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  Turbine element repairUSPTO Application #: 20080057254Title: Turbine element repair Abstract: Ion-enhanced physical vapor deposition is utilized to deposit repair material on Ti alloy turbine parts. Pulse modulation may be used to control a bias voltage and an ionization. (end of abstract)
Agent: Bachman & Lapointe, P.C. (p&w) - New Haven, CT, US Inventors: Robert L. Memmen, Igor V. Belousov, Anatoly I. Kuzmichev USPTO Applicaton #: 20080057254 - Class: 428063000 (USPTO) Related Patent Categories: Stock Material Or Miscellaneous Articles, Patched Hole Or Depression The Patent Description & Claims data below is from USPTO Patent Application 20080057254. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This is a divisional application of Ser. No. 10/734,696, filed Dec. 12, 2003, and entitled "Turbine Element Repair" which is a continuation-in-part of U.S. patent application Ser. No. 10/377,954, filed Mar. 3, 2003, and entitled "Fan and Compressor Blade Dovetail Restoration Process" and U.S. patent application Ser. No. 10/635,694, filed Aug. 5, 2003, and entitled "Turbine Element Repair" (now U.S. Pat. No. 7,216,428). BACKGROUND OF THE INVENTION [0002] The invention relates to the restoration of turbomachine parts. More particularly, the invention relates to the restoration of worn or damaged gas turbine engine fan blades and other blades and vanes. [0003] The components of gas turbine engines are subject to wear and damage. Even moderate wear and damage of certain components may interfere with optimal operation of the engine. Particular areas of concern involve the airfoils of various blades and vanes. Wear and damage may interfere with their aerodynamic efficiency, produce dynamic force imbalances, and even structurally compromise the worn/damaged parts in more extreme cases. A limited reconditioning is commonly practiced for slightly worn or damaged airfoils wherein additional material is removed below the wear/damage to provide the airfoil with a relatively efficient and clean sectional profile albeit smaller than the original or prior profile. Exemplary inspection criteria establishing the limits to which such reconditioning can be made are shown in Pratt & Whitney JT8D Engine Manual (P/N 773128), ATA 72-33-21, Inspection-01, United Technologies Corp., East Hartford Conn. Such limits may differ among airfoils depending upon the location and particular application. The limits are typically based on structural and performance considerations which limit the amount of material that may be removed. [0004] Various techniques have been proposed for more extensive restoration of worn or damaged parts of gas turbine engines. U.S. Pat. No. 4,822,248 discloses use of a plasma torch to deposit nickel- or cobalt-based superalloy material. U.S. Pat. No. 5,732,467 identifies the use of high velocity oxy-fuel (HVOF) and low pressure plasma spray (LPPS) techniques for repairing cracks in such turbine elements. U.S. Pat. No. 5,783,318 also identifies LPPS techniques in addition to laser welding and plasma transferred arc welding. U.S. Pat. No. 6,049,978 identifies further use of HVOF techniques. Such techniques have offered a limited ability to build up replacement material to restore an original or near original cross-section. However, the structural properties of the replacement material may be substantially limited relative to those of the base material. [0005] Especially for larger damage, it is known to use preformed inserts which may be welded in place to repair damage. With such inserts, the damaged area is cut away to the predetermined shape of the insert which is, in turn, welded in place. Structural limits associated with the welding limit the capability of such repair techniques to relatively low stress regions of the airfoil as with other techniques. It is common for engine repair manuals to specify the low stress areas where weld repair is permissible. Thus substantial combinations of the extent of the wear/damage and the stress to which the worn/damaged area is subject may limit use of such techniques. High stress areas often include areas near (e.g., slightly inboard of) a midspan shroud of a fan blade. SUMMARY OF THE INVENTION [0006] One aspect of the invention involves a method for restoring a machine part which has lost first material from a site (e.g., from a Ti-alloy turbomachine part during operation of the turbomachine). The part is placed in a deposition chamber. A first electric potential is applied to the part. Components for forming a repair material are ionized. The first electric potential is modulated so as to draw the ionized components to the part so that a buildup of the repair material at least partially replaces the first material. [0007] In various implementations, the modulation of the first electrical potential may be performed so as to prevent arcing from the part. The part may be heated and the heating may be modulated in conjunction with the modulation of the first electric potential. The modulation of the first electrical potential may involve maintaining a principally negative potential and applying positive pulses of relatively short duration. The ionizing may be modulated. Additional material may be removed at least partially from the site to create a base surface. The repair material may be deposited atop the base surface at least partially in place of the first material and the additional material. The repair material may comprise or consist essentially of Ti-6Al-4V, Ti-6Al-2Sn-4Zr-2Mo, Ti-8Al-1V-1Mo, or Ti-6Al-2Sn-4Zr-6Mo. The additional material may be removed, in major part, from undamaged portions of the part. The part may be a blade having a root and an airfoil and the site may be along a leading edge of the airfoil inboard of a midspan shroud of the airfoil. The first material may be lost to a depth of 2.0 mm or more. A backing element may be applied to the part protruding adjacent the site so that the deposited repair material builds up on the base surface and backing element. The backing element may be at least partially removed and adjacent deposited material and preexisting material machined to create a second base surface. More of the repair material may be deposited atop the second base surface. The method may be performed at a pressure of less than 0.01 Pa. [0008] Another aspect of the invention involves a method for restoring a Ti alloy turbine part which has lost first material from a site. The part is placed in a deposition chamber. A first electric potential is applied to the part. Components for forming a Ti-based repair material are ionized. The first electric potential is modulated so as to draw the ionized components to the part while maintaining a temperature of the part within a target range so that buildup of the repair material at least partially replaces the first material with desired properties. [0009] In various implementations, the first electric potential may have a nominal voltage of 50 V-10kV, more narrowly, 1-3 kV. A pulse repetition frequency may be 0.05-150 kHz, more narrowly, 0.5-5 kHz. A duty cycle may be 0.01-0.99, more narrowly, 0.1-0.95. An ion current density may be 1-50 mA/cm.sup.2 at a deposition rate of 10-50 .mu.m/minute, more narrowly, 2-10 mA/cm.sup.2 at a deposition rate of 15-20 .mu.m/minute. The ionizing may be pulse modulated with a pulse repetition frequency of 100-1000 Hz and a duty cycle of 0.5-0.9. Modulation of external heating of the part may be performed in conjunction with modulation of the first electric potential. [0010] Another aspect of the invention involves an apparatus for depositing material on a workpiece. The apparatus includes a deposition chamber and a deposition material source. Means are provided for forming a plasma from said deposition material source. Means are provided for applying a modulated bias electric potential to the workpiece to draw ions from the plasma to the workpiece. Means are provided for monitoring a density of the plasma and an ion current to the workpiece. A control system is coupled to the means for forming, means for applying, and means for monitoring and is programmed so as to provide feedback loop control of deposition of the material. [0011] In various implementations, the apparatus may further include means for externally heating the workpiece. [0012] Another aspect of the invention involves an apparatus for depositing material on a workpiece. The apparatus includes a deposition chamber and deposition material at least partially within the deposition chamber. A first electron beam source is positioned to direct a first electron beam to vaporize a portion of the deposition material. The ionizing electrode and an electromagnetic coil surround a flowpath from the deposition material. A bias voltage source is connected to apply an electric potential to the workpiece. A control apparatus is coupled to the bias voltage source and configured to apply said electric potential as a principally negative potential interspersed with positive pulses. [0013] In various implementations, the control apparatus may be coupled to the ionizing electrode for pulse modulation of ionization. A second electron beam source may be positioned to direct a second electron beam to the workpiece. [0014] Another aspect of the invention involves a repaired metallic part having a substrate. A repair material has a first interface with the substrate. A bond strength between the repair material and the substrate is in excess of 50 ksi. [0015] In various implementations, the repair material may be a first repair material. A second repair material may have a second interface with the substrate and a third interface with the first repair material. Second and third bond strengths between the second repair material and the substrate and first repair material, respectively, may be in excess of 50 ksi and may be between 100 ksi and 200 ksi. The substrate and repair material may comprise Ti-alloys or nickel- or cobalt-based superalloys of like nominal composition (of essentially the same composition so as to have essentially similar properties or further of identical compositions at a given concentration resolution (e.g., 2%, 1%, 0.5%, or 0.1%, by weight of the minor constituents or of all constituents.)). The repair material may have a depth of at least 2.0 mm. The substrate may have a local thickness in excess of the depth of the repair material. The substrate may comprise original unrepaired material or previously-repaired material. [0016] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 is a view of an airfoil of a fan of a gas turbine engine. [0018] FIG. 2 is a tip-inward view of the airfoil of FIG. 1. [0019] FIG. 3 is a partial sectional view of the airfoil of FIG. 1 upon damage. [0020] FIG. 4 is a partial sectional view of the airfoil of FIG. 1 upon wear. Continue reading... Full patent description for Turbine element repair Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Turbine element repair 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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