COBALT ALLOYS

BACKGROUND

Copper-beryllium alloys are widely used in a variety of applications such as aerospace bushings and machine gun liners. Exposure to beryllium, however, can cause an often-fatal lung illness. Thus, the art has developed a need for alloys including, but not limited to, beryllium-free alloys with mechanical and tribological properties competitive to those of copper-beryllium alloys.

SUMMARY

In one aspect, disclosed is an alloy comprising, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 7% nickel, 0% to about 10% tungsten, less than about 3% molybdenum, and the balance of weight percent comprising cobalt and incidental elements and impurities.

The alloy may comprise, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 3% nickel, 0% to about 10% tungsten, less than about 1% molybdenum, and the balance of weight percent comprising cobalt and incidental elements and impurities.

The alloy may comprise, by weight, 17.5% to 18.5% chromium, 0.9% to 1.1% nickel, 5.3% to 5.7% titanium, 7.3% to 7.7% iron, 1.7% to 1.9% vanadium, and the balance of weight percent comprising cobalt and incidental elements and impurities.

The alloy may comprise, by weight, 16.1% to 17.1% chromium, 2.5% to 2.9% nickel, 6.1% to 6.5% titanium, 6.9% to 7.3% iron, 1.9% to 2.1% vanadium, and the balance of weight percent comprising cobalt and incidental elements and impurities.

The alloy may consist of, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 7% nickel, 0% to about 10% tungsten, less than about 3% molybdenum, and the balance of weight percent consisting of cobalt and incidental elements and impurities.

The alloy may consist of, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 3% nickel, 0% to about 10% tungsten, less than about 1% molybdenum, and the balance of weight percent consisting of cobalt and incidental elements and impurities.

The alloy may consist of, by weight, 17.5% to 18.5% chromium, 0.9% to 1.1% nickel, 5.3% to 5.7% titanium, 7.3% to 7.7% iron, 1.7% to 1.9% vanadium, and the balance of weight percent consisting of cobalt and incidental elements and impurities.

The alloy may consist of, by weight, 16.1% to 17.1% chromium, 2.5% to 2.9% nickel, 6.1% to 6.5% titanium, 6.9% to 7.3% iron, 1.9% to 2.1% vanadium, and the balance of weight percent consisting of cobalt and incidental elements and impurities.

The alloy may comprise a low-misfit nanostructure that includes at least one of vanadium, iron, and tungsten.

The alloy may substantially avoid discontinuous grain boundary reactions or cellular growth reactions at grain boundaries.

The alloy may be characterized by an ultimate tensile strength of about 830 to about 1240 MPa at room temperature.

The alloy may be fabricated by casting or powder metallurgy methods.

In another aspect, disclosed is an alloy made by a process comprising the steps of: preparing a melt that includes, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 7% nickel, 0% to about 10% tungsten, less than about 3% molybdenum, and the balance of weight percent comprising cobalt and incidental elements and impurities; cooling the melt to room temperature; subjecting the alloy to a homogenization and solution heat treatment; and tempering the alloy.

The homogenization may be at a selected temperature (e.g., about 1020° C. to about 1125° C.) for a selected time period (e.g., about 72 hours to about 96 hours). The solution heat treatment may be at a selected temperature (e.g., about 1020° C. to about 1125° C.) for a selected time period (e.g., about 2 hours). The solution heat treatment may be followed by a water quench. The tempering may be at a selected temperature (e.g., about 750° C. to about 850° C.) for a selected time period (e.g., about 24 hours to about 75 hours). The tempering may be followed by air cooling.

The melt may comprise, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 3% nickel, 0% to about 10% tungsten, less than about 1% molybdenum, and the balance of weight percent comprising cobalt and incidental elements and impurities.

The melt may comprise, by weight, 17.5% to 18.5% chromium, 0.9% to 1.1% nickel, 5.3% to 5.7% titanium, 7.3% to 7.7% iron, 1.7% to 1.9% vanadium, and the balance of weight percent comprising cobalt and incidental elements and impurities. The homogenization may be at about 1025° C. for about 72 hours. The solution heat treatment may be at about 1025° C. for about 2 hours. The solution heat treatment may be followed by a water quench. The tempering may be at about 780° C. for about 24 hours. The tempering may be followed by air cooling.

The melt may comprise, by weight, 16.1% to 17.1% chromium, 2.5% to 2.9% nickel, 6.1% to 6.5% titanium, 6.9% to 7.3% iron, 1.9% to 2.1% vanadium, and the balance of weight percent comprising cobalt and incidental elements and impurities. The homogenization may be at about 1050° C. for about 96 hours. The solution heat treatment may be at about 1050° C. for about 2 hours. The solution heat treatment may be followed by a water quench. The tempering may be at about 780° C. for about 72 hours. The tempering may be followed by air cooling.

The melt may consist of, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 7% nickel, 0% to about 10% tungsten, less than about 3% molybdenum, and the balance of weight percent consisting of cobalt and incidental elements and impurities.

The melt may consist of, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 3% nickel, 0% to about 10% tungsten, less than about 1% molybdenum, and the balance of weight percent consisting of cobalt and incidental elements and impurities.

The melt may consist of, by weight, 17.5% to 18.5% chromium, 0.9% to 1.1% nickel, 5.3% to 5.7% titanium, 7.3% to 7.7% iron, 1.7% to 1.9% vanadium, and the balance of weight percent consisting of cobalt and incidental elements and impurities. The homogenization may be at about 1025° C. for about 72 hours. The solution heat treatment may be at about 1025° C. for about 2 hours. The solution heat treatment may be followed by a water quench. The tempering may be at about 780° C. for about 24 hours. The tempering may be followed by air cooling.

The melt may consist of, by weight, 16.1% to 17.1% chromium, 2.5% to 2.9% nickel, 6.1% to 6.5% titanium, 6.9% to 7.3% iron, 1.9% to 2.1% vanadium, and the balance of weight percent consisting of cobalt and incidental elements and impurities. The homogenization may be at about 1050° C. for about 96 hours. The solution heat treatment may be at about 1050° C. for about 2 hours. The solution heat treatment may be followed by a water quench. The tempering may be at about 780° C. for about 72 hours. The tempering may be followed by air cooling.

The alloy may comprise a low-misfit nanostructure that includes at least one of vanadium, iron, and tungsten.

The alloy may substantially avoid discontinuous grain boundary reactions or cellular growth reactions at grain boundaries.

The alloy may be characterized by an ultimate tensile strength of about 830 to about 1240 MPa at room temperature, and wherein the steps substantially avoid warm working.

The preparation of the melt may include casting or powder metallurgy methods.

In another aspect, disclosed is a manufactured article comprising an alloy that includes, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 7% nickel, 0% to about 10% tungsten, less than about 3% molybdenum, and the balance of weight percent comprising cobalt and incidental elements and impurities.

The alloy may comprise a low-misfit nanostructure that includes at least one of vanadium, iron, and tungsten.

The alloy may substantially avoid discontinuous grain boundary reactions or cellular growth reactions at grain boundaries.

The alloy may be characterized by an ultimate tensile strength of about 830 to about 1240 MPa at room temperature.

The article may be fabricated by casting or powder metallurgy methods.

The alloy may be made by a process including the steps of: preparing a melt that includes, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 7% nickel, 0% to about 10% tungsten, less than about 3% molybdenum, and the balance of weight percent comprising cobalt and incidental elements and impurities; cooling the melt to room temperature; subjecting the alloy to a homogenization and solution heat treatment; and tempering the alloy.

The alloy may be characterized by an ultimate tensile strength of about 830 to about 1240 MPa at room temperature, and wherein the steps substantially avoid warm working.

The preparation of the melt may include casting or powder metallurgy methods.

The manufactured article may be an aerospace bushing or machine gun liner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a systems-design chart illustrating processing-structure-property relationships of non-limiting embodiments of alloys falling within the scope of the disclosure.

FIG. 2 is an optical micrograph showing a non-limiting embodiment of alloys falling within the scope of the disclosure as described herein including, for example, FIG. 1, wherein the non-limiting embodiment is tempered at about 850° C. for about 8 hours.

FIG. 3 is an optical micrograph similar to FIG. 2 showing a non-limiting embodiment that is tempered at about 850° C. for about 24 hours.

FIG. 4 is a scanning electron microscope image showing a non-limiting embodiment that is tempered at about 850° C. for about 24 hours similar to FIG. 3 but at a higher magnification.

FIG. 5 is a scanning electron microscope image showing nano-scale particles that are coherent with the matrix for a non-limiting embodiment of alloys falling within the scope of the disclosure as described herein including, for example, FIGS. 1-4.

FIG. 6 is a graph plotting the estimated tensile strength of non-limiting embodiments of alloys within the scope of the disclosure as described herein including, for example, FIGS. 1-5, against the reported strength of known alloys, namely Stellite 21 and Stellite 25.

FIG. 7 depicts a process for preparing alloy 3A.

FIG. 8 depicts a thermodynamic step diagram that shows ˜21.5% (volume fraction) or strengthening phase (“L1₂” or “γ”) is predicted at the final aging temperature of 780° C. for alloy 3A.

FIG. 9 depicts the VAR crop hardness response (aging) of alloy 3A. The heat treatment schedule applied was: solution heat treatment at 1050° C. for 2 hours plus water quench, followed by aging (within 4 hours of quenching) at 780° C. for 72 hours plus air cool.

FIG. 10a depicts an optical micrograph of rotary forged alloy 3A. The alloy was etched in a solution of 5 mL H₂O₂plus 100 mL HCl. The longitudinal direction of the bar is oriented vertically in the micrograph.

FIG. 10b depicts an optical micrograph of rotary forged alloy 3A. The alloy was etched in a solution of 5 mL H₂O₂plus 100 mL HCl. The longitudinal direction of the bar is oriented vertically in the micrograph.

DETAILED DESCRIPTION

Aspects relate to an alloy and a manufactured article comprising the alloy as described herein. It should be understood that the disclosure is not limited in application to the details of construction and the arrangements of the components set forth in the following description. Other aspects and embodiments will be apparent in light of the following detailed description.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present invention. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

As used in the specification and the appended claims, the singular forms “a,” “and” and “the” include plural references unless the context clearly dictates otherwise. The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The present disclosure also contemplates other embodiments “comprising,” “consisting of” and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not.

As used herein, terms such as “face-centered cubic” or “FCC,” “hexagonal close-packed” or “HCP,” “primary carbide,” and “L1₂phase” include definitions that are generally known in the art.

Any recited range described herein is to be understood to encompass and include all values within that range, without the necessity for an explicit recitation. Use of the word “about” to describe a particular recited amount or range of amounts is meant to indicate that values very near to the recited amount are included in that amount, such as, but not limited to, values that could or naturally would be accounted for due to instrument and/or human error in forming measurements.

In a general sense, the inventors have unexpectedly found new compositions of beryllium-free alloys that achieve nano-scale precipitation strengthening in a cobalt-based FCC matrix. It is contemplated that the low stacking-fault energy of the cobalt-based FCC matrix in an alloy with more than about 10% Cr in weight percentage results in good wear resistance and a high work hardening rate. The disclosed alloys include a suitable content of chromium to provide good resistance to corrosion and erosion. Known cobalt-based alloys such as ACUBE 100 by Carpenter Technology Corporation achieve strength predominantly through warm working, with a nominal composition in weight percentage of 28% Cr, 5.5% Mo, 0.7% Mn, 0.6% Si, 0.17% N, 0.05% C, up to 1% Fe, up to 1% Ni, and the balance Co and incidental elements and impurities. The applicable product size of ACUBE 100 is thus typically limited to less than 4 inches in diameter. Moreover, when tempered at 700° C.-850° C., ACUBE 100 forms HCP precipitates that can significantly reduce ductility. Other known cobalt-based alloys such as the Stellite alloys are strengthened by primary carbides that also can limit ductility and formability. In contrast, the disclosed alloys are strengthened by precipitates that are about 100 nm or less in diameter.

Referring to FIG. 1, in an aspect, the disclosure relates to an alloy that generally includes a low-misfit nanostructure in a cobalt-based FCC matrix. Such alloys would be useful for manufactured articles including, but not limited to, the main landing gear, lugs for attaching the wings, and vertical tail hinge assembly of an aircraft. Additionally, the alloys would be useful for manufactured articles such as gun barrels and liners. The alloys would also be useful for numerous other applications wherein a low-misfit nanostructure in a cobalt-based FCC matrix is desired. As illustrated in FIG. 1, a set of suitable alloy properties can be selected depending on the desired performance of the manufactured article, namely, environmental friendliness, bearing strength, wear resistance, damage tolerance, formability, and corrosion resistance. Suitable alloy properties include non-toxicity, strength of about 830 MPa to about 1240 MPa without requiring warm working or cold working, a low coefficient of friction, a good resistance to galling and fretting, high toughness, and corrosion resistance. These alloy properties can be achieved by structural characteristics such as an FCC matrix that avoids transformation to HCP and shows a low stacking-fault energy and solid solution strengthening; a low-misfit nanostructure such as of an L1₂phase with a suitable size and fraction, the nanostructure avoiding embrittling phases; a grain structure with a suitable grain size and pinning particles, avoiding cellular reaction at the grain boundaries; and a solidification path that ends in a eutectic phase. Alloys exhibiting these structural characteristics can be accessed through the sequential processing steps shown on the left of FIG. 1. The microstructural features affected during the processing steps are connected by lines to each processing step.

The nanostructure in the disclosed alloys can be an L1₂or γ′ phase based on Co₃Ti. The disclosed alloys can reduce the lattice-parameter misfit between the precipitate phase and the FCC matrix, and thereby substantially avoid discontinuous grain boundary reactions or cellular growth reactions at the grain boundaries. It is contemplated that the interphase misfit and the precipitation of HCPη-Ni₃Ti particles can result in discontinuous grain boundary reactions or cellular growth reactions at the grain boundaries. The disclosed alloys include a suitable content of vanadium, iron, or tungsten, or a combination thereof to reduce the interphase misfit and thereby substantially avoid discontinuous grain boundary reactions or cellular growth reactions at the grain boundaries. The vanadium, iron, and/or tungsten atoms can partition at least in part to the Co₃Ti-based precipitate and reduce the lattice-parameter misfit. For example, the lattice parameter of the FCC matrix in the disclosed alloys is about 0.356 nm, and Fe, V, and/or W are expected to reduce the L1₂lattice parameter from about 0.361 nm of pure Co₃Ti to 0.359 nm or less to reduce the lattice-parameter misfit.

Still referring to FIG. 1, in a further aspect, the disclosure relates to an alloy that generally stabilizes the FCC matrix. The FCC matrix in cobalt-based alloys is metastable compared to the HCP structure, and therefore there is a tendency for FCC to transform to HCP at temperatures ranging from room temperature to a higher tempering temperature. The disclosed alloys include suitable contents of iron and nickel to substantially prevent the transformation from FCC to HCP while promoting the formation of the L1₂(γ′) strengthening phase and avoiding the formation of detrimental phases such as the Fe₂Ti Laves-phase and the η-Ni₃Ti phase.

The disclosed alloys may comprise chromium, nickel, titanium, iron, vanadium, and cobalt, along with incidental elements and impurities.

The alloys may comprise, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 7% nickel, 0% to about 10% tungsten, less than about 3% molybdenum, and the balance of weight percent comprising cobalt and incidental elements and impurities. It is understood that the alloys described herein may consist only of the above-mentioned constituents or may consist essentially of such constituents, or in other embodiments, may include additional constituents.

The alloys may comprise, by weight, about 10% to about 20% chromium, about 4% to about 7% titanium, about 1% to about 3% vanadium, 0% to about 10% iron, less than about 3% nickel, 0% to about 10% tungsten, less than about 1% molybdenum, and the balance of weight percent comprising cobalt and incidental elements and impurities.

The alloys may comprise, by weight, about 10% to about 20% chromium, about 13% to about 20% chromium, about 14% to about 20% chromium, about 15% to about 19% chromium, or about 16% to about 18% chromium. The alloys may comprise, by weight, 10% to 20% chromium, 13% to 20% chromium, 14% to 20% chromium, 15% to 19% chromium, or 16% to 18% chromium. The alloys may comprise, by weight, 15.1%, 15.2%, 15.3%, 15.4%, 15.5%, 15.6%, 15.7%, 15.8%, 15.9%, 16.0%, 16.1%, 16.2%, 16.3%, 16.4%, 16.5%, 16.6%, 16.7%, 16.8%, 16.9%, 17.0%, 17.1%, 17.2%, 17.3%, 17.4%, 17.5%, 17.6%, 17.7%, 17.8%, 17.9%, 18.0%, 18.1%, 18.2%, 18.3%, 18.4%, 18.5%, 18.6%, 18.7%, 18.8%, 18.9%, or 19.0% chromium. They alloys may comprise, by weight, about 16% chromium, about 17% chromium, or about 18% chromium.

The alloys may comprise, by weight, about 0.1% to about 5% nickel, about 0.5% to about 3.5% nickel, or about 1% to about 3% nickel. The alloys may comprise, by weight, 0.1% to 5% nickel, 0.5% to 3.5% nickel, or 1% to 3% nickel. The alloys may comprise, by weight, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, or 5.0% nickel. The alloys may comprise, by weight, less than about 7% nickel, less than about 6% nickel, less than about 5% nickel, less than about 4% nickel, less than about 3% nickel, less than about 2% nickel, or less than about 1% nickel. The alloys may comprise less than about 3% nickel. The alloys may comprise, by weight, about 1% nickel, about 2% nickel, about 3% nickel, about 4% nickel, about 5% nickel, about 6% nickel, or about 7% nickel.

The alloys may comprise, by weight, about 3% to about 8% titanium, about 4% to about 7% titanium, or about 5% to about 7% titanium. The alloys may comprise, by weight, 3% to 8% titanium, 4% to 7% titanium, or 5% to 7% titanium. The alloys may comprise, by weight, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, or 8.0% titanium. The alloys may comprise, by weight, about 5% titanium, about 6% titanium, or about 7% titanium.

The alloys may comprise, by weight, 0% to about 10% iron, about 5% to about 9% iron, or about 6% to about 8% iron. The alloys may comprise, by weight, 0% to 10% iron, 5% to 9% iron, or 6% to 8% iron. The alloys may comprise, by weight, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, or 9.0% iron. The alloys may comprise, by weight, about 6% iron, about 7% iron, or about 8% iron.

The alloys may comprise, by weight, about 0.1% to about 5% vanadium, about 0.5% to about 4% vanadium, or about 1% to about 3% vanadium. The alloys may comprise, by weight, 0.1% to 5% vanadium, 0.5% to 4% vanadium, or 1% to 3% vanadium. The alloys may comprise, by weight, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, or 4.0% vanadium. The alloys may comprise about 1%, about 2%, or about 3% vanadium.

The alloys may comprise, by weight, 0% to about 10% tungsten. The alloys may comprise, by weight, less than about 10% tungsten, less than about 9% tungsten, less than about 8% tungsten, less than about 7% tungsten, less than about 6% tungsten, less than about 5% tungsten, less than about 4% tungsten, less than about 3% tungsten, less than about 2% tungsten, less than about 1% tungsten, or 0% tungsten.

The alloys may comprise, by weight, less than about 3% molybdenum, less than about 2% molybdenum, less than about 1% molybdenum, or 0% molybdenum.

The alloys may comprise, by weight, a balance of cobalt and incidental elements and impurities. The term “incidental elements and impurities,” may include one or more of boron, carbon, manganese, nitrogen, oxygen, and sulfur.

The alloys may comprise, by weight, 17.5% to 18.5% chromium, 0.9% to 1.1% nickel, 5.3% to 5.7% titanium, 7.3% to 7.7% iron, 1.7% to 1.9% vanadium, and the balance of weight percent comprising cobalt and incidental elements and impurities. The incidental elements and impurities may include one or more of carbon (e.g., 0.004% to 0.0100%), manganese (e.g., maximum 0.002%), silicon (e.g., maximum 0.004%), phosphorus (e.g., maximum 0.002%), sulfur (e.g., maximum 0.002%), oxygen (e.g., maximum 0.006%), and nitrogen (e.g., maximum 0.0005%).

The alloys may comprise, by weight, 16.1% to 17.1% chromium, 2.5% to 2.9% nickel, 6.1% to 6.5% titanium, 6.9% to 7.3% iron, 1.9% to 2.1% vanadium, and the balance of weight percent comprising cobalt and incidental elements and impurities. The incidental elements and impurities may include one or more of carbon (e.g., 0.004% to 0.0100%), manganese (e.g., maximum 0.002%), silicon (e.g., maximum 0.004%), phosphorus (e.g., maximum 0.002%), sulfur (e.g., maximum 0.002%), oxygen (e.g., maximum 0.006%), nitrogen (e.g., maximum 0.0005%), and boron (e.g., 0.004% to 0.0100%).

The alloys may consist of, by weight, 17.5% to 18.5% chromium, 0.9% to 1.1% nickel, 5.3% to 5.7% titanium, 7.3% to 7.7% iron, 1.7% to 1.9% vanadium, and the balance of weight percent consisting of cobalt and incidental elements and impurities. The incidental elements and impurities may include one or more of carbon (e.g., 0.004% to 0.0100%), manganese (e.g., maximum 0.002%), silicon (e.g., maximum 0.004%), phosphorus (e.g., maximum 0.002%), sulfur (e.g., maximum 0.002%), oxygen (e.g., maximum 0.006%), and nitrogen (e.g., maximum 0.0005%).

The alloys may consist of, by weight, 16.1% to 17.1% chromium, 2.5% to 2.9% nickel, 6.1% to 6.5% titanium, 6.9% to 7.3% iron, 1.9% to 2.1% vanadium, and the balance of weight percent consisting of cobalt and incidental elements and impurities. The incidental elements and impurities may include one or more of carbon (e.g., 0.004% to 0.0100%), manganese (e.g., maximum 0.002%), silicon (e.g., maximum 0.004%), phosphorus (e.g., maximum 0.002%), sulfur (e.g., maximum 0.002%), oxygen (e.g., maximum 0.006%), nitrogen (e.g., maximum 0.0005%), and boron (e.g., 0.004% to 0.0100%).

The alloys may have a compressive yield strength of 800 MPa to 1,200 MPa, 810 MPa to 1190 MPa, 820 MPa to 1180 MPa, 820 MPa to 1160 MPa, or 830 MPa to 1160 MPa. The alloys may have a compressive yield strength of at least 800 MPa, at least 810 MPa, at least 820 MPa, at least 830 MPa, at least 840 MPa, at least 850 MPa, at least 860 MPa, at least 870 MPa, at least 880 MPa, at least 890 MPa, at least 900 MPa, at least 910 MPa, at least 920 MPa, at least 930 MPa, at least 940 MPa, at least 950 MPa, at least 960 MPa, at least 970 MPa, at least 980 MPa, at least 990 MPa, at least 1,000 MPa, at least 1,100 MPa, or at least 1,200 MPa. The alloys may have a compressive yield strength about of about 800 MPa, about 810 MPa, about 820 MPa, about 830 MPa, about 840 MPa, about 850 MPa, about 860 MPa, about 870 MPa, about 880 MPa, about 890 MPa, about 900 MPa, about 910 MPa, about 920 MPa, about 930 MPa, about 940 MPa, about 950 MPa, about 960 MPa, about 970 MPa, about 980 MPa, about 990 MPa, about 1,000 MPa, about 1,100 MPa, or about 1,200 MPa. The compressive yield strength may be measured according ASTM E9.

The alloys may have a 0.2% offset yield strength of 800 MPa to 1,200 MPa, 810 MPa to 1190 MPa, 820 MPa to 1180 MPa, 820 MPa to 1140 MPa, or 830 MPa to 1140 MPa. The alloys may have a 0.2% offset yield strength of at least 800 MPa, at least 810 MPa, at least 820 MPa, at least 830 MPa, at least 840 MPa, at least 850 MPa, at least 860 MPa, at least 870 MPa, at least 880 MPa, at least 890 MPa, at least 900 MPa, at least 910 MPa, at least 920 MPa, at least 930 MPa, at least 940 MPa, at least 950 MPa, at least 960 MPa, at least 970 MPa, at least 980 MPa, at least 990 MPa, at least 1,000 MPa, at least 1,100 MPa, or at least 1,200 MPa. The alloys may have a 0.2% offset yield strength of about 800 MPa, about 810 MPa, about 820 MPa, about 830 MPa, about 840 MPa, about 850 MPa, about 860 MPa, about 870 MPa, about 880 MPa, about 890 MPa, about 900 MPa, about 910 MPa, about 920 MPa, about 930 MPa, about 940 MPa, about 950 MPa, about 960 MPa, about 970 MPa, about 980 MPa, about 990 MPa, about 1,000 MPa, about 1,100 MPa, or about 1,200 MPa. The 0.2% offset yield strength may be measured according to ASTM E8.

The alloys may have a tensile strength of 1,100 MPa to 1,400 MPa, 1,150 MPa to 1,350 MPa, 1,300 MPa to 1,400 MPa, 1,330 MPa to 1,380 MPa, or 1,330 MPa to 1,370 MPa. The alloys may have a tensile strength of at least 1,100 MPa, at least 1,150 MPa, at least 1,200 MPa, at least 1,250 MPa, at least 1,300 MPa, at least 1,350 MPa, or at least 1,400 MPa. The alloys may have a tensile strength of about 1,100 MPa, about 1,150 MPa, about 1,200 MPa, about 1,250 MPa, about 1,300 MPa, about 1,350 MPa, or about 1,400 MPa. The alloys may have a tensile strength of 1,330 MPa, 1,331 MPa, 1,332 MPa, 1,333 MPa, 1,334 MPa, 1,335 MPa, 1,336 MPa, 1,337 MPa, 1,338 MPa, 1,339 MPa, 1,340 MPa, 1,341 MPa, 1,342 MPa, 1,343 MPa, 1,344 MPa, 1,345 MPa, 1,346 MPa, 1,347 MPa, 1,348 MPa, 1,349 MPa, 1,350 MPa, 1,351 MPa, 1,352 MPa, 1,353 MPa, 1,354 MPa, 1,355 MPa, 1,356 MPa, 1,357 MPa, 1,358 MPa, 1,359 MPa, 1,360 MPa, 1,361 MPa, 1,362 MPa, 1,363 MPa, 1,364 MPa, 1,365 MPa, 1,366 MPa, 1,367 MPa, 1,368 MPa, 1,369 MPa, 1,370 MPa, 1,371 MPa, 1,372 MPa, 1,373 MPa, 1,374 MPa, 1,375 MPa, 1,376 MPa, 1,377 MPa, 1,378 MPa, 1,379 MPa, 1,380 MPa, 1,381 MPa, 1,382 MPa, 1,383 MPa, 1,384 MPa, 1,385 MPa, 1,386 MPa, 1,387 MPa, 1,388 MPa, 1,389 MPa, 1,390 MPa, 1,391 MPa, 1,392 MPa, 1,393 MPa, 1,394 MPa, 1,395 MPa, 1,396 MPa, 1,397 MPa, 1,398 MPa, 1,399 MPa, or 1,400 MPa. The tensile strength may be measured according to ASTM E8.

The alloys may have an elongation of 1% to 50%, 5% to 40%, or 10% to 40%. The alloys may have an elongation of at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50%. The alloys may have an elongation of about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, or about 50%. The elongation may be measured according to ASTM E8.

The alloys may have a hardness of 35 to 38 (HRC). The alloys may have a hardness of at least 36, at least 37, or at least 38 (HRC). The alloys may have a hardness of about 36, about 37, or about 38 (HRC). The hardness may be measured according to ASTM E1842.

The alloys may have a density of 0.290 lb/in³to 0.300 lb/in³. The alloys may have a density of 0.290 lb/in³, 0.291 lb/in³, 0.292 lb/in³, 0.293 lb/in³, 0.294 lb/in³, 0.295 lb/in³, 0.296 lb/in³, 0.297 lb/in³, 0.298 lb/in³, 0.299 lb/in³, or 0.300 lb/in³. The density may be measured using standard methods.

To select compositions with a suitable microstructure, solidification paths and thermodynamic equilibria at various temperatures can be calculated with thermodynamics calculation packages such as ThermoCalc® software version N offered by Thermo-Calc Software AB of Sweden and a cobalt-based database that QuesTek Innovations LLC developed based on open-literature data.

Example 1
Alloy B86

A melt was prepared with the nominal composition in weight percentage of 18% Cr, 5.9% Ti, 4% Fe, 1.8% V, 1% Ni, and the balance Co and incidental elements and impurities. As described above, this example alloy includes a variance in the constituents in the range of plus or minus ten percent of the mean (nominal) value. The alloy in this example was arc-melted as a button. For some applications, the alloy can be prepared by casting (e.g., investment casting) or powder metallurgy methods. The as-melted button was subjected to a homogenization and solution heat treatment at about 1060° C., and tempered at about 850° C. As illustrated in FIG. 2, alloy B86 tempered at about 850° C. for about 8 hours shows annealing twins 10, indicative of an FCC matrix with low stacking-fault energy. The sample tempered at about 850° C. for about 8 hours is substantially devoid of discontinuous grain boundary reactions, cellular growth reactions, or unusual particles at the grain boundaries 20. As illustrated in FIG. 3, the sample tempered at about 850° C. for about 24 hours also is substantially devoid of discontinuous grain boundary reactions, cellular growth reactions, or unusual particles at the grain boundaries 20. Referring also to FIG. 4, scanning electron microscopy shows the annealing twins 10 for a sample tempered at about 850° C. for about 24 hours, at a higher magnification compared to FIG. 2. Referring also to FIG. 5, the sample tempered at about 850° C. for about 24 hours shows precipitates 30 that are about 100 nm or less in diameter. The nano-scale particles 30 are regularly shaped and aligned, indicative of being coherent with the matrix.

Referring to FIG. 6, the Vickers hardness number of alloy B86 increases from about 310 in the homogenized state to about 377 following tempering for about 24 hours at about 850° C. As shown in the following Table I, these hardness values are estimated to correlate to about 970 and about 1240 MPa in ultimate tensile strength (UTS) at room temperature, respectively, which is a significant improvement over known alloys like the Stellite alloys or ACUBE in the non-worked condition. For example, cast Stellite 21 may achieve about 710 MPa in UTS; powder metallurgy Stellite 21 may achieve about 1000 MPa in UTS; cast Stellite 25 is fractured-limited due to low ductility and therefore UTS is not reported; L605 (with the nominal composition in weight percentage of 10% Ni, 20% Cr, 15% W, 1.5% Mn, 0.33% C, 3% Fe, 0.4% Si, and the balance Co and incidental elements and impurities) is a common modification of Stellite 25 for wrought products with higher ductility and the UTS is 862 MPa at room temperature. It is contemplated that the strength of alloy B86 could be further increased through optional cold working.

TABLE I

Estimated

Measured
Ultimate Tensile

hardness (VHN)
Strength (MPa)

Homogenized
310 ± 14.5
970

8 hr Temper at 850° C.
357 ± 11.3

24 hr Temper at 850° C.
377 ± 4.5
1240

Example 2
Alloy 1A

A melt was prepared with a measured composition in weight percentage of 17.5% Cr, 7.7% Fe, 5.2% Ti, 2.6% Ni, 2.2% V, and the balance Co and incidental elements and impurities. This example alloy includes a variance in the constituents in the range of up to plus or minus two weight percents. The alloy was vacuum-induction-melted and vacuum-arc-remelted to a cylindrical billet measuring about 10.2 cm in diameter and weighing about 13.6 kg. The as-cast billet was subjected to a homogenization at about 1025° C. for 72 hours and solution heat treatment at about 1025° C. for 2 hours. An outer layer of the billet was removed, resulting in a round bar measuring about 8.9 cm in diameter. The round bar was hot-rolled at Special Metals, Huntington, WV. The hot rolling was performed at about 1000° C. for a reduction ratio of about eight to one, resulting in a round-cornered square bar measuring about 3.2 cm in one edge. Specimens were excised from the hot-rolled bar and subjected to a sub-solvus heat treatment and an aging heat treatment at 780° C. for 24 hours.

As listed in the following Table II, the aged alloy 1A shows a UTS comparable to a copper-beryllium alloy according to aerospace material specifications (AMS) 4533, at a much higher elongation compared. The wear resistance of the aged alloy 1A is significantly improved compared to the Cu—Be alloy, as demonstrated by lower coefficients of friction, volume loss, and wear rate.

TABLE II

Cu—Be alloy

Material Property
Alloy 1A
(AMS 4533)

Compressive Yield Strength (MPa)
830
1160

Tensile Yield Strength (MPa)
820
1140

Tensile UTS (MPa)
1340
1260

Elongation (%)
40
5.4

Coefficient of
Pin-On-Disk
0.240
0.647

Friction
Wear

Reciprocating
0.511
0.785

Wear

Volume Loss
Pin-On-Disk
0.046
0.925

(mm³)
Wear

Reciprocating
0.095
0.512

Wear

Wear Rate
Pin-On-Disk
13.73
277.00

(10⁻⁵mm³/m)
Wear

Reciprocating
28.60
153.91

Wear

Example 3
Alloy 3A

A melt was prepared with a measured composition in weight percentage of 16.6% Cr, 7.1% Fe, 6.3% Ti, 2.7% Ni, 2.0% V, and the balance Co and incidental elements and impurities. As shown in FIG. 7, the alloy was melted by Vacuum Induction Melting (VIM) at the 500 lb scale, and cast into four (4) 4-inch round by ˜40-inch long bars. These bars were welded together into a single electrode, and Vacuum Arc Remelted (VAR) into a single 6-inch round by ˜45-inch long ingot. Chemistry analysis was completed on both VIM and VAR ingots. Following production of the VIM/VAR ingot, the ingot was homogenized at 1050° C. for 96 hours. The forged product was heat treated via the following schedule: solution heat treatment at 1050° C. for 2 hours+a water quench; followed by aging (within 4 hours of quenching) at 780° C. for 72 hours+air cool. Table III shows the target and measured values (VIM and VAR) for alloy 3A.

TABLE III

Target
VIM
VAR

Element
(Min-Max)
Chemistry
Chemistry

Cr
16.6
16.69
16.5

(16.1-17.1)

Fe
7.1
7.15
7.1

(6.9-7.3)

Ti
6.3
6.14
6.2

(6.1-6.5)

Ni
2.7
2.75
2.8

(2.5-2.9)

V
2.0
2.02
2.0

(1.9-2.1)

Co + incidental
balance
balance
balance

elements and

impurities

The higher titanium level, as compared to alloy 1A, leads to a higher predicted volume fraction of strengthening precipitates (FIG. 8), and thus higher hardnesses (FIG. 9) and strengths (yield strength—Table V) in alloy 3A.

FIG. 10a and FIG. 10b show optical micrographs of rotary forged alloy 3A, 2.1-inch product, at different magnifications. The products were etched in a solution of 5 ml H₂O₂+100 mL HCl. The longitudinal direction of the bar is oriented vertically in each micrograph. The micrographs show no evidence of cellular precipitate growth at the grain boundaries, or of any hexagonal close-packed phase transformations in the matrix.

Table IV provides the final tensile properties of alloy 1A. Table V provides the final tensile properties of alloy 3A. Alloy 3A shows improved yield strength relative to alloy 1A.

TABLE IV

0.2%

Compressive
Offset

Reduction

Yield Strength
Yield
Tensile
Elongation
in Area
Hardness
Density

(ksi)
Strength
Strength
(%)
(%)
(HRC)
(lb/in³)

Alloy
119.8
119 ksi
194 ksi
40
—
36
0.296

1A

(820 MPa)
(1337 MPa)

TABLE V*

0.2% Offset

Reduction

Young's

Yield
Tensile
Elongation
in Area
Hardness
Density
Modulus

Strength
Strength
(%)
(%)
(HRC)
(lb/in³)
(Mpsi)

Alloy
126.1 ksi
199.0 ksi
32.9
27.9
37.7
0.297
36.1

3A
(869 MPa)
(1372 MPa)

*Eight specimens were evaluated; mean values are provided in Table V;

ksi = kips per square inch;

MPa = megapascal;

lb/in³= pounds per cubic inch;

Mpsi = mega pounds per square inch.

It is understood that the disclosure may embody other specific forms without departing from the spirit or central characteristics thereof The disclosure of aspects and embodiments, therefore, are to be considered as illustrative and not restrictive. While specific embodiments have been illustrated and described, other modifications may be made without significantly departing from the spirit of the invention. Unless noted otherwise, all percentages listed herein are weight percentages.

COBALT ALLOYS

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