HIGH-STRENGTH HIGH-THERMAL-CONDUCTIVITY WROUGHT NICKEL ALLOY
A nickel alloying process includes providing a metal powder containing substantially unalloyed nickel for high inherent thermal conductivity, forming a nickel alloy from the metal powder with addition of additives to form a uniform fine thermo-dynamically stable incoherent precipitate dispersion like carbides, oxides or nitrides, apply mechanical or thermo-chemical reactions to form or maintain a uniform fine dispersion of the incoherent precipitates, removing air and absorbed water from the nickel alloy, and hot extruding the nickel alloy to substantially full density and prescribed dispersion strengthened condition. A net result is a dispersion strengthened high thermal conductivity nickel alloy.
This application claims priority to U.S. Provisional Application No. 61/921,380 filed on Dec. 27, 2013 and titled High Strength High Thermal Conductivity Wrought Nickel Alloy, the disclosure of which is hereby incorporated by reference in its entirety.
FIELDThe present disclosure relates generally to alloying metals, and, more particularly, to method for producing a nickel alloy with increased thermal conductivity combined with high temperature strength capability.
BACKGROUNDWith each next generation of gas turbine engines comes increased performance, durability and reliability along with affordability. Those performance metrics are met with increased operating stresses, temperature and speed. These factors place ever increasing demands on Thermal Management System (TMS). A key component in the TMS is a heat exchanger for hot section air-to-air exchanges. The heat exchanger requires strength, temperature capability and high thermal conductivity along with manufacturability and cost. Conventional hot section heat exchanger materials are typically made of a nickel alloy for their high temperature capability and ease of fabrication. However, nickel alloys have significantly lower thermal conductivity as compared to pure nickel metal. Typical strengthening mechanisms used in those alloys, such as solid solution strengthening and precipitation hardening, cause significant electron scattering and markedly lower thermal conductivity. In some cases, the conventional nickel alloys have thermal conductivities 1/10th to 1/25th of that of pure nickel. But the relatively low strength of pure nickel makes it undesirable as an engineering or structural material.
As such, what is desired is one or more materials with high thermal conductivity and significant strength characteristics.
SUMMARYDisclosed and claimed herein is a nickel alloying process which includes providing a metal powder containing substantially unalloyed nickel, forming a nickel alloy from the metal powder, removing air and absorbed water from the nickel alloy, and hot extruding the nickel alloy. In one embodiment, the metal powder is produced by blending a substantially unalloyed nickel powder with an incoherent particle powder. In one embodiment, the metal powder is produced by blending a nickel oxide powder proportionally with a nickel-aluminum alloy powder. In the above embodiments, the nickel alloy is formed by a ball milling process. In one embodiment, the metal powder is a nickel-vanadium-carbon powder, and the nickel alloy is formed by a melting and rapid solidifying process.
Other aspects, features, and techniques will be apparent to one skilled in the relevant art in view of the following detailed description of the embodiments.
The drawings accompanying and forming part of this specification are included to depict certain aspects of the present disclosure. A clearer conception of the present disclosure, and of the components and operation of systems provided with the present disclosure, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings, wherein like reference numbers (if they occur in more than one view) designate the same elements. The present disclosure may be better understood by reference to one or more of these drawings in combination with the description presented herein. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale.
One aspect of the disclosure relates to processes of manufacturing high strength and high thermal conductivity wrought nickel alloy. Embodiments of the present disclosure will be described hereinafter with reference to the attached drawings.
One embodiment of the present disclosure provides a process to obtain higher strength in nickel alloys without significantly reducing the thermal conductivity of the alloys. In one embodiment, a process for forming a nickel alloy is based on dispersion strengthening of a nickel metal, in which a uniform ultra-fine dispersion of thermo-dynamically stable incoherent particles or precipitates is distributed in the nickel metal and produces increased strength by significantly inhibiting dislocation motion in the nickel. Specifically, Orowan Strengthening conditions are sought. The strength increase is generally proportional to the volume fraction (Vf) of the particles present in the nickel metal up to an appropriate limit. Key to dispersion strengthening is the size, distribution and Vf of the incoherent precipitates. Typically, a particle radius of about 10-20 nm, an interparticle spacing of about 100 nm or at least two times the particle size in a Vf of about 0.05 are conducive to Orowan Strengthening.
Particles of the aforementioned size range require a high magnification electron microscope to be observed. If they can be seen in an optical microscope at lower magnification, then they are described as non-metallic inclusions which are not suitable for engineering materials. Incoherent particles or precipitates covered in this disclosure include metal oxides, metal nitrides and metal carbides.
A necessary characteristic of the incoherent precipitates listed above is their thermo-dynamic stability up to the melting point of the nickel metal and resistance to coarsening over the thermo-mechanical processing range of the nickel metal during component fabrication and operation. Thermo-dynamic stability is reflected in high negative Gibbs free energy of formation, −ΔG.
A key to high thermal conductivity of the dispersion strengthened nickel is to limit any conventional alloying (solid solution strengthening and precipitation hardening) to less than 8 weight percent of combined alloying elements. In so doing, the nickel matrix will maintain its high thermal conductivity to nearly 90 W/m. K.
The nickel alloy formed in step 220 is a composite powder in which average dispersoid interparticle spacing is approximately the same as welding interspace, i.e., a uniform microstructural spacing of ultra-fine dispersant. The nickel alloy is then placed in a suitable metal container and evacuated to remove air and absorbed water in step 230. Stainless steel can be used to make such metal container. Finally the resulting nickel alloy is hot extruded to full density in step 240. In order to control recrystallized grain size and shape of the nickel alloy, a subsequent thermomechanical processing may be employed. The nickel alloy produced according to the embodiment of the present disclosure possesses a desired microstructural condition for strength and high thermal conductivity.
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It should also be recognized that the methodology of the present disclosure for retaining good thermal conductivity of Ni, while increasing the high temperature strength, can be applied to situations where other physical properties of the metal base are retained and utilized at high temperatures. For example, conversely, the electrical resistivity of pure Ni is about 1/10th of such Ni-based alloys. Aside from heat, high temperature strength DS Ni in electrical/power applications has better electrical conductivity than Ni-base alloys, and may be used to improve related performance. Other physical properties like Coefficient of Thermal Expansion and Specific Heat stay approximately the same between Ni and most of its alloys (excluding certain Fe-Ni-base low CTE compositions), i.e., these properties do not adversely influence the present disclosure.
While this disclosure has been particularly shown and described with references to exemplary embodiments thereof, it shall be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit of the claimed embodiments.
Claims
1. A nickel alloying process comprising:
- providing a metal powder containing substantially unalloyed nickel;
- forming a nickel alloy from the metal powder;
- removing air and absorbed water from the nickel alloy; and
- hot extruding the nickel alloy.
2. The nickel alloying process of claim 1, wherein the providing the metal powder comprises providing a substantially unalloyed nickel powder; providing an incoherent particle powder; and blending the substantially unalloyed nickel powder with the incoherent particle powder.
3. The nickel alloying process of claim 1, wherein the providing the metal powder comprises providing a nickel oxide powder with fine oxide dispersion; providing a nickel-aluminum alloy powder; and blending the nickel oxide powder proportionally with the nickel-aluminum alloy powder.
4. The nickel alloying process of claim 3, where the proportion between the nickel oxide powder and the nickel-aluminum alloy powder is determined by a need for the nickel oxide powder to react with the nickel-aluminum alloy powder to form nickel metal and aluminum oxide.
5. The nickel alloying process of claim 1, wherein the forming the nickel alloy comprises ball milling the metal powder under a predetermined atmosphere.
6. The nickel alloying process of claim 5, wherein the predetermined atmosphere is gaseous to promote repetitive cold-welding, deformation and fracturing of powder particles.
7. The nickel alloying process of claim 5, wherein the predetermined atmosphere is cryo-liquid to promote repetitive cold-welding, deformation and fracturing of powder particles.
8. The nickel alloying process of claim 1, wherein the providing the metal powder comprises providing the group consisting of a nickel-vanadium-carbon powder, a nickel-refractory metal-carbon powder and a nickel-refractory metal-nitrogen powder.
9. The nickel alloying process of claim 8, wherein the nickel-refractory metal-carbon powder is formulated to subsequently form a dispersion of metal carbides.
10. The nickel alloying process of claim 8, wherein the nickel-refractory metal-nitrogen powder is formulated to subsequently form a dispersion of metal nitrides.
11. The nickel alloying process of claim 1, wherein the forming the nickel alloy comprises melting the metal powder; and rapidly solidifying the melted metal powder.
12. The nickel alloying process of claim 11, wherein the melting is a vacuum induction melting.
13. The nickel alloying process of claim 11, wherein the rapidly solidifying is performed by rotary atomization using a high specific heat inert quench gas and high rotational speeds to produce fine rapidly cooled powder.
14. The nickel alloying process of claim 11, wherein the heat inert quench gas is selected from the group consisting of Helium, Hydrogen, Argon, Nitrogen and a combination thereof.
15. The nickel alloying process of claim 1, wherein the removing air and water is performed in a stainless steel container.
16. The nickel alloying process of claim 1, further comprising a thermo-mechanical processing for controlling recrystallized grain size and shape of the nickel alloy.
17. The nickel alloying process of claim 1, wherein the hot extruding includes extruding the nickel alloy to substantially full density and a prescribed dispersion strengthened metallurgical condition.
18. A nickel alloying process comprising:
- providing a substantially unalloyed nickel powder;
- providing an incoherent particle powder;
- blending the substantially unalloyed nickel powder with the incoherent particle powder;
- forming a nickel alloy from the blended powder;
- removing air and absorbed water from the nickel alloy; and
- hot extruding the nickel alloy.
19. The nickel alloying process of claim 18, wherein the forming the nickel alloy comprises ball milling the blended powder under a predetermined atmosphere.
20. The nickel alloying process of claim 19, wherein the predetermined atmosphere is gaseous to promote repetitive cold-welding, deformation and fracturing of powder particles.
21. The nickel alloying process of claim 19, wherein the predetermined atmosphere is cryo-liquid to promote repetitive cold-welding, deformation and fracturing of powder particles.
22. The nickel alloying process of claim 18, wherein the removing air and water is performed in a stainless steel container.
23. The nickel alloying process of claim 18, further comprising a thermo-mechanical processing for controlling recrystallized grain size and shape of the nickel alloy.
24. The nickel alloying process of claim 18, wherein the hot extruding includes extruding the nickel alloy to substantially full density and a prescribed dispersion strengthen metallurgical condition. cm 25-47. (canceled)
Type: Application
Filed: Dec 16, 2014
Publication Date: Nov 10, 2016
Inventors: Herbert A. Chin (Charlotte, NC), Paul L. Reynolds (Tolland, CT), Stephen P. Muron (Columbia, CT), Kevin W. Schlichting (South Glastonbury, CT), Raymond C. Benn (Madison, CT)
Application Number: 15/108,476