| Method for fabricating a thick ti64 alloy article to have a higher surface yield and tensile strengths and a lower centerline yield and tensile strengths -> Monitor Keywords |
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Method for fabricating a thick ti64 alloy article to have a higher surface yield and tensile strengths and a lower centerline yield and tensile strengthsMethod for fabricating a thick ti64 alloy article to have a higher surface yield and tensile strengths and a lower centerline yield and tensile strengths description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20090159161, Method for fabricating a thick ti64 alloy article to have a higher surface yield and tensile strengths and a lower centerline yield and tensile strengths. Brief Patent Description - Full Patent Description - Patent Application Claims
This application is a continuation-in-part of allowed U.S. application Ser. No. 10/692,985 filed Oct. 23, 2003, which is hereby incorporated by reference. This invention relates to the fabrication of thick articles of Ti64 alloy and, more particularly, to the fabrication of such articles with a controllable difference in the near-surface and centerline mechanical properties. Ti64 alloy, having a nominal composition in weight percent of 6 percent aluminum, 4 percent vanadium, 0.2 percent oxygen, balance titanium and impurities, is one of the most widely used titanium-base alloys. The Ti64 alloy is an alpha-beta titanium alloy that may be heat treated to have a range of properties that are useful in aerospace applications. Ti64 alloy is used in both thin-section and thick-section applications, and heat treated according to the section thickness. In an example of interest, Ti64 alloy is used to make thick-section forged parts of aircraft gas turbine engines, such as compressor disks, fan disks, and engine mounts, which have at least some locations with a section thickness of greater than 2¼ inches. The present approach is concerned with such thick-section articles. In the current best practice to achieve the optimal combination of strength and other properties, after forging the thick-section Ti64 articles are typically heat treated at a temperature of 1750° F., followed by an anneal heat treatment at 1300° F. The result is a 0.2 percent yield strength throughout the article of from about 120 ksi (“ksi” is an abbreviation for “thousands of pounds per square inch”) to about 140 ksi. This strength has been satisfactory for many thick-section applications. To achieve higher yield strengths in the article, a more heavily alloyed, heavier forgeable alloy such as Ti 17, having a nominal composition in weight percent of 5 percent aluminum, 4 percent molybdenum, 4 percent chromium, 2 percent tin, and 2 percent zirconium, is used. The Ti 17 alloy uses a higher percentage of expensive alloying elements than does Ti64 alloy, with the result that a large, thick-section part made of Ti 17 alloy is significantly more expensive than the same part made of Ti64 alloy. There is a need for an improved approach to achieving excellent mechanical properties in forgeable titanium alloys. The present invention fulfills this need, and further provides related advantages. The present invention provides a fabrication approach for thick-section parts made of Ti64 alloy. This approach achieves significantly improved properties where needed for the surface and near-surface regions of the thick-section parts made of this well-proven alloy. The ability to use an established alloy is an important advantage, as new procedures for melting, casting, and forging a new alloy are not required. Nor is it necessary to employ a more heavily alloyed composition such as Ti17. A method for fabricating a forged titanium-alloy article comprises the steps of providing a workpiece made of a titanium alloy having a nominal composition in weight percent of 6 percent aluminum, 4 percent vanadium, 0.2 percent oxygen, balance titanium and impurities. The titanium alloy has a beta-transus temperature. The workpiece is thereafter forged at a temperature below the beta transus temperature to make an alpha-beta forged gas turbine engine component, such as a compressor disk, a fan disk, or a gas turbine engine mount. The forged article, which is preferably a gas turbine engine component, has a thick portion thereof with a section thickness greater than 2¼ inches. The forged gas turbine engine component is thereafter heat treated by solution heat treating the forged gas turbine engine component at a temperature of from about 50° F. to about 85° F. below the beta-transus temperature, preferably for a time of from about 45 minutes to about 75 minutes. The gas turbine engine component is thereafter quenched to room temperature and thereafter aged for a minimum of 4 hours at a temperature between 900° F. and 1300° F. Desirably, the water quenching is initiated within about 20 seconds of completing the step of solution heat treating by removal of the component from the solution-treating furnace. The forged gas turbine engine component is thereafter final machined. The final machining is typically performed both to remove the high-oxygen, less ductile alpha-case at the surface and to produce the final features of the gas turbine engine component. In the usual practice, the forged gas turbine engine component is ultrasonically inspected in a rough-machined shape generated by rough machining the forging either prior to the solution heat treat or following all heat treatment. The ultrasonic inspection is performed either after the step of forging the workpiece and before the step of heat treating, or after the step of heat treating and before the step of final machining. Where the forged gas turbine engine component is a compressor or fan disk, and where the ultrasonic inspection is performed after the step of forging and before the step of heat treating, after the ultrasonic inspection rough slots may be machined into the periphery of the disk so that the subsequent heat treatment imparts the improved properties to the bottoms of the slots. The thick section of the gas turbine engine component given this heat treatment procedure desirably has a 0.2 percent yield strength of from about 120 ksi to about 140 ksi at its centerline, and a higher 0.2 percent yield strength of from about 160 ksi to about 175 ksi at a location nearer a surface thereof. The higher yield strength region of about 160-175 ksi typically extends downwardly from the surface of the gas turbine engine component to a depth of from about ¾ to about 1 inch below the surface. There is additionally an increase in the tensile strength associated with the increased yield strength. At greater depths, the gas turbine engine component has the lower yield strength range of about 120-140 ksi. In the work leading to the present invention, it was recognized that the near-surface regions of the thick gas turbine engine components are subjected to the highest stresses in service at locations about ½ inch below the final machined finished part surface. The present heat treatment procedure produces the highest yield strength and tensile strength material in the near surface regions of the thick article, where the tensile strength is most needed. The near surface regions thus perform mechanically as though they are made of a stronger material than the conventionally heat treated Ti64 material that is found toward the center regions of the thick article. The result is that the Ti64 material may be used in applications for which it would otherwise not have sufficient mechanical properties. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment. Continue reading about Method for fabricating a thick ti64 alloy article to have a higher surface yield and tensile strengths and a lower centerline yield and tensile strengths... Full patent description for Method for fabricating a thick ti64 alloy article to have a higher surface yield and tensile strengths and a lower centerline yield and tensile strengths Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for fabricating a thick ti64 alloy article to have a higher surface yield and tensile strengths and a lower centerline yield and tensile strengths patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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