Classifications

• • 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
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
  • B22D21/02—Casting exceedingly oxidisable non-ferrous metals, e.g. in inert atmosphere
  • B22D21/022—Casting heavy metals, with exceedingly high melting points, i.e. more than 1600 degrees C, e.g. W 3380 degrees C, Ta 3000 degrees C, Mo 2620 degrees C, Zr 1860 degrees C, Cr 1765 degrees C, V 1715 degrees C
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
  • B22D27/045—Directionally solidified castings
• • 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
  • B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
• • 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
• • 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
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/047—Making non-ferrous alloys by powder metallurgy comprising intermetallic compounds
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
  • C22C27/02—Alloys based on vanadium, niobium, or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C30/00—Alloys containing less than 50% by weight of each constituent
• • 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
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
  • B22F2009/041—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling by mechanical alloying, e.g. blending, milling

Definitions

• the following invention relates to a TiAl alloy for use at high temperatures, in particular in the range of 750 ° C to 900 ° C, and to their preparation and their use.
• Alloys based on intermetallic titanium aluminide compounds are used in the construction of stationary gas turbines or aircraft engines, for example as a material for moving blades, since they have the mechanical properties required for use and additionally have a low specific weight, so that the use of such alloys improves the efficiency from stationary gas turbines and aircraft engines.
• TiAl alloys based on the ⁇ - TiAl intermetallic phase in particular being used which are alloyed with niobium and molybdenum or boron and are therefore referred to as TNM or TNB alloys.
• Such alloys have as their main constituent titanium and also about 40 to 45 at.% Aluminum, 5 at.% Niobium and for example 1 at.% Molybdenum and also small amounts of boron.
• the microstructure is characterized by a high proportion of ⁇ - TiAl and also significant proportions of ⁇ 2 - Ti 3 Al, whereby further phases, such as ⁇ - phase or B19 - phase, may occur to a lesser extent.
• the known TNM or TNB alloys based on ⁇ -TiAl usually have an equiaxed ⁇ -TiAl microstructure, a lamellar microstructure or a duplex microstructure with equiaxed ⁇ -TiAl grains and lamellar regions of ⁇ -TiAl and ⁇ 2 . Ti 3 Al on.
• ⁇ -TiAl alloys in particular with lamellar microstructures, have overall very good mechanical properties up to 750 ° C., the mechanical properties deteriorate at higher temperatures due to the thermodynamic instability of the microstructure, with creep resistance in particular decreasing.
• Such an alloy should be manufacturable and processable on an industrial scale without undue effort and be used reliably in stationary gas turbines and aircraft engines.
• TiAl alloy is understood to mean an alloy whose main constituents are titanium and aluminum, so that the proportion of aluminum and titanium in at.% Or wt.% Is greater in each case than the corresponding proportion of any other alloy component.
• in.% Or wt.% Of the aluminum content may be greater than the titanium content and not only the titanium content greater than the aluminum content, as the term TiAl seems to indicate.
• a TiAl alloy according to the invention is understood to mean an alloy which is composed predominantly of intermetallic phases with the constituents titanium and / or aluminum.
• the present invention accordingly proposes a TiAl alloy as a high-temperature TiAl alloy in which, in addition to the main constituents titanium and aluminum, in particular one main constituent titanium, an aluminum fraction ⁇ 30 at.% Is present and the microstructure has a matrix of ⁇ phase in which precipitates of ⁇ - phase are incorporated.
• ⁇ -phase is also understood to mean various ⁇ -phase morphologies, such as ⁇ or ⁇ o .
• different morphologies fall under the ⁇ phase, such as ⁇ o -B8 2 , ⁇ - D8 8 or ⁇ "- transition phases.
• the volume fraction of the ⁇ phase and the ⁇ phase together should be at least 55% by volume, preferably at least 75% by volume and in particular at least 80% by volume.
• the creep resistance can be improved by a microstructure with a ⁇ -phase matrix with ⁇ precipitates embedded in, so that higher use temperatures are possible compared with the known ⁇ -TiAl alloys. Due to the In the ⁇ - phase matrix, the corresponding alloy can also be referred to as a ⁇ - TiAl alloy.
• the ratio of ⁇ -phase to ⁇ -phase corresponding to the volume fractions can be in the range from 1 to 4 to 4 to 1, in particular 1 to 3 to 3 to 1.
• the ⁇ -phase can be precipitated with particle sizes in the range of 5 nm to 500 nm, in particular 10 nm to 450 nm or 25 nm to 400 nm, and be present in the ⁇ -matrix.
• the ⁇ phase may also be present in particular globular form at grain boundaries of the TiAl alloy, with grain boundaries of all possible structural constituents coming into question.
• the alloy may be subjected to at least one heat treatment lasting from 1 to 100 hours at a temperature in the range of 20 ° C. to 400 ° C. below the ⁇ solvus temperature, so that a thermodynamically stable structure is established.
• the strength properties in particular can be favorably influenced.
• the precipitation of the ⁇ -phase can also be carried out in such a way that the ⁇ -phase is present in at least two different particle size ranges in the microstructure, wherein a first particle size range particle sizes in the range of 5 nm to 100 nm and a second particle size range particle sizes in the range of 200 nm to 500 nm.
• multi-stage aging annealing can be carried out.
• different deformation mechanisms in the alloy can be suppressed so as to increase the strength of the alloy.
• larger particle size ⁇ deposits may interfere with cutting by dislocations, while the smaller ⁇ precipitates may hinder overclimbing by the dislocations.
• the ⁇ -phase may be present as semicoherent in spherical or cubic form in the ⁇ -matrix, wherein the ⁇ -matrix may have a net-like microstructure, which allows a high creep resistance up to temperatures of 900 ° Celsius and more.
• one or more alloying elements may be added from the group including niobium, molybdenum, tungsten, zirconium, vanadium, yttrium, hafnium, silicon, carbon and cobalt.
• the alloy components niobium, molybdenum, tungsten, zirconium and cobalt are advantageous because they stabilize the ⁇ phase.
• the alloy constituents niobium and molybdenum can be provided in particular in a ratio of 1.8: 1 to 5: 1, preferably 2: 1 to 3: 1 relative to one another in the alloy, so that there is always a higher niobium content than a molybdenum content.
• niobium and molybdenum in the alloy, the higher the ratio of niobium to molybdenum can be selected in order to favor the precipitation of the ⁇ phase.
• a higher niobium content allows the formation of the ⁇ -phase, since niobium stabilizes the ⁇ -phase formation, while molybdenum essentially allows the formation of ⁇ -phases.
• the alloy components tungsten, zirconium, vanadium, yttrium and hafnium are used to form oxides and carbides, which can form finely divided precipitates, so that these alloying constituents can contribute to increasing the strength of the alloy in addition to solid solution hardening by forming the precipitates. Accordingly, the alloying constituents tungsten, zirconium, vanadium, yttrium and hafnium can be at least partially mutually substituted. The same applies to the alloy components tungsten, vanadium and cobalt on the one hand and zirconium, yttrium and hafnium on the other hand.
• cobalt can further increase the creep resistance because the alloying element cobalt can lower the stacking fault energy, thus causing dislocations to be split, making it difficult to climb the dislocations and thus increasing the creep resistance.
• the addition of silicon can improve the corrosion resistance of the alloy.
• a ⁇ -TiAl alloy according to the invention may contain 30 to 42 at.% Aluminum, in particular 30 to 35 at.% Aluminum, 5 to 25 at.% Niobium, in particular 15 to 25 at.% Niobium, 2 to 10 at.% Molybdenum, in particular 5 to 10 at.% molybdenum, 0.1 to 10 at.% cobalt, in particular 5 to 10 at.% cobalt, 0.1 to 0.5 at.% silicon and 0.1 to 0.5 at.% Hafnium and the rest of titanium.
• the individual alloy components are to be selected in accordance with the above-mentioned share ranges so that they add up to 100%. As a result, it is not always possible to fully exhaust every given share range. Rather, this depends on which other alloying components have already been selected with what proportion, so that the share areas influence each other.
• the proposed TiAl alloy can be produced by melt metallurgy, wherein the melt can be monocrystalline drawn or polycrystalline poured, so that the corresponding component of the ⁇ - TiAl alloy can be used as a single crystal, as directionally solidified component or as a polycrystalline component.
• alloy components can be mechanically alloyed, such as the alloying elements cobalt, tungsten, hafnium, vanadium and yttrium.
• the alloy may be subjected to single or multi-stage aging anneals performed in the temperature range of 20 ° C to 400 ° C below the ⁇ solvus temperature at which the ⁇ phase goes into solution.
• a corresponding TiAl alloy can be used in particular for components of stationary gas turbines or aircraft engines, such as, for example, for rotor blades.

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

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• 2014
  • 2014-02-06 EP EP14154052.6A patent/EP2905350A1/fr not_active Withdrawn
• 2015
  • 2015-02-03 US US14/612,504 patent/US10060012B2/en not_active Expired - Fee Related

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