EP0349734A1 - Intermetallische Titan-Aluminium-Verbindung und Verfahren zu ihrer Herstellung - Google Patents

Intermetallische Titan-Aluminium-Verbindung und Verfahren zu ihrer Herstellung Download PDF

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Publication number
EP0349734A1
EP0349734A1 EP89108489A EP89108489A EP0349734A1 EP 0349734 A1 EP0349734 A1 EP 0349734A1 EP 89108489 A EP89108489 A EP 89108489A EP 89108489 A EP89108489 A EP 89108489A EP 0349734 A1 EP0349734 A1 EP 0349734A1
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European Patent Office
Prior art keywords
atomic
intermetallic compound
group
temperature
elements
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EP89108489A
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English (en)
French (fr)
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EP0349734B1 (de
Inventor
Toshihiro C/O Nippon Steel Corporation Hanamura
Ryuji C/O Nippon Steel Corporation Uemori
Mitsuru C/O Nippon Steel Corporation Tanino
Jin-Ichi C/O Nippon Steel Corporation Takamura
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Nippon Steel Corp
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Nippon Steel Corp
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Priority claimed from JP63317687A external-priority patent/JP2711558B2/ja
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    • 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

Definitions

  • the present invention relates to a Ti-Al intermetallic compound having an improved room-tempera­ture ductility and high-temperature oxidation resis­tance, and is suitable for use as a high-temperature heat-resistant strength material for aircraft turbine engines, gas turbines for power generators, automobile engines, rotation bodies and the like, and further, to a process for the preparation of this intermetallic compound.
  • the Ti-Al intermetallic compound has almost the highest high-temperature specific strength among metallic materials, and furthermore, has an excellent corrosion resistance and a light weight. It was reported in Metallurgical Transaction, Vol. 6A (1975), page 1991, that a high-temperature strength of 40 kg/mm2 was obtained at 800°C, and therefore, it is considered that the Ti-Al intermetallic compound is most suitable for application to parts of gas turbines, valves and pistons of automobile engines, high-temperature dies, bearing parts and the like, due to the foregoing excel­lent characteristics.
  • the Ti-Al intermetallic compound has a compo­sition latitude in the phase diagram, and in the compo­sition range of 40 to 52 atomic % of Ti and 60 to 48 atomic % of Al, an Llo structure (basically a face-­centered tetragonal structure but wherein the Ti layers and Al layers are arranged alternately in the [001] direction) is formed in the thermally equilibriated state. Accordingly, an abnormal strengthening pheno­menon wherein the strength is increased in the single crystal state with an increase of the temperature was found, and it is known that, even in the case of polycrystal materials, the strength is not reduced at a high temperature of up to 800°C.
  • the polycrystals of the Ti-Al intermetallic compound are defective in that the ductility is low at temperatures ranging from room temperature to about 700°C.
  • the compressibility is 0.4% at room temperature and about 1.1% at 700°C (see JP-B-59-581).
  • the Ti-Al intermetallic compound has a light weight, a high heat-resistance, and an excellent corrosion resistance, it is suitable for a turbine blade to be used at high temperatures.
  • the room-temperature ductility of the Ti-Al intermetallic compound is low (the compressibility is 0.4%), a casting or forging thereof is difficult and the safety reliability at room temperature is poor, and thus a practical utilization thereof is uncertain.
  • a room-­temperature ductility is necessary.
  • a primary object of the present inven­tion is to provide a Ti-Al intermetallic compound material having a room-temperature compressibility of at least 25% and an improved high-temperature oxidation resistance.
  • a Ti-Al intermetallic compound comprising 40 to 52 atomic % of Ti and 48 to 60 atomic % of Al, and further, containing 10 to 3000 atomic ppm of at least one of the elements P, As and Sb (elements of the group V) and Se and Te (elements of the group VI), wherein the basic crystal structure of the matrix is an ordered structure of the Llo type, the room-temperature compressibility (ductility) is high, and a good high-­temperature oxidation resistance is retained.
  • a process for the preparation of a Ti-Al intermetallic compound material which comprises melting and solidifying a starting material having the above-mentioned composition in an inert gas atmosphere and, if necessary, annealing the solidified product.
  • the present inventors carried out investigations into improving the ductility in the Ti-Al intermetallic compound, and as a result, found that, in the Ti-Al intermetallic compound in which at least one of the elements P, As and Sb (elements of the group V) and Se and Te (elements of the group VI) is incorporated, the compressibility is at least 25% at room temperature and about 60% at 600°C, and the ductility at temperatures ranging from room temperature to about 700°C is greatly improved.
  • the compressibility is 0.4% and 1.1% at 700°C (see JP-A-62-215), it is considered that this remarkable performance is due to the incorporation of the above-mentioned tertiary component. Furthermore, it was found that the high-tem­perature oxidation resistance is greatly improved when compared to that of the tertiary element-free Ti-Al intermetallic compound and the Mn-added Ti-Al intermetallic compound.
  • the Ti content is adjusted to 40 to 52 atomic % to obtain a single phase of the Ti-Al intermetallic compound or a composition comprising a matrix of the Ti-Al intermetallic compound and a minor amount of a second phase of Ti3Al. If the Ti content is outside the above-mentioned range, an incorporation of another second phase occurs and good results cannot be attained. More specifically, if the Ti content is lower than 40 atomic %, Al2Ti or Al3Ti is present as the second phase and the presence of these compounds is not preferable, since they are brittle. If the Ti content exceeds 52 atomic %, the amount of Ti3Al as the second phase is increased. The high-temperature strength of Ti3Al is lower than that of TiAl, and therefore, from the viewpoint of the high-temperature strength, a large proportion of Ti3Al is not preferable.
  • the Ti content is from 40 to 50 atomic %, a single phase (Llo type ordered structure) of the Ti-Al intermetallic compound is obtained, and if the Ti content is higher than 50 atomic % and up to 52 atomic %, Ti3Al (DO19 type ordered structure) is partially included as the second phase in the above-­mentioned single phase.
  • the room-temperature ductility is improved when compared to that of the compound composed solely of the single phase, under some heating conditions.
  • the Ti content is 40 to 45 atomic %, an incorporation of Al2Ti as the second phase becomes possible under some casting or forging conditions, and the improvement of the ductility is reduced. Therefore, in the present invention, in view of the microstructure, preferably the lower limit of the Ti content is 45 atomic %.
  • an element of the group V (P, As or Sb) and/or an element of the group VI (Se or Te) is incorporated in an amount of 10 to 3000 atomic ppm.
  • the stacking fault energy is reduced and twinning easily occurs during plastic deformation, with the result that the room-tem­perature ductility is improved. This effect is enhanced with an increase of the content of the additive element, as shown in Fig. 1.
  • the element of the group V (P, As or Sb) or the element of the group VI (Se or Te) is bonded to Ti to form a compound such as TiP, TiAs, TiSb, TiSe, TiSe2 or TiTe2 in the grain boundary and the matrix, this compound acts as the initiation point of a fracture, with the result that not only the room-temperature ductility but also the workability is lowered. If the content of the additive element is lower than 10 atomic ppm, the above-mentioned object cannot be obtained.
  • TiO2 is generally formed in the outermost layer. Since TiO2 has an oxygen-depleted structure in which some of the lattice positions to be inherently occupied by O atoms are vacant in the crystal lattice, external oxygen atoms are diffused in the interior of the material through such oxygen-vacant positions and the oxidation is thus advanced inward. In TiO2 , Ti has a tetravalent positive charge and O has a divalent negative charge.
  • the concentration of the oxygen vacancy is reduced to maintain the charge balance in the interior, the paths of diffusion of external oxygen atoms through TiO2 are reduced, and the oxidation is suppressed.
  • the effect of suppressing the oxidation by the element of the group V and/or the element of the group VI is enhanced with an increase of the content of the additive element. If the content of the additive element is lower than 10 atomic ppm, the oxidation-suppressing effect is not satisfactory.
  • the content of the additive element exceeds 3000 atomic ppm, the content exceeds the dissolution limit in TiO2 and the additive element is concentrated at the interface between the TiO2 oxidation scale and the TiAl matrix to form a compound such as TiP, TiAs, TiSb, TiSe, TiSe2 or TiTe2 at the interface, with the result that a breakaway of the oxidation layer occurs there and the oxidation rate is greatly increased.
  • the content of the element of the group V (P, As or Sb) and/or the element of the group VI (Se or Te) in the Ti-Al intermetallic compound is adjusted to 10 to 3000 atomic ppm.
  • the content of the additive element is up to 1000 atomic ppm, the effect whereby oxidation is effectively suppressed at temperatures of up to 800°C can be obtained.
  • Bi has an effect of improving the oxidation resis­tance, but Bi increases the specific gravity and reduces the specific strength, and therefore, the material is disadvantageous as a high-temperature light-weight construction material. Accordingly, Bi is excluded from the element of the group V.
  • the reason why S is excluded from the element of the group VI is that the bonding between Ti and S is too strong and causes premature breakaway of the TiO2 oxidation scale. Po is excluded for the same reason as described above with respect to Bi.
  • the room-temperature ductility and the high-tem­perature oxidation resistance can be further improved.
  • a mixture formed by adding 10 to 3000 atomic ppm of at least one element selected from the group consisting of P, As, Sb, Se and Te, optionally together with Mn and Si, to 40 to 52 atomic % of Ti and 48 to 60 atomic % of Al is once placed under vacuum (under a pressure lower than 10 ⁇ 6 Torr), and then the atmosphere is replaced by Ar gas and the mixture is made molten at a temperature higher than the melting point and ranging from 1400 to 1500°C, to minimize a reaction with a crucible, and then the melt is solidified.
  • a room-tem­perature ductility can be obtained in the as-solidified state, but if the solidification product is annealed in the above-mentioned inert gas atmosphere, to obtain a uniform microstructure, the ductility is further improved.
  • the so-obtained Ti-Al intermetallic compound having the element of the group V (P, As or Sb) and/or the element of the group VI (Se or Te) incorporated therein has a compressibility of at least 25% at room tempera­ture and a compressibility of about 60% at 600°C, and the ductility is improved at temperatures ranging from room temperature to about 800°C. Since the tertiary element-free Ti-Al intermetallic compound has a com­pressibility of 0.4% at room-temperature and a com­pressibility of 1.1% at 700°C (see Japanese Unexamined Patent Publication No. 58-123847), it is obvious that the performance is greatly improved according to the present invention. Moreover, the high-temperature oxidation resistance is greatly improved compared with that of the tertiary element-free Ti-Al intermetallic compound and the Mn-added Ti-Al intermetallic compound.
  • the improvement of the room-temperature compressibility is caused by a reduc­tion of the stacking fault energy of the Ti-Al intermetallic compound by the addition of the tertiary element such as the element of the group V (P, As or Sb) or the element of the group VI (Se or Te).
  • This reduc­tion of the stacking fault energy facilitates twinning, especially crossing of twins, resulting in inproved ductility.
  • the high-temperature oxidation resistance is improved by preventing a permeation of oxygen by forming an oxide film on the surface of a material.
  • oxidation is advanced by a diffusion of oxygen through oxygen ion-vacancies in TiO 2-x formed on the surface of the sample, and accordingly, in order to improve the high-temperature oxidation resistance, the concentration of the oxygen ion-vacancies must be reduced and the rate of the inward diffusion of oxygen must be suppressed.
  • the reason why the high-temperature oxidation resistance is improved in the alloy of the present invention is considered to be because the element of the group V (P, As or Sb) or the element of the group VI (Se or Te) has a valence electron number of 5 or 6 respectively, larger than the valence electron number of Ti, i.e., 4, and therefore the tertiary element reduces the concentration of oxygen ion-vacancies in the TiO 2-x layer formed on the surface and suppresses the inward diffusion of oxygen, whereby the growth rate of the oxide layer TiO 2-x formed on the Ti-Al intermetallic compound in a high-temperature oxidizing atmosphere is reduced.
  • a mixture comprising 50 atomic % of pure sponge titanium and 50 atomic % of Al, in which 94 atomic ppm (100 weight ppm) of Se or 58 atomic ppm (100 weight ppm) of Te was incorporated, was once placed under vacuum (pressure lower than 10 ⁇ 6 Torr) in a vacuum melting furnace, the atmosphere was replaced by Ar gas, and the mixture was heated at 1500°C, made molten, and then solidified. The solidified product was then annealed at 1000°C, and a heating time of 72 hours. The results are shown in Tables 1 and 2.
  • the samples of the present invention had a greatly improved yield stress under compression deforma­tion and the room-temperature compressibility was greatly improved compared with that of the tertiary element-free Ti-Al intermetallic compound. Furthermore, the yield stress and room-temperature compressibility of the samples of the present invention were comparable to those of the Ti-Al intermetallic compound having 2% by weight of Mn added thereto.
  • the amount increased by oxidation in the Mn-added Ti-Al intermetallic compound was much larger than in the tertiary element-free Ti-Al inter­metallic compound, but in the Se- or Te-added Ti-Al intermetallic compound, the amount increased by oxida­tion was much smaller, and it was confirmed that the oxidation resistance was remarkably improved.
  • a mixture comprising 50 atomic % (63.9% by weight) of sponge Ti having a purity of 99.8% by weight and 50 atomic % (36.0% by weight) of Al having a purity of 99.99% by weight, in which 500 weight ppm of P was incorporated, was once placed under vacuum (pressure lower than 10 ⁇ 6 Torr) in a vacuum melting furnace, the atmosphere was replaced by Ar gas, and the mixture was heated at 1500°C, made molten, and then solidified. A part of the solidified product was then annealed at 1000°C for 72 hours.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)
  • Manufacture Of Alloys Or Alloy Compounds (AREA)
EP19890108489 1988-05-13 1989-05-11 Intermetallische Titan-Aluminium-Verbindung und Verfahren zu ihrer Herstellung Expired - Lifetime EP0349734B1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP11624488 1988-05-13
JP116244/88 1988-05-13
JP317687/88 1988-12-16
JP63317687A JP2711558B2 (ja) 1988-12-16 1988-12-16 ＴｉＡ▲ｌ▼金属間化合物とその製造方法

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EP0349734A1 true EP0349734A1 (de) 1990-01-10
EP0349734B1 EP0349734B1 (de) 1994-08-31

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0464366A1 (de) * 1990-07-04 1992-01-08 Asea Brown Boveri Ag Verfahren zur Herstellung eines Werkstücks aus einer dotierstoffhaltigen Legierung auf der Basis Titanaluminid
US5207982A (en) * 1990-05-04 1993-05-04 Asea Brown Boveri Ltd. High temperature alloy for machine components based on doped tial
US5908516A (en) * 1996-08-28 1999-06-01 Nguyen-Dinh; Xuan Titanium Aluminide alloys containing Boron, Chromium, Silicon and Tungsten

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3203794A (en) * 1957-04-15 1965-08-31 Crucible Steel Co America Titanium-high aluminum alloys
FR2462483A1 (fr) * 1979-07-25 1981-02-13 United Technologies Corp Alliages de titane du type tial

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3203794A (en) * 1957-04-15 1965-08-31 Crucible Steel Co America Titanium-high aluminum alloys
FR2462483A1 (fr) * 1979-07-25 1981-02-13 United Technologies Corp Alliages de titane du type tial

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5286443A (en) * 1990-04-05 1994-02-15 Asea Brown Boveri Ltd. High temperature alloy for machine components based on boron doped TiAl
US5207982A (en) * 1990-05-04 1993-05-04 Asea Brown Boveri Ltd. High temperature alloy for machine components based on doped tial
US5342577A (en) * 1990-05-04 1994-08-30 Asea Brown Boveri Ltd. High temperature alloy for machine components based on doped tial
EP0464366A1 (de) * 1990-07-04 1992-01-08 Asea Brown Boveri Ag Verfahren zur Herstellung eines Werkstücks aus einer dotierstoffhaltigen Legierung auf der Basis Titanaluminid
US5190603A (en) * 1990-07-04 1993-03-02 Asea Brown Boveri Ltd. Process for producing a workpiece from an alloy containing dopant and based on titanium aluminide
US5908516A (en) * 1996-08-28 1999-06-01 Nguyen-Dinh; Xuan Titanium Aluminide alloys containing Boron, Chromium, Silicon and Tungsten

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Publication number Publication date
DE68917815T2 (de) 1995-01-05
EP0349734B1 (de) 1994-08-31
DE68917815D1 (de) 1994-10-06

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