Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/18—High-melting or refractory metals or alloys based thereon
  • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
  • B22F5/04—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of turbine blades
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/045—Alloys based on refractory metals
  • C22C1/0458—Alloys based on titanium, zirconium or hafnium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C14/00—Alloys based on titanium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

• the present invention relates to a TiAl alloy and a method for manufacturing and turbine components using this alloy.
• Titan aluminide alloys are used in turbine components, in particular for turbines in aircraft engine construction.
• titanium aluminide alloys can be used, for example, as running and / or guide vanes in low-pressure turbines or high-pressure compressors of aircraft engines.
• titanium aluminide alloys for rotor blades and / or vanes as well as blade-disc assemblies (BLISK: artificial word for combination of blade and disc (blade, disc)) or other turbine components is due to insufficient heat resistance properties, in particular insufficient creep strength on a Operating temperature range of less than 750 ° C to 780 ° C limited.
• TiAl based alloy, TNM alloy, as well as a method of making the same and a rotor blade thereof are disclosed in US Pat EP 1 127 949 B1 described. These are TiAl alloys in which a plurality of chemical elements are additionally alloyed, resulting in a laminar microstructure of ordered ⁇ 2 phase and ordered ⁇ phase embedded in ordered ⁇ o phase.
• titanium aluminide alloys are used in the DE 10 2007 06 587 A1 described in which alloyed to the base of titanium and aluminum, niobium in a proportion of 5 to 10 atom% wherein carbon may additionally be present in an amount of 0.1 to 1 atomic%.
• the DE 10 2004 056 582 A1 also describes alloys based on titanium aluminides in which niobium is added in an amount of 5 to 10 atom%.
• the alloys may comprise levels of molybdenum in the range of 0.1 to 3 at% and of carbon in the range of 0.05 to 0.8 at%.
• a sufficient ductility especially for the sensitive use in aircraft turbines should be present.
• such an alloy should be easy to prepare and especially suitable for corresponding microstructural settings.
• methods are to be specified, how a corresponding alloy can be produced.
• the invention is based on the knowledge that an alloy based on TiAl with corresponding constituents of niobium and molybdenum offers the possibility of allocating a higher proportion of carbon, since the solubility of the carbon is particularly high in the gamma phase. Phase is significantly increased by alloying with niobium and molybdenum. However, the carbon dissolved in the mixed crystals causes a rise in hardness and an increase in creep resistance. Hafnium and zirconium form more stable carbides than titanium and molybdenum due to the higher negative enthalpy of formation. In combination with the dissolved carbon in the gamma phase, the stable special carbides allow higher operating temperatures of above 750 and up to 850 ° C than with the conventional TNM alloy.
• the composition can be chosen so that carbide formations are minimized in a controlled manner.
• the mixed crystal effect of the carbon can be enhanced by the presence of silicon.
• silicon can form the finest silicides.
• Both mixed crystal effect, special carbide formation and silicide formation have a positive effect on creep resistance.
• microalloys with yttrium, lanthanum and other rare earth elements (SE), gadolinium can be exploited to avoid uncontrolled grain growth during high temperature heat treatments which result in the setting of a creep resistant structure. This effect is attributed to the low solubility of yttrium, lanthanum and other SE, such as gadolinium in the matrix. For this reason, there is an accumulation at the grain boundaries, which has a limiting effect on the grain boundary movement at high temperatures. Elements such as yttrium also have a positive effect on the oxidation behavior at the operating temperature.
• the composition of the titanium aluminide alloy according to the invention can be adjusted so that the solidification takes place exclusively on the disordered ⁇ -phase and a peritectic solidification is excluded.
• the main constituents such as niobium, molybdenum, carbon and aluminum as well as titanium must be alloyed in appropriate matched amounts. While the components niobium and molybdenum stabilize the ⁇ -phase, the added carbon stabilizes the ⁇ -phase, so that a correspondingly balanced ratio must be set.
• the alloying element niobium may be replaced by other ⁇ -stabilizing elements such as manganese, iron, vanadium, chromium, or combinations of these elements.
• those ⁇ -stabilizing elements should be used which reduce the stacking fault energy of the ⁇ -phase and thereby reinforce the mechanical twinning especially below the brittle-ductile transition temperature.
• the effect of silicon, yttrium and other SE elements on ductility and creep resistance must be considered.
• composition of the titanium aluminide alloy according to the invention can be adjusted so that an elastic + plastic elongation at break of the alloy, especially in the unoxidized state at a temperature of 300 ° C in the range of greater than or equal to 1.0%, preferably greater than or equal to 1.3% ,
• the selected composition according to the invention of the TiAl alloy also makes it possible to adjust a fine-grained microstructure which can contribute to achieving the above-mentioned elastic + plastic elongation at break and which compensates for the ductility-reducing effect due to solid-solution hardening, special carbide and silicide formation, but nevertheless an acceptable creep resistance at temperatures above 750 ° C and up to 850 ° C.
• composition of the alloy may be selected to minimize or suppress the formation of the ⁇ -phase in the alloy at a temperature higher than 700 ° C.
• the alloy may contain as further constituents silicon, yttrium, lanthanum and other rare earth elements, such as e.g. Gadolinium, include. Silicon contributes to substitutional solid solution and precipitation hardening, while yttrium, lanthanum and other rare earth elements can be used to produce particularly homogeneous microstructures that still retain the desired elastic + plastic elongation at break by limiting grain growth during thermomechanical manufacturing processes at 300 ° C exhibit.
• the alloy may comprise, as further constituent, boron, which preferably forms borides but is also dissolved in small amounts in the mixed crystals of the alloy and thus contributes to solid solution hardening and thus an increase in strength.
• the composition of the TiAl alloy can be adjusted so that an almost complete lamellar structure is formed by a corresponding heat treatment, which has a homogeneous size distribution of the lamellar grains and suppresses the formation of globular ⁇ o and ⁇ grains.
• a structure is also known as so-called DFL (Designed fully lamellar) structure.
• globular gamma grains may be incorporated in a lamellar matrix to set acceptable ductility below the brittle-ductile transition temperature.
• the grain size may be in the lamellar structure or DFL structure in the range of an average size of the diameter of the fine-lamellar colonies of less than or equal to 200 .mu.m, preferably less than or equal to 50 microns
• Another advantage of the alloy according to the invention is that the selected alloying elements counteract the formation of ⁇ -phases, which form at higher temperatures and can have an embrittling effect. Some of the selected alloying elements reduce the ⁇ -phase stacking fault energy, thus facilitating mechanical twinning, which is positive for ductility at room temperature and 300 ° C.
• the alloys according to the invention may comprise compositions in which the aluminum content is in the range from 43 to 48 atom% aluminum, in particular 43 to 45 atom% aluminum, the molybdenum content in the range from 0.5 to 3.0 atom% molybdenum, in particular from 1.0 to 2.5 atomic% molybdenum, the niobium content in the range of 0 to 4.9 atomic% of niobium, especially 4.0 to 4.5 atomic% of niobium, ie elements of manganese, iron, vandium, chromium in each case in the range from 0 to 5 atomic% and the carbon content in the range from 0.1 to 1.0 atomic%, in particular from 0.25 to 0.9 atomic% carbon, the remainder being selected by titanium and unavoidable impurities is formed.
• a proportion of from 0.05 to 0.2 atom% boron, in particular from 0.1 to 0.15 atom% boron may be provided.
• alloys according to the invention may have further compositions of 0 to 1 atomic% silicon, in particular 0.2 to 0.5 atomic% silicon, as well as a total amount of yttrium, lanthanum and other SE elements such as gadolinium, their total in the range of 0-1 at%.
• the melting temperature of the selected SE elements should be above the operating temperature of the TiAl component.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Powder Metallurgy (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

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Cited By (7)

Citations (4)

• 2012
  • 2012-01-25 EP EP12152427.6A patent/EP2620517A1/fr not_active Withdrawn

Patent Citations (4)

Non-Patent Citations (1)

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