JP4467637B2 - Alloy based on titanium aluminum - Google Patents

Abstract

The invention concerns alloys made through the use of melting and powdered metallurgical techniques on the basis of titanium aluminides with an alloy composition of Ti-z Al-y Nb where 44.5 Atom % ≰z≰47 Atom %, 44.5 Atom % ≰z≰45.5 Atom %, and 5 Atom % ≰y≰10 Atom % with possibly the addition of B and/or C at a content between 0.05 Atom % and 0.8 Atom %. Said alloy is characterized in that it contains a molybdenum (Mo) content ranging between 0.1 Atom % to 3.0 Atom %.

Description

  The present invention uses 44.5 atomic% ≦ z ≦ 47 atomic%, especially 44.5 atomic% ≦ z ≦ 45.5 atomic%, in the case of Ti-zAl-yNb, by using melting and powder metallurgy techniques. Titanium aluminum with an alloy composition of TI-zAl-yNb with a content of 5 atomic% ≦ y ≦ 10 atomic% and a content of 0.05 atomic% to 0.8 atomic%, possibly with the addition of B and / or C It is related with the alloy made on the basis of.

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 a special interest based on the intermetallic phase γ- (TiAl) having a tetrahedral structure and also have a hexagonal structure simultaneously with the multiple phases of γ- (TiAl). A minor phase of the intermetallic phase α ₂ (Ti ₃ Al) is also included. 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 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.

EP1015605B1 EP1015650B1

"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, either through a β-mixed crystal centered cubic structure (high temperature phase) as a whole or in the presence of an α-mixed crystal and a γ-phase having a hexagonal crystal structure.

  It is further known that elemental niobium (Nb) leads to an increase in strength, creep resistance, oxygen resistance and ductility. Boron, an element that 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 elements, 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 into finely dispersed states. 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. A further object of the present invention is to enable components made of a homogeneous alloy.

  The problem is that, through the use of melting and powder metallurgy techniques, the alloy composition of Ti-zAl-yNb is 44.5 atomic% ≦ z ≦ 47 atomic%, in particular 44.5 atomic% ≦ z ≦ 45. 5 atomic%, and 5 atomic% ≦ y ≦ 10 atomic%, and the alloy further has an alloy composition formed to contain molybdenum (Mo) in the range of 0.1 atomic% to 3.0 atomic%. It is solved by having an alloy based on titanium aluminum. 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.

Furthermore, the alloy according to the present invention, when the Ti-zAl-yNb-x B , 44.5 atomic% ≦ z ≦ 47 atomic%, in particular 44.5 at% ≦ z ≦ 45.5 atomic%, 5 atomic% In the case of ≦ y ≦ 10 atomic% and 0.05 atomic% ≦ x ≦ 0.8 atomic%, or Ti-zAl-yNb-wC, 44.5 atomic% ≦ z ≦ 47 atomic%, especially 44. 5 atomic percent ≦ z ≦ 45.5 atomic percent, 5 atomic percent ≦ y ≦ 10 atomic percent, and 0.05 atomic percent ≦ w ≦ 0.8 atomic percent, each alloy having 0.1 atomic percent Molybdenum (Mo) is contained in the range of% to 3 atomic%, particularly in the range of 0.5 atomic% to 3 atomic%.

  Alternatively, when the alloy is Ti-zAl-yNb-xB-wC, 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%. It is done.

  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-45Al-8Nb-0.2C (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 in β-α-dislocations 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-phases and a small amount of α ₂ / γ-lamellar grains.

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 thickness of the thin layer group is about 200 μm, and in this case, a group that is clearly larger than 200 μm also appears.

  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-45Al-5Nb 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 the Ti-45Al-5Nb-2Mo 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 a test of Ti-45Al-5Nb-2Mo alloy in a 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.

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

Claims (6)

A melting and powder metallurgy alloy based on titanium aluminide produced by using the alloy, in addition to titanium (Ti), aluminum (Al), niobium (Nb) and molybdenum (Mo) A quinary alloy containing one or more of boron (B) and carbon (C),
When the alloy is composed of Ti, Al, Nb, Mo and B, the Al content is 44.5 atomic% or more and 47 atomic% or less, and the Nb content is 5 atomic% or more and 10 atomic%. The Mo content is 0.1 atomic% or more and 3.0 atomic% or less, the B content is 0.05 atomic% or more and 0.8 atomic% or less, and the balance is Ti. Is defined as
When the alloy is composed of Ti, Al, Nb, Mo and C, the Al content is 44.5 atomic% or more and 47 atomic% or less, and the Nb content is 5 atomic% or more and 10 atomic%. The Mo content is 0.1 atomic% or more and 3.0 atomic% or less, the C content is 0.05 atomic% or more and 0.8 atomic% or less, and the balance is Ti. Is defined as
When the alloy is composed of Ti, Al, Nb, Mo, B, and C, the Al content is 44.5 atomic% or more and 47 atomic% or less, and the Nb content is 5 atomic% or more and 10 Atomic percent or less, Mo content of 0.1 atomic percent or more and 3.0 atomic percent or less, B content of 0.05 atomic percent or more and 0.8 atomic percent or less, The content is specified to be 0.05 atomic percent or more and 0.8 atomic percent or less, and the balance is Ti.
alloy based on titanium aluminide, wherein a high strength γ- titanium aluminum alloy have a fine dispersion of β- phases are formed. 2. The titanium-aluminum-based alloy according to claim 1 , wherein, in any one of the compositions, the Al content is 44.5 at% or more and 45.5 at% or less. Structural materials made from alloy based on the titanium aluminum according to claim 1 or 2. A method for producing an alloy based on titanium aluminum, wherein the alloy is made of boron (B) or carbon (C) in addition to titanium (Ti), aluminum (Al), niobium (Nb) and molybdenum (Mo ). A 5 or 6-element alloy containing any one or more of them,
When the alloy is composed of Ti, Al, Nb, Mo and B, the Al content is 44.5 atomic% or more and 47 atomic% or less, and the Nb content is 5 atomic% or more and 10 atomic%. The Mo content is 0.1 atomic% or more and 3.0 atomic% or less, the B content is 0.05 atomic% or more and 0.8 atomic% or less, and the balance is Ti. Is defined as
When the alloy is composed of Ti, Al, Nb, Mo and C, the Al content is 44.5 atomic% or more and 47 atomic% or less, and the Nb content is 5 atomic% or more and 10 atomic%. The Mo content is 0.1 atomic% or more and 3.0 atomic% or less, the C content is 0.05 atomic% or more and 0.8 atomic% or less, and the balance is Ti. Is defined as
When the alloy is composed of Ti, Al, Nb, Mo, B, and C, the Al content is 44.5 atomic% or more and 47 atomic% or less, and the Nb content is 5 atomic% or more and 10 Atomic percent or less, Mo content of 0.1 atomic percent or more and 3.0 atomic percent or less, B content of 0.05 atomic percent or more and 0.8 atomic percent or less, The content is specified to be 0.05 atomic percent or more and 0.8 atomic percent or less, and the balance is Ti.
Melting and is produced by using the powder metallurgy technology, the manufacturing method of the alloy based on titanium aluminide, wherein a high strength γ- titanium aluminum alloy have a fine dispersion of β- phases are formed. 5. The method for producing a titanium-aluminum-based alloy according to claim 4 , wherein in any one of the compositions, the Al content is 44.5 atomic% or more and 45.5 atomic% or less. Structural materials produced from the claims 4 or 5 alloy based on titanium aluminide produced by the manufacturing method of the alloy according to.

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