The present subject matter, in general, relates to alloys for high temperature applications and, in particular, relates to nickel-base eutectic alloys.
Nickel (Ni) based superalloys are used as materials in applications that are exposed to high temperatures for long periods. Examples of such applications are gas turbine engines, where a reasonable strength at high temperatures, stability of microstructure, oxidation resistance, and low density of the materials are important considerations. Such Ni-based superalloys can be used in a wrought form, or consolidated form from powder, or in a cast form.
In an example, wrought alloys include IN718 described in U.S. Pat. No. 3,046,108. The nominal composition of the alloy described in this invention is Ni-17% Fe-19% Cr-3.15Mo-5.15% (Nb+Ta)-5% Al, and it has a density of 8.19 gm/cm3. This alloy retains its yield strength, which is 950 Mega Pascal (MPa) at about 650° C. in large sections. Further, the alloy is strengthened by a fine distribution of intermetallic precipitates based on the intermetallic compound, Ni3Al, designated as γ′ and an intermetallic compound based on Ni3Nb in a matrix containing Ni and Fe (designated γ″). Another commonly used wrought alloy used in disc and blade applications of gas turbine engines, UDIMET 720 with a nominal composition Ni-16% Cr-14.75% Co-3% Mo-1.25% W-5% Ti-2.5% Al-0.01% C-0.0275% Zr-0.15% B and a density of 8.08 gm/cm3 by weight, was introduced in 1986 (UDIMET is a Registered Trade Mark of Special Metals Corporation), and has a slightly improved strength at 700° C.
An alternative approach for large high temperature applications is based on consolidation of alloy powders. The usage of powder permits higher alloying levels without attendant segregation of elements in the product. For example, the U.S. Pat. No. 5,104,614 discloses the composition of alloy designated as N18 which retains high temperature yield strength to about 1000 MPa at 750° C. The use of powder permits higher alloying levels without attendant segregation of elements in the product. The nominal composition of N18 is Ni-11.5% Cr-15.7% Co-6.5% Mo-0.6W-4.5% Al-4.35% Ti-0.45Hf by weight and this alloy is strengthened by a fine dispersion of the intermetallic compound γ′ in a matrix of γ.
Further, in certain high temperature applications, cast alloys are used. Such alloys may be in the equiaxed, directionally solidified or single crystal form. For example, U.S. Pat. No. 5,366,695 describes a single crystal composition, known commercially as CMSX10, which is nominally Ni-5.7% Al-0.2% Ti-2% Cr-3% Co-5% W-8% Ta-6% Re-0.4% Mo-0.33% Hf by weight and has a density of 9.05 gm/cm3. This alloy is also precipitation-strengthened by high volume fractions of γ′ and retains high temperature yield strength of about 950 MPa to temperatures greater than 850° C. The process used to manufacture a material using the cast alloys limits its application to manufacturing of products having thin sections and limited dimensions. The materials represented by this class of alloys are used as turbine aerofoils in gas turbines. Further examples of such single crystal alloys strengthened by high volume fractions of γ′ can be found in U.S. Pat. No. 6,966,956 and US Patent Publication No US2010/0143182, which teach improvement of the long term stability and oxidation resistance of such alloys.
Alloys as described above are derived from the beneficial effects of a fine dispersion of an intermetallic compound Ni3Al in a disordered matrix strengthened by various elements that contribute to solid solution strengthening and also limit atomic mobility at high temperatures. Such γ′-strengthened cast alloy compositions strengthened cast alloy compositions can be reinforced by unidirectionally aligned, coarsely spaced, carbide fibers through directional solidification of eutectic compositions, as described, for example, in U.S. Pat. No. 3,904,402. These materials retain strength levels of about 950 MPa to nearly 870° C. Similarly, U.S. Pat. No. 4,111,723 discloses another example directionally solidified eutectic alloy with molybdenum fibers. Due to a unidirectional alignment of fibers, the properties of these directionally solidified eutectic alloys are anisotropic, with poor transverse properties. Further, the process of manufacture of such eutectic alloys requires low solidification rates, which may lead to long manufacturing cycles.
Ni based alloys have emerged as materials of choice for high temperature applications in the range 600° C. to 1110° C. based on the properties of the disordered matrix γ phase and the intermetallic compound γ′ of the Ni based alloys. However, the high temperature properties of such Ni based alloys are ultimately limited by presence of the disordered matrix γ phase. U.S. Pat. No. 5,336,340 discloses a different metallurgical approach consisting of a combination of the intermetallic compound Ni2AlTi (β′) and Ni3Al (γ′) dispersed in a matrix of the intermetallic compound NiAl (β) in the Ni—Ti—Al system. Such alloys are shown to possess extremely high strength, ranging from 1000 MPa to 1455 MPa at room temperature and retain high strength up to 1200 MPa at 700° C. However, the alloys have only been tested in compression and no evidence of tensile ductility, which is important for engineering applications, has been provided.
It is known that finer scale structures arising from eutectic or peritectic reactions in iron, magnesium, titanium and aluminium alloys with disordered matrix phases and intermetallic compounds offer improved combinations of compressive strength and ductility. However, it is also well known in the prior art that intermetallic compounds offer improved high temperature properties but suffer from the problems of ambient temperature ductility.
The present invention exploits the interaction between eutectic and peritectic reactions that form intermetallic compounds, including γ′ in certain binary systems with Ni as the base, to form fine scale structures constituted entirely of different combinations of intermetallic compounds in ternary and more complex systems.
This summary is provided to introduce a distinctive metallurgical approach and concepts related to combinations of multiple intermetallic phases in different fine-scale eutectic combinations in the nickel-aluminium-zirconium system with high temperature strength, oxidation resistance, microstructural stability and relatively low density. The concepts are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for determining or limiting the scope of the claimed subject matter.
In one embodiment, the present subject matter describes a group of alloy compositions in a Nickel-Aluminium-Zirconium (Ni—Al—Zr) system corresponding to a concentration range of about 9-20% Al and about 4-14% Zr by atomic percentages, and the balance being Ni. In another embodiment, the present subject matter includes at least one eutectic constituent including at least two, of the intermetallic compounds or phases Ni3Al, NiAl, Ni5Zr, Ni7Zr2 and their derivatives that are realized within the aforementioned composition group.
In another embodiment, the present subject matter includes the aforementioned eutectic constituents combined with various primary solidification phases based on the aforementioned intermetallic compounds that are realized within the afore-mentioned group of compositions. The alloys according to present subject matter exhibit high compressive strengths ranging from about 0.85 Giga Pascal (GPa) to about 2.2 GPa, compressive ductilities ranging from about 3 to 9%, with similar tensile strength, and ductility up to 4% in the cast condition. Further, the alloys retain strength in the range 0.85 GPa to 1.9 GPa up to temperatures of 700° C.
In yet another embodiment, these alloys exhibit oxidation resistance and microstructural stability up to temperatures of about 1100° C.
The detailed description is provided with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.
The present subject matter utilizes an interaction between eutectic and peritectic reactions that form intermetallic compounds, including γ′ in certain binary systems with Ni as the base, to form fine scale structures constituted of different combinations of intermetallic compounds in ternary and further complex systems. The alloys described herein exhibit superior strength over conventional Ni base superalloys at temperatures up to 700° C. Such alloys also have high oxidation resistance and micro-structural stability at elevated temperatures up to about 1100° C. Further, the alloys possess reasonable tensile ductility at ambient temperature In addition, the alloys exhibit a comparatively low density ranging from 7.3-7.9 gm/cm3. Furthermore, the aforementioned properties of the alloys have been realized with alloying additions to Ni, such as Al and Zr that have a relatively low cost.
In one embodiment, the alloys in accordance with present subject matter have varying compositions of Nickel (Ni), Aluminum (Al), and Zirconium (Zr), primarily based on Ni. Such varying compositions of the alloys include Al and Zr, which are present in a concentration range of about 9 to 20%, and about 4 to 14%, respectively, the balance being Ni. The aforementioned composition range is described in
Further to the preparation, the alloys were melted in a laboratory scale non-consumable are melting unit and remelted several times to ensure homogeneity. A portion of the alloys was re-melted and suction cast into a cylindrical water-cooled copper (Cu) crucible. A combination of X-ray diffraction, electron probe microanalysis, and scanning electron microscopy in the back-scattered mode were used to analyze compositions and structures of various microstructural constituents. It is, however, understood that such alloys and their products may be manufactured by alternative methods known to those skilled in the art, such as wrought forms, or from consolidation of powder, or in equiaxed, directionally solidified or single crystal cast forms.
In another embodiment of the present subject matter, the alloy compositions include a combination of eutectic constituents further including the intermetallic phases Ni3Al denoted by γ′, Ni5Zr, Ni7Zr2 and NiAl denoted by β, in various proportions.
In another embodiment,
Further, in another embodiment, alloys including the eutectic structures as well as the alloys including primary solidification phases in addition to the eutectic structures have been tested in compression, at room temperature and at 700° C. Samples for compression testing were derived from the suction cast samples following American Society for testing and materials (ASTM) standards.
In order to illustrate relevant compositions from which substantially high strengths that can realized,
Further, the resistance to fracture, of various primary solidification phases and eutectic constituents as present within Alloys A to I, is probed by examining the corners of hardness indents made at various regions of the microstructure of Alloys A to I with a Vickers indent at a load of 200 gm.
As known in the art, heavy duty applications of structural materials require a reasonable tensile ductility present within the structural materials.
As a part of another embodiment of the present subject matter, a number of experiments have been conducted upon Alloy B to determine various properties thereof in order to investigate the high temperature stability of the alloys of the present subject matter. However, the present subject matter is not restricted by the results of the below-mentioned experiments, which may be extended to cover experiments conducted over Alloys A, C, D, E, F, G, H, I, J, K, and L. The high temperature stability of the alloys has been investigated by exposure of Alloy B to high temperature for varying amounts of time followed by an examination of the microstructure.
Also as a part of the high temperature stability, weight gain of Alloy B was determined after exposure to air at different temperature both under static and cyclic oxidation conditions. Such studies were carried out in a thermo gravimetric analyzer. Samples were heated at rate of 20° C./min and held for different times and temperatures for the static study. In the case of cyclic tests samples, each cycle consisted of heating to a particular temperature at a rate of 20° C./min and cooling at same rate down to 300° C.
In yet another embodiment of the present subject matter, the alloys listed in Table 1 may include limited alloying additives or trace additives. These additives also retain the eutectic constituents within the alloys of the present subject matter. The effect of limited alloying additions or the presence of trace additions in improving the properties of the alloys listed in Table 1 is considered by way of examples. The addition of such additives does not substantively affect the nature of the intermetallic phases, their derivatives, their combinations and their distribution as illustrated in
Similarly, additions of Niobium (Nb), Molybdenum (Mo), and Tungsten (W) may be used to suitably alter the properties of the aforementioned intermetallic compounds. Further, Boron (B) may be added to affect grain boundary strength in materials of this class.
Table 2 illustrates the additional alloying elements that may be added to alter properties of described Ni-based alloys.
Table 3 illustrates the compressive yield strength properties of some alloys with such additional alloying elements, as an example. Such alloying additions are to be understood as examples with respect to the microstructure and various intermetallic phases and their
derivatives that correspond to embodiments of this present subject matter.
Number | Date | Country | Kind |
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900/CHE/2012 | Mar 2012 | IN | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/IN2012/000387 | 6/4/2012 | WO | 00 | 5/20/2015 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2013/132508 | 9/12/2013 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
3046108 | Eiselstein | Jul 1962 | A |
3904402 | Smashey | Sep 1975 | A |
4111723 | Lemkey | Sep 1978 | A |
4731221 | Liu | Mar 1988 | A |
5104614 | Ducrocq et al. | Apr 1992 | A |
5336340 | Cahn | Aug 1994 | A |
5366695 | Erickson | Nov 1994 | A |
6190467 | Jackson et al. | Feb 2001 | B1 |
6482355 | Santella et al. | Nov 2002 | B1 |
6966956 | Koizumi et al. | Nov 2005 | B2 |
20080008618 | Sato et al. | Jan 2008 | A1 |
20100143182 | Sato et al. | Jun 2010 | A1 |
Number | Date | Country |
---|---|---|
101148729 | Mar 2008 | CN |
1 767 667 | Sep 2010 | EP |
Entry |
---|
Decker et al., “The Mechanism of Beneficial Effects of Boron and Zirconium on Creep-Rupture Properties of a Complex Heat-Resistant Alloy,” Report 57 to the National Advisory Committee for Aeronautics, Project 1478-11, Oct. 1957. |
Jayanth et al., “Phase Equilibria in the Ni-Rich Region of the Ni—Al—Zr system,” MRS Proceedings 19, pp. 395-398, Dec. 1982. |
Kim et al., “Phase transformation and microstructure of NiAl/Ni3Al alloys containing Ti,” Scripta Materialia 48(4), pp. 443-448, Feb. 2003. |
Extended European Search Report, dated Dec. 10, 2015, for European Application No. 12870721.3-1362/2823074, 9 pages. |
Inoue et al., “Formation of non-equilibrium b.c.c. phase with high tensile strength in Ni—Al—Zr system by rapid solidification,” Materials Science and Engineering A181-A182:1072-1075, 1994. |
International Search Report, dated Sep. 19, 2012, for International Application No. PCT/IN2012/000387, 4 pages. |
Miura et al., “Reinvestigation of Ni-Solid Solution/Liquid Equilibria in Ni—Al Binary and Ni—Al—Zr Ternary Systems,” Journal of Phase Equilibria 22(4):457-462, 2001. |
Tsau et al., “Microstructures and mechanical properties of Ni—Al—Fe—X intermetallics based on Ni-25AL-27.5Fe alloy,” Materials Chemistry and Physics 65:136-143, 2000. |
Written Opinion of the International Searching Authority, dated Sep. 19, 2012, for International Application No. PCT/IN2012/000387, 4 pages. |
Number | Date | Country | |
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20150292062 A1 | Oct 2015 | US |