CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional

Application No. 61 /865,731 , filed on August 14, 2013. The entire disclosure of the above application is incorporated herein by reference.

STATEMENT OF GOVERNMENT RIGHTS

[0002] The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the U.S. 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 method for applying coatings to non-planar surfaces or areas where movement is restricted, and more particularly to apparatuses and methods for performing laser peening and High Velocity Accelerated Laser Deposition (HVLAD) on non-planar surfaces or surfaces in areas where movement is restricted.

BACKGROUND

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

[0005] High Velocity Laser Accelerated Deposition (HVLAD) is a proprietary photonic method developed by Lawrence Livermore National Laboratory of Livermore, CA, for producing highly corrosion resistant coatings with virtually unmatched interfacial bond strength. With HVLAD, a high-intensity laser pulse is focused onto an advancing film-like target material which is covered by a thin layer of water. The laser pulse generates a high-temperature plasma, and with it a very large pressure that shears out a patch of film-like material, accelerating it to hypersonic velocities. The accelerated patch hits the substrate at an oblique angle, where the high impact velocity induces plastic flow at the film-substrate interface. This produces shear flow due to the oblique incidence, thereby resulting in the intimate mixing of target and substrate materials at the interface. The intimate mixing of target and substrate materials creates an exceptionally strong interfacial bond. An important aspect of the technique is that neither the temperature of the film material, nor that of the substrate, is substantially raised during the process; as such the process does not induce phase changes or alloy composition changes and thus allows for the exceptionally strongly bonded coatings of alloys and materials that might not otherwise be possible. The strength of the "localized explosive bond" achieved with HVLAD approaches the ultimate tensile strength of the bulk material itself. Thus, HVLAD uses advanced lasers to produce high-performance corrosion and wear resistant coatings with interfacial bond strengths previously achieved only through explosive bonding. Additional specific details on the HVLAD process may be found in U.S. patent application serial no. 13/229,840, filed September 12, 2012, and assigned to Lawrence Livermore National Security LLC, the entire disclosure of which is hereby incorporated by reference into the present application.

[0006] Compared to traditional chemical and physical vapor deposition (CVD and PVD), HVLAD offers the following distinct advantages: (1 ) room temperature deposition in air; (2) elimination of problematic powder handling required by flame, plasma, high-velocity oxy-fuel and cold-spray processes; (3) wide range of coating compositions; (4) congruent deposition of alloys; (5) an order-of-magnitude enhancement in bond strength over that possible with conventional methods; (6) elimination of residual porosity; (7) extremely high mass flux rates exceeding 15 mils/mm2/pulse; and (8) utilization of cost- competitive photonic tooling, developed and built domestically, thereby providing the U.S. a competitive advantage for the production of advanced new materials.

[0007] HVLAD enables the continuous deposition of the world's most corrosion resistant materials, including titanium and refractory metals, on a wide variety of substrates requiring protection. The HVLAD deposition process can be done at ambient temperature and in open air with no special containment. For example, aluminum alloys can now be clad with corrosion-resistant titanium alloys for aerospace and marine applications. This new laser-based coating process can be used to clad inexpensive high-temperature oxide-dispersion- strengthened, or ODS, steels, which has been proposed for use in future fossil, solar and nuclear power plants, with exceptionally corrosion resistant high- temperature materials such as tantalum. This enables the operation of such plants at temperatures, approaching 900 degrees centigrade. It will be appreciated that unprotected ODS steel undergoes extreme corrosive attack in high temperature molten salt coolants, whereas tantalum and other protective coatings prevent such attack, thereby enabling operation in such extreme environments. By extending the operating temperature to such high levels, dramatic improvements in the efficiency of energy conversion become possible.

[0008] The HVLAD process leverages high-power pulsed laser technology developed by Lawrence Livermore National Laboratory (LLNL) for laser inertial confinement fusion, known as laser ICF. Such laser technology serves as the foundation stone for the National Ignition Facility, at present the world's most energetic laser facility whose mission is to create fusion ignition in a laboratory for the first time.

[0009] HVLAD protective coatings and cladding with high-integrity interfacial bonds are capable of extending the operating temperature of energy conversion equipment, thereby achieving improvements in efficiency and extending the life of valuable equipment, thereby potentially saving the U.S. economy tens of billions of dollars every year. For example, the annual cost of corrosion due to the deterioration of the nation's infrastructure is estimated to be at least $22 billion, with the loss of another estimated $22 billion due to the corrosion of planes, ships, vehicles and other equipment owned by the U.S. Department of Defense. New proprietary HVLAD coatings and cladding are expected to help prevent such loss.

[0010] Coatings produced with conventional chemical and physical vapor deposition processes are typically completed at a relatively slow rate due to mass transport limitations. Low mass flux, or flow, and roughness amplification place limitations on coating thicknesses as well. Typically, conventional thermal and cold-spray coatings have bond strengths only on the order of 10,000 psi, while the substrate and coating materials have ultimate tensile strengths of 100,000 to 500,000 psi. Furthermore, such coating processes rely on difficult-to-handle powder feeds through a hypersonic nozzle.

[0011] Another advantage of the HVLAD system is that it is highly cost competitive. The HVLAD beam delivering robot can be configured nearly exactly as that now used cost effectively in the laser peening process for treating F-22 fighter jets, Navy arrestment hook shanks, and gas and steam turbine blades. Thus, almost no additional capital investment is required for initial deployment of the HVLAD system in applying coatings in such applications.

[0012] HVLAD can be beneficial in a wide variety of industrial applications as well. For example, a thin layer of titanium on critical areas of aircraft and ship hulls could be a very cost effective means of corrosion prevention, yet allow for a conventional ship hull design of steel.

[0013] In addition, protective coatings of various types are essential for ensuring long service lives for components in high-temperature power plants. These coatings help prevent the initiation and propagation of various modes of corrosion, including uniform corrosion, pitting, crevice corrosion, erosion- corrosion, fretting corrosion, stress corrosion cracking, corrosion fatigue, and hydrogen-induced cracking. By enabling the operation of power plants at higher temperatures through the use of high-temperature material coatings, substantial increases in process efficiency can be realized.

[0014] HVLAD coatings could make possible the use of high- temperature materials in power plants, leading to an increase in efficiency of up to possibly up to 20% or more, and resulting in significant savings for the economy and the environment. By making it possible to operate power plants at higher temperature through the use of high-temperature materials, substantial increases in process efficiency may potentially be realized. Increasing the operating temperature of an energy conversion system from 325 ^' i °C (-600K) to 900 ^' i °C (-1200K), the efficiency might be increased by as much as 20% in fossil-fuel, solar-thermal, and nuclear power plants. While ODS FM steels have very good high-temperature strength, these materials lack corrosion resistance in exotic high-temperature coolants such as flowing molten fluoride salts and liquid metals. The HVLAD process can be used to deposit high-temperature, corrosion-resistant coatings of very expensive corrosion-resistant alloys such as Ta-10W on less corrosion-resistant structural materials such as ODS steel, with bond strengths limited by the yield strength of the coating or substrate material.

[0015] At the present time however, there is no effective means for manipulating the various components of the HVLAD system into areas with limited access, such as the insides of large and small conduits. Enabling coatings to be applied to difficult to access areas of structures or on the insides of large and small conduits would allow the HVLAD methodology to be significantly expanded.

SUMMARY

[0016] In one aspect the present disclosure relates to an apparatus for use with a high velocity laser deposition (HVLAD) process for depositing a coating on a non-planar surface of a structure. The apparatus may make use of a housing articulable about at least two non-parallel axes so as to be able to follow a contour of the non-planar surface of the structure. A film may be carried on the housing which has a first surface facing away from the structure and a second surface facing toward the structure. A tamping medium may be configured to cover the first surface of the film. A laser source may be used to direct a laser beam at the first surface of the film at an oblique angle to the first surface of the film, which causes removal of a portion of the film and depositing the removed portion on the surface of the structure.

[0017] In another aspect the present disclosure relates to an apparatus for use with a high velocity laser deposition (HVLAD) process for depositing a coating on a non-planar surface of a structure. The apparatus may comprise a housing articulable about three non-parallel axes so as to be able to follow a contour of the non-planar surface of the structure. A target film may be carried on the housing and may have a first surface facing away from the structure and a second surface facing toward the structure. A tamping medium may be configured to contact the first surface of the target film during the HVLAD operation. A laser source may be used for generating a laser beam directed at the first surface of the target film to remove and deposit a portion of the target film on the surface of the structure.

[0018] In still another aspect the present disclosure relates to a method for implementing a high velocity laser deposition (HVLAD) process for depositing a coating on a non-planar surface of a structure. The method may comprise providing a housing articulable about at least two non-parallel axes so as to be able to follow a contour of the non-planar surface of the structure. A target film may be carried on the housing and may have a first surface facing away from the structure and a second surface facing toward the structure. A tamping medium may be used which is configured to cover the first surface of the target film. A laser beam may be directed at the first surface of the target film at an oblique angle to the first surface of the target film, and used to remove a portion of the target film, and to deposit the removed portion of the target film on the surface of the structure. The method may involve controlling movement of the housing about the at least two non-parallel axes to maintain a desired spatial relationship between the target film and the non-planar surface of the structure while the HVLAD process is carried out.

[0019] 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 THE DRAWINGS

[0020] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0021] Figure 1 is a high level side cross sectional view of one embodiment of a multi-axis apparatus in accordance with the present disclosure for positioning the components of an HVLAD deposition system inside a conduit and coating a non-planar surface.

[0022] Figure 2 is a high level side view of another embodiment of a multi-axis apparatus of the present disclosure that makes use of a tamping medium which is carried on a beam facing side of the target film which is being deposited on the surface;

[0023] Figure 3 is a perspective view of another embodiment of a multi-axis apparatus of the present disclosure which makes use of a three axis head for controlling movement of a housing, which carries the HVLAD components, about three axes; and

[0024] Figure 4 is an enlarged perspective view of the housing shown in Figure 3 showing in greater detail the components used in the HVLAD process mounted on the housing.

DETAILED DESCRIPTION

[0025] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0026] Referring to Figure 1 there is shown a multi-axis apparatus 10 for carrying out the HVLAD deposition process. The multi-axis apparatus 10 (hereinafter simply "apparatus 10") may be moved linearly along axis 12 and also rotated about axis 12, as indicated by arc 14 to enable coatings to be applied to non-planar surfaces. By "non-planar" surfaces it is meant surfaces that are not flat. Figure 1 illustrates the apparatus 10 being used to apply a coating 16 to an inside surface 18a of a circular pipe 18.

[0027] The apparatus 10 may include a housing 20 having a hollow beam pipe 22 that communicates with an interior area of the housing. The entire housing 20 may be translated linearly along axis 12 and/or rotated about axis 12 through a suitable conventional translation/rotation mechanism 22. Mechanism 22 may comprise one or more servo motors, stepper motors, linear drive actuators, or any other conventional electronically controlled motive means for moving the entire housing 20 linearly and/or rotationally as needed relative to axis 12. A suitable controller 24 may be used to control the mechanism 22. The controller 24 may be controlled in response to a user input or it may operate in accordance with a program that automatically controls movement of the apparatus 10 in accordance with the dimensions of the pipe 18.

[0028] The apparatus 10 further may include a tamping injection port 26 through which a tamping medium, for example a tamping fluid 28 such as water, may be injected. A high power pulsed laser beam 30 may be directed through the beam pipe 22 onto a shaped mirror 32 (i.e., flat or concave) and reflected at a desired angle (i.e., an oblique angle) onto the surface of a target film 34. The target film 34 may contain material which is to be deposited on the inside surface 18a of the pipe 18. The target film 34 may be carried on a supply spool 36 and wound onto a takeup spool 38 as the HVLAD process is carried out. The controller 24 may control advancement of the target film 34 by controlling at least one of the spools 36 and 38, in this example the takeup spool 38, as the HVLAD process is carried out. A window 40 on the housing 20 allows a portion of the target film 34 carrying coating material to be removed, accelerated and deposited on the interior surface 18a of the pipe 18 at an oblique angle relative to the interior surface 18a. A tamping fluid return conduit 42 may be used to permit return flow of the tamping fluid 28 to a tamping fluid reservoir (not shown) and to enable recirculation of the tamping fluid during the HVLAD process. An air knife line (i.e., conduit) 44 may be used to carry a pressurized flow of fluid, such as air 44a, which is directed at the mirror 32 to continuously clean a surface of the mirror which is reflecting the laser beam 30.

[0029] The apparatus 10 in Figure 1 may also include an optional stabilizing assembly 46 for stabilizing the housing 20 within the pipe 18. The stabilizing assembly 46 in one implementation may comprise two or more rollers 48 spaced about the perimeter of the housing 20 that help maintain the housing in a predetermined radial position within the pipe 18 as the housing 20 is translated and rotated while performing the HVLAD process. Alternatively, a circumferential bladder may be used which surrounds an outer surface of the housing 20 to maintain the housing in a predetermined orientation within the pipe 18. The precise configuration of the stabilizing assembly 46 may depend on the shape/contour/configuration of the structure being coated by the apparatus 10. [0030] Referring briefly to Figure 2, an apparatus 100 in accordance with another embodiment of the present disclosure is shown. The apparatus 100 is similar to the apparatus 10 and components of the apparatus 100 that are identical to those described for the apparatus 10 have been identified with the same reference numbers used in Figure 1 and a prime (') designation. With the apparatus 10, however, instead of the tamping fluid 28 being provided via a jet or stream, a tamping medium 28a is carried on a beam-facing side of the film 36'. The tamping medium may comprise water or any other suitable fluid. This eliminates the need to inject the tamping fluid 28 shown in Figure 1 . The fluid line 42 shown in Figure 1 instead operates as an evacuation line 42' to allow tamping debris present inside the housing 20' to be carried out of the housing.

[0031] Figures 3 and 4 illustrate an apparatus 200 in accordance with another embodiment of the present disclosure in which a 3-axis articulating head 202 is used to perform the HVLAD process. As shown particularly well in Figure 4, the articulating head 202 carries a housing 202a on which is supported a supply spool 204 of target film 206, a takeup spool 208, a pair of idler spools 210 and 212, and a fluid (e.g., water) delivery conduit fixture 214 for delivering a jet spray of tamping fluid 216 to the surface of the film 206. The spools 204, 208, 210 and 212 are arranged to permit a laser beam 218, as well as the tamping fluid 216, to impinge a surface of the target film 206 at a desired oblique angle.

[0032] Figures 3 and 4 illustrate the apparatus 200 being used to coat the surface of a planar plate 220. However, it will be appreciated that the articulating head 202 is able to move about three perpendicular axes as noted by arc sections 222, 224 and 226, which enables the apparatus 200 to follow the contour of virtually any non-planar surface. Such non-planar surfaces may be cylindrical, elliptical, complexly curved, or virtually any other non-planar shape. And of course, the apparatus 200 may be used to coat planar surfaces as well. During the overall HVLAD operation (described more fully in the co-pending application recited herein), each of the apparatuses 10, 100 and 200 use their respective high power pulsed laser beam (30, 30' or 218) to remove a section of the target film (34, 34' or 206) which is accelerated towards and onto the facing surface of either the pipe 18 or other non-planar surface. The laser beam 30/307218 may be moved synchronously with the housing 20/202a to maintain the desired angular alignment of the laser beam relative to the surface of the target film 34/347206. The laser beam 30/307218 may form a high-intensity laser pulse which is focused onto the target film 34/347206, which is itself covered by a thin layer of the tamping fluid 30/30', which may be water. The laser pulse generates a high-temperature plasma and a large pressure that shears out a patch-like section of the target film 34/347206. This accelerates the sheared out patch of target film to a hypersonic velocity. The accelerated patch hits the surface 18a at an oblique angle where the high impact velocity induces plastic flow at the film-substrate interface. This produces shear flow due to the oblique incidence, thereby resulting in the intimate mixing of target and substrate materials at the interface. The intimate mixing of target and substrate materials creates an exceptionally strong, permanent interfacial bond. The strength of the bond may approach the tensile strength of the material itself to which the removed film section is bonded. The motion of the housing 20/202a is controlled about a plurality of non-parallel axes so as to maintain a spatial relationship between the target film 34/347206 and the non-planar surface as the HVLAD process is carried out.

[0033] Each of the apparatuses 10, 100 and 200 thus allow the HVLAD process to be used to coat non-planar surfaces. This enables the HVLAD process to be employed on structures, such as the insides of conduits or on virtually any non-planar surface (e.g., aircraft wing and fuselage, helicopter rotor blades, etc.). Even planar structures enclosed within some other structure, which makes use of the HVLAD process to coat the structure difficult or impractical, may potentially be coated by implementing the HVLAD process with one of the apparatuses 10, 100, and 200.

[0034] The apparatuses 10, 100 and 200 are expected to find particular utility in coating structures used in connection with solar/thermal power generating systems, fossil-fueled power plants and nuclear power plants. This is expected to enable structures/components used with these facilities to operate at even higher temperatures, and thus potentially significantly enhance the efficiency of such facilities. The HVLAD process, as implemented using the apparatuses 10, 100 and 200, is expected to have significant utility in connection with applying coatings to non-planar components/structures made from oxide dispersion strengthened (ODS) ferritic-martensitic (FM) steels. The HVLAD coating process is expected to significantly enhance the corrosion resistance of such steels. The foregoing examples represent just a very limited number of applications that the apparatuses 10, 100 and 200 could be employed in to coat non-planar surfaces or surfaces in restricted areas where the HVLAD coating process would otherwise be difficult or impossible carry out.

[0035] While various embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the present disclosure. The examples illustrate the various embodiments and are not intended to limit the present disclosure. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.