Cold Spray Deposition with Pulsed Laser Sintering

Abstract

A material deposition method is provided for depositing a layer of a first material onto a substrate composed of a second material. The method includes accelerating an inert gas through a nozzle as a supersonic jet; inserting a powder of the first material into the nozzle; directing said jet with the powder towards the substrate to produce a film of the first material onto the substrate; and aiming a coherent electromagnetic beam from a laser towards the substrate to sinter the film into the layer. The first material can be Inconel 625 or a refractive high entropy alloy.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] The invention is a Continuation-in-Part, claims priority to and incorporates by reference in its entirety U.S. patent application Ser. No. 17 / 732,775 filed Apr. 29, 2022 and assigned Navy Case 114305.STATEMENT OF GOVERNMENT INTEREST

[0002] The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.BACKGROUND

[0003] The invention relates generally to annealing treatment of an inorganic mineral deposit on a substrate. In particular, the invention relates to laser sintering of a metallic and / or ceramic material deposited onto a structure by cold spray.

[0004] Many hypersonic applications have thus far been limited to single use (e.g., missile nose cone) or high maintenance and high cost applications (e.g., space shuttle tiles). The need for material solutions under repeated use and expanded survivability is critical for military and technological dominance. Environmental variables that are trivial in sub-hypersonic applications pose catastrophic failures at hypersonic velocities. A single water droplet or dust particle at hypersonic velocities poses enormous risks in vehicle survivability and increase conditional restrictions for use.

[0005] Such vulnerabilities of aerospace structures under hypersonic conditions necessitates extreme temperature and impact resistant coatings that can absorb thermal stresses as well as kinetic collision within a vitiated atmospheric environment. Such techniques to apply an appropriate coating are yet unavailable in the current state-of-the-art.SUMMARY

[0006] Conventional coating deposition techniques yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, various exemplary embodiments provide a material deposition method for depositing a layer of a first material onto a substrate composed of a second material. The method includes accelerating an inert gas through a nozzle as a supersonic jet; inserting a powder of the first material into the nozzle; directing said jet with the powder towards the substrate to produce a film of the first material onto the substrate; and aiming a coherent electromagnetic beam from a pulsed laser towards the substrate to sinter the film into the layer.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which:

[0008] FIG. 1 is a representational view of a cold spray operation;

[0009] FIG. 2 is a representational view of a laser sinter operation;

[0010] FIG. 3 is a representational view of an exemplary combined spray and sinter operation;

[0011] FIG. 4 is a representational view of an airfoil with detail view of a protective coating from the exemplary operation;

[0012] FIG. 5 is a representational view of an aircraft or a missile being coated by the exemplary process using mechanical robots;

[0013] FIG. 6 is a block diagram view of the material deposition process;

[0014] FIG. 7 is a tabular view of a grain growth;

[0015] FIG. 8 is a graphical view of X-ray diffraction (XRD) used to quantify coating microstructure;

[0016] FIG. 9A, 9B, 9C and 9D are photographic cross-sectional views of deposited material layers; and

[0017] FIG. 10 is a cross-sectional view of material layers and their crystalline structures.DETAILED DESCRIPTION

[0018] In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

[0019] The disclosure generally employs quantity units with the following abbreviations: length in meters (m), mass in grams (g), time in seconds(s), angles in degrees (°), force in newtons (N), temperature in degrees Celsius (° C.), pressure in atmospheres (atm) or pascals (Pa), electric potential in volts (V), resistance and impedance in ohms (Ω), energy in joules (J), power in watts (W) and frequencies in hertz (Hz). Supplemental measures can be derived from these, such as density in grams-per-cubic-centimeters (g / cm3) and the like.

[0020] Conventional hypersonic material solutions for hypersonic flight or de-orbital re-entry have exorbitant costs and poor survivability beyond a single use mission. Materials capable of withstanding repeated hypersonic environments are generally very costly, heavy, brittle, and / or require high-temperature processing (>2,000° C.). Such characteristics render such materials unsuitable as structural elements for frame with which to contain a hypersonic aircraft. There is a critical need for methods in depositing and tailoring coatings of high-temp materials on light-weight, low-cost substructures.

[0021] There are two inherent problems restricting hypersonic applications First, high temp metal alloy coatings often need heat treatment (>2,000° C.) following deposition which would compromise the integrity of a low-temp substructure such as aluminum (melting temperature Tm=660° C.). Second, conventional metal alloy-or-composite coating methods are limited to small form-factors to fit inside vacuum chambers and suffer with poor uniformity.

[0022] High temperature coatings are often high in cost and / or weight. Exemplary embodiments enable lower cost, lighter weight structures, yet provide localized heat treatment isolated to the coatings by the short pulse width of pulsed laser sintering. The objective of this disclosure is to describe the exemplary process of cold flow deposition of a metal alloy layer onto a substructure, followed by pulsed laser sintering to anneal the deposited layer. Short pulses of energy enable a small heat affected zone (HAZ) and further enable selective heating of the coating without compromising the substructure. This densifies the materials and improves adhesion.

[0023] Exemplary embodiments cover the gas entrainment concept of depositing a coating of high temperature material to protect a substrate structural component from ambient conditions in hypersonic flight. One potential example of this technology involves providing a coating of Inconel or other high-melting-point alloy of several dozen nanometers to millimeters in thickness onto a comparably low temperature structural material, such as aluminum.

[0024] The exemplary process enables coatings (<25 μm to >10 mm) of high-temperature metal alloy-or-composite to be deposited onto a substrate, and afterwards heat treated, such as by laser sintering. This enables incorporation of a low-cost substructure with a superior strength-to-weight ratio over alternatives necessary in the absence of heat treatment. Materials that have been successfully deposited by exemplary embodiments include Inconel 625 and an alloy of tungsten-tantalum-niobium-molybdenium (WTaNbMo).

[0025] This exemplary technique introduces the integration of cold spray (CS) deposition with pulsed laser sintering (PLS). Unlike other thermal spray deposition methods, cold spray is a supersonic powder deposition process capable of depositing virtually any material (e.g., metal, ceramic, polymer) at room temperature. Within the scope of the claimed features, alternatives to cold spray include plasma spray, which can be subjected to analogous laser treatment.

[0026] Such conditions avoid oxidation via using an inert gas and facilitate a huge variety of substructure materials. The inherent tensile film stress of many thermal spray methods suffers from delamination and adhesion loss. However, film stress in room temperature cold spray coating are compressive, offering higher film strength while eliminating oxidation than alternative deposition techniques.

[0027] Subsequent processing using pulsed laser sintering enables spatially selective heat treatment, confined to the coated material, enabling modification in film stress, densification, improved adhesion, morphology, in situ alloying, and even the potential for film repair. Additionally, this exemplary process has potential for radiation shielding in nuclear reactor systems, further broadening the benefit to the Department of Defense.

[0028] Most notably, both the cold spray and pulsed laser sintering are scalable and three-dimensionally compatible for large form-factor, conforming surfaces processed under room temperature ambient conditions. These complementary processes enable a broad range of military, nuclear, space, and commercial applications.

[0029] Cold Spray (CS) is a supersonic particle deposition method that accelerates metal powder through a nozzle above a critical velocity for particle deformation and adhesion. CS is compatible for coating large three dimensional (3D) surfaces but results in high stress coatings. Reducing film stress requires thermal treatment at temperatures that would compromise lower temperature substructures. Pulsed laser sintering can selectively apply heat to an isolated region on a surface coating without compromising substructure.

[0030] Pulsed laser heat treatment can eliminate thermal conduction to a selected heat affected zone (HAZ), allowing a tailored heat treatment, spanning from annealing, sintering, melting, to ablating. Laser heat treatment can repair crystalline damage, reduce film stress, modify crystalline microstructure (columnar versus equiaxial grains), improve film adhesion, enable in situ alloying, as well as surface smoothing and texturing. Patent Application Publication 2022 / 0359226 discloses techniques regarding laser sintering thin films of semiconductor nanoparticles.

[0031] Further efforts will include obtaining cold spray services from the Army Research Laboratories (ARL) facilities located at Penn State University, for which samples have been acquired. High temperature powder materials and aluminum substrates are to be provided by Naval Surface Warfare Center—Dahlgren Division (NSWCDD) for delivery to Penn State for cold spray deposition services.

[0032] Following receipt of cold sprayed samples, as-deposited coatings will be fully characterized prior to laser sintering experiments. A comprehensive material characterization includes, but is not limited to: X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) to be conducted at NSWCDD.

[0033] Further characterization is expected by utilizing the collaborative relationship with the Nanomaterials Characterization Labs (NMCL) at the University of Virginia. This will include focused ion beam (FIB) cross-sectioning to study the morphology, microstructure, composition, and elemental distribution. Transmission electron microscopy (TEM) will then be performed to look at the microstructure and electron backscatter diffraction (EBSD). Additional strength of materials characterization using a Vickers hardness test are planned.

[0034] Coatings composed of metal alloy and composite films will be a game changer for military applications where materials are exposed to a harsh environment. These include alloy coatings for high ablation high temperature environments, such those encountered by hypersonic and re-entry space vehicles leading edges and actuator, rocket combustion chambers, and vertical missile launcher are but a few examples.

[0035] Techniques for selective depth laser sintering (SDLS) of metal-or-composite alloy coated surfaces on less heat tolerant substrates for the purpose of reducing film stress and tailored morphology: applying metallic and composite conformal coatings to 3D surfaces via thermal spray and subsequent laser sintering techniques.

[0036] No conventional method can deposit uniform, homogenous conformal coatings of a high melting point temperature metal alloy-or-composite on 3D varying surfaces. All conventional techniques require plasma, high temperature application, or vacuum chamber sputtering. These alternative methods are incompatible with many substrates in terms of size, shape, or material types and furthermore suffer from non-uniformity on complex shapes, slow deposition rates, size restrictions, and poor homogeneity.

[0037] For example, hypersonic surfaces such as nose-cones, wings, or fan blades need to survive extreme temperatures and ablative environments, yet weight restrictions limit materials choices. The exemplary technique would enable a room temperature deposition of a refractive high entropy alloy (RHEA) coating such as tungsten-talmium-molybdimin-niobium (WTaMoNb) on a less heat tolerant air frame material using cold spray.

[0038] In particular, cold spray constitutes a thermal spray technique that aerosols metal powder accelerated to supersonic speeds at room temperature. This powder strikes a substrate's surface. This enables deposition of ultra-high temperature metal alloys onto the substrate. One caveat of cold spray is the presence of residual stress in the coating. Pulsed laser treatment spatially provides localized heat treatment with almost zero heat affect zone (HAZ), or thermal conduction.

[0039] This means a metal alloy (e.g., RHEA) coating with a high (>2,500° C.) melting point can be uniformly deposited and sintered onto a low temperature object for hypersonic applications. Additionally, both cold spray and laser sintering are completely capable of treating complicated 3D surfaces while being performed at room temperature.

[0040] FIG. 1 shows an elevation representational view 100 of a cold spray deposition process system 110 for coating an obverse surface of a substrate 120. A low pressure gas supply 130 feeds an inert gas through a valve 135 into a gas heater 140 that surrounds coils 145 through which the gas flows into a baffle chamber 150 that includes a (sonic) throat, beyond which the gas expands to supersonic speeds in a supersonic nozzle 160. The gas can be for example, nitrogen (N2) or argon (Ar).

[0041] A powder hopper 170 contains a powder of coating material, which falls into a sieve 175 and through a valve 180. The flowing gas entrains the falling powder through aspiration. Both the gas and the powder enter into the nozzle 160 to produce a cold spray 185 that deposits the coating material 190 as a layer onto the substrate 120. The heater 140 controls the gas temperature (such as by heat exchange) to compensate for thermal energy release from expansion through the nozzle 160.

[0042] FIG. 2 shows an elevation representational view 200 of a laser sinter process system 210. A laser 220 emits an electromagnetic beam through focusing optics 230 and a beam scanner (galvo) 240 to project electromagnetic energy 250 to a coating material 260 that heats to perform annealing, sintering or melting after being deposited onto the substrate 120. The beam can preferably be in the infrared portion of the spectrum and cycled at about 50 KHz as pulses-per-second. The pulse width is highly dependent on the material being processed, but generally resides in the nanosecond regime. For most metals, the wavelength is not critical. Other materials may possess unique absorption characteristics, such as semiconductors.

[0043] FIG. 3 shows an elevation view 300 of an exemplary process 310 of cold spray deposition 110 depositing a coating 190 followed by laser sinter annealing 210 to sinter the coating as the final layer 260. Both process systems 110 and 210 travel in directions 320 (left-to-right) relative to the substrate 120.

[0044] FIG. 4 shows an elevation cross-sectional view 400 of an airfoil 410 with detail 420 showing cold spray coating. An enlargement 430 of the detail 420 shows a leading edge 440 with multiple coating layers 450, which are subsequently sintered to protect the airfoil from hypersonic thermal conditions. This technique illustrates how layers can be combined iteratively, to deposit thicker coatings on regions that require greater thermal or kinetic protection.

[0045] FIG. 5 shows a representational view 500 of a 3D object with an extremely large form factor, such as a generic missile 510 being coated with cold spray and laser sinter operations. A pair of mechanical robotic arms 520 flanks the missile 510. Each arm 520 holds one of the operators for cold flow 110 or sintering 210 for traveling along the axial length of the missile 510, which can simultaneously turn on its symmetry axis.

[0046] In this manner, the cold flow process 110 travels along an axial direction 530 along the aircraft or missile surface to deposit the powder coating 190, followed by the sintering process 210 that travels independently along the axial direction 540 to fuse the powder as the final layer 260.

[0047] FIG. 6 shows a block diagram view 600 of phases and their operations. Three phases are shown: first 610, second 620 and third 630. The first two phases 610 and 620 involve Inconel, while the third phase 630 involves WTaNbMo. The first phase 610 includes ball milling 640 of Inconel into pellets, which then undergo pressing 650 onto a substrate 120.

[0048] For the second and third phases 620 and 630, laser sintering 660 replaces these milling and pressing operations. This deposition is followed by baseline material and quality characterization 670 by various techniques described previously. Next, the pressed Inconel undergoes laser sintering 680 up to 600° C. Finally the deposited and sintered layer is evaluated again in a post-sinter characterization 690.

[0049] The second and third phases 620 and 630 include cold spray deposition 660 of powder deposit. This material is Inconel for the second phase 620 and WTaNbMo for the third phase 630. For both phases, baseline characterization 670 follows, and subsequently laser sintering 680 is applied to the deposited layer 190 to form the sintered layer 260. The third phase further includes an ODU process 685. Both phases 620 and 630 conclude with post-sinter characterization 690.

[0050] FIG. 7 shows a tabular view 700 of grain growth from laser sintering as a measure of material homogeneity of the sintered layer 260. Column 710 includes peak angle, 720 provides average pellet diameters in nanometers, while column 730 includes post laser sintering diameters. Finally column 740 presents the differences in nanometers, showing positive increase in grain growth resulting from laser sintering.

[0051] FIG. 8 shows a graphical view 800 of pellet size distribution. Peak angle 2θ810 (in degrees) denotes the abscissa, while intensity 820 (counts) denotes the ordinate. A legend 830 identifies SNX 640 and SN6 650 traces, with the highest value being for SNX 640 at about 870 counts corresponding to peak angle of 43°. XRD spectra provide evidence that properties of the material being deposited can be maintained or modified depending on the laser parameters. Oxidation can be nearly eliminated, while the sprayed powder can be either maintained or tailored to achieve select conditions, such as alloying, reduction in coating stress or merely densification.

[0052] FIGS. 9A, 9B, 9C and 9D show magnified cross-sectional photographic views 900 of pre- and post-sintering. Photograph 910 shows Inconel powder, while photograph 920 shows the powder after ball milling 640 and pressing 650. Photograph 930 shows the layer 260 after laser sintering 680. Photograph 940 shows crack depth of 40 μm at 25° C., while photograph 950 shows crack depth increased, indicating greater homogeneity with increased crack depth of 76 μm at 600° C.

[0053] Photograph 910 is repeated alongside photograph 960 showing deposited and sintered Inconel in a smooth distribution. These photographs illustrate successful densification of the material deposited by cold spray. Additionally, these confirm that layers of >40 μm can be laser treated for densification at ambient (i.e., room) temperature, and this can be increased by heating the substrate by select laser parameters.

[0054] FIG. 10 shows cross-sectional views 1000 of crystalline structures. Photograph 1010 shows how grain formation can be tailored for unique properties to improve heat conduction or electrical properties. Diagram 1020 shows that when the substrate 120 cools, columnar grain formation can be achieved, and photograph 1030 shows that when the substrate 120 is heated, a more equiaxial grain formation tends to occur.

[0055] Exemplary embodiments with cold spray followed by laser sintering provide several advantages over conventional techniques for deposition of inorganic high temperature compounds on substrate surfaces to improve temperature resistance.

[0056] Cold Spray enables custom coatings on structures of any size or shape.

[0057] Cold Spray enables uniform or tapered thickness to minimize weight and enables higher protection of high-impact locations.

[0058] Laser sintering (LS) combined with CS enables heat treatment for densification, restructuring, and annealing to reduce film stress.

[0059] Combining CS and LS Lightweight lower temperature substructures can be used, coated with high temperature alloys.

[0060] Tapered thickness and even graded alloy or morphology can be used for heat conduction and

[0061] Pulsed laser sintering enables low heat affected zone (HAZ) to allow localized heat treatment / annealing to reduce substructure heating while minimizing oxidation of the coating.

[0062] Pre-cold spray surfaces can be laser textured to improve adhesion.

[0063] While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.

Claims

1. A material deposition method for providing a layer of a first material onto a substrate composed of a second material, said method comprising:accelerating an inert gas through a nozzle as a supersonic jet;inserting a powder of the first material into said nozzle;directing said jet with said powder towards the substrate to produce a film of the first material onto the substrate; andaiming a coherent electromagnetic beam from a laser towards the substrate to sinter said film into the layer.

2. The method according to claim 1, wherein the first material has a higher melting point temperature than the second material.

3. The method according to claim 1, further including heating said inert gas prior to accelerating.

4. The method according to claim 1, wherein the first material is Inconel 625.

5. The method according to claim 1, wherein the first material is a refractive high entropy alloy.

6. The method according to claim 5, wherein the first material is tungsten-tantalum-niobium-molybdenium (WTaNbMo).

7. The method according to claim 1, further including pulsing said electromagnetic beam during aiming.

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