Single-phase nickel alloy for additive manufacturing

Abstract

Provided is a nickel-based alloy comprising, in weight%, the following parts and as a remainder Ni: Fe: 17.0 to 20.0, Cr: 18.5 to 23.0, W: 0.5 to 1.0, C: 0.005 to 0.025, B: 0.001 to 0.009, Zr: 0.0005 to 0.01, and Si: 0.02 to 0.3, Mo: 8.0 to 10.0, Co: 1.0 to 2.0, and conditionally Al: up to 0.15, Ti: up to 0.15, Hf: up to 0.005, Ta: up to 0.005, Nb: up to 0.005, V: up to 0.006, Y: up to 0.003, Sc: up to 0.001, Zn: up to 0.001, Mg: up to 0.010, Na: up to 0.004, Pb: up to 0.0005, Sn: up to 0.003, and unavoidable impurities. Further, related powder materials, related additive manufacturing methods and assemblies are provided, which may be manufactured according to the methods shown.

Description

[0001] The present invention relates to nickel-based alloys for additive manufacturing, which are particularly suitable for powder bed-based manufacturing methods. In addition, a related powdered substrate, an additive manufacturing method, and a component manufactured by or manufacturable by the method shown are provided.

[0002] Preferably, the component represents a component of a turbine, such as a component applied in the flow path hardware of a gas turbine, such as a seal component or a liner component. Therefore, the component is preferably made of a related superalloy. In an alternative, the component may belong to high-performance components, such as components applied in the power generation, aviation, or automotive industries.

[0003] Additive Manufacturing (AM) or three-dimensional (3D) printing is a promising manufacturing technology that enables the production of complex structures and objects that cannot be easily achieved via conventional manufacturing processes. In many additive manufacturing technologies, especially laser powder bed fusion (L-PBF), the powder is subjected to melting and then rapid solidification. The solidification can occur at a temperature gradient and / or even at a cooling rate of 10 4 K / s to 10 6 K / s.

[0004] There is a continuous need in the industry to find new materials for additive manufacturing and new components and / or solutions that can be realized, for example, via industrial manufacturing devices. In addition, AM stands out due to its short process step chain, which enables material savings and particularly short delivery times.

[0005] Additive manufacturing generally includes powder bed fusion methods, such as selective laser melting (SLM) or laser powder bed fusion (L-PBF), selective laser sintering (SLS), and electron beam melting (EBM). The related machine hardware or devices for such methods typically include a manufacturing or building platform on which, after feeding a layer of substrate (the substrate can then be melted and subsequently solidified, for example, by an energy beam such as a laser), the component is built layer by layer. The layer thickness is determined by a recoater that, for example, automatically moves above the powder bed and removes excess material from the manufacturing plane or building space.

[0006] In addition, additive manufacturing methods involve "Directed Energy Deposition (DED)", such as laser cladding, electron beam welding or plasma welding, metal inkjet molding (MIM), so-called sheet lamination methods, or even thermal spraying (VPS, LPPS) methods.

[0007] Accordingly, the present invention may relate to Ni-based alloys and associated metal powders for additive manufacturing, and / or to the use of such metal powders for additive manufacturing, and to a method for producing a target component by AM.

[0008] In particular, the known Hastelloy X is a rather weldable class of single-phase nickel superalloys. Hastelloy X (HX) (single-phase austenitic (solution-strengthened) nickel-based superalloy) is actually one of the most promising Ni superalloy powders for additive L-PBF processing.

[0009] This alloy can be used to manufacture components such as gas turbine engines, combustion chamber components, and high-temperature gas-cooled reactors. Accordingly, the properties of interest for use of HX at high temperatures and exposure to non-protective atmospheres include tensile strength, high-temperature low-cycle fatigue, creep durability, creep-rupture, creep-fatigue interaction, subcritical crack growth, thermal stability, and oxidation resistance.

[0010] The as-built (AB) microstructure achieved by L-PBF is, for example, different from the microstructure of conventional (forged) counterparts. Similar to most single-phase alloys with an FCC (face-centered cubic) structure, the grain morphology in the AB condition is columnar. The microstructure includes a cellular and / or dendritic solidification structure caused by relatively large constitutional supercooling, where alloying elements are micro-segregated to the cell boundaries due to rapid solidification (see above).

[0011] These features may affect both the static and dynamic properties at room temperature and high temperatures. The special microstructure features associated with L-PBF processing can be homogenized by a high-temperature (solution) annealing treatment, for example, by a diffusion-controlled reaction. The high-temperature properties, especially creep resistance, can be enhanced by microstructure homogenization, in particular by removing unwanted phases in the micro-segregation regions, thereby changing the grain morphology and promoting grain size increase by recrystallization and grain growth.

[0012] However, considering cost efficiency, directly utilizing the as-built microstructure of (single-phase) superalloys adds special value to the AM process chain, as the structural advantages can be directly utilized, and this is directly related to significant progress in process reproducibility and reliability.

[0013] Accordingly, an object of the present invention is to provide improved alloys, powdered alloys and manufacturing methods in the material categories shown. A particular object of the present invention is to provide a modification of the known "Hastelloy X" composition having an improved characteristic curve thermomechanical behavior in high-temperature applications. Such improved alloys may involve modifications to the chemical composition of Hastelloy X, which are in powder form and suitable for AM, particularly suitable for generative manufacturing, hybrid manufacturing such as additionally building structures on a prefabricated substrate, and / or repair methods for turbine components.

[0014] The object mentioned is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0015] One aspect of the present invention relates to a nickel-based alloy, which comprises the following parts by weight and Ni as the balance: 17.0 to 20.0 iron (Fe), 18.5 to 23.0 chromium (Cr), 0.5 to 1.0 tungsten (W), 0.005 to 0.025 carbon (C), 0.001 to 0.009 boron (B), 0.0005 to 0.01 zirconium (Zr), 0.02 to 0.3 silicon (Si), 8.0 to 10.0 molybdenum (Mo), 1.0 to 2.0 cobalt (Co), and conditionally, i.e., if due to the production route, for example, through fluidization, it is inevitable or coincidental or inherently present: up to 0.15 aluminum (Al), up to 0.15 titanium (Ti), up to 0.005 hafnium (Hf), up to 0.005 tantalum (Ta), up to 0.005 niobium (Nb), up to 0.006 vanadium (V), up to 0.003 yttrium (Y), up to 0.001 scandium (Sc), up to 0.001 zinc (Zn), up to 0.010 magnesium (Mg), up to 0.004 sodium (Na), up to 0.0005 lead (Pb), up to 0.003 tin (Sn), and possible inevitable impurities, and the possible inevitable impurities may (if any) include sulfur (S), phosphorus (P), nitrogen (N) and oxygen (O).

[0016] The chemical properties of such alloy compositions are particularly outstanding in terms of significantly improved creep (stress-rupture) performance under as-built (as-manufactured) conditions. In addition, for example, due to the avoidance of high-temperature solution and homogenization and grain growth of additively manufactured products, the manufacturing complexity of the manufacturing method is significantly reduced and possible structural deformations and dimensional changes are minimized, which otherwise may require further treatment by high-temperature heat treatment.

[0017] In one embodiment, the alloy contains C in the range of 0.010 to 0.020 (further specifying the above carbon range). As will be further described in the exemplary embodiments below, this specified carbon range confers particular advantages in terms of, for example, the creep strength, fatigue behavior, and / or susceptibility to solidification cracking of the alloy.

[0018] In one embodiment, the alloy contains Si in the range of 0.02 to 0.25 (further specifying the above silicon range). As will be further described below, this specified silicon range also confers particular advantages in terms of, for example, the creep strength, fatigue behavior, and / or susceptibility to solidification cracking of the alloy.

[0019] In one embodiment, the alloy contains Cr in the range of 20.5 to 23.0 (further specifying the above chromium range). As will be further described below, this specified chromium range also confers particular advantages in terms of, for example, the creep strength, fatigue behavior, and / or susceptibility to solidification cracking of the alloy.

[0020] In one embodiment, the alloy contains B in the range of 0.002 to 0.005 (further specifying the above boron range). As will be further described below, this specified boron range also confers particular advantages in terms of, for example, the creep strength and / or susceptibility to solidification cracking of the alloy. More particularly, this boron content defines an optimal level or trade-off of said properties. As described below, boron advantageously inhibits carbide formation at grain boundaries, thereby effectively delaying the onset of fatigue behavior (such as fracture time).

[0021] In one embodiment, the alloy contains Zr in the range of 0.0005 to 0.004 (further specifying the above zirconium range). As will be further described below, this specified zirconium range also confers particular advantages in terms of, for example, the creep strength, fatigue behavior, and / or susceptibility to solidification cracking of the alloy.

[0022] In one embodiment, as inevitable impurities, the alloy contains in particular up to 0.025 wt% of oxygen and / or up to 0.005 of nitrogen, since trace amounts of these elements are generally inevitable but not harmful in the gas atomization practice of powders and / or alloy materials.

[0023] In one embodiment, the nickel-based alloy contains elements according to the relationship C + B + Zr + Hf < 0.04 in wt%. This embodiment is particularly advantageous because the total share of at least C, B, and Zr in the alloy composition should be controlled or limited accordingly. In contrast, an increased solidification range (see below) and / or an increased concentration of these elements may disadvantageously result in a greater susceptibility to solidification cracking during laser-based AM processing.

[0024] In one embodiment, the nickel-based alloy contains elements according to the relationship Al + Ti + Hf + Nb + Ta + Zr < 0.15 in wt%. This specified absolute relationship of the shown elements reasonably defines an upper limit in terms of, for example, the creep strength, fatigue behavior, and / or susceptibility to solidification cracking of the alloy.

[0025] In one embodiment, the nickel-based alloy is a single-phase alloy. According to this embodiment, it should be understood that although the alloy of the present invention is complex in composition, it remains simple in structure, for example, without precipitates.

[0026] Another aspect of the present invention relates to a powder material of the described alloy, preferably for additive manufacturing of components.

[0027] Another aspect of the present invention relates to additive manufacturing of components from a powdered base material of the alloy, wherein the method is preferably a powder bed fusion or laser metal deposition method.

[0028] In one embodiment, the method is a repair and / or hybrid manufacturing method. In the latter case, the method may include additive building on a pre-existing or pre-fabricated component such as a substrate or support.

[0029] Another aspect of the present invention relates to a component including a structure manufactured by or manufacturable by the described method, wherein the structure further includes, for example, a V-shaped texture pattern.

[0030] The advantages and embodiments related to the described alloy and / or the described powder material are equally valid or equally applicable to the described method and / or the described component, and vice versa.

[0031] Furthermore, features and advantageous embodiments become apparent from the following description of exemplary embodiments in conjunction with the accompanying drawings.

[0032] Figure 1 a and Figure 1 b each show scanning electron microscopy (SEM) images of the as-manufactured (as-built) alloy microstructure at different resolutions.

[0033] Figure 2 The results of stress-rupture tests of related conventional alloys are also shown in the SEM photographs.

[0034] Figure 3 The mobility (diffusion coefficient) of boron relative to carbon in the FCC nickel matrix is shown in the context of the present invention.

[0035] Figure 4 The equilibrium phase diagram of Hastelloy-X type material in FCC structure is shown, where the mass percentage of boron is plotted on the vertical axis.

[0036] Figure 5 The "Scheil" solidification ranges are shown in the table (right column) for different percentages of carbon (upper left column) and boron (lower left).

[0037] Figure 6 The linear relationship of rupture time plotted against boron content in ppm (parts per million) on the ordinate is shown in the form of an Arrhenius-type equation.

[0038] Figure 7 Results of the creep ductility (elongation) of the structure in percentage as a function of boron content in ppm are shown.

[0039] In the figures, similar, same-kind, and same-acting elements may have the same reference numerals. These figures are not necessarily drawn to true scale but may be enlarged or reduced to permit a better understanding of the principles shown. Rather, the figures described should be interpreted in a broad sense and as a qualitative basis, which permits those skilled in the art to apply the teachings provided in various ways.

[0040] As used herein, the term "and / or" shall mean that each of the listed elements may be used alone or in combination with two or more of the other listed elements.

[0041] Figure 1 a shows a cut sample from a single-phase austenitic alloy, e.g., an SEM micrograph from the chemical composition of Hastelloy X. The microstructure belongs to the as-built microstructure from the L-PBF additive manufacturing method. It has been shown that the grain morphology at the weld beads (see melt pools) overlaps and is similar to a special v-shaped or v-shaped-like shape. This is Figure 1 a particularly represented by a V-shaped line oriented at a 45° angle with respect to the build direction (BD), which points upward in the image. The transverse direction TD is also indicated as pointing in a direction perpendicular to the BD.

[0042] By observing Figure 1 the SEM photograph at an amplified resolution of b, the v-shaped-like texture pattern P becomes even more evident. The v-shaped or V-shaped morphology can be explained by the continuous competition between epitaxial growth along the heat dissipation direction HD (highlighted by a thin dashed line in Figure 1 a) and heterogeneous nucleation along or with the thermal gradient pointing towards the center of each melt pool or the v-shaped pattern. These patterns P evolve particularly in the overlapping zones of remelting, which ultimately leads to small and periodic angular offsets of the crystal lattice of grains with a high dislocation density.

[0043] Figure 2The fracture crack propagation path is shown by the black areas in the SEM images, indicating how cracks form at the V-shaped grain boundaries. At least when diffusion creep is dominant, the V-shaped grains can actually control the fracture mechanism and result in a shorter creep life of the structure. The structural growth and connection of micropores nucleated at the location of the precipitates, especially the grain boundary carbides, are accompanied by the connection of microcracks along the "V-shaped" grain boundaries. In a given material class, this is a special feature of the L-PBF process and shows an orientation of approximately 45° with respect to the stress rupture load direction (i.e., the plane with the maximum resolved shear stress) before the final failure of the relevant structure.

[0044] Starting from Figure 3 there is provided an (improved) alloy composition according to the invention, for example an improved powdered alloy for additive manufacturing routes such as laser metal deposition or L-PBF, which is used for generation or repair applications.

[0045] The provided nickel-based alloy contains the following parts in weight % and Ni as the balance: 17.0 to 20.0 of Fe, 18.5 to 23.0 of chromium Cr, 0.5 to 1.0 of W, 0.005 to 0.025 of C, 0.001 to 0.009 of boron B, 0.0005 to 0.01 of zirconium Zr, 0.02 to 0.3 of silicon Si, 8.0 to 10.0 of molybdenum Mo, 1.0 to 2.0 of cobalt Co, and conditionally or if present, for example, unavoidably or coincidentally or inherently due to the production route: up to 0.15 of Al, up to 0.15 of Ti, up to 0.005 of Hf, up to 0.005 of Ta, up to 0.005 of Nb, up to 0.006 of V, up to 0.003 of Y, up to 0.001 of Sc, up to 0.001 of Zn, up to 0.010 of Mg, up to 0.004 of Na, up to 0.0005 of Pb, up to 0.003 of Sn, and possible unavoidable impurities, which may include S, P, N, and / or O.

[0046] As a particular advantage of the invention, the carbide formation at the grain boundaries is suppressed due to the given composition. Therefore, the micropore formation may also be delayed in time (e.g., during the life of a component made of the alloy according to the invention). This is particularly attributed to the addition of B and Zr as alloying elements to the indicated composition within defined ranges.

[0047] By varying the boron in the chemical composition, during the high-temperature loading of the relevant structure, the delay in the formation of said pores occurs and the development of carbides at the grain interfaces is prevented. This significantly increases the creep resistance because boron, which is highly soluble (see Figure 3)It diffuses to the grain boundaries and occupies the carbon positions or prevents carbon from diffusing to the grain boundaries. That is, carbon diffusion is inhibited. Therefore, the life of the relevant components can be significantly increased and the fracture time tr can be reduced.

[0048] This can be explained by the fact that boron has a higher mobility relative to carbon in the (FCC) Ni crystal, causing B to diffuse to the grain boundaries faster, as Figure 3 shown. In addition, in order to reduce impurity segregation at the grain boundaries, Zr is added in a smaller fraction. In addition, zirconium is introduced as an alloying element to achieve sulfur scavenging.

[0049] In an even more preferred composition, the provided alloy contains carbon, silicon, chromium, boron, and zirconium (instead of the ranges shown above) in weight percent: 0.010 to 0.020 C, 0.02 to 0.25 Si, 20.5 to 23.0 Cr, 0.002 to 0.005 B, 0.0005 to 0.004 Zr, and optional or inevitable impurities, such as up to 0.025 O and up to 0.005 N.

[0050] In this context, a reliable limit for C is up to 0.025 wt% at 0.005 wt% of B.

[0051] A rather conservative and possibly even more favorable limit for C is up to 0.020 wt% at 0.005 wt% of B.

[0052] The provided nickel-based alloy may also contain elements according to the relationship (in weight percent): C + B + Zr + Hf < 0.04.

[0053] At least the elements C, B, and Zr generally increase the solidification range. However, in laser-based AM processing, an increase in the concentration of these elements may unfavorably lead to solidification cracking susceptibility. Therefore, their overall percentage in the alloy composition should be limited.

[0054] Regarding boron, the maximum solubility limit of this element in a given nickel matrix at high temperature is thus preferably about 0.005 in weight percent (see Figure 4 ).

[0055] Figure 4 The equilibrium phase diagram of the standard composition of (FCC) Hastelloy X is clearly shown, where only the boron content is plotted on the ordinate. The point at 50 ppm (equal to 0.005 weight percent (wt%)) is a reasonable upper limit.

[0056] Regarding the above-mentioned role of boron, for suppressing carbide formation, B is beneficial for increasing the creep strength. However, adding boron in an amount greater than the stated limit results in the formation of detrimental borides. Due to the rapid solidification rate of laser-based AM, the amount of B should be limited to a supersaturated FCC matrix. This particularly allows for the faster diffusion of boron to grain boundaries (compared to carbon) during the high-temperature operation of relevant components. Therefore, in practice, a maximum amount of not greater than approximately 0.005 wt% B is recommended.

[0057] Regarding carbon, as already outlined above, in the presence of 0.005 wt% B, a maximum amount or optimal level of 0.02 wt% still ensures a reduced solidification range compared to conventional Hastelloy X (containing, for example, 0.05 wt% to 0.10 wt% carbon).

[0058] The alloy composition of the present invention further comprises elements in the following relationship or close to the following relationship by weight percent: Al + Ti + Hf + Nb + Ta + Zr < 0.15.

[0059] Figure 5 shows the "Scheil" solidification temperature ranges (in °C) for different carbon and boron fractions (left column). In the upper left column, the carbon fraction is shown at a fixed boron content of 0.003 wt%. In the lower left column, on the other hand, the boron fraction is shown at a fixed carbon content of 0.02 wt%. The right column then lists the said solidification ranges of Scheil under the assumption of allowing the formation of a so-called second phase from the remaining liquid.

[0060] The assumptions from the "Scheil" equation are particularly suitable for simulating the situation in L-PBF AM regarding its inherently large temperature gradients.

[0061] The rather short "Scheil" range can qualitatively indicate that the (solidification) cracking risk is comparably small, because the smaller solidification temperature (range) enables the relevant alloy to better accommodate microcracks, while a larger range indicates an increased likelihood of cracking (i.e., cracks between the already solidified structural dendrites and the remaining (interdendritic) liquid during solidification).

[0062] In Figure 5 a specific range of 120 °C is prominently marked, indicating a threshold within the context of the present invention below which the solidification cracking risk can remain rather low or tolerable.

[0063] Adding Zr to, for example, 100 ppm may not significantly change the solidification range. However, an increasing Zr content or an excessive Zr content will lead to the formation of detrimental grain boundary ZrC at high temperatures.

[0064] As found in the literature, in the solution annealed state (under the same test conditions as those carried out during the testing of the alloys of the present invention), the rupture time (tr) of the commercial (forged) alloys is from 110 to 160 hours, while the manufacturer's data sheet indicates that the expected rupture time tr is about 100 hours. In contrast, with a gradually significant increase in creep ductility, the composition of the present invention advantageously causes a rupture time of up to about 500 hours.

[0065] In Figure 6 , for tr at 816 °C at each B level is presented in the form of the Arrhenius equation (i.e., log(tr) versus B weight % in ppm). Clearly, a linear correlation between B weight % and tr was found. In other words, a slight increase in boron in the alloy results in a significant increase in the rupture time tr.

[0066] This indicates that under high temperature conditions (see 816 °C, 103 MPa thermo-mechanical loading) and for the boron contents studied in this case, the delay of the rupture time tr is driven by the diffusion control mechanism as described above. According to additional modeling perspectives, by incorporating 0.004 wt% of B, tr could be even further increased up to 650 to 700 hours.

[0067] In a similar manner as shown in Figure 6 , Figure 7 further shows the creep ductility parameters tested as a function of boron content. Clearly, within the given range, the creep ductility increases almost linearly with the boron content as well.

[0068] The alloys and / or components as mentioned herein may particularly relate to components or articles of complex shape, such as components or articles having a structured wire section. Preferably, the component may form part of a steam turbine component or a gas turbine component, such as blades, vanes, shrouds, shields such as thermal shields, tips, segments, inserts, injectors, seals, transition pieces, burners, nozzles, filters, orifices, liners, distributors, domes, boosters, cones, spray guns, plates, resonators, pistons or any corresponding retrofit kits. Alternatively, the component may relate to additional or similar components.

Claims

1. A nickel-based alloy comprising the following parts by weight % and the balance being Ni: Fe: 17.0 to 20.0, Cr: 18.5 to 23.0, W: 0.5 to 1.0, C: 0.005 to 0.025, B: 0.001 to 0.009, Zr: 0.0005 to 0.01, Si: 0.02 to 0.3, Mo: 8.0 to 10.0, Co: 1.0 to 2.0, and optionally, Al: up to 0.15, Ti: up to 0.15, Hf: up to 0.005, Ta: up to 0.005, Nb: up to 0.005, V: up to 0.006, Y: up to 0.003, Sc: up to 0.001, Zn: up to 0.001, Mg: up to 0.010, Na: up to 0.004, Pb: up to 0.0005, Sn: up to 0.003, and unavoidable impurities.

2. The nickel-based alloy according to claim 1, comprising, by weight %, C: 0.010 to 0.020, Si: 0.02 to 0.25, Cr: 20.5 to 23.0, Mo: 8.0 to 10.0, Co: 1.0 to 2.0, W: 0.5 to 1.0, Fe: 17.0 to 20.0, B: 0.002 to 0.005, Zr: 0.0005 to 0.004, and optionally, Al: up to 0.15, Ti: up to 0.15, Hf: up to 0.005, Ta: up to 0.005, Nb: up to 0.005, V: up to 0.006, Y: up to 0.003, Sc: up to 0.001, Zn: up to 0.001, Mg: up to 0.010, Na: up to 0.004, Pb: up to 0.0005, Sn: up to 0.003, unavoidable impurities, in particular O: up to 0.025, and N up to 0.

005.

3. The nickel-based alloy according to claim 1 or 2, comprising elements according to the following relationship by weight %: C + B + Zr + Hf < 0.

04.

4. The nickel-based alloy according to claim 1 or 2, comprising elements according to the following relationship by weight %: Al + Ti + Hf + Nb + Ta + Zr < 0.

15.

5. The nickel-based alloy according to one of the preceding claims, the nickel-based alloy being a single-phase alloy.

6. A powder material of an alloy according to one of the preceding claims for additive manufacturing of a component.

7. A method for additive manufacturing a component from a powdered alloy substrate according to one of the preceding claims, the method being powder bed fusion or laser metal deposition.

8. The method according to claim 7, the method being a repair and / or hybrid manufacturing method.

9. A component comprising a structure manufactured by the method according to claim 7 or 8.

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