Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L3/00—Lift-valve, i.e. cut-off apparatus with closure members having at least a component of their opening and closing motion perpendicular to the closing faces; Parts or accessories thereof
  • F01L3/02—Selecting particular materials for valve-members or valve-seats; Valve-members or valve-seats composed of two or more materials
• • 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
• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
  • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
  • F01D5/12—Blades
  • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
  • F05D2300/00—Materials; Properties thereof
  • F05D2300/20—Oxide or non-oxide ceramics
  • F05D2300/22—Non-oxide ceramics
  • F05D2300/228—Nitrides
  • F05D2300/2284—Nitrides of titanium

Definitions

• the invention relates to components based on intermetallic ⁇ -TiAl alloys with a graded microstructure transition between spatially separated areas, each with a different microstructure, and a method for their production.
• Intermetallic ⁇ -TiAl alloys have received great attention in recent years due to their combination of unique material properties. Their advantageous mechanical and thermophysical properties with low specific weight recommend their use in the aerospace industry. The high temperature and corrosion resistance makes the material interesting for fast moving components in machines, e.g. for valves in internal combustion engines or for blades in gas turbines.
• the technical alloys currently used, based on ⁇ -TiAl have a multi-phase structure and, in addition to the ordered tetragonal ⁇ -TiAl, contain the ordered hexagonal ⁇ 2 -Ti 3 Al as the main phase, typically with 5-15% by volume.
• Refractory metals as alloying elements can lead to the formation of a metastable, cubic, body-centered phase, which occurs either as the ⁇ phase (unordered) or as the B2 phase (ordered). These alloy additives improve oxidation resistance and creep resistance. Si, B and C are used in small quantities to fine-tune the cast structure.
• TiAl alloys are usually produced by multiple melting in a vacuum arc furnace as ingots (VAR - Vacuum Are Remelting). Alternatively, the production of alloys based on ⁇ -TiAl by means of permanent mold casting from a cold-wall induction or plasma furnace or by means of
• the range of structural mechanical properties of a ⁇ -TiAl alloy is known to be significantly expanded over that of cast structures by means of massive forming at temperatures in the range between 900 ° C and 1400 ° C. Massive forming creates a dynamically recrystallized fine-grained structure.
• the 4 basic structure types near- ⁇ structure (globular ⁇ grains with ⁇ 2 phase at grain boundaries and triple points), duplex Structure (globular ⁇ grains and lamellar ⁇ 2 / ⁇ at approximately equal proportions), nearly lamellar structures (grains made from oi 2 / ⁇ lamella and isolated globular ⁇ grains) and fully lamellar structures (grains made from c 2 / ⁇ - Slats) (see Fig. 2).
• Fine-grained near- ⁇ and duplex structures have good room temperature ductility, high elongation at break and high tensile strength and thus high fatigue strength, but at the same time low creep resistance and low fracture toughness.
• structures with comparatively coarser grains and with a pronounced lamellar structure show a significantly better creep resistance and a higher fracture toughness, but on the other hand also a lower fatigue strength and elongation at break.
• ⁇ -base TiAl alloys solidified from the melt are generally used.
• the aftertreatments consist either in special heat treatment cycles (see D. Zhang, P. Kobold, V. Güther and H. Clemens: Influence of Heat Treatments on Colony Size and Lamellar Spacing in a Ti-46A1- 2Cr-2Mo- 0.25Si-0.3B Alloy, Zeitschrift für Metallischen, 91 (2000) 3, see page 205) or in various forming steps.
• DE-C-43 18 424 C2 describes a process for the production of moldings from ⁇ -TiAl alloys, for example also in the form of valves and valve disks for engines.
• a cast blank is first deformed in the temperature range from 1050 ° C to 1300 ° C under quasi-isothermal conditions with a high degree of deformation, the part is then cooled and finally at
• Components are often required, and this includes, for example, valves for internal combustion engines and rotor blades for gas turbines, for which different, in some cases very different, material properties are required in individual component areas, in particular also with regard to their thermomechanical properties. So far, this has generally been met by assembling a component from areas of different materials, eg by means of non-positive and / or material joining. Valves for internal combustion engines are today made, for example, from different types of steel for the 1 stem and for the plate area, the parts being connected to one another by friction welding.
• poppet valves for internal combustion engines made of ⁇ -based TiAl alloys consist of a one-piece, e.g. a melted blank or manufactured by hot isostatic pressing of alloy powders.
• the raw part is uniformly brought to thermomechanical material properties by means of a first forming process which correspond to the later requirements for the plate area of the valve.
• a second forming process by means of extrusion and simultaneous shaping to the desired component mass, the semi-finished product, which has already been formed, is shaped further into the shaft in an appropriately equipped extrusion mold and in application of process parameters adapted to the material requirements.
• the thermomechanical material properties required for a valve stem are formed in this section.
• the extrusion process for the part is "broken off" in a press mold with a conical transition between the inlet and outlet areas at the point in time that a finished valve with twice formed, slim
• Shank area with a once formed, thick plate area and with a conical transition zone is created.
• the structure, in particular grain shape and size, between the plate and shaft area change in a graded manner, which is determined by the forming parameters of the two forming steps.
• This method also comprises several forming steps and is therefore complex and expensive.
• the object of the present invention is for components made of alloys based on ⁇ -TiAl, which in the final state have local areas with different thermomechanical requirement profiles and should have a transition zone with regard to the material properties, one versus the other State of the art to create a more economical manufacturing process and a comparatively inexpensive component produced by this process.
• the aim here is to utilize the entire possible range of structure-determined property profiles by setting different basic structures in one component.
• structures that are as well adapted to the requirements as possible are to be generated and thermomechanical properties are to be generated that are qualitatively superior or at least not inferior to those of components obtained by known processes with multi-stage forming, the components being inferior but should be cheaper to manufacture.
• a one-piece component made of an intermetallic alloy based on ⁇ -TiAl with a graded microstructure transition between spatially adjacent areas of different microstructures, which has at least in one area a lamellar structure consisting of c 2 / ⁇ -lamellas and has a near- ⁇ structure, duplex structure or fine lamellar structure in at least one further area, a transition zone with a graded structure being present between these areas, in which the lamellar cast structure gradually merges into the other structure mentioned.
• the lamellar casting structure consisting of cü 2 / ⁇ -lamellae was preferably produced by directional solidification of a molten alloy.
• the near- ⁇ structure, duplex structure or fine-lamellar structure has preferably been produced in the at least one further area by solid forming and, if appropriate, by post-treatment from the cast structure.
• the object is further achieved by a method for producing components of this type, a suitable TiAl melt being produced in a customary manner in a first step, and the TiAl melt in a second step using solidification is converted into a semi-finished product which has a lamellar cast structure consisting of ⁇ 2 / ⁇ -TiAl lamellae, and - in a third step in a partial area or in partial areas of the semi-finished product, the lamellar, made of cü 2 / ⁇ - Existing cast aluminum TiAl lamellas are transformed into a near- ⁇ -structure, duplex structure or fine-lamellar structure by massive forming in a temperature range from 900 ° C to 1400 ° C.
• a pore-free, cylindrical semifinished product is produced from the TiAl melt by means of continuous casting, which is then massively deformed by extruding a rod area.
• the TiAl melt becomes a cylindrical one by means of centrifugal casting
• areas of high tensile strength, ductility and fatigue strength with areas of high fracture toughness and high creep resistance can be realized in one and the same component.
• Components produced according to the invention consist in the fact that the selection of the manufacturing steps in comparison to the prior art enables considerable savings in manufacturing costs to be achieved.
• the economic advantage results from the technical knowledge that multiple reshaping of the semi-finished product with a cast structure can be dispensed with in such components.
• phase diagram TiAl shows an excerpt from the phase diagram TiAl, the oblique line between a and ⁇ + ⁇ being the ⁇ -transus, which strongly depends on the Al content. and a heat treatment of a material dynamically recrystallized by forming leads to a fully lamellar structure above the transus, and to a nearly lamellar, duplex or globular near- ⁇ structure depending on the temperature,
• Fig. 3 shows the scheme of melting homogeneous semi-finished TiAl according to A. L. Dowson et al. , Microstructure and Chemical Homogeneity of Plasma - Are Cold-Hearth
• FIG. 4 shows a metallographic micrograph of the plate area of a valve produced according to the invention, the picture in the plate showing the coarse-grained lamellar cast structure made of o! 2 / ⁇ -lamella shows and it can be seen that this structure in the conical part of the
• Fig. 5 is a light micrograph of the lamellar
• Fig. 6 is a light micrograph of the globular deformed structure in the shaft area in higher
• the special casting method according to the invention described in more detail below allows even unforeseen advantageous material properties with a comparatively large and thus individually tailored to the respective material requirements variation range of property combinations.
• it can be made from a semi-finished product to achieve a dynamically recrystallized structure with thermomechanical properties that deviate greatly from the properties of the cast semifinished product.
• the properties of the dynamically crystallized structure can also be varied by adapting the process parameters.
• intermetallic ⁇ -TiAl alloy encompasses a wide range of individual alloys.
• An essential alloy range is due to the molecular formula
• This group of materials also includes orthorhombic titanium aluminide base alloys, for example with a typical alloy composition T1-25A1-20 Nb (atomic%). Their comparatively higher specific weight makes this group less interesting for those applications in which components are exposed to fast and oscillating movements, as is the case with valves in internal combustion engines, for example.
• the structures which can be set according to the invention from the phases and basic structures described at the outset result as a result of the method steps according to the invention, according to which corresponding components are produced.
• a property profile can be set to a large extent, as is required for the finished component in the component area not further formed, e.g. the profile of the plate part in a valve for internal combustion engines.
• the semifinished product in the form of the cast blank is then subjected to massive shaping in the temperature range between 900 ° C. and 1400 ° C. by extrusion or by means of an equivalent shaping process and is brought into a shape which is matched to the dimensions of the end product.
• the rods are extruded only over part of their total length in an extrusion die of profile dimensions that at least approximately correspond to the final dimensions of the component in the formed area, for example dimensions of a valve for internal combustion engines with a conical transition between the stem and plate area, ie the extrusion mold has a tapered cross-section between the inlet area and the outlet area.
• the semifinished product is increasingly deformed in the conically tapering die area and thus continuously transferred from the structural state of the cast structure to the recrystallized structural state achieved by extrusion.
• the experience already available makes it possible for the person skilled in the art to change certain thermomechanical properties of the material in a targeted manner using appropriate forming parameters within material-related limits and to optimize them to meet special requirements.
• Preferred components according to the invention are valves for internal combustion engines. This applies in particular to emerging future applications. While one so far
• Valves are stressed in the stem area at rather moderate temperatures by strong alternating loads (fatigue).
• the demands on the material in terms of strength and ductility are correspondingly high.
• these components of intermetallic ⁇ -TiAl alloys according to the invention achieve these locally different thermomechanical properties in an outstanding manner.
• Additional, particularly suitable components are blades of gas turbines, which require different thermomechanical properties at the base of the blade than in the peripheral area of the blade.
• the invention is described in detail using the following example for valves for internal combustion engines.
• a TiAl starting alloy with the composition Ti-46Al-8.5Nb- (1-3) (Ta, Si, B, C, Y) (data in atomic%) is melt-metallurgically converted into a rod material with a diameter of 40 mm manufactured, which corresponds approximately to the diameter of a valve plate.
• the alloy is produced by mixing titanium sponge, Al granules and a multi-component master alloy AINbTaSiBYC, in which the atomic ratios between the alloy elements Nb, Ta, Si, B, C and Y correspond to those in the final TiAl alloy.
• a stable rod is pressed from the material mixture, which is used as a melting electrode in a vacuum arc furnace and remelted into a primary ingot.
• the primary ingot has an inhomogeneous alloy composition and is therefore melted and homogenized again in a plasma furnace (cold hearth) in a skull made of the same material, which is in a water-cooled copper crucible.
• the melt flows through a channel heated by a plasma torch into a strand extraction device, at the upper end of which a third homogenization takes place in the molten phase by means of a cold wall induction crucible.
• the molten TiAl alloy is pulled down as a block or rod, whereby the material solidifies in a non-porous manner.
• the process is shown schematically in Fig. 3 and is by A.L. Dowson et al.
• the coil is dimensioned such that the energy is sufficient for the complete melting of the alloy located in the coil.
• the semi-finished product obtained in this way has a lamellar cast structure with colony sizes of the lamella packs between 100 ⁇ m and 500 ⁇ m, but at the same time has excellent material homogeneity.
• the individual rods thus obtained as semi-finished products are divided into cylindrical segments, brought to a temperature of 1200 ° C. under protective gas and pressed in protective gas by extrusion into a heated die with a valve shape. The forming ratio in the shaft area is approx.
• the present invention is not limited to the example set out above, rather the invention also encompasses components for other, not mentioned applications in which a corresponding structure is required or advantageous for the application.
• the material ⁇ -base TiAl alloy is not limited to the alloy compositions explicitly mentioned.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• General Engineering & Computer Science (AREA)
• Crystallography & Structural Chemistry (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Cutting Tools, Boring Holders, And Turrets (AREA)
• Analysing Materials By The Use Of Radiation (AREA)
• Ceramic Products (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Laminated Bodies (AREA)

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• 2000
  • 2000-05-17 DE DE10024343A patent/DE10024343A1/de not_active Withdrawn
• 2001
  • 2001-05-17 EP EP01936369A patent/EP1287173B1/fr not_active Expired - Lifetime
  • 2001-05-17 AU AU2001262295A patent/AU2001262295A1/en not_active Abandoned
  • 2001-05-17 DE DE50113507T patent/DE50113507D1/de not_active Expired - Lifetime
  • 2001-05-17 ES ES01936369T patent/ES2298238T3/es not_active Expired - Lifetime
  • 2001-05-17 AT AT01936369T patent/ATE384146T1/de active
  • 2001-05-17 JP JP2001584596A patent/JP2003533594A/ja active Pending
  • 2001-05-17 US US10/276,404 patent/US20040045644A1/en not_active Abandoned
  • 2001-05-17 WO PCT/EP2001/005621 patent/WO2001088214A1/fr active IP Right Grant

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