JP2009097095A - Titanium-aluminum based alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable production of a titanium-aluminum alloy with a fine and uniform structural form since guaranteeing of the minimum amount of ductility is essential to the production of a turbine and an engine by a titanium-aluminum alloy. <P>SOLUTION: The titanium-aluminum based alloy is produced by using a melting and powder metallurgy technique. The alloy consists of Ti-zAl-yNb, wherein z is in a range of 44.5 atom%≤z≤45.5 atom% and y is in a range of 5 atom%≤y≤10 atom%, optionally addition of B and/or C with content ranging between 0.05 atom% and 0.8 atom%. The alloy is characterized in that it contains a molybdenum (Mo) ranging between 0.1 atom% and 3.0 atom%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention uses melting and powder metallurgy techniques to achieve 44.5 atomic% ≦ z ≦ 47 atomic%, especially 44.5 atomic% ≦ z ≦ 45.5 atoms in the case of Ti-z Al-y Nb. %, 5 atomic% ≦ y ≦ 10 atomic%, and an alloy composition of Ti-z Al-y Nb with a content of 0.05 atomic% to 0.8 atomic% and possibly B and / or C addition. The present invention relates to an alloy prepared on the basis of titanium aluminum.

Titanium aluminum alloys have the property of making them very suitable as lightweight work materials, especially for use at high temperatures. As industrial applications, these alloys have special interest based on the intermetallic phase γ- (TiAl) with a tetrahedral structure, and also have a hexagonal structure simultaneously with the multiphase of γ- (TiAl) Also includes a minor phase of intermetallic phase α ₂ (Ti ₃ Al). These γ-titanium aluminum alloys are suitable for moving parts at high operating temperatures, such as light weight (3.85-4.2 g / cm ³ ), high elastic modulus, high strength and high creep resistance up to 700 ° C. It is characterized by its attractive properties as a lightweight work material. Examples of such uses are turbine blades, engine valves, hot air ventilators in aircraft engines and stationary gas turbines.

EP1 015 605 B1 EP1 015 650 B1 "Structural Intermetallics 1997" by YW. Kim, DM Dimiduk, MV Nathanal, R. Darolia, CT Liu, PL Martin, DB Miracle, R. Wagner, M. Yamaguchi, (TMS: Warrendale, Pennsylvania), 1996 , Page 531

  In the technically important area of alloys having an aluminum content of 45 atomic% to 49 atomic%, a series of phase transitions appear during solidification of the melt and subsequent cooling. Solidification can occur in two peritectic reactions, which generally go through a β-mixed crystal centered cubic structure (high temperature phase) or coexisting an α-mixed crystal and a γ-phase having a hexagonal crystal structure.

  Furthermore, it is known that elemental niobium (Nb) leads to an increase in strength, creep resistance, oxygen resistance and ductility. The element, boron, which is partially insoluble in the γ-phase, can result in fine grains both in the cast state and within the α-region after being reshaped by subsequent heat treatment. As a result of the low aluminum content and high concentration of β-stabilizing element, the increased β-phase portion in the structure causes coarse dispersion of this phase and leads to weak mechanical properties.

  The mechanical properties of γ-titanium aluminum alloys are highly anisotropic with respect to their deformation and fracture properties, but also due to the structural anisotropy due to the preferred use of multilayer structures or dual structures. For the desired use of structure and structure in the production from titanium aluminum derived components, casting methods, various powder metallurgy, and remolding steps, and combinations of these production methods can be used.

  According to Non-Patent Document 1, in the course of various development programs, the influence of numerous alloying elements on the structure, composition adjustment in various manufacturing processes, and individual characteristics were investigated. The relationships discovered thereby are as complex as for other systematized metals such as steel, and could only be summarized in a very general form by limited rules. Thus, certain mixing parts can have exceptional combinations of properties.

A titanium aluminum alloy is known from Patent Document 1 and has a structurally and chemically uniform structure. In this case, most phases of γ (TiAl) and α ₂ (Ti ₃ Al) are separated in a finely dispersed state. The disclosed titanium aluminum alloys having an aluminum content of 45 atomic% are distinguished by exceptionally good mechanical and high temperature properties.

  A common problem with any titanium aluminum alloy is low ductility. For a long time, it has not succeeded in improving the low fracture resistance (compared with Non-Patent Document 1) of a titanium aluminum alloy which is generated due to high brittleness and intermetallic phase properties given in advance. For many of the above uses, a plastic rupture elongation of 1% or more is actually sufficient. For turbine and engine production, however, it is essential that this minimum amount of ductility be guaranteed in industrial production over large batch numbers. Since ductility depends sensitively on the structure in the industrial production process, it is very difficult to reliably obtain a remarkably uniform structure shape. For high tensile strength alloys, the maximum allowable defect size, such as maximum grain or single layer mass size, is very small, and therefore very high structural uniformity is desired for such alloys. This uniformity, however, is difficult to achieve due to unavoidable variations in alloy mixtures derived from, for example, plus or minus 0.5 atomic percent in aluminum content.

  Of the many possible structural types of γ-titanium aluminum alloys at present, only thin layers and double structures are considered for high temperature use. Upon cooling from the monolayer region, the α-mixed crystal appears first, while the γ-phase plate is crystallographically oriented and separated from the α-mixed crystal.

  In comparison, a double structure consisting of thin layer assemblies and γ-grains occurs when the material is heated in the second phase region α + γ. Then, in cooling, the α-grains existing in the second phase region change into a thin-layer group that becomes two phases again. Eventually, coarse components are present in the γ-titanium aluminum alloy because large α-grains are formed while running through the α-region. In practice, this occurs during solidification when a large α-phase stem crystal is formed from the melt. Therefore, α-mixed single layer regions should be avoided as much as possible during processing. In practice, however, fluctuations in plasticity and processing temperature appear and thereby locally change the structure of the machined part, so that it is inevitable to form a large thin layer group.

  From this state of the art, the present invention is to enable the production of a titanium aluminum alloy having a fine and uniform structural form, and according to the purpose, a variant of the alloy composition is made into an alloy. Manufacture of inevitable temperature changes that appear during the production process in industrial practice with little or no significant effect on the homogeneity of the alloy, and without requiring any fundamental changes, especially in the manufacturing process Is to make it possible. Therefore, a further object of the present invention is to allow a component made of a homogeneous alloy.

  This problem is achieved through the use of melting and powder metallurgy techniques in the case of Ti-z Al-y Nb alloy composition, 44.5 atomic% ≦ z ≦ 47 atomic%, in particular 44.5 atomic% ≦ z ≦. 45.5 atomic%, and 5 atomic% ≦ y ≦ 10 atomic%, and the alloy is further formed to contain molybdenum (Mo) in the range of 0.1 atomic% to 3.0 atomic%. It is solved by an alloy based on titanium aluminum having a composition. The balance of the alloy is made of Ti (titanium).

  Studies have shown that alloying titanium aluminum with molybdenum with niobium and molybdenum usually results in an alloy where the β-phase is not stable over the entire temperature range, and thus, in a routine process, such as extrusion The method dissolves the remainder of the hot β-phase and a better alloy structural morphology is obtained. In this way, a β-phase volume portion is realized without roughening the grain over the entire temperature range corresponding to the production process. This type of alloy according to the invention is therefore a homogeneous structure with high strength due to fine grain and a very uniform β-phase dispersion.

  Accordingly, the alloys disclosed by the present invention are suitable as lightweight work materials for high temperature use such as turbine blades or engine and turbine components. The alloys of the present invention are made by using cast metallurgy, melt metallurgy, or powder metallurgy methods, or by using these methods in combination with reshaping techniques.

  In particular, in the case of Ti- (44.5 atomic% to 45.5 atomic%) Al- (5 atomic% to 10 atomic%) Nb, molybdenum is contained at a content of about 1.0 atomic% to 3.0 atomic%. The addition results in a good microstructure with high structural uniformity.

  Further, in the case of Ti-z Al-y Nb-x, the alloy according to the present invention is 44.5 atomic% ≦ z ≦ 47 atomic%, particularly 44.5 atomic% ≦ z ≦ 45.5 atomic%, 5 atoms. % ≦ y ≦ 10 atomic% and 0.05 atomic% ≦ x ≦ 0.8 atomic%, or in the case of Ti-z Al—y Nb—w C, 44.5 atomic% ≦ z ≦ 47 atomic% In particular 44.5 atomic% ≦ z ≦ 45.5 atomic%, 5 atomic% ≦ y ≦ 10 atomic%, and 0.05 atomic% ≦ w ≦ 0.8 atomic%, Molybdenum (Mo) is contained in the range of 0.1 atomic% to 3 atomic%, particularly in the range of 0.5 atomic% to 3 atomic%.

  Alternatively, when the alloy is Ti—z Al—y Nb—x Bw C, 44.5 atomic% ≦ z ≦ 47 atomic%, in particular 44.5 atomic% ≦ z ≦ 45.5 atomic%, 5 atomic% ≦ y ≦ 10 atomic%, 0.05 atomic% ≦ x ≦ 0.8 atomic% and 0.05 atomic% ≦ w ≦ 0.8 atomic%, and addition of molybdenum in the range of 0.1 atomic% to 3 atomic% Made by.

  With a given alloy and similar alloy ratios, a high strength γ-titanium aluminum alloy with a β-phase fine grain dispersion is created for a wide range of processing temperatures.

  In the case of the present invention, efforts to structural stability and process security thereby seek to obtain inclusion of body-centered cubic β-phase, so that the appearance of a single phase region spans the entire temperature range throughout the manufacturing process. And is achieved to be avoided in use. In principle, for any industrial titanium aluminum alloy at temperatures above 1350 ° C., the β-phase appears according to the high temperature phase.

  From literature it is known that this phase can be stabilized by various elements such as Mo, W, Nb, Cr, Mn and V at low temperatures. However, a special problem with alloys in which these elements are present is that the β-stabilizing elements must be adjusted very closely to the Al content. Furthermore, the addition of these elements has an undesirable exchange effect which causes a high β-phase part and a coarse dispersion of this phase. Such a structure is most disadvantageous for mechanical properties. Furthermore, the nature of the β-phase depends on the alloying elements and their composition. In particular, the structure must be chosen such that the precipitation of the brittle ω-phase from the β-phase is virtually always eliminated. From this relationship, the alloy composition is provided such that an optimum composition for the mechanical properties and β-phase dispersion can be achieved for a wide range of processing temperatures. At the same time, the best possible strength properties are achieved.

  According to a preferred form of the invention, the alloy also contains boron, preferably boron having a content of 0.05 atomic% to 0.8 atomic% in the region of the alloy. The addition of boron advantageously leads to the formation of a stable precipitate, which likewise contributes to the mechanical strength and structural stability of the alloy.

  The problems of the present invention are further solved by components made from the alloys of the present invention. A comparison is made against the above to avoid repetition.

  In the following, the present invention will be described by means of exemplary embodiments with reference to the attached conceptual diagram without limiting the general idea of the invention. Regarding publication, reference is made to all details of the invention, but it is less rigorous than is described in text.

  FIG. 1 shows two photographs of the structure in a cast block made from a Ti-45 Al-8 Nb-0.2 C (atomic%) alloy. The picture, as well as further pictures in the following figures, were taken with backscattered electrons in a scanning electron microscope.

The structure (FIG. 1) shows a thin layer assembly of α ₂ -phase and γ-phase derived from a former γ-thin layer. The former γ-thin layers are separated by brightly photographed β-phase or B2-phase grain stripes. Next, the α-thin layer formed at the β-α-dislocation collapses and further cools to become an α ₂ -thin layer and a γ-thin layer.

In FIGS. 2a-2c, further photographs of the Ti-45Al-8Nb-0.2C alloy structure taken with a scanning electron microscope after different processing steps are shown. FIG. 2a shows the structure after it has been extruded at 1230 ° C. The extrusion direction runs horizontally. The structure showed α ₂ -and β-phase grains, with the body-centered cubic β-phase disappearing.

FIG. 2b shows the structure of the alloy after extrusion at 1230 ° C. and after a further forging step at 1100 ° C. This structure shows α ₂ -and γ-phase and a small amount of α ₂ / γ-thin-layer clusters.

FIG. 2c shows the structure of the alloy after extrusion at 1230 ° C. and subsequent heat treatment at 1330 ° C. This structure likewise represents grains of α ₂ -and γ-phase. The picture shows a complete thin layer structure with thin layers of α ₂ -and γ-phase. The thin-layer group size is about 200 μm, and at that time, groups that are clearly larger than 200 μm also appear.

  Similar to the structure illustrated in FIG. 2a, the body-centered cubic phase does not appear in the structure illustrated in FIGS. 2b and 2c. Therefore, the β-phase that has been heat-treated in this temperature range after extrusion is not thermodynamically stable.

  3a and 3b represent scanning electron micrographs of the alloy structure according to the present invention. Starting with a Ti-45 Al-5 Nb alloy, 2 atomic percent of the alloying reagent molybdenum was added. This starting alloy Ti-45Al-5Nb-2Mo is based on the composition described in Patent Document 2.

  FIGS. 3a and 3b show the structure of this alloy of the invention observed after extrusion at 1250 ° C. and subsequent heat treatment at 1030 ° C. (FIG. 3a) and at 1270 ° C. (FIG. 3b).

The structure of FIG. 3a represents α ₂ -phase, γ-phase and brightly visible β-phase grains, the latter being arranged in a striped pattern. The structure in FIG. 3b shows α ₂ -and γ-phase thin layer clusters and again brightly visible β-phase grains precipitated from the γ-phase.

  The structure of FIGS. 3a and 3b is fine and very uniform, indicating a uniform dispersion of the β-phase. After heat treatment at 1030 ° C., a spherical structure appears, in which it has striped β-phase grains parallel to the extrusion direction, while the material heat treated at 1270 ° C. It represents a complete thin-layer structure with very uniform and uniformly dispersed β-grains (FIG. 3b).

  The cluster size of Ti-45 Al-5 Nb-2 Mo alloy is 20-30 μm and is therefore at least 5 times smaller than that of the complete thin layer structure of γ-titanium aluminum alloy. Furthermore, since the γ-phase was removed in the β-phase, the β-grains were very finely divided. Thus, in short, a very fine and uniform structure was achieved.

  Tests show this fine and uniform structural morphology after heat treatment has been done for the entire high temperature region up to 1320 ° C. The structure clearly shows that over the entire temperature range suitable for the manufacturing process, a sufficient volume of β-phase is provided and grain growth is effectively suppressed.

  In a tensile test performed on a material heat treated at 1030 ° C., an elongation limit of 867 MPa, a tensile strength of 816 MPa, and a plastic elongation of 1.8% at break were measured at room temperature.

  FIG. 4 shows the tension-elongation polarity measured from the test of Ti-45 Al-5 Nb-2 Mo alloy in the tensile test. The test material was extruded at 1250 ° C., then heat treated at 1030 ° C. for 2 hours, and then cooled in the furnace. The curves taken at 700 ° C and 900 ° C indicate that the alloy is suitable for many high temperature applications. By alloying a small amount of molybdenum, a very uniform microstructure is formed in the alloy, whereby the alloy can be used well as a high temperature work material.

  Further, in FIG. 4, the results of a tensile test on the material of the present invention at room temperature (25 ° C.) are illustrated, in which the tension σ expressed in MPa is expressed with respect to the elongation ε expressed in%. Has been. As a result, there was an increase in the elongation limit that has not been observed for γ-titanium aluminum alloys in other ways. This is a sign of a particularly fine and uniform structure. The increase in elongation limit can react to local tension due to plastic flow, which is very advantageous for ductility and damage resistance.

  The homogeneity of the alloys of the invention within the appropriate processing temperature range is not affected by changes in temperature or composition, which is technically unavoidable.

  The titanium aluminum alloy of the present invention is made through the use of metallurgical casting or powder metal technology. For example, the alloys of the present invention can be processed by hot forging, hot compression, and hot extrusion and hot rolling.

  The present invention allows for the production of titanium aluminum alloys with a very uniform microstructure and high strength, despite the alloy composition changes and unavoidable treatments that appear in industrial surface treatments as previously. The advantage is that it is possible.

  The titanium aluminum alloy of the present invention achieves high strength and good room temperature ductility at temperatures ranging from 700 ° C to 800 ° C. The alloy is therefore suitable for a large number of application areas and can be used, for example, for highly loaded elements or as a particularly high temperature titanium aluminum alloy.

4 is a scanning electron micrograph of a cast block having an alloy of Ti-45 Al-8 Nb-0.2 C (atomic%). It is the photograph of the structure image | photographed with the scanning electron microscope in the alloy of Ti-45 Al-8 Nb-0.2 C (atomic%) after a different process process. It is the photograph of the structure image | photographed with the scanning electron microscope in the alloy of Ti-45 Al-8 Nb-0.2 C (atomic%) after a different process process. It is the photograph of the structure image | photographed with the scanning electron microscope in the alloy of Ti-45 Al-8 Nb-0.2 C (atomic%) after a different process process. 2 is a photograph of the structure after different processing steps in an alloy of the present invention of Ti-45 Al-5 Nb-2 Mo (atomic%). 2 is a photograph of the structure after different processing steps in an alloy of the present invention of Ti-45 Al-5 Nb-2 Mo (atomic%). It is a graph of the tension-elongation curve of the test result of the alloy of Ti-45 Al-5 Nb-2 Mo (atomic%).

Claims (7)

  An alloy based on titanium aluminum produced by using melting and powder metallurgy technology, and having an alloy composition of Ti-z Al-y Nb-x B, 44.5 atomic% ≦ z In an alloy having ≦ 47 atomic%, 5 atomic% ≦ y ≦ 10 atomic%, and 0.05 atomic% ≦ x ≦ 0.8 atomic%, the total amount of Ti, Al, Nb, B and Mo is 100 An alloy containing molybdenum (Mo) in a range from 0.1 atomic% to 3 atomic% based on the atomic%, and a β phase appearing at a temperature up to 1320 ° C. 2. The alloy according to claim 1 , wherein Ti—z Al—y Nb—x B is 44.5 atomic% ≦ z ≦ 45.5 atomic%.   An alloy based on titanium aluminum manufactured by using melting and powder metallurgy technology, and having an alloy composition of Ti-z Al-y Nb-w C, 44.5 atomic% ≦ z In an alloy having ≦ 47 atomic%, 5 atomic% ≦ y ≦ 10 atomic%, and 0.05 atomic% ≦ w ≦ 0.8 atomic%, the total amount of Ti, Al, Nb, C, and Mo is An alloy containing molybdenum (Mo) in a range of 0.5 atomic% to 3 atomic% with reference to 100 atomic% and a β phase appearing at a temperature of 1320 ° C. The alloy according to claim 3 , characterized in that Ti-z Al-y Nb-w C is 44.5 atomic% ≤ z ≤ 45.5 atomic%.   An alloy based on titanium aluminum manufactured by using melting and powder metallurgy technology, and having an alloy composition of Ti-z Al-y Nb-x Bw C, 44.5 atomic% ≦ In an alloy having z ≦ 47 atomic%, 5 atomic% ≦ y 10 atomic%, 0.05 atomic% ≦ x ≦ 0.8 atomic%, and 0.05 atomic% ≦ w ≦ 0.8 atomic%, Ti, Molybdenum (Mo) is contained in the range from 0.1 atomic% to 3 atomic% based on the total amount of Al, Nb, B, C and Mo being 100 atomic%, and at a temperature up to 1320 ° C. An alloy characterized by the appearance of β phase. The alloy according to claim 5 , characterized in that Ti-z Al-y Nb-x Bw C is 44.5 atomic% ≤ z ≤ 45.5 atomic%. A component manufactured from the alloy according to any one of claims 1-6 .

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