Systems and methods for phase-engineered laser beam shaping for improved microstructure and defect control

Abstract

The present disclosure relates to a method, using a using a laser source, to carry out a processing operation on a molten metal to enable control over a resulting microstructure, defects, and / or stresses of a printed part formed, or of a weld formed by laser welding. In some implementations the method may involve using the laser source to generate a laser beam; controlling the phase of the laser beam to create a wavefront having an orbital angular momentum; and using the orbital angular momentum of the wavefront to transfer an optical torque onto the molten metal. This imparts a degree of control over at least one of density or grain microstructure of at least one of the printed part or the weld.

Description

SYSTEMS AND METHODS FOR PHASE-ENGINEERED LASER BEAM SHAPING FOR IMPROVED MICROSTRUCTURE AND DEFECT CONTROLCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a PCT International Application of United States Patent Application No. 63 / 671 ,619, filed on July 15, 2024. The disclosure of the above application is incorporated herein by reference.FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC for the operation of Lawrence Livermore National Laboratory.FIELD

[0003] The present disclosure relates to systems and methods for laser beam shaping during an additive manufacturing (AM) operation or a laser welding operation for the purpose of positively influencing the interaction of laser light with molten metal during laser welding or during an AM operation, to enable control over the resulting microstructure, defects and stresses of the part or surface being acted on by the laser light.BACKGROUND

[0004] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0005] Metal additive manufacturing (AM) enables manufacturing of intricate and complex geometries beyond the limitations of conventional approaches. However, AM produced parts typically have mechanical properties that differ from conventional manufacturing. This results from microstructural differences such as the presence of elongated grains or high concentrations of dislocations in AM material.

[0006] Of the different metal AM methods, laser powder bed fusion (LPBF) presents particular challenges due to the relatively small powders (typically 10 - 50 pm) used and the interactions of the metal with the tightly focused laser. Common defects,such as incomplete melting, gas porosity, and high residual stresses, are difficult to avoid and present significant challenges for reliable printing. These challenges often result in small windows of acceptable processing parameters that can give the optimal properties. Optimizing one property will often deteriorate another property, i.e. optimizing density can decrease microstructure uniformity or residual stress or alternately improving microstructure uniformity can decrease density.

[0007] A large contributor to these issues is that the typical LPBF laser beam profile used are of a Gaussian shape; these beams are non-optimal for the laser AM process because of detrimental laser-material interactions during printing such as keyholing (laser-vapor interactions), spatter and porosity (melt pool instabilities) and anisotropic mechanical properties (large thermal gradients). Gaussian beams suffer from strong intensity localization at the beam waist and possess high sensitivity to focal plane positioning, limiting optothermal control. Even simple amplitude-structured laser beam shapes can improve on the Gaussian induced problems and lead to grain refinement and stabilized melt pools, reducing spatter and porosity.

[0008] To address the above and other metal AM fabrication challenges, what is needed is a method and system for creating and controlling a laser source with controlled phase, polarization and amplitude (intensity) to influence the interaction of a laser light produced by the laser source with molten metal during laser welding and / or additive manufacturing, so as to enable control over the resulting microstructure, defects, and / or stresses of a printed metal component or laser weld.SUMMARY

[0009] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0010] In one aspect the present disclosure relates to a method, using a laser source, to carry out a processing operation on a molten metal to enable control over a resulting microstructure, defects, and / or stresses of a printed part formed, or of a weld formed by laser welding. In one implementation the method may comprise using the laser source to generate a laser beam; controlling the phase of the laser beam to create a wavefront having an orbital angular momentum; and using the orbital angular momentum of the wavefront to transfer an optical torque onto the molten metal. This imparts a degree of control over at least one of density or grain microstructure of at least one of the printed part or the weld.

[0011] In another aspect of the present disclosure the phase of the wavefront is controlled such that phase vortex is created in which a polarization of the laser beam is spatially invariant throughout a cross section of the laser beam.

[0012] In another aspect of the present disclosure the phase of the wavefront is controlled such that a polarization vortex is created in which a polarization direction of the laser beam changes continuously relative to an axial center of the wavefront of the laser beam (spatially variant).

[0013] In another aspect of the present disclosure the method further comprises controlling an amplitude (intensity distribution) of the laser beam.

[0014] In another aspect the present disclosure relates to a method, using a laser source, to carry out a processing operation on a molten metal to enable control over a resulting microstructure, defects, and / or stresses of a printed part formed, or of a weld formed by laser welding. The method may comprise using the laser source to generate a laser beam; controlling the phase of the laser beam to impart an orbital angular momentum (OAM) onto the wavefront, to create a wavefront having at least one of a phase vortex or a polarization vortex; and using at least one of the phase vortex or the polarization vortex the orbital angular momentum of the wavefront to transfer an optical torque onto the molten metal through different modes of coupling. This serves to control at least one of density or grain microstructure of at least one of the printed part or the weld.

[0015] In another aspect of the present disclosure the phase of the laser beam is controlled to create the phase vortex, and wherein the phase vortex causes a polarization of the laser beam to be spatially invariant throughout a cross section of the laser beam.

[0016] In another aspect of the present disclosure the phase of the laser beam is controlled to create the polarization vortex, and wherein the polarization vortex causes a polarization of the laser beam to be spatially variant throughout a cross section of the laser beam.

[0017] In another aspect of the present disclosure the method further comprises controlling an amplitude of the laser beam.

[0018] In another aspect of the present disclosure using the laser comprises using at least one of a continuous wave laser or a pulsed laser for generating the laser beam, and wherein the laser beam has a wavelength between 250-2000 nm, or around 10600 nm where certain materials have higher absorptivity.

[0019] In another aspect, the present disclosure relates to a system for use in at least one of a laser based additive manufacturing application or a welding application to control at least one of a microstructure, defects, and / or stresses of a printed part formed from molten metal using the system, or of a weld formed using molten metal by the system. The system may comprise a laser configured to generate a laser beam, and a plurality of optics components for receiving the laser beam and controlling a phase of a wavefront of the laser beam. The controlled phase creates the wavefront with an orbital angular momentum. The orbital angular momentum transfers an optical torque onto the molten metal as the laser beam impinges the molten metal to impart a degree of control over at least one of density or grain microstructure of at least one of the printed part or the weld.

[0020] In another aspect of the present disclosure the laser comprises at least one of a continuous wave laser or a pulsed laser.

[0021] In another aspect of the present disclosure the system further comprising an electronic controller for controlling operation of the laser.

[0022] In another aspect of the present disclosure the plurality of optics includes a polarizing beam splitter for converting the laser beam emanating from the laser into a p linear polarized beam and an s linear polarized beam.

[0023] In another aspect of the present disclosure the plurality of optics further comprises a quarter wave plate beam for receiving the linear (p or s) polarized beam and creating a circularly (left circular or right circular) polarized beam of light.

[0024] In another aspect of the present disclosure, the plurality of optics further comprises a half wave plate for receiving the linear (p or s) polarized beam and converting the direction of the circularly (left circular or right circular) polarized beam of light from a first rotational direction to a second rotational direction.

[0025] In another aspect of the present disclosure the plurality of optics further comprises a segmented wave plate configured to receive and convert the circularly (left circular or right circular) polarized beam of light having the second rotational direction to a polarization vortex beam in which both the phase and the polarization of the beam are spatially variant.

[0026] In another aspect of the present disclosure the plurality of optics further comprises a telescope and an f-theta lens acting as a focusing optics to focus the polarization vortex beam.

[0027] In another aspect of the present disclosure the system further comprises a scanning subsystem for scanning the linearly (p or s) polarized beam having the second rotational direction within an X / Y plane.

[0028] In another aspect of the present disclosure the scanning subsystem comprises galvanometer scanner subsystem.

[0029] In another aspect of the present disclosure the laser comprises at least one of a continuous wave laser or a pulsed laser.

[0030] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.BRIEF DESCRIPTION OF DRAWINGS

[0031] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0032] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

[0033] Figure 1 is a high level block diagram illustration of one embodiment of a system in accordance with the present disclosure;

[0034] Figure 1 a shows in highly simplified illustrations the differences between amplitude, phase vortex and polarization of light;

[0035] Figure 2 illustrates transverse cross section EBSD (Electron Backscatter Diffraction) maps of SS3161 L melt pools phase created using phase vortex and polarization vortex controlled beams with the different colors representing different crystallographic orientations of metal grains and the lines outlining the individual grains;

[0036] Figure 3 illustrates portions of SEM images that show a longitudinal cross section analysis on SS 316L melt pools, which indicates the strong grain refinement induced by phase vortex and polarization vortex light beams;

[0037] Figure 4 shows graphs which illustrate keyholing that occurs with a conventional Gaussian beam, a vortex beam with m=1 and a vortex beam with m=2;

[0038] Figure 5 shows EBSD maps created using scanning electron microscopy on SS 316L cubes printed to illustrate how polarization influences texture of the printed material; and

[0039] Figure 6 shows Archimedes measurements of part densities which indicate polarization dependence, and more particularly how spiral polarization achieves even better absorption efficiency and even further improves part density over radial polarization.DETAILED DESCRIPTION

[0040] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0041] While conventional light beams typically carry linear momentum, engineering the phase of an incident beam can induce spin-orbit coupling and result in wavefronts with a spiral trajectory, and consequently, enable such 'phase vortex' beams to propagate with spin angular momentum (“SAM”) and orbital angular momentum (“OAM”). While SAM can be obtained by the more conventional circularly polarized (without the need for phase variations) light, the OAM is a consequence of having a phase vortex. The OAM increases with the order of the phase vortex beam, and can be transferred on to materials as torque onto materials. The OAM can also couple to the melt pool through other mechanisms such as through bulk absorption, azimuthal intensity gradients (which can impart an asymmetric temperature gradient leading to surface tension gradients) or through capillary effects. At high power densities in laser welding and AM, a vapor plume can form above the melt pool. The vortex beam could also impart OAM to the vapor plume, which can further induce complex flow patterns to the melt pool. Other effects such as magnetohydrodynamic coupling cannot be ruled out. The various embodiments and methods of the present invention incorporate and use such vortex beams and the resulting transfer of OAM, as an optical knob (by engineering the order of the beam) to impart some degree of control into fluid dynamic instabilities, for example turbulent or modified flows, and influence the microstructural evolution during the process. The vortex beams and resulting transfer of OAM can eliminate or aid significantly in the reduction of spatter and porosity and reduce the propensity for keyholing (an unstable melting condition that forms a deep cavity in the melt pool).

[0042] In particular, the systems and methods of the present disclosure are able to create and control a laser source with controlled phase and amplitude (intensity). This enables influencing the interaction of laser light with molten metal during laser welding and / or additive manufacturing, which in turn enables control over the resulting microstructure, defects, and stresses of a printed metal component or laser weld. Thesystems and methods described herein may be used, as just one example, in laser powder bed fusion (LPBF). The LPBF process is a process for producing metallic components with wide ranging geometries and site-specific properties. This process is performed by spreading a thin layer of metal powder and selectively melting / welding the powder into a substrate at the desired locations. This operation is repeated in a layer-by- layer process to build up 3D part. The laser beam properties have a large effect on the interaction of the laser with the molten metal and therefore the resulting physical properties of resolidified metal. In general, any process that involves high power lasers for melting a material (such as welding, directed energy deposition) can be controlled by the use of vortex beams.

[0043] Referring to Figure 1 , one embodiment of a system 10 in accordance with the present disclosure is shown. In this example the system 10 generates phase vortex beams from the output of a continuous wave Yb fiber laser 12 emitting light at a selected wavelength. In some embodiments, however, the laser may be a pulsed laser, and the operation of the system 10, and the performance results obtained, will be similar or identical regardless of whether a continuous wave laser or a pulsed laser is used. In some embodiments the wavelength may be 250-2000 nm, or in some embodiments at 10600 nm where certain materials have higher absorptivity. In one embodiment the wavelength is 1080 nm. In some embodiments the power of the laser may vary between about 50 W and 50000 W, depending on the material being processed and other factors.

[0044] A polarizing beam splitter 14 is used to convert the unpolarized laser beam 12a into two linear polarizations “p”, indicated by reference number 12a1 , and “s”, indicated by reference number 12a2. The s polarized light (beam 12a2) is sent into a beam dump 16. The p polarized light (beam 12a1 ) is sent through a quarter wave plate 18 to obtain circularly polarized light. A half wave plate 20 installed prior to the quarter wave plate 16 converts the direction of the circularly polarized light, in this example from right circular to left circular. Those skilled in the art will also appreciate that similar effects are to be expected even if one lets the s polarized light pass through and reflect the p polarized light. This choice only affects the direction of circular polarization (left circular vs. right circular) after the beam passes through the quarter wave plate. The effect will remain qualitatively the same irrespective of whether left circular or right circular light is passed through the segmented wave plate.

[0045] With further reference to Figure 1 , the left circularly polarized light is then passed through a birefringent segmented wave plate (SWP) 22. The SWP 22converts the circularly polarized input to a polarization vortex beam in which both the phase and the polarization of the beam are spatially variant. The beam that passes through the SWP 22 is then directed through a plurality of focusing optics 24. In some embodiments the focusing optics may comprise a telescope and f-theta lens. The beam then impinges a galvanometric scanner subassembly 26. The galvanometric scanner subassembly 26 may have a pair of galvanometric scanners for controllably scanning the beam over an X / Y plane on a build plate 28.

[0046] It will be appreciated that the order (‘m’) of the SWP 22 determines the order of the vortex beam. If a non-birefringent SWP 22 is used instead, the output beam that passes through it will carry the polarization of the beam incident on the SWP. In some embodiments a beam profiler may be used to image the intensity profile of the beam at the build plate 28. While not shown in the drawings, a beam profiler would operate similar to a camera, but offers even better capabilities as in higher dynamic range, higher damage thresholds, etc. In some embodiments a polarimeter is used to determine the direction of polarization using a Stoke’s polarimetry framework.

[0047] Referring further to Figure 1 , in some embodiments the system 10 may also include an electronic controller 30 for controlling and / or monitoring one or more components of the system, and / or monitoring the printing process being carried out. In some embodiments the electronic controller 30 may include a memory 32 (e.g., volatile and / or non-volatile RAM / ROM / DRAM, etc.) for storing software for executing printing operations and / or control algorithms for assisting with beam control. In some embodiments the memory 32 may also store one or more databases 34 used to contain lookup tables, materials data, amplitude control data, frequency and / or phase control data, etc. In some embodiments a motion control subsystem 38 (e.g., DC stepper motors, linear actuators, etc.) may be used to control scanning of the galvanometer scanners of the subsystem 26. In some embodiments the motion control subsystem 38 may also be used to control movement of the build plate 28 within the X / Y plane, and / or within each of the X, Y and Z planes.

[0048] Figure 1 a illustrates how accessing phase and polarization of a light beam enables additional degrees of freedom to influence light-matter interactions. With phase vortex control, the polarization of the light within the beam will be the same as that of the beam incident on the segmented wave plate). With polarization vortex control, the polarization of the light within the beam is spatially variant. Unlike conventional beams where the polarization is the same at each position within the beam, the direction ofpolarization in a phase-vortex beam varies (in a radial, azimuthal or spiral fashion) within the beam intensity profile .

[0049] The co-inventors hypothesize that phase vortex beams likely impart the spin and orbital angular momentum onto the melt pools, causing additional liquid stirring or modified Marangoni flows, which changes how nucleation takes place and results in an “equiaxed” (equal axes) grain structure of the re-solidified metal. Using same energy density, power and scan speed for the two laser melt tracks, one using a vortex beam the other using a Gaussian beam, vortex beams nearly eliminate the elongated (columnar) grains observed in a Gaussian beam. This is illustrated in Figure 2, where the grain structure resulting from the use of a Gaussian beam is shown. The elimination of the elongated grains, which is accomplished using a vortex beam, is shown in Figure 2. This result is likely due to three dominant effects. The first is dendrite fragmentation during solidification, with the dendrite fragments forming “new” grains ahead of the solid / liquid interface that is at the back of the melt pool. It is a similar effect to that seen in welding where a fast solidification rate in the presence of a low thermal gradient of results in equiaxed grains because of the same effect. The second effect is the stirring induced by the coupling of GAM sub-locally through absorption or temperature in the melt pool, or the emanated vapor plume above the melt pool (which can perturb the meltpool through altered vapor-fluid interactions) that could create swirling or stirring effect. This stirring will create short-lived cavitation events forming sub-micron-scale bubbles or pores (similar to stirring a cup of coffee to induce frothing), which serve as sites for new grains to be nucleated. The third effect is that the thermal gradients in the melt pool are reduced as a consequence of the annular amplitude / intensity profile) imparted by phasevortex beams. The “ring” shape will reduce thermal gradients from the center to the periphery of the melt pool, in comparison to a Gaussian beam which overheats the center of the melt pool. However, the stirring induced by GAM transfer onto the melt pool seems to be a significantly more dominant factor in grain refinement, compared to achieving grain refinement by only reducing thermal gradients. This is due to the fact that unity order vortex beams still result in elongated grains that are strongly oriented towards the direction of the laser scan direction (from the back of the melt pool at the solid / liquid interface, rather than ahead of it as seen in the vortex beams) as seen in Figure 3. On the other hand higher order vortex beams (m=2) with comparable intensity profiles and beam diameters result in fully equiaxed grains, as observed not just in transverse cross section images, but also longitudinally in the melt pool (shown in Fig. 3). This observationshows that increasing the strength of OAM (by increasing the beam order) is the more dominating mechanism, as compared to thermal gradients or other fluid dynamic effects, during the solidification process of the melt pool.

[0050] Apart from the proposed effects on microstructure, it is hypothesized that the ring-shaped intensity profile of vortex beams will stabilize the flows within the melt pool. It is believed that this reduces the propensity for keyhole formation compared to conventionally used Gaussian beams, due to a redistribution of the intensity profile and consequently energy delivered to the melt pool (from the center to the melt pool edges). Figure 4 shows graphs of keyhole formation for different values of “m” for a Gaussian beam, a vortex beam with m=1 , and a vortex beam with m=2. From Figure 4, it can be observed that the propensity for keyhole formation (indicated by the difference in slope between the black and red lines), is much lower in the case of the vortex beams. It is believed that the implementation of a phase vortex beam, irrespective of the polarization can reduce the propensity for keyholing and reduce porosity, which will improve the part density of structures printed under otherwise identical conditions. Note that the proposed approach of incorporating polarization and phase vortex beams is also applicable in directed energy deposition (DED), laser welding and other process where a laser beam is used for melting the surface of metals or alloys and results in solidification, cooling and grain structure evolution. The presence of small, equiaxed grain boundaries will improve resistance to propagation of cracks, pores and defects and further improve mechanical properties of welded or AM (LPBF, DED and other lasermelting dependent processes) / LPBF-printed materials.

[0051] Referring to Figure 2, two simulated transverse cross sections of SS3161 L melt pools phase are shown which were created using phase vortex and polarization vortex controlled beams. These illustrations show the strong grain refinement achieved with phase vortex and polarization vortex beams.

[0052] Figure 3 shows portions of SEM images of a longitudinal cross section analysis on SS 316L melt pools using Gaussian, phase vortex (m-=1 ) and polarization vortex beam. This again illustrates the strong grain refinement induced by high-order vortex beams.

[0053] Figure 5 shows EBSD (Electron Backscatter Diffraction) maps created using scanning electron microscopy on SS 316L cubes printed to exhibit polarization dependent texture. These EBSD maps illustrate how grain texture is sensitive to the polarization direction of vortex beams, where texture is the propensity for a material tohave a certain crystallographic orientation. Strongly textured materials have many grains of similar orientation while weakly textured materials have random orientations. The inverse pole figures of Figure 5 show the difference in orientation propensity of the left side (spirally polarized m=1 vortex beam) to be strongly (101 ), or strongly textured toward that orientation. Whereas the (azimuthally polarized m=1 vortex beam) (right side) is much weaker in the (101 ) direction and has a secondary preferential orientation close to (201 ), demonstrating some control over texture with polarization changes (despite the phase distribution in both beams being the same) in the current invention.

[0054] Figure 6 shows Archimedes measurements of part densities which indicate polarization dependence, and more particularly how spiral polarization influences absorption efficiency and even further improves part density over radial polarization.

[0055] The various embodiments and methods discussed herein thus utilize full control of all of the properties of light to garner more control over the AM process, improving control over laser / material interactions, allowing better control of the melt-pool and solidification and ultimately reducing defects and enabling the ability to closely control microstructure.

[0056] Example uses of the present invention include controlling microstructure in position-dependent manner during LPBF, widening the processing window for maximum density without leading to defect formation during LPBF, and controlling microstructure during laser welding / laser DED.

[0057] Although the descriptions above and in the Appendices contain many details and specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from aclaimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments.

[0058] Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art. In the claims, reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element or component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 1 12, sixth paragraph, unless the element is expressly recited using the phrase “means for.”

[0059] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

[0060] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed,that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0061] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0062] When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. As used herein, the term “about”, when used immediately previous to a specific recited value, denotes the specific recited value as well as all values, inclusive, from + / - 10% of the specific recited value.

[0063] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0064] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Claims

CLAIMSWhat is claimed is:1 . A method, using a laser source, to carry out a processing operation on a molten metal to enable control over a resulting microstructure, defects, and / or stresses of a printed part formed, or of a weld formed by laser welding, comprising: using the laser source to generate a laser beam; controlling the phase of the laser beam to create a wavefront having an orbital angular momentum; and using the orbital angular momentum of the wavefront to transfer an optical torque onto the molten metal to impart a degree of control over at least one of density or grain microstructure of at least one of the printed part or the weld.

2. The method of claim 1 , wherein the phase of the wavefront is controlled such that phase vortex is created in which a polarization of the laser beam is spatially invariant throughout a cross section of the laser beam.

3. The method of claim 1 , wherein the phase of the wavefront is controlled such that a polarization vortex is created in which a polarization direction of the laser beam changes continuously relative to an axial center of the wavefront of the laser beam (spatially variant).

4. The method of claim 1 , further comprising controlling an amplitude (intensity distribution) of the laser beam.

5. A method, using a laser source, to carry out a processing operation on a molten metal to enable control over a resulting microstructure, defects, and / or stresses of a printed part formed, or of a weld formed by laser welding, the method comprising: using the laser source to generate a laser beam; controlling the phase of the laser beam to impart an orbital angular momentum (OAM) onto the wavefront, to create a wavefront having at least one of a phase vortex or a polarization vortex; andusing at least one of the phase vortex or the polarization vortex the orbital angular momentum of the wavefront to transfer an optical torque onto the molten metal through different modes of coupling, to control at least one of density or grain microstructure of at least one of the printed part or the weld.

6. The method of claim 5, wherein the phase of the laser beam is controlled to create the phase vortex, and wherein the phase vortex causes a polarization of the laser beam to be spatially invariant throughout a cross section of the laser beam.

7. The method of claim 5, wherein the phase of the laser beam is controlled to create the polarization vortex, and wherein the polarization vortex causes a polarization of the laser beam to be spatially variant throughout a cross section of the laser beam.

8. The method of claim 5, further comprising controlling an amplitude of the laser beam.

9. The method of claim 1 , wherein using the laser comprises using at least one of a continuous wave laser or a pulsed laser for generating the laser beam, and wherein the laser beam has a wavelength between 250-2000 nm, or around 10600 nm where certain materials have higher absorptivity.

10. A system for use in at least one of a laser based additive manufacturing application or a welding application to control at least one of a microstructure, defects, and / or stresses of a printed part formed from molten metal using the system, or of a weld formed using molten metal by the system, the system comprising: a laser configured to generate a laser beam; a plurality of optics components for receiving the laser beam and controlling a phase of a wavefront of the laser beam; the controlled phase creating the wavefront with an orbital angular momentum, the orbital angular momentum transferring an optical torque onto the molten metal as the laser beam impinges the molten metal to impart a degree of control over at least one of density or grain microstructure of at least one of the printed part or the weld.1 1. The system of claim 10, wherein the laser comprises at least one of a continuous wave laser or a pulsed laser.

12. The system of claim 10, further comprising an electronic controller for controlling operation of the laser.

13. The system of claim 10, wherein the plurality of optics includes a polarizing beam splitter for converting the laser beam emanating from the laser into a p linear polarized beam and an s linear polarized beam.

14. The system of claim 13, wherein the plurality of optics further comprises a quarter wave plate beam for receiving the linear (p or s) polarized beam and creating a circularly (left circular or right circular) polarized beam of light.

15. The system of claim 14, wherein the plurality of optics further comprises a half wave plate for receiving the linear (p or s) polarized beam and converting the direction of the circularly (left circular or right circular) polarized beam of light from a first rotational direction to a second rotational direction.

16. The system of claim 15, wherein the plurality of optics further comprises a segmented wave plate configured to receive and convert the circularly (left circular or right circular) polarized beam of light having the second rotational direction to a polarization vortex beam in which both the phase and the polarization of the beam are spatially variant.

17. The system of claim 16, wherein the plurality of optics further comprises a telescope and an f-theta lens acting as a focusing optics to focus the polarization vortex beam.

18. The system of claim 17, further comprising a scanning subsystem for scanning the linearly (p or s) polarized beam having the second rotational direction within an X / Y plane.

19. The system of claim 18, wherein the scanning subsystem comprises galvanometer scanner subsystem.

20. The system of claim 10, wherein the laser comprises at least one of a continuous wave laser or a pulsed laser.

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