Patent Publication Number: US-2018029131-A1

Title: Powdered Titanium Alloy Composition and Article Formed Therefrom

Description:
FIELD 
     This application generally relates to titanium alloys and, more particularly, to titanium alloys for powder metallurgy. 
     BACKGROUND 
     Titanium alloys offer high tensile strength over a broad temperature range, yet are relatively light weight. Ti-6Al-4V is perhaps the most common and widely used titanium alloy. In wrought form, Ti-6Al-4V has a relatively low density (about 4.47 g/cm 3 ), yet exhibits exceptional mechanical properties, such as a yield strength in excess of 120 ksi (thousand pounds per square inch), an ultimate tensile strength in excess of 130 ksi, an elongation of at least 10 percent, and a fatigue limit (10 million plus cycles) in excess of 90 ksi. Furthermore, titanium alloys are resistant to corrosion. Therefore, titanium alloys, Ti-6Al-4V specifically, are used in various demanding applications, such as aircraft components, medical devices and the like. 
     Powder metallurgy manufacturing techniques, such as die pressing, metal injection molding, direct hot isostatic pressing and the like, result in the formation of net (or near net) articles. Therefore, powder metallurgy manufacturing techniques offer the opportunity for significant cost savings by significantly reducing (if not completely eliminating) the need for machining operations, which are time intensive and wasteful of materials. 
     Ti-6Al-4V powders are available, and have been formed into various articles using powder metallurgy manufacturing techniques. However, articles formed from Ti-6Al-4V powders do not have the same mechanical properties as articles formed from wrought Ti-6Al-4V. For example, the fatigue limit of articles formed from Ti-6Al-4V powders can be 20 to 30 percent less that the fatigue limit of articles formed from wrought Ti-6Al-4V (e.g., 70 ksi for powdered versus 95 ksi for wrought). In many applications, such a significant reduction in the fatigue limit may not be acceptable. 
     Accordingly, those skilled in the art continue with research and development efforts in the field of titanium alloys. 
     SUMMARY 
     In one embodiment, the disclosed titanium alloy consists essentially of about 7.0 to about 9.0 percent by weight vanadium (V), about 3.0 to about 4.5 percent by weight aluminum (Al), about 0.8 to about 1.5 percent by weight iron (Fe), about 0.14 to about 0.22 percent by weight oxygen (O), optionally about 0.8 to about 2.4 percent by weight chromium (Cr), and the balance titanium. 
     In another embodiment, the disclosed titanium alloy consists essentially of about 7.0 to about 8.5 percent by weight vanadium (V), about 3.5 to about 4.5 percent by weight aluminum (Al), about 0.9 to about 1.5 percent by weight iron (Fe), about 0.15 to about 0.22 percent by weight oxygen (O), and the balance titanium. 
     In another embodiment, the disclosed titanium alloy consists essentially of about 7.5 to about 9.0 percent by weight vanadium (V), about 3.0 to about 4.0 percent by weight aluminum (Al), about 0.8 to about 1.3 percent by weight iron (Fe), about 0.14 to about 0.20 percent by weight oxygen (O), about 0.8 to about 2.4 percent by weight chromium (Cr), and the balance titanium. 
     In one embodiment, the disclosed powdered titanium alloy composition consists essentially of about 7.0 to about 9.0 percent by weight vanadium (V), about 3.0 to about 4.5 percent by weight aluminum (Al), about 0.8 to about 1.5 percent by weight iron (Fe), about 0.14 to about 0.22 percent by weight oxygen (O), optionally about 0.8 to about 2.4 percent by weight chromium (Cr), and the balance titanium. 
     In another embodiment, the disclosed powdered titanium alloy composition consists essentially of about 7.0 to about 8.5 percent by weight vanadium (V), about 3.5 to about 4.5 percent by weight aluminum (Al), about 0.9 to about 1.5 percent by weight iron (Fe), about 0.15 to about 0.22 percent by weight oxygen (O), and the balance titanium. 
     In another embodiment, the disclosed powdered titanium alloy composition consists essentially of about 7.5 to about 9.0 percent by weight vanadium (V), about 3.0 to about 4.0 percent by weight aluminum (Al), about 0.8 to about 1.3 percent by weight iron (Fe), about 0.14 to about 0.20 percent by weight oxygen (O), about 0.8 to about 2.4 percent by weight chromium (Cr), and the balance titanium. 
     Other embodiments of the disclosed titanium alloy composition will become apparent from the following detailed description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram depicting one embodiment of the disclosed method for manufacturing an article; 
         FIG. 2  is a flow diagram of an aircraft manufacturing and service methodology; and 
         FIG. 3  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed is an alpha-beta titanium alloy that may be used in wrought or powdered form. Significantly, articles formed from the disclosed titanium alloy using powder metallurgy manufacturing techniques may have mechanical properties, such as fatigue limit, that are at least as good as (if not better than) the mechanical properties of articles formed from wrought Ti-6Al-4V. Therefore, the disclosed titanium alloy is an alternative to Ti-6Al-4V that is particularly suitable for use in powder metallurgy. 
     In a first embodiment, disclosed is an alpha-beta titanium alloy having the composition shown in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Element 
                 Range (wt %) 
               
               
                   
                   
               
             
            
               
                   
                 Vanadium 
                 7.0-9.0 
               
               
                   
                 Aluminum 
                 3.0-4.5 
               
               
                   
                 Iron 
                 0.8-1.5 
               
               
                   
                 Oxygen 
                 0.14-0.22 
               
               
                   
                 Chromium 
                 0 or 0.8-2.4 
               
               
                   
                 Titanium 
                 Balance 
               
               
                   
                   
               
            
           
         
       
     
     Chromium (Cr) is an optional component of the alpha-beta titanium alloy of the first embodiment. When present, the concentration of chromium may range from about 0.8 percent by weight to about 2.4 percent by weight, such as from about 1.8 percent by weight to about 2.4 percent by weight. 
     Thus, the alpha-beta titanium alloy of the first embodiment consists essentially of titanium (Ti), vanadium (V), aluminum (Al), iron (Fe), oxygen (O) and, optionally, chromium (Cr). 
     Those skilled in the art will appreciate that various impurities, which do not substantially affect the physical properties of the alpha-beta titanium alloy of the first embodiment, may also be present, and the presence of such impurities will not result in a departure from the scope of the present disclosure. For example, the impurities content of the alpha-beta titanium alloy of the first embodiment may be controlled as shown in Table 2. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Impurity 
                 Maximum (wt %) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Carbon 
                 0.10 
               
               
                   
                 Nitrogen 
                 0.05 
               
               
                   
                 Chlorine 
                 0.05 
               
               
                   
                 Hydrogen 
                 0.015 
               
               
                   
                 Silicon 
                 0.05 
               
               
                   
                 Yttrium 
                 0.005 
               
               
                   
                 Sodium 
                 0.01 
               
               
                   
                 Magnesium 
                 0.10 
               
               
                   
                 Other Elements, Each 
                 0.10 
               
               
                   
                 Other Elements, Total 
                 0.30 
               
               
                   
                   
               
            
           
         
       
     
     In a second embodiment, disclosed is an alpha-beta titanium alloy having the composition shown in Table 3. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Element 
                 Range (wt %) 
               
               
                   
                   
               
             
            
               
                   
                 Vanadium 
                 7.0-8.5 
               
               
                   
                 Aluminum 
                 3.5-4.5 
               
               
                   
                 Iron 
                 0.9-1.5 
               
               
                   
                 Oxygen 
                 0.15-0.22 
               
               
                   
                 Titanium 
                 Balance 
               
               
                   
                   
               
            
           
         
       
     
     Thus, the alpha-beta titanium alloy of the second embodiment consists essentially of titanium (Ti), vanadium (V), aluminum (Al), iron (Fe) and oxygen (O). The impurities content of the alpha-beta titanium alloy of the second embodiment may be controlled as shown in Table 2. 
     One specific, non-limiting example of a titanium alloy of the second embodiment has the composition shown in Table 4. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Element 
                 Target (wt %) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Vanadium 
                 7.5 
               
               
                   
                 Aluminum 
                 4.0 
               
               
                   
                 Iron 
                 1.2 
               
               
                   
                 Oxygen 
                 0.20 
               
               
                   
                 Titanium 
                 Balance 
               
               
                   
                   
               
            
           
         
       
     
     In a third embodiment, disclosed is an alpha-beta titanium alloy having the composition shown in Table 5. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Element 
                 Range (wt %) 
               
               
                   
                   
               
             
            
               
                   
                 Vanadium 
                 7.5-9.0 
               
               
                   
                 Aluminum 
                 3.0-4.0 
               
               
                   
                 Chromium 
                 0.8-2.4 
               
               
                   
                 Iron 
                 0.8-1.3 
               
               
                   
                 Oxygen 
                 0.14-0.20 
               
               
                   
                 Titanium 
                 Balance 
               
               
                   
                   
               
            
           
         
       
     
     Thus, the alpha-beta titanium alloy of the third embodiment consists essentially of titanium (Ti), vanadium (V), aluminum (Al), chromium (Cr), iron (Fe) and oxygen (O). The impurities content of the alpha-beta titanium alloy of the third embodiment may be controlled as shown in Table 2. 
     One specific, non-limiting example of a titanium alloy of the third embodiment has the composition shown in Table 6. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Element 
                 Target (wt %) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Vanadium 
                 8.0 
               
               
                   
                 Aluminum 
                 3.5 
               
               
                   
                 Chromium 
                 2.0 
               
               
                   
                 Iron 
                 1.0 
               
               
                   
                 Oxygen 
                 0.18 
               
               
                   
                 Titanium 
                 Balance 
               
               
                   
                   
               
            
           
         
       
     
     In one variation of the third embodiment, the disclosed alpha-beta titanium alloy may have the composition shown in Table 7. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Element 
                 Range (wt %) 
               
               
                   
                   
               
             
            
               
                   
                 Vanadium 
                 7.5-9.0 
               
               
                   
                 Aluminum 
                 3.0-4.0 
               
               
                   
                 Chromium 
                 1.8-2.4 
               
               
                   
                 Iron 
                 0.8-1.3 
               
               
                   
                 Oxygen 
                 0.14-0.20 
               
               
                   
                 Titanium 
                 Balance 
               
               
                   
                   
               
            
           
         
       
     
     The disclosed titanium alloy may be used to manufacture various articles, such as aircraft parts and components, using traditional casting or forging processes, or hybrid processes such as powder metallurgy combined with forging, or rolling, or extrusion, or welding (solid state (linear or rotational friction or inertia) or traditional melting fusion or with filler). Additionally the disclosed titanium alloys may be used for various net shape and near net shape fabrication processes such as additive manufacturing laser, electron beam, plasma arc melting techniques and powder metallurgy additive laser or electron beam sintering techniques. The disclosed titanium alloy may also be used in powdered form to manufacture various articles using powder metallurgy manufacturing techniques. As noted herein, the powdered form of the disclosed titanium alloy (the disclosed powdered titanium alloy composition) is significantly attractive, particularly vis-a-vis Ti-6Al-4V in powdered form, due to an anticipated improvement in the mechanical properties, particularly fatigue limit, of the resulting articles. 
     Various powdered forms of the disclosed titanium alloy may be used without departing from the scope of the present disclosure. Regarding shape, the powder particles of the disclosed powdered titanium alloy composition may be spherical, flakey, spongy, cylindrical, blocky, acicular or the like. Powder particle shape may be substantially uniform throughout the powdered titanium alloy composition (e.g., all spherical particles) or multiple different shapes may be included in a particular powdered titanium alloy composition. Regarding size, the powder particles of the disclosed powdered titanium alloy composition may have a broad particle size distribution (e.g., a mixture of relatively large and relative small particles) or a narrow particle size distribution (e.g., substantially uniform particle size). 
     In one expression, the disclosed powdered titanium alloy composition may be prepared as a physical mixture of at least two distinct powder compositions. As one specific, non-limiting example, the disclosed powdered titanium alloy composition may be prepared by mixing a first powder composition (a substantially pure titanium powder) with a second powder composition (a master alloy powder) in sufficient proportions to achieve the compositional limits recited in Table 1. 
     In another expression, the disclosed powdered titanium alloy composition includes a single powder component, and each powder particle of the single powder component has substantially the same composition. Specifically, each powder particle of the single powder component has a composition within the compositional limits recited in Table 1. Such a powdered titanium alloy composition may be prepared, for example, by atomization, wherein a molten mass having a composition within the compositional limits recited in Table 1 is forced through an orifice. 
     Also disclosed is a method for manufacturing articles using the disclosed powdered titanium alloy composition. Referring to  FIG. 1 , one embodiment of the disclosed method for manufacturing an article, generally designated  10 , may begin at Block  12  with the step of preparing a powdered titanium alloy composition. The powdered titanium alloy composition prepared at Block  12  may have a composition falling within the compositional limits recited in Table 1. 
     At Block  14 , the powdered titanium alloy composition may be compacted to form a shaped mass. Various compaction techniques may be used without departing from the scope of the present disclosure. As one example, the compaction step (Block  14 ) may include die pressing. As another example, the compaction step (Block  14 ) may include cold isostatic pressing. As another example, the compaction step (Block  14 ) may include metal injection molding. As yet another example, the compaction step (Block  14 ) may include direct hot isostatic pressing. 
     At Block  16 , the shaped mass may optionally be sintered. Sintering may be required when the compaction step (Block  14 ) does not simultaneously sinter/consolidate. For example, the sintering step (Block  16 ) may include heating the shaped mass to an elevated temperature (e.g., about 2,000° F. to about 2,500° F.) and maintaining the shaped mass at the elevated temperature for at least a minimum amount of time (e.g., at least 60 minutes, such as about 90 minutes to about 150 minutes). 
     At Block  18 , the shaped mass (e.g., the sintered shaped mass) may optionally be subjected to hot isostatic pressing (“HIP”) to reduce (if not eliminate) voids in the sintered shaped mass. For example, the hot isostatic pressing step (Block  18 ) may be performed at a pressure ranging from about 13 ksi to about 16 ksi and a temperature ranging from about 1,475° F. to about 1,800° F., and the elevated pressure and temperature may be applied for at least about 60 minutes, such as for about 120 minutes to about 300 minutes. 
     At Block  20 , the shaped mass (e.g., the HIPed and sintered shaped mass) may optionally be solution treated. For example, solution treatment may include reheating the shaped mass from room temperature to a temperature ranging from about 1400° F. to about 1725° F., and maintaining at temperature for approximately 1 hour before rapidly cooling/quench using various quench media, such as, but not limited to, water, ethylene glycol, liquid polymer additives and gas atmospheres/partial pressures that could include argon, nitrogen and helium, individually or combined, along with forced atmosphere fan cooling. 
     At Block  22 , the shaped mass (e.g., the solution treated, HIPed and sintered shaped mass) may optionally be aged. For example, aging may include reheating the shaped mass from room temperature to a temperature ranging from about 900° F. to about 1400° F., and maintaining the shaped mass at temperature for about 2 to about 8 hours before cooling back to room temperature. 
     Accordingly, the disclosed method  10  may be used to efficiently manufacture articles of various shapes and sized, including articles (e.g., aircraft parts) having complex geometries. Because the articles are produced to net (or near net) shapes, little or no machining is required to finalize the article, thereby significantly reducing both material and labor costs. 
     Articles formed from the disclosed powdered titanium alloy composition may exhibit excellent mechanical properties. Indeed, it is believed that articles formed from powdered forms of the titanium alloy compositions presented in Tables 4 and 6 will exhibit an ultimate tensile strength (ASTM-E8) of at least 130 ksi, a yield strength (ASTM-E8) of at least 120 ksi and an elongation (ASTM-E8) of at least 10 percent, which is comparable to that achieved using wrought or powdered Ti-6Al-4V. Furthermore, it is believed that articles formed from powdered forms of the titanium alloy compositions presented in Tables 4 and 6 will exhibit a fatigue limit of at least 95 ksi, which is comparable to that achieved using wrought Ti-6Al-4V, but significantly better than that achieved using powdered Ti-6Al-4V. Standard fatigue test methods can include, but are not limited to, alternating and mean stress imposed on various fatigue test specimen designs, such as, but not limited to, rotational bending, cantilever flat, axial dog bone, torsion, tension, three (3) or four (4) point bending. 
     Examples of the disclosure may be described in the context of an aircraft manufacturing and service method  100 , as shown in  FIG. 2 , and an aircraft  102 , as shown in  FIG. 3 . During pre-production, the aircraft manufacturing and service method  100  may include specification and design  104  of the aircraft  102  and material procurement  106 . During production, component/subassembly manufacturing  108  and system integration  110  of the aircraft  102  takes place. Thereafter, the aircraft  102  may go through certification and delivery  112  in order to be placed in service  114 . While in service by a customer, the aircraft  102  is scheduled for routine maintenance and service  116 , which may also include modification, reconfiguration, refurbishment and the like. 
     Each of the processes of method  100  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 3 , the aircraft  102  produced by example method  100  may include an airframe  118  with a plurality of systems  120  and an interior  122 . Examples of the plurality of systems  120  may include one or more of a propulsion system  124 , an electrical system  126 , a hydraulic system  128 , and an environmental system  130 . Any number of other systems may be included. 
     The disclosed titanium alloy composition may be employed during any one or more of the stages of the aircraft manufacturing and service method  100 . As one example, components or subassemblies corresponding to component/subassembly manufacturing  108 , system integration  110 , and or maintenance and service  116  may be fabricated or manufactured using the disclosed titanium alloy composition. As another example, the airframe  118  may be constructed using the disclosed titanium alloy composition. Also, one or more apparatus examples, method examples, or a combination thereof may be utilized during component/subassembly manufacturing  108  and/or system integration  110 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  102 , such as the airframe  118  and/or the interior  122 . Similarly, one or more of system examples, method examples, or a combination thereof may be utilized while the aircraft  102  is in service, for example and without limitation, to maintenance and service  116 . 
     The disclosed titanium alloy composition is described in the context of an aircraft; however, one of ordinary skill in the art will readily recognize that the disclosed titanium alloy composition may be utilized for a variety of applications. For example, the disclosed titanium alloy composition may be implemented in various types of vehicle including, for example, helicopters, passenger ships, automobiles, marine products (boat, motors, etc.) and the like. 
     Although various embodiments of the disclosed titanium alloy composition and article formed therefrom have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.