Improved h230 additive manufactured products and process therefor

Abstract

An H230 nickel-based alloy powder object having improved tensile and elongation strength due to fine carbide particles in the grain and grain boundary is obtained through additive manufacturing using rapid cooling of the powder layers which are melted and solidified into an underlying layer to produce a precursor which can then be heat treated without quenching to produce the final object.

Description

IMPROVED H230 ADDITIVE MANUFACTURED PRODUCTS AND PROCESS THEREFORCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a Completion Application of co-pending U.S. Provisional Application, Serial No. 63 / 636,924, filed on April 22, 2024, for “Improved H230 Additive Manufactured Products and Process Therefor,” the disclosure of which is hereby incorporated by reference in its entirety, including the drawings.PRIOR ART

[0002] As is known to those skilled in the art to which the present invention pertains in 1978 during the “cobalt crisis,” Haynes 230 alloy powder (H230) was developed. H230 powder is a nickel-based solid solution strengthened super alloy, which includes chromium, molybdenum, tungsten and other adjuvants. Objects fabricated from this powder are superior in high temperature mechanical strength and corrosion resistance. The wrought alloy maintains reasonable strength up to temperatures exceeding 1093 °C. However, in a traditional mill process for wrought alloy manufacturing, large size carbides particles or dispersoids are formed and often agglomerate which become detrimental clusters. These carbides are too large in size to be considered an effective strengthening factor. However, these excessively large carbides can potentially be the source of significant strengthening mechanisms if they can be broken up into fine carbides and distributed uniformly in an object to be manufactured.

[0003] It is this, as well as the enhancement of H230 powder, to which the present invention is directed.SUMMARY OF THE INVENTION

[0004] In a first aspect hereof, an improved solid solution H230 alloy powder product having a high-volume fraction of dispersed fine carbides is formed by solid solution strengthening along with Carbide Dispersion Strengthening (CDS) by additive manufacturing or 3D printing an H230 precursor product using rapid cooling. The rapid cooling of the powder layers as they are deposited and then melted and solidified into the preceding or underlying layers enables production of useful precursors or matrices without quenching. The so-obtained precursors or matrices are then heat treated to obtain the desired strengthened products.

[0005] The present invention, in a further aspect, provides for oxide dispersion strengthening (ODS), as well.

[0006] For a more complete understanding of the present invention, reference is made to the following detailed description and accompanying drawing in which:BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a photograph of both large and grain boundary carbides in wrought H230;

[0008] FIG. 2 is a photograph showing ultra fine carbides evenly distributed in an additive manufactured H230 object in accordance herewith;

[0009] FIG. 3 is a table showing an H230 tensile properties comparison of wrought versus additive manufactured H230 product at room temperature, 760°C and 982°C.

[0010] FIGS. 4(a) and (b), respectively, depict optical images of wrought plate (0.75”) and bar stock (0.5”) showing the effects of thermal mechanical working on microstructures and carbide distribution;

[0011] FIGS. 5A, (a) and (b), respectively, are optical images (2,000x) of LPBF AM H230 objects manufactured according hereto in a vertical build orientation and a horizontal build orientation showing the fine carbide particle distribution at 982°C;

[0012] FIGS. 5B (a) and (b), respectively, are optical images of a vertical orientation and horizontal orientation showing both fine grain carbide distribution and larger grain boundaries at 1177° C manufactured according hereto;

[0013] FIG. 6 is a graph of yield strength versus temperature between an H230 printed object hereof and other tungsten super alloy manufactured objects.DETAILED DESCRIPTION OF THE INVENTION

[0014] When a liquid is supercooled below its melting temperature, crystallization sets in, and a supercritical epitaxial growth occurs. This can be realized by metal additive manufacturing using laser powder bed fusion (LPBF). In using LPBF, small powder volumes are successively rendered molten. The volumes fuse together and immediately solidify at extremely high cooling rates because the heat is mainly extracted through the adjacent underlying bulk material.

[0015] Applying this principal and in accordance with a first aspect hereof, there is provided a method for additive manufacturing H230-based alloy powder products having improved tensile strength and elongation. As is well known, H230 alloy powder is a commercially available nickel -based powder which also contains amounts of tungsten, chromium and molybdenum as well as other metals.

[0016] The present method for producing H230 objects generally comprises:(a) providing an inert atmosphere chamber maintained at about room temperature and equipped with an energy source for melting a quantity of H230 alloy powder;(b) providing a base in the chamber for building a product;(c) depositing a first layer of an H230 alloy powder on the base;(d) rapidly melting and cooling the first layer into the base as the powder is being deposited;(e) rapidly depositing, melting and cooling successive layers of the powder until a meta state supersaturated solution solid intermediate product or matrix or precursor is obtained and removed from the chamber;

[0017] In forming the precursor, depending on the nature of the object, the base may, or may not be integrated thereinto. When not integrated, it is detached by any conventional means as is known to the skilled artisan.

[0018] Thereafter, the precursor is heat treated to obtain a final product.

[0019] The final product comprises ultrafine carbides in the grain and grain boundary for tensile strengthening.

[0020] With more particularity, it has been found that H230 alloy powder-based products prepared by laser powder bed fusion additive manufacturing (PBF-laser or LPBF) the layers when deposited, melted and coupled with rapid solidification of the powder as it is deposited, enables the preservation of significant amounts of both tungsten and carbon in a super saturated solid solution matrix state without significant formation of tungsten carbide, as well as chromium carbide or molybdenum carbide particles. The additive manufactured products formed hereby define a precursor for obtaining ultrafine precipitates for dispersively strengthening the matrix properties, e.g., tensile and elongation strengthening. The matrix or precursor keeps the super saturated solid solution in a meta state.

[0021] The so-obtained precursor, when heat treated, provides a strengthened final engineered shape product having ultrafine carbide particles evenly distributed throughout the grain and slightly larger carbide particles in the grain boundary.

[0022] The rapid solidification controls and distributes the solutes evenly throughout the precursor matrix on a volumetric basis. By controlling the rapid melting and solidification, objects in a supersaturated solid solution state can be produced in the final engineering shape without the need for quenching while eliminating any concern regarding potential complex geometry part distortion in complex geometric objects which may otherwise occur during quenching.

[0023] From the meta state of the supersaturated solid solution, a simple heat treatment of about 1200°F or above, preferably about 1800°F or higher for about 30 to about 60 minutes, large amounts of ultrafme carbides are formed in the nickel-based matrix and grain boundary of the final product. These ultrafme carbides are temperature stable beyond the nickel base matrix and therefore, the so-produced alloy products are enhanced at elevated temperatures beyond y’or y” strengthening (since both primes have solvus temperature substantially lower than the nickel base matrix).

[0024] Ordinarily, the fine carbide particles will range in size from about a few nanometers in the grain to larger particles in the grain boundary.

[0025] As is known to the skilled artisan, to achieve the results hereof, rapid cooling will generally range from about >10'3°C / sec to about >10'5°C / sec where the layers go from a superheated liquid to below 1500°F contemporaneously with the depositing and melting of the powder into the underlying or preceding powder layers.

[0026] In a second aspect hereof, in addition to the carbide dispersion strengthening, oxide dispersion strengthening can also be incorporated hereinto. This is achieved by admixing or blending minor amounts of at least one high temperature rare earth oxide with the H230 powder prior to printing. Representative oxide powders include, for example, hafnium oxide, yttrium oxide and the like, as well as mixtures thereof.

[0027] Where used, the oxide source will be present in an amount ranging from about 0.2% to about 5.0% by weight based on the weight of the powders. Preferably, the oxide source is present in an amount ranging from about 1.0% to about 3.0% by weight based on the total weight of the powder or wrought.

[0028] In a particularly preferred aspect hereof, the oxide source is a mixture of hafnium oxide and yttrium oxide in a 1:1 weight ratio although these oxides can be used individually within the stated weight ranges.

[0029] The oxide source(s) is added to H230 to the powder by mixing or blending it into the powder at ambient conditions using conventional mixing techniques.

[0030] In manufacturing objects or products in accordance with the present invention, conventional additive manufacturing techniques are applied.

[0031] Like other additive manufacturing processes, LPBF machines also start with a 3D CAD (Computer-Aided Design) file that is loaded into the machine. After this, the machine starts to prepare for the printing process by heating a bed or build platform to a consistent temperature. Typically, a layer of 0.1 mm-thick material is spread over the build platform. The first layer of the object to be printed or its support structure is then drawn by fusing the powdered particles, either by a laser or electron beam. This is followed by a new layer of powder that is spreadacross the previous layer using a blade or a roller. A hopper or a reservoir located below or beside the bed provides a fresh material supply.

[0032] The process starts by slicing the 3D CAD file data into layers, usually from 20 to 100 micrometers thick, creating a 2D cross-section of each layer; this file format is the industry standard .stl file used on most layer-based 3D printing or stereolithography technologies. This file is then loaded into a file preparation software package that assigns parameters, values and physical supports that allow the file to be interpreted and built by different types of additive manufacturing machines.

[0033] While selective laser melting, thin layers of atomized metal powder are evenly distributed using a re-coating mechanism onto a substrate plate, usually metal, that is fastened to an indexing platform that moves in the vertical (Z) axis. Typically, this takes place inside a chamber containing a tightly controlled atmosphere of inert gas, either argon or nitrogen, at oxygen levels below 1000 parts per million. Once each layer has been distributed, each 2D slice of the part geometry is fused by selectively melting the powder. This is accomplished with a high-power laser beam, usually an ytterbium fiber laser with hundreds of watts. The laser beam is directed in the X and Y directions with two high frequency scanning mirrors and remains in focus along the layer utilizing an F-Theta lens arrangement. The laser energy is intense and focused enough to permit full melting (fusion) of the particles to form a solid structure. The process is repeated layer after layer until the part is complete.

[0034] Thus, the present process includes: (a) computer modeling an object to be produced; (b) transmitting the model to an appropriate slicer where the model is converted into two dimensional “slices” with appropriate software, wherefrom (c) the sliced images are sent to a 3D printer which deposits the powder with rapid cooling in layers in a printing chamberaccording to the software instructions sent by the slicer and as described hereinabove. As noted above, the printing itself is carried out at room temperature in a vacuum chamber in an inert atmosphere, such as argon, using, preferably, a laser or other high-density energy-source device, along with rapid cooling, which melts the powder into a layer therebelow as it traverses along a predetermined computer-controlled path to create a product precursor which, when heat treated, provides the final engineered shape product. As noted above, the precursor shaped object need not be quenched before being heat treated.

[0035] For a more complete understanding of the present invention, reference is made to the following non-limiting illustrative examples. In the examples, all parts are by weight, absent contrary indications.EXAMPLE I

[0036] To test the efficacy of the present invention, a series of H230 alloy powder cylindrical blanks suitable for the fabrication of round threaded end tensile samples were fabricated in an argon atmosphere-containing vacuum chamber maintained at about room temperature and equipped with a high energy laser, using a commercially available H230 powder.

[0037] Initially, a first layer of the powder is deposited on a base or support plate. Next, a second layer of powder is deposited thereover and melted into the first layer, rapidly cooled and then solidified into the first layer using the laser according to conventional additive manufacturing processing. This sequential layer-after-layer deposition of melting and solidification with rapid cooling was continued until the desired blanks were obtained.

[0038] As shown in Table 1, in forming the blanks, the H230 alloy powder had the following chemical composition:TABLE 1 - CompositionElement min maxCarbon 0.05 0.15Manganese 0.30 1.00Silicon 0.25 0.75Phosphorus — 0.03Sulfur — 0.015Chromium 20.00 24.00Molybdenum 1.00 3.00Tungsten 13.00 15.00Aluminum 0.20 0.50Lanthanum 0.005 0.05Cobalt — 5.00Titanium — 0.10Boron — 0.015Iron — 3.00Copper — 0.50Nickel Remainder

[0039] As the second layer and succeeding layers were being deposited, they were cooled at a rate of about >10'3C° / second as they were melted into the preceding or underlying layers.

[0040] After the blanks were fabricated without quenching, they were subjected to a series of strength and tensile property tests.

[0041] In the first testing, the orientation of the samples was parallel to the Z direction.All elevated temperature tests were conducted on the blanks in the “as built” condition. No post build heat treatments were performed, except as set forth in Fig. 3, which identifies the materials testing state.

[0042] The testing ranging from room temperature to 760°C was performed according to ASTM E8 and high temperature testing was conducted according to ASTM E21.

[0043] High temperature uniaxial tensile testing was conducted according to ASTM E21 standard and room temperature tensile testing was conducted according to ASTM E8

[0044] Fig. 3 shows a tensile property comparison of wrought versus the additive manufactured nature of the blanks at room temperature, 760°C and 982°C. The additive manufactured objects or blanks exhibited significantly higher strengths under different heat treatment conditions.

[0045] The uniaxial tension tests were conducted at 982°C, 1093°C, 1149°C and 1177°C.

[0046] The uniformly distributed carbides are stable throughout the testing temperatures from 1177°C up to about 1214°C.

[0047] Similarly, the strain rate sensitivity m and the stress dependence n show that plastic deformation of the PBF-laser H230 product is controlled by a combination of dislocation slip and diffusion mediated recovery processing within the green interior.

[0048] Furthermore, and referring to Figs. 4, 5A and 5B, comparisons are shown, wherein Fig. 4 shows the comparison between conventional wrought plate and bar stock. Fig. 5A shows the results of similar product fabricated using the additive manufacturing PBF-laser H230 process of Example I. Fig. 5B depicts optical images of PBF-laser AM H230 in both vertical and horizontal orientations clearly showing the discreet carbides in both orientations and the larger grain boundary carbides when tested at 1177°C.

[0049] Referring to Figs. 1 and 2, which show that the post treatment or subsequent heat treating of so-produced precursors enables uniformly distributed fine carbides. Fig. 1 shows a prior art object of wrought H230 and Fig. 2 shows a significantly improved strengthened alloy having evenly distributed fine carbides when manufactured in accordance herewith.

[0050] Fig. 6 shows the improved tensile strength of H230 objects or products achieved by the present method (H230+) when compared to present commercially available tungstencontaining H230 powder and Hl 88 powder. It is readily perceived that the present method enables the manufacture of H230 products having improved tensile strength.

[0051] According to the present invention, additive manufactured objects exhibit stability over elevated temperature ranges of up to about 1246°C. This is attributable to the dispersion of fine carbide particles in the grain of approximately 200 nanometers to 800 nanometers in diameter and slightly larger carbides in the grain boundaries.

[0052] It should be noted that the present invention is equally applicable to any commercially available H230 alloy powder in compliance with UNS N06230 specification.

[0053] It is apparent from the preceding that a very fine uniform distribution of carbides leading to higher strength levels, as compared to wrought H230 alloys, is achieved by the practice of the present invention. The fine carbides within the grains of the additive manufactured microstructure act as a fine particle distribution, thereby reducing slip distance and providing this higher strength level observed in an additive manufactured H230 object.

[0054] Although the present invention has been directed to the use of H230 powder, it should be noted that it is theorized that the present process may be applicable to other wrought materials having a significant tungsten and carbon content.

[0055] It should also be noted that the present process is applicable to manufacturing many products, including heat exchangers, primary structures, conduction chambers, heat shields, thermal protection systems, and the like.

Claims

CLAIMS1. A method for improving the strength of H230 alloy powder additive manufactured products comprising:(a) providing an inert atmosphere chamber maintained at about room temperature and equipped with an energy source for melting a quantity of H230 alloy powder;(b) providing a base in the chamber upon which to build a product;(c) depositing a first layer of the H230 alloy powder on the base;(d) rapidly melting and cooling the first layer into the base as the powder is being deposited; and(e) rapidly depositing, melting and cooling successive layers of the powder until a meta state supersaturated solid solution precursor is obtained of final engineered shape;2. The method of Claim 1 which further comprises:(a) thereafter, heat treating the so-obtained precursor to obtain a final product; and(b) wherein the final product comprises strengthening ultrafme carbides in the grain and grain boundary.

3. The method of Claim 2 wherein the final product is heat treated without quenching the precursor.

4. An additive manufactured product produced according to the method of Claim 2.

5. The method of Claim 3 wherein the precursor is heat treated at a temperature ranging from about at least 1200°F for a time period of about 30 to about 60 minutes to provide a final product.

6. An additive manufactured product according to Claim 3.

7. An additive manufacture product produced according to the method of Claim 6.

8. The method of Claim 1 wherein the H230 powder is a high temperature refractory alloy powder consisting essentially of:(a) from about 95% to 99.5% by weight of an H230 powder; and(b) from 0.5% to about 95% by weight of a rare earth oxide powder.

9. The method of Claim 8 wherein the rare earth metal oxide is selected from the group consisting of hafnium oxide and yttrium oxide.

10. The method of Claim 9 wherein the rare earth metal oxide is hafnium oxide.

11. The method of Claim 9 wherein the rare earth metal oxide is yttrium oxide.

12. The method of Claim 9 wherein the rare earth metal oxide is a 1 : 1 weight ratio mixture of hafnium oxide and yttrium oxide.

13. The method of Claim 1 wherein the additive manufacturing process is a laser powder bed fusion process.

14. The method of Claim 1 which further comprises detaching the precursor from the base.

15. The method of Claim 1 wherein the base is integrated into the precursor.

6. A method for additive manufacturing an H230 alloy powder object, comprising:(a) preparing a CAD file of an object to be produced;(b) slicing the file by creating a 2D cross-section of each of the layers; and(c) printing the object with selective laser powder bed fusion melting according to the method of Claim 1.

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