of mold 10. Mold 10 is illustrated in
The coated reinforcement insert 14 can be positioned in each mold cavity 12 of mold 10 by any suitable insert positioning means. For purposes of illustration and not limitation,
The molten metallic material then is introduced (e.g. gravity poured) into the mold 10 via a pour cup 10c, which conveys the molten metallic material via a down sprue 10p and runners 10r to the mold cavities 12 where the molten metallic material fills each mold cavity, surrounds the reinforcement insert 14 therein, and solidifies to form a composite casting in each mold cavity. The composite casting comprises reinforcement insert 14 disposed in a metallic matrix formed by the solidified metallic material with the ceramic coating material between the reinforcement insert and the metallic matrix. In the illustrative embodiment of the present invention discussed above, the metallic matrix comprises titanium or a titanium alloy and the reinforcement insert comprises silicon carbide, silicon nitride, or an intermetallic compound disposed in the matrix.
The composite castings produced in the mold 10 are freed by a knock-out operation where the mold is struck with a hammer to knock off the ceramic mold material followed by sand blasting to remove remaining ceramic mold material on the composite castings.
After the composite castings are removed from the mold 10, they optionally can be subjected to a hot isostatic pressing (HIP) operation as described in U.S. Pat. No. 5,981,083, already incorporated herein by reference.
The following EXAMPLES are offered to further illustrate but not limit the invention.
Referring to
In particular, a pair of SiC reinforcement inserts of the type shown in
Deposition of the yttria or erbia ceramic coating was conducted using electron beam physical vapor deposition equipment and processing described in U.S. Pat. No. 5,716,720 with the temperature control lid feature of U.S. Pat. No. 6,688,254 to control SiC reinforcement insert (substrate) temperature during the coating deposition process, both of these patents being incorporated herein by reference. The temperature of the SiC reinforcement insert was maintained in the range of 1825 to 1920 degrees F. during deposition using the temperature control lid feature of U.S. Pat. No. 6,688,254.
In depositing the yttria or erbia ceramic coating pursuant to this example, the source material of yttria (yttrium oxide) or erbia (erbium oxide) was a cylinder with nominal dimensions of 2.5 inches diameter and 7.5 inches in length wherein the electron beam impinged the end of the cylinder. The processing sequence employed a vacuum of 1×10−4 torr in the loading chamber where the SiC reinforcement insert was mounted on the part manipulator. The reinforcement insert mounted with a flat major side adjacent the part manipulator then was moved into the preheat chamber through an open valve connecting the loading chamber and the preheat chamber. The reinforcement insert was heated to 1900 to 1950 degrees F. in the preheat chamber by radiant heating from resistively heated graphite heating elements. The preheated reinforcement insert then was moved into the coating chamber above the end of the cylinder of yttria or erbia source material. In the coating chamber, the electron beam (power level of 80-90 kW) from an electron gun was scanned over the end of a cylinder of yttria or erbia source material to evaporate it. For yttria or erbia source material, oxygen was introduced into the coating chamber to produce a pressure of 1-20 microns. The SiC reinforcement insert was rotated by the part manipulator above the source material in the cloud of evaporated yttria or erbia material in the coating chamber. Rotation of the reinforcement insert was conducted in the range of 1-15 rpm. Once the proper coating time and thus coating thickness was produced on the major side of the reinforcement insert, the manipulator was retracted to locate the insert back into the loading chamber where it cooled. The valve between the loading chamber and the preheating chamber was closed. Once cool, the loading chamber was opened and the SiC reinforcement insert was removed. The insert then was reloaded on the part manipulator for coating of the opposite major side thereof, which was mounted against the part manipulator during the first coating cycle and thus was not coated. The narrow edges of the SiC reinforcement insert received two coating layers of yttria or erbia as a result of the two coating cycles needed to coat both major sides of the insert.
Deposition was conducted for a time to produce the desired thickness of yttria or erbia on each side of the reinforcement insert. In particular, a continuous yttria or erbia coating approximately 0.001 to 0.002 inch in thickness was deposited on the side of the SiC reinforcement insert depending upon the source material employed.
The two pairs of coated reinforcement inserts clamped in the titanium clamps described above and shown in
Although the invention has been shown and described with respect to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.
