Patent Description:
This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

Cold spraying is a type of additive process in which a stream of solid particles is accelerated to high speeds by a carrier gas through a nozzle toward a substrate. The particles have enough kinetic energy such that upon impact with the substrate, they deform plastically and bond metallurgical-ly/mechanically to the substrate to form a coating. Although, metallurgical bonding is preferred, all the particles may not be necessarily bonded in a metallurgical fashion.

The particles are accelerated to a critical velocity such that the coating can be created. This critical velocity can depend on the properties of the particles and to a lesser degree on the material of the substrate (i.e., deformability, shape, size, temperature, etc.).

It is hypothesized that the particles adhere to the substrate when their kinetic energy is converted to a sufficient level of thermal and strain (mechanical) energy leading to a phenomenon known in art as "adiabatic shear instability. " It has been observed that the deposition efficiency of a given material is increased as the temperature of the particles is increased up to a certain extent, which is typically achieved by increasing the carrier gas temperature. The carrier gas temperature also influences the gas dynamics through the convergent-divergent nozzle that is typically used in a cold spray process. In other words, all things remaining constant, a higher carrier gas temperature leads to a higher gas velocity in the divergent section of the nozzle, which in turn may lead to higher particle velocity.

Related <CIT>, taught a method for increasing the particle temperature in the divergent section of the nozzle (independent of the carrier gas temperature), by deploying a laser beam coaxially to the nozzle where the taught rectangular nozzle design along with the particle feeding methodology in the divergent section, enabled enhanced distribution and interaction of the particles with the laser beam within the divergent section of the nozzle to increase the temperature of the particles. In other words, the teachings of the referenced related art provided for a mechanism to independently control the particle temperature and the gas dynamics (velocity) for a given nozzle. Further, a portion of the laser beam also is transmitted to the substrate to enhance the deposition quality.

To deposit a coating, the cold spray nozzle is typically traversed on a substrate while maintaining a suitable target distance. This results in a coating along a small track (typically similar to the width of the nozzle exit) on the substrate. To coat a substrate having an area larger than the nozzle exit width, the nozzle is scanned on the substrate multiple times, typically in a raster pattern with the help of a motion system such as a robot. The nozzle exit width is limited by the gas dynamics requirements for a given convergent-divergent nozzle, to achieve the desired particle velocity as well as the distribution. In other words, for a given gas with a given inlet temperature and pressure, the geometry of the convergent section, the divergent section as well as the throat connecting the two sections, determine the gas flow behavior, which in turn influences the particle velocity and the particle distribution. It is not straight forward to just increase the nozzle cross section area to coat a larger substrate. For practical applications, it is recommended to optimize the geometry of the nozzle so that the necessary flow dynamics can be achieved with standard industrial equipment (gas supply, heater, powder feeder etc.) economically.

One particular difficulty associated with cold spray process arises from defects on the underlying substrate surface. When the surface has an imperfection such as a gap or undulation between two coating passes (tracks), the discontinuity/imperfection may continue to develop in the subsequent layers as the coating builds up. Therefore, it is not recommended to build a thicker layer in a single pass, which may become the precursor to the undulations in the final coating. Further, while coating circular/conical objects with varying surface area, extensive process optimization is required to manage the deposit thickness from the origin towards the periphery or from the vertex towards the base, as the coating mass changes significantly.

From the aforementioned, it is apparent that uniform coatings on large substrates with varying surface area by a single cold spray nozzle, is not easily achieved. New methods and devices are needed for efficient coating fabrication.

<CIT> discloses a cold spray apparatus according to the preamble of claim <NUM>. However, this application suffers from similar drawbacks. From <CIT> a cold spray apparatus including a single nozzle is known. With such a design it is difficult to coat a substrate having an area larger than the nozzle exit width by scanning on the substrate multiple times, typically in a raster pattern with the help of a motion system such as a robot.

Similar devices which suffer from the same drawbacks are known from <CIT>, from <CIT> and from <CIT>.

The following summary is provided to facilitate an understanding of some of the innovative features unique to the present disclosure and is not intended to be a full description. A full appreciation of the various aspects of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole. The claimed invention is defined by the appended claims.

In view of this it is an object of the invention to disclose a cold spray apparatus that is capable of coating complex large substrates with high accuracy and efficiency, without necessitating complex tool path optimization and in turn eliminating/minimizing defect growth and subsequent finish machining operation.

This object is solved by a cold spray apparatus according to claim <NUM>. Further embodiments are subject of the dependent claims.

Provided is a cold spray apparatus for applying a coating of particles to a substrate, comprising a plurality of nozzles, including each nozzle defining an inner passage that terminates at a common exit for the entire assembly. The nozzle assembly also includes a particle supply members in communication with the inner passages. The particle supply members supply the particles to flow and accelerate through the inner passages and out of the nozzle via the common nozzle exit toward the substrate to be coated thereon. Furthermore, each nozzle includes a laser beam that is transmitted through the inner passage and exits via the common nozzle exit toward the substrate. The laser heats at least one of the particles within the inner passage and the substrate to promote coating of the substrate with the particles.

Provided are methods that solve one or more problems of the prior art optionally by providing in at least one aspect a method for enhancing the interaction of the particles with the laser beam within the inner passage of the nozzle, and thereby improving the energy absorption. This includes minimizing backward scattering of the laser beam by injecting particles in the divergent section of the nozzle, distributing the particles uniformly therein and hence increasing the interaction of the particles with the laser beam.

In some aspects, methods for integrating the particle stream from each nozzle into a common particle stream having substantially uniform particle distribution density and directing the combined stream with substantially uniform particle characteristics towards the substrate are provided to increase the deposition efficiency and uniformity. This optionally includes terminating each nozzle's inner passage at an optimal distance from the common exit of the apparatus assembly.

In yet another aspect, not part of the claimed invention, methods for coating complex substrates are provided. This optionally includes organizing a plurality of nozzles, having a predetermined common exit geometry that mimics the substrate geometric profile to be coated or built. Yet further, this also optionally includes supplying a desired amount of particles to each nozzle to achieve differential coating mass on the substrate, which in turn develops a desired geometric profile or conformality.

Accordingly, it becomes possible to solve the above aforementioned problems and to coat complex substrates with high accuracy and efficiency.

The scope of the claimed invention is limited by the claims.

The drawings are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Exemplary aspects will become more fully understood from the detailed description and the accompanying drawings, wherein:.

Detailed aspects are disclosed herein; however, it is to be understood that the disclosed aspects are merely exemplary in nature and may be embodied in various and alternative forms within the scope of the claims. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the invention and/or as a representative basis for teaching one skilled in the art to variously employ the present invention.

As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, including "at least one," unless the content clearly indicates otherwise" As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. The term "or a combination thereof" means a combination including at least one of the foregoing elements.

It will be further understood that terms such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Throughout this specification, where publications are referenced the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.

Referring initially to <FIG>, a cold spray nozzle assembly <NUM> is illustrated according to various exemplary embodiments of related U. Application No. <NUM>/<NUM>,<NUM>. The cold spray nozzle assembly <NUM> can be used for applying a coating of particles <NUM> to a substrate as will be described in greater detail below.

The assembly <NUM> can include a nozzle <NUM> having a substantially straight longitudinal axis X. As shown in <FIG>, the nozzle <NUM> can define an inner passage <NUM> that extends parallel to the axis X. The inner passage <NUM> can also include a nozzle entrance 22a and a nozzle exit 22c at opposite ends thereof (<FIG>). As shown in <FIG>, the inner passage <NUM> can include a convergent section <NUM> adjacent the nozzle entrance 22a and a divergent section <NUM> adjacent the nozzle exit 22c. More specifically, both the convergent and divergent sections <NUM>, <NUM> can be progressively tapered. The convergent section <NUM> narrows moving away from the entrance 22a, and the divergent section <NUM> widens moving toward the exit 22c. The convergent section <NUM> is connected to the divergent section <NUM> to define a throat 22b (<FIG>). As will be discussed, the particles <NUM> flow through the inner passage <NUM>, and the convergent and divergent sections <NUM>, <NUM> ensure an appropriate flow field in the passage <NUM> such that the particles <NUM> move at a sufficient velocity to coat the substrate (not shown).

As shown in <FIG>, the nozzle <NUM> is substantially rectangular in shape. More specifically, the inner passage <NUM> (<FIG>) has a substantially rectangular cross section taken perpendicular to the axis X. The entire inner passage <NUM> can have a similar substantially rectangular cross section along the entire axis X of the passage <NUM>; however, it will be apparent that the area of such a cross section will change along the axis X due to the progressive tapering of the convergent and divergent sections <NUM>, <NUM>. It will also be appreciated that the inner passage <NUM> and the exit 22c can alternatively have any suitable non-circular shape, including square shape.

Furthermore, as shown in <FIG>, the nozzle <NUM> includes one or more particle supply inlets 13a, 13b. The nozzle <NUM> can include any number of inlets 13a, 13b, and the inlets 13a, 13b are disposed in the divergent section <NUM> of the inner passage <NUM>. In the preferred embodiment shown in <FIG>, there are two inlets 13a, 13b disposed symmetrically on opposite sides of the axis X. The particle supply inlets 28a, 28b (<FIG>) can each extend transverse to the axis X. For instance, the particle supply inlets 28a, 28b can each be disposed at a positive acute angle relative to the axis X and generally toward the exit 22c. Further, the assembly <NUM> can include a particle supply member (not shown). The particle supply member can be in (fluid) communication with the inner passage <NUM> of the nozzle <NUM> via the inlets 28a, 28b. For instance, the particle supply member can include one or more tubes that are received in and operably coupled to the inlets 28a, 28b, respectively. Thus, as will be discussed, the particles <NUM> can be supplied from the supply member to flow through the inlets 28a, 28b, through the inner passage <NUM>, and out of the nozzle exit 22c toward the substrate to coat it with the particles <NUM>.

As shown in <FIG>, the assembly <NUM> according to the claimed invention includes a gas supply member <NUM>. The gas supply member <NUM> is in fluid communication with a gas source (not shown). The gas source can supply any suitable gas to pressurize the inner passage <NUM> of the nozzle <NUM>. Moreover, the assembly <NUM> includes a laser source <NUM>. The laser source <NUM> can be of any suitable type, such as a diode laser of a known type. The laser source <NUM> can optionally include a fiber-optic cable <NUM> and at least one or more (e.g., three shown here) optical elements 25a, 25b, 25c (<FIG>). The laser source <NUM> can be operably coupled to the first branch <NUM> of the pressure tube <NUM> so as to be substantially coaxial with the axis X. As will be discussed, the laser <NUM> emits a laser beam <NUM> (<FIG>) that is transmitted through the entrance 22a of the inner passage <NUM> of the nozzle <NUM> and out of the nozzle <NUM> via the exit 22c toward the substrate. The laser beam <NUM> can be directed substantially parallel to and coaxial to the axis X toward the substrate, although some degree of spread of the beam <NUM> inward or away from the X axis may optionally be preferred. The laser beam <NUM> heats particles below the particles' melting point. In some embodiments, laser beam <NUM> can heat particles below the particles' melting point only in and downstream of the divergent sections <NUM>.

Additionally, the assembly <NUM> can further include a handling device as well as process controller (not shown). The handling device can be of any suitable type, such as a robotic handling device. The controller can be of any suitable type, such as a programmable computer. The controller can be in communication with the laser source, the handling device, the gas supply source, and the particle supply source for operating each. The controller can also optionally be in communication with the pressure tube <NUM> for receiving feedback regarding the pressure and temperature inside the pressure tube <NUM>.

Now attention is drawn to an optional operational mode of the cold spray nozzle disclosed herein, wherein the method of the operational mode is not part of the claimed invention. The controller can move the assembly <NUM> into a desired position relative to the substrate using the handling device. The controller can cause the gas supply member to supply gas into the inner passage <NUM> and to the substrate before and during operation of the laser source <NUM>. After the laser <NUM> has begun operating, the controller can cause the particle supply member to supply the particles <NUM>. The particles <NUM> can be accelerated by the gas up to or beyond a critical velocity within the inner passage <NUM> and directed toward the substrate. In some embodiments, the particle supply member supplying the particles <NUM> can be supplied directly to the divergent sections <NUM> to flow in the gas supplied by the gas supply member, accelerate within the divergent sections <NUM>, and out of the nozzle assembly via the nozzle exit toward the substrate to coat the substrate. The energy of the laser beam <NUM> can heat the particles <NUM> during flight toward the substrate. Because the particles <NUM> are heated, the particles <NUM> can plastically deform more readily when the particles <NUM> impact the substrate. Furthermore, the energy of the laser beam <NUM> can continue to heat the substrate as the particles <NUM> are ejected toward the substrate. Thus, the substrate can plastically deform more readily. The handling device can continuously move the assembly <NUM> to evenly coat the substrate with the particles <NUM> on predetermined areas. It will be appreciated that the operational mode described above is merely an example and shouldn't be interpreted as limiting.

It is noteworthy that the teachings of related <CIT> include a substantially rectangular nozzle geometry, side particle injection mode, and the coaxial laser coupling, produce unanticipated benefits and advantages compared to the prior art. Because of the substantially rectangular cross section of the inner passage <NUM> (<FIG>) and because of the injection of particles at a suitable location along the minor axis plane (28a, 28b) in the divergent section of the inner passage <NUM>, the particles <NUM> can be distributed more uniformly across the inner passage <NUM>, resulting in more uniform particulate velocities, leading to a fairly even thickness on the substrate (further illustrated in <FIG>) as compared with prior art systems. The significance of uniform particulate velocity should be appreciated in the context of critical velocity. It is well known that in cold spray applications, the particles must achieve a critical velocity for effective deposition. Particles with velocities below the critical velocity do not metallurgically bond to the target, whereas particle velocity much higher than the critical velocity does not provide any additional benefits, but consumes higher energy. It will be appreciated that the teachings of related U. Application No. <NUM>/<NUM>,<NUM> provide the best combination of both uniform particle distribution across the nozzle exit, and uniform particle velocities with lower standard deviation. Furthermore, having "a laser that emits a laser beam that is transmitted through the inner passage" thereby provides additional heat energy to the particle within the nozzle, independent of the supply gas as the heat source. Yet further, the taught laser coupling methodology provides for the development of a laser beam profile that mimics the internal passage of the nozzle due to progressive internal reflection. Effective energy transfer occurs due to the uniform particle distribution in the divergent section of the nozzle as well as the beam shape modulation, which provides the maximum chance for interaction of the laser beam with the particles. Accordingly, the finished part can be more aesthetically pleasing, can fit better to other parts, and can have better properties due to in-situ annealing. Moreover, the specific claimed combination results in improved performance unattainable by the prior art.

Although, the teachings of the above referenced related <CIT> provide for; (i) the development of a uniform particle distribution profile as the particle stream emerges towards the target, (ii) the development of laser beam profile that mimics the internal passage of the rectangular nozzle due to progressive internal reflection, (iii) a uniform exposure of the particles to the laser beam leading to uniform absorption, (iv) no back reflection of the laser beam towards the source that can damage the laser optics, and (v) the uniform treatment of the coated material by the residual laser beam emerging out of the nozzle, which mimics the cross section of the nozzle exit, there remain several unsolved problems that can benefit the cold spray process further. The teachings of the claimed invention provide for at least some of the unsolved problems as discussed below.

Now referring to <FIG>, a brake rotor <NUM> is to be coated by a cold spray nozzle assembly <NUM> described above. It will be appreciated that the coating needs to be applied only to the braking surface <NUM>. The entire braking surface <NUM> can optionally be coated by moving the cold spray nozzle assembly <NUM> with the help of a handling device (not shown) such as a robot over the braking surface <NUM>, following a complex and time consuming raster pattern that will ensure a uniform coating thickness, while avoiding coating the unwanted area <NUM>. Alternatively, a combination of rotary motion of the rotor and step wise radial motion of the nozzle assembly, may be simpler and less time consuming. It is to be appreciated that for a given coating thickness, the mass of the coating segment <NUM>, <NUM> and <NUM> will vary significantly. Since the nozzle can only coat a small track at a time, the effective residence time of the nozzle at a given track will vary considerably as it moves step wise along the radial direction to keep the coating thickness uniform. Further, the desired coating thickness may not be achieved in a single pass as it will likely leave undulations between successive tracks. In cold spray, the underlying undulations/defects continue to grow as the coating builds up. In summary, extensive process optimization will be necessary to achieve a uniform coating on part <NUM>, which yet may not avoid defective coating as well as the need for considenable amount of finish machining. Particularly the growth of defects is problematic while coating such large surfaces.

Now referring to <FIG>, a multi nozzle cold spray apparatus <NUM> according to the claimed invention is disclosed that can apply a uniform coating of particles <NUM> across the entire substrate <NUM> as will be described in greater detail below. It will be appreciated that the width of particle stream <NUM> can optionally be identical to the width of the substrate <NUM>, however, that may not be sufficient to ensure a uniform coating. Other important particle stream characteristics are necessary to ensure uniform coating and will be described in greater detail below. Further, with the help of a handling device (e.g., robot) the apparatus <NUM> can be traversed along the length of the substrate <NUM> to coat the entire surface facing the particle stream <NUM>. Alternatively, the substrate <NUM> can be traversed while keeping the apparatus <NUM> stationary to achieve the coating.

The exemplary embodiment of the cold spray apparatus <NUM> according to the claimed invention shown in <FIG>, includes a nozzle assembly <NUM> having a substantially straight longitudinal axis X and further comprising of a plurality of internal passages. The number of internal passages can be at least two and optionally can be <NUM> or <NUM> or <NUM> or <NUM> or many, depending on the width of the required coating as well as the geometric characteristics of the internal passages. Additionally, the geometric characteristics of these internal passages mimic the preferred embodiment <NUM> (<FIG>), to a large extent. Further, the apparatus <NUM> can include a gas supply member <NUM>, operably in communication with a pressure chamber <NUM>, a plurality of particle supply members 43a through 43f, operably in communication with internal passages of the nozzle assembly <NUM>. The cross sectional views of apparatus <NUM> (<FIG>) taken transverse to the axis X at different locations are provided in <FIG>. The cross section <NUM> taken adjacent to the pressure chamber <NUM> shows five tapered inlets 58a, 58b, 58c, 58d and 58e. Further, cross section <NUM> includes five passages 56a, 56b, 56c, 56d and 56e, which are substantially smaller than the inlets shown in cross section <NUM>. Additionally, the cross sectional area of the internal passages (54a, 54b, 54c, 54d and 54e) progressively increase in size toward the exit <NUM> as shown in cross section <NUM>. Furthermore, adjacent to the nozzle exit <NUM>, there is only one substantially large passage <NUM>, resulting from the merger of the all the passages illustrated above.

Further details of nozzle assembly <NUM> is shown in <FIG>, which is the cross sectional view <NUM> taken along the symmetric plane of the multi nozzle apparatus <NUM>. The inner passages 64a, 64b, 64c, 64d and 64e extend substantially parallel to the axis X. These passages optionally can be similar (not necessarily same) to each other, however in a preferred embodiment of the claimed invention shown here, they are optionally kept identical. Further details of only one passage 64a are discussed below and it is understood that all other passages (64b, 64c, 64d and 64e) possess similar characteristics. The inner passage 64a includes a nozzle entrance 62a and a nozzle exit 66a at opposite ends thereof. As shown in <FIG>, the inner passage 64a includes a convergent section 72a adjacent the nozzle entrance 62a and a divergent section 75a adjacent the nozzle exit 66a. More specifically, both the convergent and divergent sections 72a, 75a can be progressively tapered. The convergent section 72a narrows moving away from the entrance 62a, and the divergent section 75a widens moving toward the exit 66a. The convergent section 62a is connected to the divergent section 75a to define a throat 73a (<FIG>). The particles flow through the inner passage 64a, and the convergent and divergent sections 72a, 75a ensure an appropriate flow field in the passage 64a such that the particles move at a sufficient velocity before they enter the common nozzle assembly exit <NUM>. Each inner passage can receive the accelerating carrier gas from a common pressure chamber <NUM>, or optionally the pressure chamber can be separated.

Additionally, each inner passage includes a plurality of particle supply inlets. The inner passage can include any number of inlets, and the inlets can optionally be disposed in any suitable location. In the preferred embodiment shown in <FIG>, there are two inlets 74a, 74b for internal passage 64a, disposed symmetrically on opposite sides of the passage. The particle supply inlets 74a, 74b (<FIG>) each extend transverse to the axis X. For instance, the particle supply inlets 74a, 74b can each be disposed at a positive acute angle relative to the axis X and generally toward the exit 66a (<FIG>). Further, the assembly <NUM> can include a particle supply source (not shown). The particle supply source can be in (fluid) communication with the inner passages of the nozzle via the particle supply members 43a through 43f. For instance, the particle supply member can include one or more tubes that are received in and operably coupled to the inlets. Thus, as will be discussed, the particles <NUM> can be supplied from the supply source to flow through the inlets 74a, 74b, through the inner passage 64a, and out of the nozzle exit 66a toward the substrate to coat it with the particles <NUM>.

Furthermore, the apparatus assembly <NUM> includes a laser source <NUM>. The laser source <NUM> can be of any suitable type, such as a diode laser of a known type. Each inner passage of the nozzle assembly <NUM> includes a laser beam. The laser source <NUM> can optionally include a fiber-optic cable <NUM>. In a preferred embodiment shown in <FIG>, fiber <NUM> brings in one laser beam from a source (not shown), which can optionally split into a plurality of laser beams through a semitransparent mirrors assembly 68a. The semitransparent mirror assembly can be any known type that enable a desired fraction of the laser beam to be transmitted through each mirror and reflecting the remaining fraction in substantially parallel direction of axis X. Subsequently, each reflected fraction of the laser beam is processed through at least one or more (e.g., two shown here) optical element (e.g., lens) assemblies 68b, 68c (<FIG>). The laser source <NUM> can be operably coupled to the first branch <NUM> (<FIG>) of the pressure tube <NUM> so as to keep all the laser beams substantially coaxial with the axis X. Further details on the laser beam propagation through the will be provided below.

Now referring to <FIG>, each inner passage of the apparatus assembly <NUM> can optionally terminate at <NUM> away from the exit <NUM>. For convenience, the distance between the throat of the inner passage <NUM> (divergence section) to the termination point <NUM> is defined as ML and the between the throat of the inner passage <NUM> to the exit <NUM> is defined as DL. It will be appreciated that the divergence angle of each inner passage will remain constant to maintain a progressive taper of the inner passage in axis X direction, however, the projected exit width <NUM> of each inner passage will depend on DL. Further, the total maximum opening width <NUM> of the apparatus assembly <NUM> will be the sum total of the projected exit width <NUM> of all channels. Further, a term nozzle overlap is defined as: [(DL-ML)/DL]*<NUM>. When ML is equal to DL, i.e., each internal passage terminates at the exit <NUM>, resulting in a <NUM>% over lap. It will be appreciated that the wall between each internal passage will have a finite dimension, and therefore, fabricating a nozzle assembly having <NUM>% overlap is practically difficult. For example, if a plurality of individual nozzle assembly <NUM> (<FIG>) were physically joined together, it will lead to a situation where ML is greater than DL resulting in a negative overlap. In a preferred embodiment <NUM> shown in <FIG>, the overlap can optionally be between <NUM>% and <NUM>%. The influence of the overlap on the particulate characteristics and the resulting coating will be discussed in greater detail below.

To demonstrate the specific benefits of the teaching of the present invention, flow simulations for different overlap percentages are presented below. The simulations were carried out employing flow simulation software Fluent <NUM>. The following conditions (typically used in our process) were employed in each simulation case: Gas Pressure-500psi, Gas temperature-<NUM>, Powder Feed Rate- <NUM> per minute per inner passage, Particle size- <NUM>, Material- Steel, DL- <NUM> inch, and divergence angle (<NUM>)- <NUM> degree. Further for flow simulation, Reynolds Stress Model with pressure velocity coupled and quick discretization for density and momentum were employed. Additionally, particle injection scheme of DPM with stochastic tracking (Random walk model) was adopted. Furthermore, the teachings of related <CIT> include a substantially rectangular internal passage, side particle injection along minor axis plane, and the coaxial laser coupling that produce unanticipated benefits and advantages compared to the prior art, were incorporated in the simulation.

Referring to <FIG>, the particle impact map <NUM> on a target substrate situated <NUM> away from the nozzle assembly exit <NUM> (<FIG>) for different overlap percentages is presented. Further, the corresponding particle velocity magnitude is also superimposed on this map according to a gray scale <NUM>; the lighter shade indicates higher velocity whereas the darker shade indicates lower velocity. Now referring to the case of -<NUM>% overlap which is achieved by simply adjoining a plurality (five here) of nozzles <NUM>, significant gaps <NUM> in the particle distribution map are observed. These gaps indicate that no coating will be forming on those areas of the target. Further attention is drawn to the zones <NUM> that have recorded particle impacts indicating a fairly uniform distribution of the particles in those areas. Further, the lighter shade in much of the map also indicates that a significant number of particles achieved uniform higher velocities except for those at the edges of each patch (<NUM>). The cold spray developer community has conventionally tried to achieve uniform higher velocity (above the critical velocity required to achieve particle adhesion at the target) for maximum number of particles which leads to maximum deposition efficiency. Further, it is generally believed that axial injection provides the maximum particles velocities. However, one skilled in the art wouldn't normally expect a significant number of particles attaining high particle velocities and a uniform distribution profile with side injection in the divergent section as shown in <FIG>. It will be appreciated that the teachings of related <CIT> include a substantially rectangular internal passage geometry along with the side particle injection mode, leads to results that are contrary to conventional wisdom. As will be demonstrated below, an axial injection may not provide such uniform particle velocity as well as uniform distribution across the entire nozzle opening. It will be appreciated that for an overlap of - <NUM>%, the uncoated area <NUM> is expected to be more than that doesn't have particle impact as the velocities of the adjacent particles (darker shade) are quite low and they are not expected to bond with the target.

Further, when the overlap is <NUM>%, although the particle map shows uniform coverage, zones <NUM> with significantly low velocities are present and it is anticipated that coatings will not be formed in those areas. This is further substantiated from <FIG> which provides the maximum, the average and the minimum particle velocities for different overlap percentages. As seen from this plot, the lowest particle velocity (<NUM>) is achieved for <NUM>% overlap. Furthermore, with <NUM>% overlap there is a significant reduction in the particles with lower velocities (darker shade), while at <NUM>% overlap, almost all particles show uniform higher velocities (lighter shade). Additionally, at <NUM>% overlap, no specific improvement in particle velocity shading is observed, however, the length of the particle impact zone is substantially reduced. The significance of the length of the particle impact zone is that, the longer it is, the more target area can be coated in a single traverse of the apparatus <NUM> (<FIG>), provided that the impacting particles have the needed critical velocity and uniformity in distribution. Therefore, overlaps beyond a point may not provide any additional benefits, but on the other hand may lead to thicker and narrower coatings that may not be desired. Further insight to optimal overlap percentage can be gained from the particle velocity distribution map shown in <FIG>. As will be appreciated, for best coating results, it is desirable that all particles attain a velocity that is higher than the critical velocity of the material being deposited. However, it is practically difficult to get all the particles developing velocities higher than the critical velocity. In other words, in a given cold spray nozzle, there always will be some particles that fail to attain the critical velocity, however, it is always a design goal to provide the maximum number of particle with velocities higher than the critical velocity. Further, it is also desired that these particles are distributed uniformly across the particle stream such that uniform coating can be fabricated. With that background, referring to <FIG>, it is observed that at -<NUM>% overlap there are significant number of particles that attain velocities higher than the critical velocity <NUM>. However, in the region between two particle streams <NUM>, there are no particles and obviously no coating will be formed in that zone. Further, at <NUM>% overlap there are significant number of particles that attain velocities higher than the critical velocity <NUM>, however, the region between two particle streams <NUM>, although sees particles, but with velocities lower that the desired critical velocity <NUM>. As a result, no coating is expected to form in zone <NUM>. In contrast, at <NUM>% overlap, there are many particles in the region between two particle streams <NUM> that possess velocities higher than the critical velocity <NUM> and expected to form a coating in that region. As the overlap grows to <NUM>%, the number of particles with velocities higher than the critical velocity <NUM> has grown considerably in region <NUM> and an overall good coating across the particle streams is expected. Further, with <NUM>% overlap, although the width of particles stream shrunk, but the number of particles with velocities higher than the critical velocity in region <NUM> didn't appear to increase any further. Therefore, any added benefit is not expected from <NUM>% overlap, but on the other hand it may be detrimental in terms reducing the coating width. Therefore, the preferred overlap can optionally be between <NUM> and <NUM>%, but, it can be further lower depending upon the material's critical velocity. For example, an overlap of <NUM> may have enough number of good particles in region <NUM> for a material whose critical velocity is substantially lower than <NUM>.

Now referring to <FIG>, the laser source <NUM> provides a laser beam 124a that is transmitted through the entrance 62a (<FIG>) of the inner passage 64a (<FIG>) of the nozzle <NUM> and out of the inner passage 64a via the exit 66a toward the substrate according to an embodiment of the claimed invention. The laser beam 124a is directed substantially parallel to and coaxial to the axis X toward the substrate, although some degree of spread of the beam 124a inward or away from the X axis may optionally be preferred. Laser absorption is a line of sight process. For a central laser beam 124a to pass through the inner passage, the laser beam has to achieve a minimum dimension at or around the throat 63a (<FIG>) of the inner passage, which means it achieves a maximum power density (total power/beam cross sectional areas) near the throat. If particles were injected axially through the throat 63a as commonly practiced in industry, the particle stream also has to pass through the throat simultaneously with the laser beam. As a result, the particles will block a major portion of the laser beam at the throat leading to back reflection, beam distortion, and non-uniform absorption. Back reflection can damage the optics 121a, 122a, 123a. The side injection scheme via 74a and 74b (<FIG>) beyond the throat (i.e. in the divergent section) of the present invention allows the laser beam to interact with the particles beyond its focal point and in the divergent section of the inner passage. Any scattered fraction of the laser beam in the divergent section of the inner passage will not travel back to the optics via the throat 63a. Furthermore, due to the progressive divergence of the inner passage beyond the throat as well as the substantially rectangular cross section, forward scattering and multiple internal reflections will be promoted leading to a laser beam profile 125a that mimics the internal passage. The net results are: (a) uniform exposure of the particles to the laser beam leading to uniform absorption, and (b) no back reflection of the laser beam towards the source that can damage the laser optics. A circular beam cross section with Gaussian intensity distribution transforming into a rectangular profile with top hat distribution is caused by this specific combination of particle injection scheme, nozzle shape, as well as laser coupling with the nozzle. Same benefits can occur to all other laser beams transmitting through all other internal passages in the preferred embodiment <NUM> shown in <FIG>. It will be appreciated that the common exit passage <NUM>(<FIG>) assumes a substantially rectangular shape as each internal passage. All the modulated laser beam emanating from each inner passage via exit 66a can further scatter and modulate into a single beam <NUM> mimicking the cross section profile of the common exit passage <NUM> and thereby causing uniform treatment of the coated material by the residual laser beam emerging out of the nozzle exit <NUM> (<FIG>).

Referring to <FIG>, embodiment <NUM> of the claimed invention can be utilized to simultaneously coat both braking surfaces of a brake rotor. It includes two multi nozzle cold spray apparatuses 134a and 134b. Apparatus 134b can be kept stationary in place to coat <NUM> the entire surface <NUM> simultaneously while rotating the brake rotor with a motor <NUM>. As discussed earlier, the coating mass will vary significantly along the radial direction. Therefore, the injected mass of particles can progressively change from inside channels toward the outmost channels of the apparatus 134b. Further, the beam power passing through each channel can progressively vary to provide equivalent heat energy per unit mass of the coating. This can be achieved by appropriate optical elements used in the laser source <NUM> (<FIG>). Accordingly, a uniform coating without raster marks and the related defects can be fabricated rapidly.

Although the multi nozzle cold spray apparatus <NUM> can coat a large area without raster patterns and defects, it can also be used to fabricate coatings similar to that can be obtained by a single nozzle <NUM>. <FIG> presents the simulated particle distribution map as well as the corresponding particles velocity distribution maps when the apparatus <NUM> was operated in different modes. A <NUM>% over lap was considered in these simulations. Particle distribution map <NUM> was obtained when the particles and the carrier gas were injected only in one internal passage, which is equivalent to operating one single nozzle <NUM>. It will be appreciated that to run the apparatus in a single channel mode, the carrier gas will continue to flow through the channels that are not in use because the internal passages receive the carrier gas from the common pressure chamber <NUM>. Alternatively, the pressure chamber <NUM> can be separated to feed each internal passage separately. Referring to <FIG>, the internal passage 64a can optionally receive carrier gas from pressure tube 151a, which is isolated from the neighboring pressure tube by a wall 152a. It will be appreciated that only a partial view of symmetric half portion <NUM> of the nozzle assembly <NUM> is shown in <FIG>. Further, the pressure tube 151a is in fluid communication with a gas supply source via control valve 153a. Accordingly, each internal passage (64a, 64b, 64c, 64d and 64e of <FIG>) can optionally receive carrier gas from its corresponding pressure tube, which is isolated from its neighboring pressure tube by a wall. Further, each pressure tube is in fluid communication with a gas supply source via its corresponding control valve. Particle distribution map <NUM> (<FIG>) was obtained when the particles and the carrier gas were injected only through <NUM> adjacent internal passages. The corresponding particle velocity distributions are presented in map <NUM> and <NUM>. As can be seen the influence of the common exit nozzle <NUM> (<FIG>) on the particle distribution map (i.e., the width of the coating) is not significant. Further simulations were carried by supplying carrier gas to all five internal passages, but feeding particles only to <NUM> adjacent internal passages. As seen in map <NUM>, the number of particles possessing velocities above the critical velocity <NUM> increased significantly. However, the particle distribution map wasn't noticeably different from <NUM>. Accordingly, the material deposition efficiency can be significantly increased in this mode.

As discussed earlier, axial injection is believed to provide higher particle velocity compared to side injection as provided in this disclosure. To demonstrate the impact of axial particle injection to the multi nozzle cold spray apparatus <NUM> on the particle velocity and distribution, simulations were carried out utilizing the procedures described above. Now referring to <FIG>, target particle distribution map <NUM>' shows quite non uniform distribution comprising of zones <NUM> with a lot of particles and zones <NUM> with a few particles. Further the particle velocity distribution map <NUM>" shows that although some particles achieved significantly higher velocities <NUM> than the critical velocity <NUM>, but their fraction was low. A large fraction of the particles <NUM> showed velocities lower than the critical velocity <NUM>. Further, from graph <NUM>‴, it is seen that although the maximum particle velocity <NUM> for axial injection was higher than the case of side injection, the mean particle velocity <NUM> was slightly lower for the case of axial injection. Additionally, the spread between maximum and minimum particle velocity was the largest for the case of axial injection. It will be appreciated that the multi nozzle cold spray apparatus <NUM> as disclosed here provides the most uniform particle distribution as well as the minimum spread (standard deviation) of particle velocities, beneficially impacting the resulting coating.

Referring to <FIG>, the multi nozzle cold spray apparatus <NUM> comprises of a common exit <NUM> that has a parabolic profile <NUM>. If all the internal passages remain same, the overlap will vary along the parabola. To obtain an optimal particulate distribution as well as velocity characteristics, this overlap can be adjusted. The use of such a nozzle to coat a parabolic surface <NUM> is shown in <FIG>. Accordingly, such an apparatus can also be used to build parabolic objects. Another multi nozzle cold spray apparatus <NUM> is shown in <FIG> and it can include a tapered exit <NUM>. Also, this apparatus will have a varying overlap and an optimal overlap needs to be selected to ensure a good deposit. <FIG> shows the use of such apparatus in coating a conical surface <NUM> where the coating mass varies radially, which can be adjusted by varying the particle feed. Further, the tapered nozzle exit can ensure a fixed target distance. Additionally, the apparatus <NUM> can be used to build objects having a conical profile <NUM>. Accordingly, many different common exit nozzle profiles can be adopted to achieve different deposition profiles. This also can optionally include supplying a desired amount of particles to each nozzle to achieve differential coating mass on the substrate, which in turn develops a desired geometric profile or conformality.

Claim 1:
A cold spray apparatus for applying a coating of particles to a substrate comprising:
a nozzle assembly comprising a plurality of nozzles (<NUM>), each nozzle (<NUM>) having an inner passage (<NUM>), the inner passage (<NUM>) extending in a flow direction from a convergent section (<NUM>) adjacent a nozzle entrance (22a) through a throat (22b) to a divergent section (<NUM>) adjacent a nozzle exit (22c), wherein the inner passage (<NUM>) of each nozzle (<NUM>) terminates at a common nozzle exit (22c) for the entire assembly;
a gas supply member (<NUM>) configured for supplying a gas to inner passage (<NUM>) of each nozzle (<NUM>) to flow through the inner passage (<NUM>) of the nozzle (<NUM>) and accelerate through inner passage (<NUM>) by passage through the convergent section (<NUM>), the throat (22b), and the divergent section (<NUM>) of the inner passage (<NUM>);
a particle supply member in direct communication with the inner passage (<NUM>) of each nozzle (<NUM>), the particle supply member configured for supplying the particles to flow in the gas supplied by the gas supply member (<NUM>) and out of the nozzle (<NUM>) via the nozzle exit (22c) toward the substrate to coat the substrate;
wherein a laser source (<NUM>) is provided that emits a laser beam that is transmitted through the inner passage (<NUM>) of each nozzle (<NUM>) containing the supplied gas, the laser heating the particles below the particles' melting point and heating the substrate to promote cold spray coating of the substrate with the particles;
wherein the nozzle assembly has a substantially rectangular nozzle geometry including side powder injection points (13a, 13b; 28a, 28b) located in the divergent section (<NUM>) of the inner passage (<NUM>); and
wherein the laser source (<NUM>) is configured to effect a coaxial laser coupling.