Patent Description:
Bond performance of a structural adhesive joint requires a reliable and repeatable pre-bond surface structure. Traditionally, titanium substrates have been treated by processes such as a grit blast process, an alkaline etching process, and/or an acid or basic anodizing process to achieve a fresh oxide layer and a desirable surface roughness prior to bonding. However, the bond quality achievable from substrate surface subjected to a grit blast process is often inconsistent. As a result, the durability of the bond process may be inconsistent. Etching and anodizing processes are wet chemistry batch processes and require large quantity of hazard chemical solutions by immersion of entire parts.

A titanium substrate present within an environment containing oxygen (e.g., an "air" environment) will have an oxide layer formed on the surface of the substrate. Such an oxide layer is typically a solid layer, poorly bonded, and does not provide a desirable adhesive bonding surface.

What is needed is a method for treating a contoured titanium substrate surface that results in a desirable oxide layer that improves bond performance when an adhesive is applied to the surface.

<CIT>, XP <NUM> (describing all the features of the preamble of claims <NUM>, <NUM> and <NUM>), and <CIT> disclose prior art bonding methods.

According to an aspect of the present disclosure, a method for treating a surface of a contoured titanium substrate used for adhesively bonded engine components is provided as set forth in claim <NUM>.

According to another aspect of the present disclosure, a method of adhering a titanium substrate to a second substrate is provided as set forth in claim <NUM>.

According to another aspect of the present disclosure, a method of preparing an airfoil for bonding is provided according to claim <NUM>.

In any of the aspects or embodiments described above and herein, the energy applied from the fiber laser system to the surface of the titanium substrate to create the produced oxide layer may also remove one or more contaminants present on the surface of the titanium substrate.

In any of the aspects or embodiments described above and herein, the energy applied from the fiber laser system to the surface of the titanium substrate to create the produced oxide layer may also remove a natural oxide layer present on the surface of the titanium substrate.

In any of the aspects or embodiments described above and herein, the method may further include applying energy from the fiber laser system to the surface of the titanium substrate in an amount that removes a preexisting oxide layer, the removal of the preexisting oxide layer occurring prior to the creation of the produced oxide layer.

In any of the aspects or embodiments described above and herein, the produced oxide layer may be a layer of a titanium oxide having a thickness on the order of about <NUM> nanometers (nm) to about <NUM>.

In any of the aspects or embodiments described above and herein, the thickness of the produced oxide layer may be on the order of about <NUM> to about <NUM>.

In any of the aspects or embodiments described above and herein, the open porous morphology of the produced oxide layer may be configured to permit an adhesive to infiltrate and reside within at least a portion of the produced oxide layer.

In any of the aspects or embodiments described above and herein, the produced oxide layer may be configured such that the nanoscale open porous morphology is substantially accessible from an exposed surface of the produced oxide layer.

In any of the aspects or embodiments described above and herein, the nanoscale porous structures may be present throughout an entirety of a thickness of the produced oxide layer.

In any of the aspects or embodiments described above and herein, the energy from the fiber laser system may be applied to the surface of the titanium substrate in a manner that causes the energy to reflect and scatter into non-line of sight surface features.

The foregoing features, elements, steps, or methods may be combined in various combinations without exclusivity, unless expressly indicated herein otherwise. These features, elements, steps, or methods as well as the operation of the disclosed embodiments will become more apparent in light of the following description and accompanying drawings.

Referring to <FIG>, embodiments of the present disclosure include methods for treating the surface of a titanium substrate <NUM> to produce a surface that promotes bonding of the surface with an adhesive material <NUM> such as a primer or adhesive. The aforesaid adhesive <NUM> provides at least part of a material that will enable the titanium substrate <NUM> to be joined with a second substrate <NUM> (e.g., a metallic substrate, a composite substrate, etc.). The surface of the titanium substrate <NUM> to be joined (e.g., via an adhesive bond) to the second substrate <NUM> will be referred to hereinafter as a "prebond surface <NUM>". The present disclosure is not limited to treating the prebond surface <NUM> of any particular type of titanium substrate <NUM>. Unless indicated otherwise herein, the term "titanium" as used herein includes any type of titanium alloy, and is not therefore limited to any particular titanium alloy. The present disclosure is also not limited to treating the surface of a titanium substrate <NUM> for use with any particular adhesive. Depending upon the type of substrate bonding desired, the adhesive may be a primer or an adhesive, or any material that is useful in producing an adhesive bond, and may include combinations of such materials.

The present disclosure methods have particular utility is treating components that may be used in a gas turbine engine, but are not limited to treating gas turbine engine components. <FIG> illustrates a gas turbine engine <NUM> including a fan section <NUM>, a low-pressure compressor section <NUM>, a high-pressure compressor section <NUM>, a combustor section <NUM>, a high-pressure turbine section <NUM>, and a low-pressure turbine section <NUM>. Air drawn into the fan section <NUM> is directed into the compressor sections <NUM>, <NUM> where it is worked to a higher pressure. The worked air subsequently passes through the combustor section <NUM> where fuel is added and ignited. The worked air and combustion products enter and power the turbine sections <NUM>, <NUM> before exiting the engine. The fan section <NUM> includes a plurality of fan blades <NUM> connected to, and radially extending out from, a fan hub <NUM>. The fan section <NUM> is rotatable about centerline <NUM> of the engine. <FIG> illustrates an exemplary fan blade <NUM> having a root <NUM> and an airfoil <NUM>. <FIG> illustrates a diagrammatic cross-section of a fan blade airfoil <NUM>. The airfoil <NUM> is defined by a leading edge <NUM>, a trailing edge <NUM>, a tip <NUM>, a suction side surface <NUM>, and a pressure side surface <NUM>. As can be seen in <FIG>, in some instances an insert <NUM> (referred to as "a leading edge insert") may be attached to the airfoil <NUM> at the leading edge <NUM> of the fan blade <NUM>. The leading edge insert <NUM> is a non-limiting example of a titanium substrate that may be treated according to present disclosure methods. As stated above, however, the present disclosure is not limited to treating airfoil leading edge inserts and the insert <NUM> is described herein solely for the purpose of providing an example that illustrates the utility of the present disclosure; e.g., an application where the titanium substrate may be subjected to significant forces and environmental factors, and how the enhanced bond quality and durability the bond performance made possible by the present disclosure method improves such applications.

Embodiments of the present disclosure utilize a fiber laser system <NUM> to treat a surface of a titanium substrate <NUM> in a manner that produces an oxide layer 32B ("produced oxide layer 32B") with an open porous morphology <NUM>. <FIG> is a diagrammatic illustration showing a prebond surface <NUM> of a titanium substrate <NUM> with a produced oxide layer 32B. An adhesive <NUM> is shown residing within an open porous morphology of the produced oxide layer 32B, with some amount of the adhesive <NUM> disposed at or above the exposed surface of the oxide layer 32B. <FIG> is purposefully shown not to scale to facilitate the description provided herein. There are numerous different types of fiber laser systems <NUM> commercially produced. Moreover, any particular fiber laser system <NUM> may be operated using a variety of different parameters including but not limited to beam size, laser power, laser frequency, scan speed, pulse rate/duration, etc. A fiber laser system <NUM> that is used with a titanium substrate is an infrared fiber laser system that is operable to produce pulse energy in the range of about <NUM> to <NUM> mJ and can operate at a pitch of about <NUM> to <NUM>, using a laser beam having a diameter of about <NUM>. Fiber lasers capable of ablating and treating the titanium surface may be supplied by TRUMPF, Rofin-Sinar, Advalue Photonics, Coherent, IPG Photonics, FOBA and others. A specific example of an acceptable fiber laser system is a <NUM> watt pulsed fiber laser, vertical configuration produced by the IPG Photonics Corporation of Oxford, MA USA, with a focal length of <NUM>.

Referring to <FIG>, the fiber laser system <NUM> may be configured to move the laser output (i.e., the "laser beam <NUM>") relative to a stationary substrate <NUM>, or alternatively the system <NUM> may be configured to move the substrate relative to a stationary laser beam, or some combination thereof. The relative movement between the laser beam <NUM> and the substrate <NUM> may follow a predetermined pattern; e.g., a two dimensional pattern or a three-dimensional pattern, etc. The present disclosure is not limited to any particular application methodology other than as indicated herein.

In some embodiments, the present disclosure may utilize a fiber laser system <NUM> that employs a single laser beam <NUM> to treat a surface of a titanium substrate <NUM> in a manner that produces an oxide layer 32B with an open porous morphology <NUM>; e.g., see <FIG>. In other embodiments, the present disclosure may utilize a fiber laser system <NUM> that employs a plurality of laser beams <NUM> to treat a surface of a titanium substrate <NUM> in a manner that produces an oxide layer 32B with an open porous morphology <NUM>; e.g., see <FIG>.

As stated above, a titanium substrate <NUM> present within an environment containing oxygen (e.g., an "air" environment) will typically have a preexisting oxide layer 32A formed naturally on the prebond surface <NUM> of the titanium substrate <NUM> (see <FIG>); i.e., an oxide layer <NUM> formed solely by exposure of the titanium substrate <NUM> to an air environment. In many instances, the aforesaid preexisting oxide layer 32A is a solid layer and its bond to the underlying substrate <NUM> and/or adhesive <NUM> may lack significant bonding strength. For at least these reasons, it has been discovered that the preexisting oxide layer 32A may not provide a desirable surface for adhesive bonding. In many instances, the aforesaid prebond surface <NUM> may also have some amount of contaminants (e.g., dirt, oils, etc.) disposed on the prebond surface <NUM>. These contaminants (which may collectively be referred to as a contaminant layer <NUM>) may detrimentally affect the attachment/bonding of an adhesive to the substrate surface.

In some embodiments of the present disclosure, a fiber laser system <NUM> may be utilized to introduce energy into a prebond surface <NUM> of a titanium substrate <NUM> in an amount that is sufficient to remove the contaminant layer <NUM> from the prebond surface <NUM>; e.g., remove materials residing on the prebond surface <NUM> other than the substrate material itself, or a preexisting oxide layer 32A formed on the prebond surface <NUM>. Contaminants present on the prebond surface <NUM> may, however, be removed by other means. In some embodiments of the present disclosure, a fiber laser system <NUM> may be utilized to introduce energy into the metallic prebond surface <NUM> in an amount that is sufficient to remove (e.g., by ablation) the preexisting oxide layer 32A. In some embodiments, the preexisting oxide layer 32A present on the prebond surface <NUM> may, however, be removed by other means.

Once the preexisting oxide layer 32A is removed (and contaminant layer <NUM> as applicable), a fiber laser system <NUM> may be utilized to introduce energy into the prebond surface <NUM> in an amount that is sufficient to transform a depth of the prebond surface <NUM> of the substrate <NUM> into a produced oxide layer 32B having an open porous morphology <NUM> that is contiguous with the exposed surface of the prebond surface <NUM> (e.g., See <FIG>). The produced oxide layer 32B is a layer of a titanium oxide (e.g., a TiOx layer) having a thickness <NUM> on the order of about <NUM> nanometers (nm) to about <NUM>, which thickness <NUM> is more typically in the range of about <NUM> to about <NUM>. For clarity sake, the thickness <NUM> of the produced oxide layer 32B may be determined along a line perpendicular to the prebond surface <NUM> extending into the underlying titanium substrate <NUM>, and the thickness <NUM> of the layer 32B is the distance the layer 32B is present along that line at a given point from the exposed surface of the produced oxide layer 32B inward toward the underlying titanium substrate <NUM>.

The term "open porous morphology" is used to indicate that the produced oxide layer 32B has open pores configured to permit an adhesive <NUM> (See <FIG>) applied to the exposed surface of the oxide layer 32B to infiltrate and reside within the aforesaid surface. The open pores may be randomly distributed within the oxide layer 32B and are configured to be substantially accessible from the exposed surface of the oxide layer 32B; i.e., substantially accessible such that the adhesive <NUM> applied to the surface is able to infiltrate and reside within the aforesaid nanoscale open pores. The nanoscale open pores are present in at least a portion of the thickness <NUM> of the oxide layer 32B extending from the exposed surface of the layer 32B, and may be present in substantially the entire thickness <NUM> of the layer 32B.

The present disclosure method can be applied to contoured titanium components; i.e., applied to a component surface having at least one portion that is contoured with one or more geometric features that prevent direct line of sight laser beam impingement. A substantial percentage of the incident light in a laser treatment process is either scattered or reflected. Under conventional surface laser treatments, the scattered and/or reflected laser light adds minimal or no energy to the substrate impinged upon. It is typical, for example, for <NUM>-<NUM>% of laser light incident to a titanium alloy to be either scattered or reflected. Fiber lasers are known to produce a higher quality beam relative to other laser types, consequently providing a more accurately controlled focal beam relative to other types of laser systems given the same surface morphology. In those instances where a substrate portion is accessible by a line of sight ("LOS") laser beam, as specific geometry features (e.g., the inner surface of v-notch, cylinder, or cavity, etc.) permit, the aforesaid scattering and/or reflection is taken into account under the present disclosure to arrive at the energy necessary to create an oxide layer <NUM> with the desired open porous morphology <NUM>; e.g., the amount of incident laser light and energy attendant thereto may be increased to account for the reflection and/or scattering.

LOS laser systems are often limited by their LOS nature. For example, in some instances a portion of a non-planar substrate <NUM> (e.g., a contoured substrate) may not be accessible by the laser beam produced by a LOS laser system. <FIG> and <FIG> diagrammatically illustrate a substrate <NUM> having a V-notch type of feature that is not accessible via a laser system that utilizes a LOS laser beam.

The present disclosure, in contrast, utilizes a fiber laser and leverages the aforesaid scattering and/or reflection to apply the requisite energy into the surface regions that cannot be accessed by a non-LOS laser system; e.g., to remove contaminants <NUM>, to remove a preexisting solid oxide layer 32A, to create a produced oxide layer 32B having an open porous morphology <NUM>, and/or combinations thereof.

For example, under the present disclosure the angle of incidence of the laser beam produced by the fiber laser system <NUM> may be altered to increase the reflected light energy into a non-LOS substrate surface region (i.e., a "non-LOS surface feature"). The present disclosure further leverages the quality of the laser beam produced by a fiber laser system <NUM>. As stated above, fiber lasers are known to produce one of the highest beam qualities of available laser systems. The flexibility of a fiber laser to alter the angle of incidence of the laser beam permits the laser beam to be applied at an angle wherein the reflected portion of the laser beam will enter further into the non-LOS substrate surface region. The quality of the laser beam produced by the laser fiber system <NUM> increases the amount of energy that may be provided to the surface via reflectance and scattering. The surface characteristics of the prebond surface <NUM> (e.g., roughness, etc.) may affect the scattering and/or reflectance of the laser beam. Consequently, the present disclosure contemplates configuring the laser fiber system <NUM> output in view thereof; e.g., adjusting the output power of the system to produce the requisite reflected laser beam having sufficient power for the treatment described herein. <FIG> and <FIG> diagrammatically illustrate a substrate having a V-notch type of feature that is not accessible via a LOS impingement process. In <FIG>, the angle of incidence of the laser beam <NUM> is altered relative to line perpendicular to one of the substrate <NUM> surfaces. As a result, an increased amount of energy from the laser beam <NUM> is reflected into the V-notch and is available therefore for the oxide layer treatment. In <FIG>, the laser beam <NUM> is manipulated relative to the V-notch (or vice versa) so that the laser beam <NUM> is directed into the V-notch. In this example, the geometry of the V-notch relative to the angle of incidence of the laser beam <NUM> results in an increase in the amount of light reflected and/or scattered within the interior of the V-notch. As a result, the interior surfaces of the V-notch are subjected to an increased amount of energy from the laser beam <NUM> for the surface treatment.

Testing to evaluate bond performance and cracking resistance was performed to evaluate several surface preparation techniques; e.g., surface preparation by an alkaline etching process, by an anodizing process, by a Nd YAG laser process, and by a fiber laser process. The graph of Crack Growth versus time shown in <FIG> depicts the cracking resistance data collected. The results indicate that surface preparation performed by fiber laser process exhibited better bond performance and crack resistance on a titanium surface relative to the same type of substrate surface subjected to an alkaline etch process, an anodizing process, or a Nd YAG laser process. The aforesaid testing also indicated that a desirable failure mode (e.g., <NUM>% cohesive) was achieved as well. The aforesaid tested was performed in accordance with ASTM D3762, except that titanium test samples were used. Surface characterization showed that both macro-roughness and micro-roughness observed with the fiber laser treated titanium surface. A thick open porous morphology oxide layer <NUM> (e.g., about <NUM> to <NUM>) was also formed that promotes desirable strong chemical interaction and mechanical interlocking to enhance adhesive bonding. In some isolated areas, a thick porous oxide layer (e.g., about <NUM> to <NUM>) was also observed.

The following examples are provided to illustrate the utility of the present disclosure. The non-limiting examples illustrate method embodiments of the present disclosure applied to a prebond surface <NUM> of a titanium alloy substrate having a layer of contaminants and a preexisting oxide layer 32A disposed on the aforesaid prebond surface <NUM>. The following examples are also described in terms of one or more laser beam sources from a fiber laser system <NUM> that are configured to traverse across the prebond surface <NUM> in the direction indicated by arrow <NUM> (or vice versa). As indicated above, the present disclosure is not limited to any particular laser application pattern relative to the prebond surface <NUM>.

In a first example shown in <FIG>, the fiber laser system <NUM> includes a laser beam source <NUM> that is configured to introduce energy into the prebond surface <NUM> in an amount that is sufficient to remove contaminants <NUM> from the prebond surface <NUM>, to remove the preexisting oxide layer 32A present on the prebond surface <NUM>, and to transform a predetermined depth of the prebond surface <NUM> into a produced oxide layer 32B having an open porous morphology <NUM>.

In a second example shown in <FIG>, the fiber laser system <NUM> includes a first laser beam source 30A and a second laser beam source 30B. The first laser beam source 30A is configured to introduce energy into the prebond surface <NUM> in an amount that is sufficient to remove contaminants <NUM> from the prebond surface <NUM> and to remove the preexisting oxide layer 32A present on the prebond surface <NUM>. The second laser beam source 30B is configured to introduce energy into the prebond surface <NUM> in an amount that is sufficient to transform a predetermined depth of the prebond surface <NUM> into a produced oxide layer 32B having an open porous morphology <NUM>.

The above examples are intended to be illustrative of some embodiments of the present disclosure, and the present disclosure is not limited to these examples. As stated above, in some embodiments the fiber laser system <NUM> may employ more than one laser beam source <NUM> to accomplish certain functionalities (e.g., remove contaminants, remove preexisting oxide layer, form an open porous morphology <NUM>, etc.). Furthermore, as described above the present disclosure provides improved methodologies for treating contoured surfaces having one or more non-LOS surface features. As can be seen in <FIG> and <FIG>, embodiments of the present disclosure utilize the fiber laser system <NUM> to introduce laser energy into non-LOS surface features. The above method examples are applicable to treating prebond surfaces <NUM> within non-LOS surface features.

As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural forms thereof unless the context clearly indicates otherwise. Unless otherwise indicated, all numbers expressing conditions, concentrations, dimensions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about".

Where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain steps may be performed concurrently in a parallel process when possible, as well as performed sequentially. Therefore, the particular order of the steps set forth in the description should not be construed as a limitation.

Claim 1:
A method for treating a surface of a contoured titanium substrate (<NUM>) used for adhesively bonded engine components, comprising:
applying energy from a laser system (<NUM>) to a contoured surface of a titanium substrate (<NUM>),
the method being characterised in that:
the laser system (<NUM>) is an infrared fiber laser system that produces pulse energy in the range of about <NUM> to <NUM> mJ and at a pitch of about <NUM> to <NUM> using a laser beam having a diameter of about <NUM>, and the laser energy is distributed to the contoured titanium surface by at least one of direct line of sight, reflection, or scattering of one or more laser beam (<NUM>), wherein the step of applying energy from the fiber laser system (<NUM>) to the contoured surface of the titanium substrate (<NUM>) creates a produced oxide layer (32B) within the titanium substrate (<NUM>), the produced oxide layer (32B) including a nanoscale open porous morphology (<NUM>).