WO2019118437A1

WO2019118437A1 - Methods of transforming grains in additively manufactured products

Info

Publication number: WO2019118437A1
Application number: PCT/US2018/064915
Authority: WO
Inventors: Gen SATOH; Yimin RUAN; JR. Daniel M. MYERS
Original assignee: Arconic Inc.
Priority date: 2017-12-11
Filing date: 2018-12-11
Publication date: 2019-06-20

Abstract

Broadly, the present disclosure relates to methods for transforming grains in additively manufactured products. In this regard, the methods generally include producing an additively manufactured product, where at least a portion of the additively manufactured product comprises a plurality of first grains, selectively directing an energy source toward a segment of the portion comprising the first grains, thereby producing a molten pool segment, cooling the molten pool segment, thereby producing a transformed segment having second grains (transformed grains).

Description

METHODS OF TRANSFORMING GRAINS IN ADDITIVELY MANUFACTURED

PRODUCTS

FIELD OF THE INVENTION

[0001] This patent application relates to methods of transforming grains in additively manufactured products.

BACKGROUND

[0002] Additive manufacturing is defined as“a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies.” ASTM F2792-l2a entitled “Standard Terminology for Additively Manufacturing Technologies”. Wire feedstocks may be used in some additive manufacturing techniques to produce additive manufactured products.

SUMMARY OF THE DISCLOSURE

[0003] Broadly, the present disclosure relates to methods for transforming grains in additively manufactured products. In this regard, the methods generally include producing at least a portion additively manufactured product having a plurality of first grains, directing an energy source toward a segment of the portion thereby producing a molten pool segment, and cooling the molten pool to produce a transformed segment having a plurality of second grains. The transformed segment may realize a grain structure having second grains with an average grain size not greater than 90% of the average grain size of the first grains. This method may be repeated to produce a plurality of transformed segments, and may also be coupled with additively manufactured processes to transform the grains of additively manufactured products during production.

[0004] Due to the transformation of at least some of the first grains to second grains, the additively manufactured products may realize improved properties, such as, increased tensile properties, ductility, and fatigue crack growth resistance, among many others.

[0005] In one embodiment, a method comprises: (a) producing an additively manufactured product having a length (x), width (y) and a height (z), where at least a portion of the additively manufactured product comprises a plurality of first grains, an average aspect ratio of the first grains is at least 2: 1 in an Z:X plane, and an average grain size of the first grains is at least 0.5 mm; (b) selectively directing an energy source toward a segment of the portion, thereby producing a molten pool segment, where an aspect ratio of a depth to a width of the molten pool segment is at least 1.5: 1; (c) cooling the molten pool segment, thereby producing a transformed segment, where the transformed segment comprises a plurality of second grains, and an average grain size of the second grains is not greater than 90% of the average grain size of the first grains.

[0006] In some of the above embodiments, the producing comprises additively manufacturing the additively manufactured product, where the additively manufacturing comprises: (i) using the energy source to heat a feedstock (e.g., a wire, a powder, and combinations thereof) above the liquidus point of the additively manufactured product to be formed, thereby creating a molten pool; (ii) cooling the molten pool at a cooling rate of at least 0.l°C per second, where, due to the steps (i) and (ii), a portion of the additively manufactured product is produced, the portion comprising at least some of the first grains; (iii) repeating steps (i)-(ii) until the final additively manufactured product is completed, the final additively manufactured comprising a plurality of the portions and the plurality of the first grains, where steps (b) - (c) are performed on at least one of the plurality of portions.

[0007] In some of the above embodiments, during the directing step (b), the energy source is continuously powered and moved, thereby producing at least one continuous molten pool segment.

[0008] In some of the above embodiments, steps (b) - (c) are repeated at least once on at least one portion of the plurality of portions, thereby realizing a plurality of transformed segments.

[0009] In some of the above embodiments, at least some of the plurality of transformed segments are segregated from each other.

[0010] In some of the above embodiments, at least some of the plurality of transformed segments are adjacent each other.

[0011] In some of the above embodiments, the depth of at least one molten pool segment is at least 2 mm. In some of the above embodiments, the depth of at least one molten pool segment is at least 5 mm. In some of the above embodiments, the depth of at least one molten pool segment is at least 10 mm. In some of the above embodiments, the depth of at least one molten pool segment is at least 20 mm.

[0012] In some of the above embodiments, the aspect ratio of at least one molten pool segment is at least 2: 1. In some of the above embodiments, the aspect ratio of at least one molten pool segment is at least 3: 1. In some of the above embodiments, the aspect ratio of at least one molten pool segment is at least 4: 1. In some of the above embodiments, the aspect ratio of at least one molten pool segment is at least 5: 1. In some of the above embodiments, the aspect ratio of at least one molten pool segment is at least 6: 1. [0013] In some of the above embodiments, the second grains of at least one transformed segment comprises an average grain size not greater than 75% of the average grain size of the first grains. In some of the above embodiments, the second grains of at least one transformed segment comprises an average grain size not greater than 50% of the average grain size of the first grains. In some of the above embodiments, the second grains of at least one transformed segment comprises an average grain size not greater than 25% of the average grain size of the first grains.

[0014] In some of the above embodiments, at least one transformed segment comprises a length (L) that is at least 10% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In some of the above embodiments, at least one transformed segment comprises a length (L) that is at least 25% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In some of the above embodiments, at least one transformed segment comprises a length (L) that is at least 40% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In some of the above embodiments, at least one transformed segment comprises a length (L) that is at least 50% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In some of the above embodiments, at least one transformed segment comprises a length (L) that is at least 65% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In some of the above embodiments, at least one transformed segment comprises a length (L) that is at least 75% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In some of the above embodiments, at least one transformed segment comprises a length (L) that is at least 90% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In some of the above embodiments, at least one transformed segment comprises a length (L) that is at least 100% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product.

[0015] In some of the above embodiments, at least one transformed segment comprises a length (L) that is equivalent to at least 1 additively manufactured layer. In some of the above embodiments, at least one transformed segment comprises a length (L) that is equivalent to at least 2 additively manufactured layers. In some of the above embodiments, at least one transformed segment comprises a length (L) that is equivalent to at least 5 additively manufactured layers. In some of the above embodiments, at least one transformed segment comprises a length (L) that is equivalent to at least 10 additively manufactured layers. In some of the above embodiments, at least one transformed segment comprises a length (L) that is equivalent to at least 15 additively manufactured layers. In some of the above embodiments, at least one transformed segment comprises a length (L) that is equivalent to at least 20 additively manufactured layers. In some of the above embodiments, at least one transformed segment comprises a length (L) that is equivalent to at least 30 additively manufactured layers.

[0016] In some of the above embodiments, the second grains comprise equiaxed grains.

[0017] In some of the above embodiments, the additive manufacturing comprises operating in a vacuum at a pressure of not greater than 1000 ptorr. In some of the above embodiments, the additive manufacturing comprises operating in a vacuum at a pressure of not greater than 500 ptorr. In some of the above embodiments, the additive manufacturing comprises operating in a vacuum at a pressure of not greater than 300 ptorr. In some of the above embodiments, the additive manufacturing comprises operating in a vacuum at a pressure of not greater than 200 ptorr.

[0018] In some of the above embodiments, the additively manufactured product comprises at least one of an aluminum alloy, titanium alloy (e.g., a titanium aluminide alloy), cobalt alloy, nickel alloy, iron alloy, or chromium alloy.

[0019] In some of the above embodiments, the additively manufactured product comprises a titanium alloy. In some of the above embodiments, a titanium alloy is a titanium aluminide alloy. In some of the above embodiments, the additively manufactured product comprises titanium alloy Ti-6Al-4V.

[0020] In some of the above embodiments, the additively manufactured product is in the form of an automotive component or an aerospace component.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. la shows an embodiment for producing an additively manufactured product having at least some transformed grains.

[0022] FIG. lb shows an embodiment for producing an additively manufactured product having at least some transformed grains.

[0023] FIG. 2 shows an embodiment for producing an additively manufactured product having at least some transformed grains, wherein the additive manufacturing process is coupled with the grain transformation process. [0024] FIG. 3 shows a schematic representation of a cross-sectional view of an additively manufactured product having first grains.

[0025] FIG. 4 shows a schematic representation of a cross-sectional view of the additively manufactured product of FIG. 3 having first grains, with a powered energy source directed toward the additively manufactured product producing a molten pool segment.

[0026] FIG. 5 shows a schematic representation of a cross-sectional view of the transformed segment produced by directing the powered energy source in FIG. 4.

[0027] FIG. 6 shows a schematic representation of a cross-sectional view of the mode of heat transfer realized by the molten pool segment in FIG. 4.

[0028] FIG. 7 shows a schematic representation of a cross-sectional view of the additively manufactured product of FIG. 3 having both adjacent and segregated transformed segments.

[0029] FIG. 8 shows a schematic representation of a cross-sectional view of the additively manufactured product of FIG. 3 having a continuous molten pool segment.

[0030] FIG. 9 shows a schematic representation of a cross-sectional view of an additively manufactured product comprised of three portions and a plurality of segregated, but aligned transformed segments.

[0031] FIG. 10 shows a schematic representation of a cross-sectional view of an additively manufactured product comprised of three portions and a plurality of transformed segments that are segregated within each portion, but adjacent through portions.

DETAILED DESCRIPTION

i. General Methods

[0032] In one embodiment, and referring now to FIG. la, a method for producing an additively manufactured product having at least some transformed grains is shown (100). As illustrated, an additively manufactured product is produced (110) and then an energy source is directed toward the additively manufactured product to produce a molten pool segment (120). The molten pool segment is then cooled (130), thereby producing an additively manufactured product having at least some transformed grains.

[0033] More particularly, and now referring to FIG. lb, a method for producing an additively manufactured product having at least some transformed grains is shown (100). First, an additively manufactured product is produced (110). In this regard, the additively manufactured product may be characterized by a length (x), width (y), and height (z) (111). The Z direction is also known as the“build direction”. At least a portion of the additively manufactured product may include a plurality of first grains (112). In this regard, the first grains generally realize an average aspect ratio of at least 2: 1 (Z:X) (113) and an average grain size of at least 0.5 mm (114). After production of the additively manufactured product (110), an energy source may be directed and powered toward a segment of a portion of the additively manufactured product that includes at least some first grains, thereby realizing the production of a molten pool segment (120). In this regard, the molten pool segment may be characterized by an aspect ratio (i.e., depth to the width) of at least 1.5 to 1 (121). In this manner, production of the molten pool segment includes supplying energy, via a powered energy source, thereby heating at least some of the segment to a temperature above its liquidus temperature. Following production (120), the molten pool segment may be cooled, thereby producing a transformed segment (130). The transformed segment may include a plurality of second grains, wherein the average grain size of the second grains is not greater than 90% of the first grains (132). In one embodiment, the average grain size of the second grains is not greater than 75% of the average grain size of the first grains. In another embodiment, the average grain size of the second grains is not greater than 50% of the average grain size of the first grains. In yet another embodiment, the average grain size of the second grains is not greater than 25% of the average grain size of the first grains. In some embodiments, the second grains comprise equiaxed grains.

[0034] While reference to,“second grains” is made to herein, an additively manufactured product having at least some transformed grains may be comprised of third grains, fourth grains, etc., to the n^th number of grains. For instance, in some embodiments an additively manufactured product having transformed grains therein may be comprised of a plurality of transformed grains (i.e., second grains, third grains, and n^th grains). In this regard, the energy source may be adjusted to produce the n^th grains, for instance, by varying the aspect ratio of the produced molten pool segments. A variety of transformed grains (e.g., second grains, third grains, and n^th grains) may be useful for the purpose of tailoring the grains within specific portions of additively manufactured products. Thus, in one embodiment, an additively manufactured product comprises a plurality of transformed grains, wherein the plurality of transformed grains includes at least second grains and third grains.

[0035] As used herein,“aspect ratio” means the ratio of a first dimension of an object (e.g., length (L) of a grain; depth (D) of a molten pool segment) to a second dimension of an object (e.g., width (W) of a grain; width (W) of a molten pool segment). [0036] As used herein, the word“grain” takes on the meaning defined in ASTM El 12

§3.2.2, i.e.,“the area within the confines of the original (primary) boundary observed on the two-dimensional plane of-polish or that volume enclosed by the original (primary) boundary in the three-dimensional object”. Grain dimensions are determined in two-dimensional space, in accordance with the“Heyn Lineal Intercept Procedure” method described in ASTM standard El 12-13, entitled,“Standard Test Methods for Determining Average Grain Size”.

[0037] As used herein“grain size” means the size of a grain as determined in accordance with the“Heyn Lineal Intercept Procedure” method described in ASTM standard El 12-13, entitled,“Standard Test Methods for Determining Average Grain Size”, wherein a minimum of five micrographs are taken parallel to the height (z) dimension of the additively manufactured product, and wherein the micrographs are analyzed at approximately 50% of the maximum length (x) and width (y) dimensions (i.e., in the middle of the product). If the average grain size determination is being made with respect to transformed grains, the micrographs should be taken at points where the transformation is thought to have occurred as close to the 50% maximum of the length (x) and width (y) dimensions. In this regard, the grain size may be determined in the Z:X and/or Z:Y planes. In this regard, the first grains may generally realize an aspect ratio in the Z:X and Z:Y planes that differ from the X:Y plane due to the growth of the first grains being generally in the Z-direction. Thus, the transformation of the grains is measured relative to the Z:X and Z:Y planes, as opposed to all three Z:X, Z:Y, and X:Y planes.

[0038] As used herein,“additive manufacturing” means,“a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies”, as defined in ASTM F2792-l2a entitled “Standard Terminology for Additively Manufacturing Technologies”.

[0039] Due to the producing (i.e., additive manufacturing) (110), at least a portion of the additively manufactured product may comprise first grains wherein the first grains realize an average grain size of at least 0.5 mm. In one embodiment, the first grains realize an average grain size of at least 0.6 mm. In another embodiment, the first grains realize an average grain size of at least 0.7 mm. In yet another embodiment, the first grains realize an average grain size of at least 0.8 mm. In another embodiment, the first grains realize an average grain size of at least 0.9 mm.

[0040] The directing of an energy source toward a segment of the portion may produce a molten pool segment. In other words, the energy source, when powered, may supply enough energy to the segment such that at least some of the segment is heated to a temperature above its liquidus. In this regard, the directing (120) may be sufficient to realize a molten pool segment having an aspect ratio of at least 1.5 to 1 (depth to width). In one embodiment, a molten pool segment realizes an aspect ratio of at least 2: 1. In another embodiment, a molten pool segment realizes an aspect ratio of at least 3: 1. In yet another embodiment, a molten pool segment realizes an aspect ratio of at least 4: 1. In another embodiment, a molten pool segment realizes an aspect ratio of at least 5: 1. In yet another embodiment, a molten pool segment realizes an aspect ratio of at least 6: 1. Energy sources that may be used to produce the molten pool segment(s) include, but are not limited to, an electron beam (EB), a plasma arc, or any suitable laser. As described in further detail below, an energy source may be used to additively manufacture products. In this regard, the energy source used for additive manufactured may be the same energy source used to produce a molten pool segment or segments. However, a secondary or a plurality of energy sources may be used to produce additively manufactured products having transformed grains. Furthermore, a plurality of energy sources may be used to perform the additive manufacturing and grain transformation processes. For instance, one or more energy sources may perform the additive manufacturing while one or more energy sources performs the grain transformation steps (e.g., concomitantly; separately).

[0041] Transformation of the first grains to second grains may be sufficient to realize additively manufactured products with improved physical properties. For instance, the additively manufactured product may realize increased tensile properties, ductility, and fatigue crack growth resistance, among many others. In this regard, the second grains may generally realize an average grain size of not greater than 90% of the first grains. In one embodiment, the average grain size of the second grains is not greater than 75% of the average grain size of the first grains. In another embodiment, the average grain size of the second grains is not greater than 50% of the average grain size of the first grains. In yet another embodiment, the average grain size of the second grains is not greater than 25% of the average grain size of the first grains. In some embodiments, the second grains comprise equiaxed grains.

[0042] As used herein,“equiaxed grains” means grains having an average aspect ratio of not greater than 1.5 to 1 as measured in the Z:Y and Z:X planes as determined by the“Heyn Lineal Intercept Procedure” method described in ASTM standard El 12-13, entitled, “Standard Test Methods for Determining Average Grain Size”. ii. Specific Methods

[0043] The methods for transforming the grains in additively manufactured products may be coupled to additively manufactured processes, and additive manufacturing apparatuses. In this regard, and now referring to FIG. 2, a method for transforming grains during an additive manufacturing process is illustrated (200). In this manner, a portion of an additively manufactured product may be produced (210). The production may generally include (i) using an energy source to heat a feedstock (e.g., a wire, a powder, and combinations thereof) above the liquidus point of the additively manufactured product to be formed (211), thereby creating a molten pool (212), followed by (ii) cooling the molten pool to a temperature below its solidus (213). The cooling of the molten pool (213) may generally be performed at a rate of at least 0. l°C per second (214). Once the molten pool has cooled (e.g., to a temperature below its solidus), this process may be repeated until a portion of the additively manufactured product is produced (210). In this regard, the portion may comprise at least some of the first grains. The steps (i)-(ii) may be repeated until a final additively manufactured product is completed, wherein the final additively manufactured product comprises a plurality of portions and a plurality of first grains.

[0044] During, or following production of a portion or a plurality of portions, the energy source may be directed toward a segment of a portion to produce a molten pool segment (220). The molten pool segment may be cooled, thereby producing a transformed segment (230). The directing (220) and cooling (230) may be performed at least once on at least one portion. In this regard, production of an additively manufactured product may include a plurality of production steps (210), and a plurality of directing (220) and cooling steps (230). For instance, the directing (220) and cooling (230) (e.g., by radiative effects, convection, and/or by conduction to a substrate) may be performed any number of times on at least one layer of additively manufactured material. In this manner, the directing (220) and cooling (230) (e.g., transformation of first grains to second grains) may be performed any number of times between the additive manufacturing of a portion or portions. The production (210), directing (220), and cooling (230) may be performed in any suitable order until the completion of an additively manufactured product (240). Thus, the additively manufactured products described herein may comprise a plurality of portions, and at least one transformed segment.

[0045] An additively manufactured product having a plurality of transformed segments (i.e., at least two transformed segments) may be produced by a variety of methods. In some embodiments, the plurality of transformed segments may be segregated from each other. In other words, the transformed segments may be separated by a suitable distance. The suitable distance may be chosen, for instance, on the basis of the desired properties of the additively manufactured product. For instance, an additively manufactured product having a transformed segment, or plurality of transformed segments may realize isotropy within the additively manufactured product sufficient to utilize non-destructive inspection techniques (e.g., ultrasonic methods). In other embodiments, the plurality of transformed segments may be adjacent to each other. That is, the transformed segments may at least be touching, or may overlap each other. Thus, in some embodiments an additively manufactured product may comprise a plurality of transformed segments, wherein at least a portion of the plurality of transformed segments are segregated, and wherein at least another portion of the plurality of transformed segments are adjacent. In this regard, during the production of an additively manufactured product, any combination of segregated and adjacent segments may be produced according to the desired properties of the additively manufactured product. Further, the segregated and adjacent transformed segments may be tailored to realize desired properties within specific portions of the additively manufactured product.

[0046] In another aspect of the invention, a variety of combinations of segregated and adjacent transformed segments may be produced within a plurality of portions of an additively manufactured product. For instance, a first portion of an additively manufactured product may be produced, and a first plurality of segregated and/or adjacent transformed segments may be produced within the first portion. Then, at least a second portion may be produced, and a second plurality of segregated and/or adjacent transformed segments may be produced within the second portion. In this regard, the transformed segments of the first plurality of transformed segments may be segregated and/or adjacent to the transformed segments of the second plurality of transformed segments. Thus, any combination of adjacent and/or transformed segments may be realized in the three-dimensional space of an additively manufactured product. For instance, at least a first plurality of transformed segments and a second plurality of transformed segments may be both segregated but aligned (see FIG. 9). Further, at least a first plurality of transformed segments and a second plurality of transformed segments may be adjacent throughout at least a first portion and second portion of an additively manufactured product (see FIG. 10). Thus, an additively manufactured product may include any combination of segregated and/or transformed segments, relative to any dimension (i.e., x, y, and z) within an additively manufactured product. [0047] The methods described herein may be used to produce molten pool segments individually. In other words, the directing (220) and cooling (230) may occur separately. However, as one may appreciate, a continuous method for transforming first grains to second grains may also be utilized. In this regard, during the directing (220), the energy source or the additively manufactured product may be continuously powered and moved, thereby producing a continuous molten pool segment. In this regard, a continuous molten pool segment is a molten pool segment that continuously increases in size in the direction of movement of the energy source. Due to the extent of the movement, a portion of a continuous molten pool segment may cool to below its solidus during repositioning. In this regard, a continuous molten pool segment may comprise both molten portions and solid portions during the directing of the energy source.

[0048] As noted above, the methods for producing additively manufactured products having transformed grains may involve repeating the transformation steps, and the additive manufacturing steps (e.g., manufacturing at least one layer). In this regard, any number of transformation steps may be performed, following any number of additive manufacturing steps. By non-limiting example, an additive manufacturing step, wherein the step includes producing a layer of the additively manufactured product, may be repeated two times to produce two additively manufactured layers. Then, a transformation step may be performed, thereby realizing transformation of at least some of the first grains of the 2 layers, wherein each layer is 1 mm in the Z direction. In this regard, the depth of the molten pool segment realized by directing the energy source may be at least 2 mm, in order to transform the produced portion (e.g., the layers). In one embodiment, the depth of at least one molten pool segment is at least 2 mm. In another embodiment, the depth of at least one molten pool segment is at least 5 mm. In yet another embodiment, the depth of at least one molten pool segment is at least 10 mm. In another embodiment, the depth of at least one molten pool segment is at least 20 mm. Thus, multiple layers may be penetrated by the energy source, thereby producing transformed segments that penetrate multiple layers within the additively manufactured product.

[0049] In one approach, the transformed segment comprises a length that is at least 10 % of at least one of the length (x), the width (y), or the height (z) of the additively manufactured product. By non-limiting example, an additively manufactured product of 100 mm in the height (z) direction may be produced. Then, a molten pool segment having a depth (D) of 10 mm may be produced in the height (z) direction of the additively manufactured product. Thus, upon cooling of the molten pool segment to a transformed segment, the additively manufactured product would comprise a transformed segment that is 10% of the height (z) of the additively manufactured product. In one embodiment, the transformed segment is at least 25% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In another embodiment, the transformed segment is at least 40% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In another embodiment, the transformed segment is at least 50% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In yet another embodiment, the transformed segment is at least 65% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In another embodiment, the transformed segment is at least 75% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In yet another embodiment, the transformed segment is at least 90% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product. In another embodiment, the transformed segment is the same dimension (i.e., 100%) of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product.

[0050] In another approach, the transformed segment comprises a length equivalent to at least 1 additively manufactured layer. By non-limiting example, an additive manufacturing step, wherein the step includes producing a layer of the additively manufactured product may be performed. Then, a transformation step may be performed, thereby realizing transformation of at least some of the first grains of the singular layer. In one embodiment, the transformed segment comprises a length equivalent to at least 2 additively manufactured layers. In another embodiment, the transformed segment comprises a length equivalent to at least 5 additively manufactured layers. In yet another embodiment, the transformed segment comprises a length equivalent to at least 10 additively manufactured layers. In another embodiment, the transformed segment comprises a length equivalent to at least 15 additively manufactured layers. In yet another embodiment, the transformed segment comprises a length equivalent to at least 20 additively manufactured layers. In another embodiment, the transformed segment comprises a length equivalent to at least 30 additively manufactured layers.

iii. Additive Manufacturing Apparatus

[0051] The additively manufactured products described herein may be produced using any suitable additive manufacturing apparatus. In one approach, electron beam (EB) or plasma arc techniques are utilized. Electron beam techniques may facilitate production of larger parts than readily produced via laser additive manufacturing techniques. In one embodiment, a method comprises feeding a wire (e.g., in some instances < 8 mm in diameter; in other instances < 4.74 mm) to the wire feeder portion of an electron beam gun. The electron beam (EB) may heat the wire above the liquidus point of the additively manufactured product to be formed, followed by solidification of the molten pool to form the deposited material (e.g., a portion of the additively manufactured product).

[0052] In some embodiments, the additive manufacturing process is performed in a vacuum. The additive manufacturing may be performed in a vacuum, for instance, to prevent oxidation of materials prone to oxidation (e.g., titanium alloys) during deposition. In one embodiment, the additive manufacturing apparatus comprises a vacuum chamber. In this manner, when the additive manufacturing is performed in a vacuum environment, the average pressure (e.g., during the deposition) of the additive manufacturing apparatus may be not greater than 1000 ptorr. Producing additively manufactured products in a vacuum may generally result in low cooling rates of the molten pool(s) and molten pool segment(s). In this regard, cooling rates of at least 0.l°C/s may be realized due to heat transfer occurring primarily by (1) conduction to the additive manufacturing substrate, and/or the produced additively manufactured portion(s), and (2) by radiative effects. In this regard, the cooling rates realized by performing additive manufacturing in vacuum may be lower than those that are performed in ambient air, where the heat transfer may primarily occur by convection from the air. In one embodiment, the average pressure of the additive manufacturing apparatus during production is not greater than 500 ptorr. In another embodiment, the average pressure of the additive manufacturing apparatus during production is not greater than 300 ptorr. In yet another embodiment, the average pressure of the additive manufacturing apparatus during production is not greater than 200 ptorr.

[0053] As used herein,“substrate” means a material having at least one surface that additively manufactured products are deposited onto. For instance, an additively manufactured product may be deposited onto a substrate in order to transfer heat produced during additive manufacturing (e.g., to cool molten pools). In this regard, substrates may be disposable portions of the additively manufactured product that are removed prior to realization of an end-use product. Alternatively, a substrate may be incorporated as an integral part of the additively manufactured product (e.g., see U.S. Patent Pub. No. 2015013144). Suitable forms of substrates include plates, extrusions, forgings, and castings, among others. [0054] The cooling rates of molten pools producing during additive manufacturing in a vacuum may generally be lower than those performed in the ambient air. While not being bound by any theory, it is generally believed that the low cooling rates of molten pools are responsible for the production and characteristics of the first grains (e.g., average grain size of at least 0.5 mm and an aspect ratio of at least 2: 1 (Z:X)). Similarly, while not being bound by any theory, it is believed that the dimensions of the molten pool segments described herein may result in a higher rate of heat transfer to the substrate due to conduction to the substrate and/or the produced additively manufactured portion(s). In this regard, the aspect ratio of molten pool segments of at least 1.5: 1 may help facilitate the realization of the transformed grains within the transformed segment upon cooling.

iv. Suitable Materials

[0055] Transformation of the first grains of the additively manufactured products described herein to second grains may be performed on any suitable metal, or metal alloy. In this regard, a suitable metal alloy such as an aluminum alloy, titanium alloy (e.g., titanium aluminide alloys), cobalt alloy, nickel alloy, iron alloy, chromium alloy, and/or combinations thereof, among others.

[0056] As used herein,“aluminum alloy” means a metal alloy having aluminum as the predominant alloying element.“Titanium alloy” means a metal alloy having titanium as the predominant alloying element. “Titanium aluminide alloy” means a metal alloy having titanium and aluminum as the predominant alloying elements, wherein the amount of aluminum is at least 10 wt. % Al, and wherein the metal alloy includes at least one of the phases of g-TiAl, a₂-Ti₃Al, and TiAh. “Cobalt alloy” means a metal alloy having cobalt as the predominant alloying element.“Nickel alloy” means a metal alloy having nickel as the predominant alloying element. “Iron alloy” means a metal alloy having iron as the predominant alloying element (e.g., steels; stainless steels). “Chromium alloy” means a metal alloy having chromium as the predominant alloying element.

[0057] In one embodiment, an additively manufactured product comprises an aluminum alloy. In one embodiment, an additively manufactured product comprises a titanium alloy. In one embodiment, an additively manufactured product comprises a cobalt alloy. In one embodiment, an additively manufactured product comprises a nickel alloy. In one embodiment, an additively manufactured product comprises an iron alloy. In one embodiment, an additively manufactured product comprises a chromium alloy.

[0058] Some titanium alloys that may be used include those described in ASTM B348. For instance, some useful titanium alloys described in ASTM B348 include Ti-6Al-4V (grade 5), Ti-5Al-2.5Sn (grade 6), and Ti-3Al-2.5V (grade 9). Other useful titanium alloys may include Ti-6Al-6V-2Sn, Ti-Al-2Sn-4Zr-6Mo, Ti-6Al-2Mo-2Cr, and Ti-6Al-2Sn-4Zr- 2Mo, among others. In one embodiment, an additively manufactured product comprises titanium alloy Ti-6Al-4V.

[0059] As used herein,“Ti-6Al-4V” means a grade 5 titanium alloy comprising from about 5.5 wt. % Al to about 6.75 wt. % Al, from about 3.5 wt. % V to about 4.5 wt. % V, a maximum of 0.40 wt. % Fe, a maximum of 0.2 wt. % O, a maximum of 0.015 wt. % H, a maximum of 0.05 wt. % N, a maximum of 0.40 wt. % other impurities, and the balance being Ti. As may be appreciated, similar specifications exist for other titanium grades. v. Product Applications

[0060] Additively manufactured products made using the methods described herein may be suitable for a variety of applications. For instance, the additively manufactured products described herein may be suitable in aerospace and/or automotive applications. In one embodiment, an additively manufactured product is used in a ground transportation application. Non-limiting examples of aerospace applications may include heat exchangers and turbines (e.g., turbocharger impeller wheels). Non-limiting examples of automotive applications may include interior or exterior trim/appliques, pistons, valves, and/or turbochargers. Other examples include any components close to a hot area of the vehicle, such as engine components and/or exhaust components, such as the manifold.

[0061] In another aspect, the additively manufactured products may be utilized in a structural application. In one embodiment, an additively manufactured product is utilized in an aerospace structural application. For instance, the additively manufactured products may be in the form of various aerospace structural components, including floor beams, seat rails, fuselage framing, bulkheads, spars, ribs, longerons, and brackets, among others. In another embodiment, an additively manufactured product is utilized in an automotive structural application. For instance, the additively manufactured products may be in the form of various automotive structural components including nodes of space frames, shock towers, and subframes, among others. In one embodiment, an additively manufactured product is a body-in-white (BIW) automotive product.

[0062] In another aspect, the additively manufactured products may be utilized in an industrial engineering application. For instance, the additively manufactured products may be in the form of various industrial engineering products, such as tread-plate, tool boxes, bolting decks, bridge decks, and ramps, among others. [0063] In some embodiments, the additively manufactured products of the present disclosure may be utilized in a variety of products including the likes of medical devices, transportation systems and security systems, to name a few. In other embodiments, the additively manufactured products may be incorporated in goods including the likes of car panels, media players, bottles and cans, office supplies, packages and containers, among others.

[0064] In some embodiments, the additively manufactured products of the present disclosure may be utilized in a variety of products including non-consumer products including the likes of medical devices, transportation systems and security systems, to name a few. In other embodiments, the additively manufactured products may be incorporated in goods including the likes of car panels, media players, bottles and cans, office supplies, packages and containers, among others.

[0065] Aside from the applications described above, the additively manufactured products of the present disclosure may also be utilized in a variety of consumer products, such as any consumer electronic products, including laptops, cell phones, cameras, mobile music players, handheld devices, computers, televisions, microwave, cookware, washer/dryer, refrigerator, sporting goods, or any other consumer electronic product requiring durability and selective visual appearance. In one embodiment, the visual appearance of the consumer electronic product meets consumer acceptance standards.

EXAMPLES

[0066] Referring now to FIG. 3, a cross-sectional view of an additively manufactured product (300) is illustrated. The cross-section of the additively manufactured product (300) is bound by an upper edge (310), a lower edge (320), a left edge (315), and a right edge (325). Contained by the bounds, the additively manufactured product (300) includes an upper portion (340) (e.g., the upper half of the portion of the additively manufactured product) associated with the upper edge (310), and a lower portion (350) (e.g., the lower half of the portion of the additively manufactured product) associated with the lower edge (320). The additively manufactured product, as illustrated, includes a plurality of first grains (330). The plurality of first grains (330) realize an average aspect ratio of at least 2: 1 in the Z:X plane and an average grain size of at least 0.5 mm (not to scale in FIG. 3). Generally, the first grains are large grains that grow in the direction of heat flow during additive manufacturing (e.g., during cooling of welds). [0067] During production of the additively manufactured product, at least some of the first grains (330) may be transformed. For instance, and referring now to FIG. 4, an energy source (400) may be used to direct an energy beam (410) toward a portion of the additively manufactured product (300), thereby producing a molten pool segment (412). In the illustrated embodiment, the molten pool segment (412) contiguously penetrates the upper side (310) and upper portion (340), but does not penetrate the lower portion (350). The molten pool segment comprises a width (W) (414) and a depth (D) (416). As illustrated, the molten pool segment (412) realizes an aspect ratio (depth:width) of at least 2: 1.

[0068] Referring now to FIG. 5, a molten pool segment may cool when the energy source is not powered (400), thereby producing a transformed segment (512). The transformed segment (512) may comprise second grains (530) that realize an average grain size not greater than 90% of the average grain size of the first grains (230). As illustrated, the transformed segment (512) generally comprises equiaxed grains (defined above).

[0069] Referring now to FIG. 6, the rate of cooling of the molten pool segment may govern the average grain size, and the orientation of the second grains. In this regard, the direction of heat flow (601) may influence the rate of cooling. For instance, the illustrated molten pool segment experiences heat flow in the X-directions, thereby facilitating production of the transformed segment and the transformed grains.

[0070] Referring now to FIG. 7, a cross-sectional view of an additively manufactured product having both adjacent transformed segments (710) and segregated transformed segments (720) is shown (700). As illustrated, there are three adjacent transformed segments (710), and two segregated transformed segments (720). In this regard, the three adjacent transformed segments (710) are segregated from the two segregated transformed segments (720).

[0071] Referring now to FIG. 8, a cross-sectional view of an additively manufactured product having a continuous transformed segment is illustrated (800). As illustrated, the energy source moves from left to right (810). As the energy source is powered and continuously moved, a continuous molten pool segment is formed (820). As illustrated, the transformed grains form when the powered energy source moves from left to right (810).

[0072] Referring now to FIG. 9, a cross-sectional view of an additively manufactured product is shown (900). The additively manufactured product comprises a first portion (901), a second portion (902), and a third portion (903). The first portion includes a first plurality of transformed segments (910). Similarly, the second portion (902) includes a second plurality of transformed segments (920), and the third portion (903) includes a third plurality of transformed segments (930). In this regard, the first plurality of transformed segments (910) are segregated from one another within the first portion (901). Similarly, the second plurality of transformed segments (920) are segregated within the second portion (902), and the third plurality of transformed segments (930) are segregated within the third portion (903). Furthermore, the first plurality of transformed segments (910) are segregated from the second plurality of transformed segments (920) and third plurality of transformed segments (930). However, the first, second, and third plurality of transformed segments (910, 920, and 930) are segregated, but are aligned in the Z-direction of the additively manufactured product.

[0073] Referring now to FIG. 10, a cross-sectional view of an additively manufactured product is shown (1000). The additively manufactured product comprises a first portion (1001), a second portion (1002), and a third portion (1003). The first portion includes a first plurality of transformed segments (1010). Similarly, the second portion (1002) includes a second plurality of transformed segments (1020), and the third portion (1003) includes a third plurality of transformed segments (1030). In this regard, the first plurality of transformed segments (1010) are segregated from one another within the first portion (1001). Similarly, the second plurality of transformed segments (1020) are segregated within the second portion (1002), and the third plurality of transformed segments (1030) are segregated within the third portion (1003). However, the first plurality of transformed segments (1010) slightly overlap, i.e., are adjacent with the second plurality of transformed segments (1020). Similarly, the second plurality of transformed segments (1020) are adjacent with the third plurality of transformed segments (1030).

[0074] While the embodiments described in the examples herein show an energy source that is 90° to the X-direction, the energy source may be directed toward the additively manufactured product in any direction. Further, as noted above, the methods described herein may utilize a plurality of energy sources to perform the additive manufacturing steps and/or grain transformation steps. In this regard, it should be understood that the illustrated embodiments are not intended to limit the scope of the claims to any particular configuration of the additively manufactured product and energy source(s). Furthermore, certain terms used in the examples, such as, but not limited to, upper portion, upper half, upper edge, lower portion, lower half, lower edge, left edge, right edge, are used merely for illustrative purposes, and in no way serve to limit the scope of the claims.

[0075] Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention which are intended to be illustrative, and not restrictive.

[0076] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases "in one embodiment" and "in some embodiments" as used herein do not necessarily refer to the same embodiment s), though it may. Furthermore, the phrases "in another embodiment" and "in some other embodiments" as used herein do not necessarily refer to a different embodiment, although it may. Thus, as described above in the specification, and below in the claims, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.

[0077] In addition, as used herein, the term "or" is an inclusive "or" operator, and is equivalent to the term "and/or," unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of "a," "an," and "the" include plural references, unless the context clearly dictates otherwise.

[0078] Although the various aspects of the presently disclosed embodiments have been illustrated above by reference to examples and preferred embodiments, it will be appreciated that the scope of the presently disclosed embodiments are defined not by the foregoing description but by the following claims properly construed under principles of patent law.

Claims

CLAIMS What is claimed is:

1. A method comprising:

(a) producing an additively manufactured product having a length (x), width (y) and a height (z);

wherein at least a portion of the additively manufactured product comprises a plurality of first grains;

wherein an average aspect ratio of the first grains is at least 2: 1 in an Z:X plane;

wherein an average grain size of the first grains is at least 0.5 mm;

(b) selectively directing an energy source toward a segment of the portion, thereby producing a molten pool segment;

wherein an aspect ratio of a depth to a width of the molten pool segment is at least 1.5: 1;

(c) cooling the molten pool segment, thereby producing a transformed segment; wherein the transformed segment comprises a plurality of second grains; and wherein an average grain size of the second grains is not greater than 90% of the average grain size of the first grains.

2. The method of claim 1, wherein the producing comprises:

additively manufacturing the additively manufactured product, wherein the additively manufacturing comprises:

(i) using the energy source to heat a wire feedstock above the liquidus point of the additively manufactured product to be formed, thereby creating a molten pool;

(ii) cooling the molten pool at a cooling rate of at least 0.l°C per second; wherein, due to the steps (i) and (ii), a portion of the additively manufactured product is produced, the portion comprising at least some of the first grains;

(iii) repeating steps (i)-(ii) until the final additively manufactured product is completed, the final additively manufactured comprising a plurality of the portions and the plurality of the first grains;

wherein steps (b) - (c) are performed on at least one of the plurality of portions.

3. The method of claim 1, wherein the producing comprises: additively manufacturing the additively manufactured product, wherein the additively manufacturing comprises:

(i) using the energy source to heat a powder feedstock above the liquidus point of the additively manufactured product to be formed, thereby creating a molten pool;

(ii) cooling the molten pool at a cooling rate of at least 0.l°C per second;

wherein, due to the steps (i) and (ii), a portion of the additively manufactured product is produced, the portion comprising at least some of the first grains;

4. The method of any of the preceding claims, wherein during the directing step (b), the energy source is continuously powered and moved, thereby producing at least one continuous molten pool segment.

5. The method of any of the preceding claims, further comprising:

wherein steps (b) - (c) are repeated at least once on at least one portion of the plurality of portions, thereby realizing a plurality of transformed segments.

6. The method of any of the preceding claims, wherein at least some of the plurality of transformed segments are segregated from each other.

7. The method of any of the preceding claims, wherein at least some of the plurality of transformed segments are adjacent each other.

8. The method of any of the preceding claims, wherein the depth of at least one molten pool segment is at least 2 mm, or 5 mm, or 10 mm, or 20 mm.

9. The method of any of the preceding claims, wherein the aspect ratio of at least one molten pool segment is at least 2: 1, or 3: 1, or 4: 1, or 5: 1, or 6: 1.

10. The method of any of the preceding claims, wherein the second grains of at least one transformed segment comprises an average grain size not greater than 75%, or 50%, or 25% of the average grain size of the first grains.

11. The method of any of the preceding claims, wherein at least one transformed segment comprises a length (L) that is at least 10%, or 25%, or 40%, or 50%, or 65%, or 75%, or 90%, or 100% of at least one of the length (x), the width (y) or the height (z) of the additively manufactured product.

12. The method of any of the preceding claims, wherein at least one transformed segment comprises a length (L) that is equivalent to at least 1, or 2, or 5, or 10, or 15, or 20, or 30 additively manufactured layers.

13. The method of any of the preceding claims, wherein the second grains comprise equiaxed grains.

14. The method of any of the preceding claims, wherein the additive manufacturing comprises operating in a vacuum at a pressure of not greater than 1000 ptorr, or 500 ptorr, or 300 ptorr, or 200 ptorr.

15. The method of any of the preceding claims, wherein the additively manufactured product comprises at least one of an aluminum alloy, titanium alloy, cobalt alloy, nickel alloy, iron alloy, or chromium alloy.

16. The method of any of the preceding claims, wherein the additively manufactured product comprises a titanium alloy.

17. The method of any of the preceding claims, wherein the additively manufactured product comprises titanium alloy Ti-6Al-4V.

18. The method of any of the preceding claims, wherein the additively manufactured product is in the form of an automotive component or an aerospace component.

19. A method comprising:

wherein an average grain size of the first grains is at least 0.5 mm;

(c) cooling the molten pool segment, thereby producing a transformed segment; wherein the transformed segment comprises a plurality of second grains; wherein an average grain size of the second grains is not greater than 90% of the average grain size of the first grains; and

wherein the second grains comprise equiaxed grains.

20. A method comprising:

wherein an average grain size of the first grains is at least 0.5 mm;

(c) cooling the molten pool segment, thereby producing a transformed segment; wherein the transformed segment comprises a plurality of second grains; and wherein an average grain size of the second grains is not greater than 25% of the average grain size of the first grains.