AU2005100278A8 - Simultaneous production of gamma titanium aluminide (gamma-TiAl) and grossite (CaAl4O7) (KRH-process for production gamma titanium aluminide (gamma-TiAl) and grossite (CaAl4O7)) - Google Patents

Description

S&FRef: 713913

AUSTRALIA

PATENTS ACT 1990 INNOVATION PATENT SPECIFICATION Name and Address of Applicants: Alireza Kamali, of c/o Malek Ashtar University of Technology, Department of Materials and Chemistry, Shahid Babay Highway, Tehran, Iran Hekmat Razavizadeh, of c/o Iran University of Science and Technology, Department of Metallurgy and Minerals, Narmak, Tehran, Iran Seyed Mohammad Mehdi Hadavi, of c/o Malek Ahstar University of Technology, Department of Materials and Chemistry, Shahid Babay Highway, Tehran, Iran Actual Inventor(s): Alireza Kamali Hekmat Razavizadeh Seyed Mohammad Mehdi Hadavi Address for Service: Invention Title: Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Simultaneous production of gamma titanium aluminide (y-TiAl) and grossite (CaA1 4 0 7

(KRH-

process for production gamma titanium aluminide (y-TiAl) and grossite (CaA140 7 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5843c [R:\LIBF]1 5714.doc:TYB SIMULTANEOUS PRODUCTION OF GAMMA TITANIUM ALUMINIDE (y- O TiAl) AND GROSSITE (CaAl 4 0 7 (KRH- PROCESS FOR PRODUCTION SGAMMA TITANIUM ALUMINIDE (y-TiAl) AND GROSSITE (CaAl 4 0 7 0 Technical Field The present invention relates to a process for the simultaneous production of Stitanium aluminide and grossite. The present invention also relates to a titanium aluminide or a grossite prepared by the process.

00 Background of the Invention Titanium aluminides and grossite have special applications as high temperature materials.

Titanium aluminium-based alloys (Ti-Al) ("titanium aluminides") have unique properties such as high specific strength, excellent oxidation resistance and acceptable mechanical properties at high temperature. Consequently these alloys are used as structural materials in high temperature applications. For example, superalloys used in manufacturing of turbine engines can be replaced by titanium aluminides. This replacement is desirable since titanium aluminides are not as heavy as superalloys and can therefore be used in industrial applications in devices such as compressors and turbine blades in jet engines, components of competitive car engines and aircraft, spacecraft and missile frames especially for hypersonic applications. The application of TiAl-based alloys however is restrained by the absence of effective and non-expensive manufacturing technologies for their preparation and also the titanium aluminides produced can be brittle or have an non-homogeneous microstructure which is reflected in a strong variation in mechanical properties. Conventional processing routes used today for the production of y- TiAl are complicated and expensive and can be summarized as follows: 1) Ingot metallurgy (IM) References V. Guether et al., in y-Titanium Aluminides 1999 (eds Y.W Kim et al) TMS, Warrendale, PA 1999 page 225; and H. Kestler et al., in Titanium and Titanium Alloys (eds Cleyens and Peters) Viley VCH, 2003, p 3 5 1.

In this method small electrodes are pressed from a mixture of the alloy components.

The composition of the electrodes is chosen to compensate for the known evaporation loss of aluminium and specific alloying during the following VAR (vacuum arc remelting) process. In a first VAR step, the electrode is melted in a water-cooled crucible to a primary ingot. In a second VAR step, the primary ingot is remelted in order to improve the chemical homogeneity of the entire ingot. This procedure therefore involves multiple melting of the components in the vacuum arc remelting furnace. This process is therefore costly, complicated and time consuming.

2) Powder metallurgy (PM) [R:\LIBFF]713913.doc:RMC In the powder metallurgy process, the aluminum and titanium powders are melted O in a water cooled copper crucible using skull melting. At the bottom of the crucible, a C transfer system consisting of an induction heated, water cooled copper funnel forms a a melt stream and guides the stream into a gas nozzle, which can be operated either with helium or argon. The complete facility comprises a melting chamber, an atomization 0tower and other facilities. A detailed technical description of the PIGA (Plasma Melting Inert Gas Atomization) as well as processing parameters, cooling rates and results of 0 powder analyses are given in R.Gering, F.P. Schimansky and R.Wagner, Institute for SMaterials Research, Geesthcht, 1992, page 215. In this method, the high partial pressure S 10 of aluminium in the melting condition can result in high evaporation losses. Generally this process is used for sheet rolling because y-TiA1 based alloy powders can be hot isostatically pressed (HIP) to a billet that can be sheet rolled without prior homogenizing heat treatment or forging. The process is both time consuming and costly and uses expensive and complicated equipment.

3) Other Methods 3-1) Combustion Synthesis (CS) Combustion synthesis or self-propagating high temperature synthesis (SHS) is used to produce a product comprising intermetallic phases. If the combination of the thermochemical and thermophysical properties of the system is appropriate, a high temperature reaction front is initiated, which then propagates through the reactants. For this purpose aluminum and titanium are mixed and cold pressed to obtain cylindrical pellets. These pellets are then ignited by means of an electrical coil. Preparation by combustion synthesis is performed using thermal explosion or self propagating modes.

The combustion process needs some preheating to ignite. The exothermic reaction takes place after aluminum melting and an aluminium melting front identified (References: N.

Bertoline et al., Intermetallics,ll (2003), pages 41-49; Li Peijie and et al., Materials Letters 58 (2004), pages 1861-1864 and U.A. Anselmi-Tamburini et al., Science and Technology (Chimica Industria), 2000, pages 1-10. Recently, a new method, based on the use of an electric field to activate the SHS reaction has been developed. Through this method (field activated combustion synthesis (FACS)), the synthesis of TiAl has been demonstrated R. Orru, G. Cad and Z.A.Munir, Metallurgical and Materials Transactions A,vol30A,1999.

3-2) Electroslag Remelting The possibility of manufacturing an ingot of intermetallic compounds on a TiA1 base by the method of electroslag remelting in a chamber furnace under active flux has been examined. Ingots obtained by the method have a typical cast material structure and [R:\LIBFF]713913.doc:RMC _1 increased porosity (up to The cast metal has chemical and structure homogeneity A.D.Ryabtser et al., Problem of SEM-2000 Nrl-C. 75-78 Donetsk National Technical C University, Artyoma str.58 Donetsk 83000, Ukraine -rato@fizmet.dgtu.donetsk.ua.

a On the other hand, calcium dialuminate (CaA1 4 0- 7 or grossite, unlike most refractory ceramics, has a low thermal expansion coefficient and a high resistance to Sthermal shock. Therefore grossite as a structural material has a special attraction in high temperature applications.

00 0 Object of the Invention It is an object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages or at least provide a suitable alternative.

Summary of the Invention In a first aspect, the present invention provides a process for simultaneous preparation of a titanium aluminide and grossite, the process comprising: combining titanium dioxide (TiO 2 aluminium calcium (Ca) and a chlorate or perchlorate compound in a vessel; heating the combination at an elevated temperature and for a sufficient time to form a product comprising titanium aluminide and grossite (CaA1407).

In a second aspect, the present invention provides titanium aluminide or grossite prepared by the process of the first aspect of the invention.

Definitions The following definitions are intended as general definitions and should in no way limit the scope of the present invention to those terms alone, but are put forth for a better understanding of the following description.

Unless the context requires otherwise or specifically stated to the contrary, integers, steps, or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements.

Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated step or element or integer or group of steps or elements or integers, but not the exclusion of any other step or element or integer or group of elements or integers. Thus, in the context of this specification, the term "comprising" means including principally, but not necessarily solely".

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to [R:\LIBFF]713913.doc:RMC or indicated in this specification, individually or collectively, and any and all O combinations or any two or more of said steps or features.

CN All the references cited in this application are specifically incorporated by reference a are incorporated herein in their entirety. Inclusion herein of any given reference is not intended to indicate that the reference is generally known in Australia or elsewhere.

SBrief Description of the Drawings A preferred form of the present invention will now be described by way of example Swith reference to the accompanying drawings wherein: Figure 1 is a vessel suitable for use in the process of the present invention.

Detailed Description of the Preferred Embodiments There is disclosed herein a process for simultaneous preparation of a titanium aluminide and grossite, the process comprising: combining titanium dioxide (TiO 2 aluminium calcium (Ca) and a chlorate or perchlorate compound in a vessel; heating the combination at an elevated temperature and for a sufficient time to form a product comprising titanium aluminide and grossite (CaA1 4 0 7 In one embodiment, by the process of the invention titanium aluminide in a bulk form as the main product and grossite (CaA140 7 in form of slag as a by-product may be produced. In one embodiment both the titanium aluminide and the grossite are fused in this process. In one embodiment the titanium aluminide and the grossite may be separated from each other.

In one embodiment, the titanium aluminide produced by the process is gamma titanium aluminide (7-TiAl).

In one embodiment the elevated temperature is at a temperature at which reaction occurs between the components. Suitably the temperature is in a range from about 400°C to about 600°C. For example 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590 C or 600°C. Suitably the pressure is about 1 atmosphere although it will be appreciated that the pressure inside the vessel may be higher.

In one embodiment the chlorate or perchlorate is potassium perchlorate or potassium chlorate although other perchlorates or chlorates may be used.

In one embodiment the compounds are powderised prior to combination or following combination but prior to heating the combination. In one embodiment the particle size is less 100 micrometers.

In one embodiment the powders are combined and mixed in the following mole ratio: [R:\LIBFF]713913.doc:RMC TiO 2 25.08: Al 63.71: Ca 7.52 and KC10 4 3.68. Suitable ranges include TiO 2 24 to 26 moles, Al 63 to 65 moles, Ca 6 to 8 moles and KC10 4 2 to 5 moles. The powders may be mixed by means of a mixer prior to being poured into a ceramic crucible where they a are may be further pounded by means of a mallet. The crucible may then be sealed by means of a ceramic bung. In one embodiment the crucible is placed in a steel vessel, which may be a flanged steel vessel (other vessels could be used but steel is chosen for economical reasons) and the empty space within the vessel filled with magnesium oxide 0 (MgO) and/or aluminium oxide powders (A1 2 0 3 The presence of these powders is desirable for preventing damage to the ceramic crucible which may occur as a result of S 10o severe shaking during the reaction process and also prevents oxygen from entering the r ceramic crucible. The steel vessel may be sealed by means of screwing with a steel bung.

The steel vessel may then be placed into an electric vessel which may have already been preheated to a temperature from about 200'C to about 400'C. The vessel is then further heated in the furnace up to a maximum temperature of about 1700'C, typically to a temperature of from about 400 0 C to about 600'C where combustion synthesis takes place between the raw materials, the combustion synthesis being activated by heat. After combustion synthesis, the vessel may be cooled and the product removed. The product may comprise two separate parts: a) y- TiA1 in a bulk form as the main product; and b) grossite (CaA140 7 as a by-product in the form of slag. Both TiA1 and grossite may be fused. TiA1 can be separated from grossite, for example by using a hammer.

Alternatively the products can be separated by means of their density with grossite present in slag floating on the top which can be scooped off.

Reference is now made to the accompanying drawing, which shows a vessel suitable for use in the present invention. Referring to FIG. 1, a vessel according to one embodiment of this invention comprises a flanged steel container 1 that is sealed 2 by screwing with a steel bung 3. A magnesium oxide (MgO) or aluminium oxide (A1- 2 0 3 crucible 4 is placed in the steel container 1 into which the charge 5 (a mixture of TiO 2 Al, Ca and KC10 4 powders) has been previously poured. A ceramic bung 6 is located above the crucible 4 and the empty space inside the steel container 1 filled with magnesium oxide (MgO) or aluminium oxide (A1 2 0 3 powder 7.

The present invention has the advantages that titanium aluminide and grossite can be prepared without the need to use expensive and complicated equipment.

The invention will now be described with reference to the following examples which should not be construed as being limiting on the invention.

Example 1: [R:\LIBFF]713913.doc:RMC 120g TiO 2 103g Al, 18g Ca and 30g KC10 4 (all in the form of a powder) as raw O materials were combined and mixed in a mixer. The mixture as charge was then poured C1 into a magnesium oxide (MgO) crucible. The ceramic crucible containing the mixture Swas then placed in a flanged steel vessel and the empty space of the vessel was filled with magnesium oxide powder. A steel bung was then screwed into the vessel to make it air- Stight. The vessel was then placed into an electric furnace at 300 0 C. The vessel was then heated in the furnace to the reaction temperature (about 400°C to about 600°C). After 00 cooling, the product was removed from the vessel. Analysis showed that the product r"- N contained 75g y-TiAl and 160g grossite (CaA140 7 Example 2: 720g TiO 2 618g Al, 109g Ca and 210g KC10 4 (all in the form of a powder) as raw O materials were combined and treated in the same manner as Example 1. The product comprised 576g y-TiAl and 943g grossite (CaA1 4 0 7 Example 3: 1046g TiO 2 898g Al, 158g Ca and 305g KC10 4 (all in the form of a power) as raw materials were combined and treated in the same manner as Example 1. The product comprised 875g y-TiA1 and 1380g grossite (CaA140 7 Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.

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Claims (3)

1. 2. The process according to claim 1 where the elevated temperature is at least 00 400 0 C and the compounds are combined in the form of a powder and mixed in the Sfollowing mole ratio: TiO 2 24 to 26 moles, Al 63 to 65 moles, Ca 6 to 8 moles and KC10 4 2 to 5 moles.
2. 3. The process according to claim 1 or 2 further comprising separating the Stitanium aluminide from the grossite.
3. 4. A process for preparing titanium aluminide and grossite, said process substantially as hereinbefore described with reference to any one of the examples and/or the accompanying drawing. Titanium aluminide or grossite prepared by the process of any one of claims 1 to 4. DATED this First Day of April, 2005 Alireza Kamali Hekmat Razavizadeh Seyed Mohammad Mehdi Hadavi Patent Attorneys for the Applicants SPRUSON FERGUSON [R:\LIBFF]713913.doc:RMC