Patent Publication Number: US-2023158594-A1

Title: Anti-corrosive braze coatings

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 63/282,911 filed Nov. 24, 2021 for “ANTI-CORROSIVE BRAZE COATINGS” by D. Teigen, K. Rose, C. Kuha, and K. Wachter. 
    
    
     BACKGROUND 
     The present disclosure relates to air data probes, and more particularly, to air data probes with improved corrosion resistance. 
     Air data probe devices can be utilized in, e.g., aerospace applications for measuring environmental parameters usable to determine air data outputs. For instance, air data probes can measure pitot pressure, static pressure, or other parameters of airflow across the air data probe that are usable for determining air data outputs, such as pressure altitude, altitude rate (e.g., vertical speed), airspeed, Mach number, angle of attack, angle of sideslip, or other air data outputs. Such air data probes often include one or more air data sensing ports, such as static pressure ports located on the side of the probe integral to the surface of the probe that are pneumatically connected to sensors that sense the atmospheric pressure outside of the aircraft. Certain flight conditions can cause ice accumulation within an air data probe, degrading air data probe performance. 
     SUMMARY 
     In one embodiment, a corrosion-resistant air data probe includes a hollow tube having at least one opening, an inner surface of the hollow tube defining an interior cavity, a heating element, and a continuous layer of a braze material. The heating element is disposed adjacent to the inner surface, within the interior cavity. The continuous layer of the braze material completely covers the heating element and covers at least a portion of the inner surface. 
     In another embodiment, a method of fabricating an air data probe includes applying a braze material to an inner surface of an air data probe, positioning the air data probe in a first orientation relative to a direction of gravity, heating the air data probe while in the first orientation to braze a braze material to the inner surface and a heating coil disposed adjacent to the inner surface, applying additional braze material to the inner surface after heating the air data probe while in the first orientation, positioning the air data probe in a second orientation relative to the direction of gravity, and heating the air data probe while in the second orientation to braze the additional braze material to the inner surface and the heating coil. The air data probe comprises a hollow tube having at least one opening, an interior cavity of the hollow tube is defined by the inner surface, and the hollow tube is oriented along an axis. The second orientation is rotated about the axis relative to the first orientation. 
     The present summary is provided only by way of example, and not limitation. Other aspects of the present disclosure will be appreciated in view of the entirety of the present disclosure, including the entire text, claims, and accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an example of an air data probe. 
         FIG.  2    is a cross-sectional image of an example of an air data probe. 
         FIG.  3    is a cross-sectional image of an example of an air data probe having a partial anti-corrosive braze layer. 
         FIG.  4 A  is a cross-sectional image of an example of an air data probe having an anti-corrosive braze layer. 
         FIG.  4 B  is a cross-sectional image the heating element of the air data probe of  FIG.  4 A . 
         FIG.  5    is a flow diagram of an example of a method of fabricating a corrosion-resistant air data probe. 
     
    
    
     While the above-identified figures set forth one or more embodiments of the present disclosure, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features and components not specifically shown in the drawings. 
     DETAILED DESCRIPTION 
     The present disclosure includes systems and methods of for improving corrosion resistance of air data probes. More specifically, the systems and methods disclosed herein use a layer of brazed material to protect heating elements and/or air data probe surfaces from corrosion. The systems and methods disclosed herein advantageously reduce the susceptibility of air data probes to corrosion-based failure. 
       FIG.  1    is a perspective view of air data probe  10 . Air data probe  10  includes tube  14  and sensing ports  26  and  28 . In the depicted example, tube  14  includes a barrel- or cylinder-shaped portion and a tapered or conically-shaped section leading to sensing port  28 . However, tube  14  can have other suitable geometries. Sensing ports  26  and  28  are formed integrally with tube  14  and are pneumatically connected to one or more sensors. Sensing ports  26  and  28  allow air data probe  10  to sense air data when air data probe  10  is placed in a flow or air. As depicted, sensing port  26  is a pitot pressure sensing port and sensing port  28  is a static pressure sensing port. However, air data probe  10  can have other combinations of one or more sensing ports for sensing a variety of air data. 
       FIG.  2    is a cross-sectional image of prior art air data probe  100 . Air data probe  100  has overall structure as disclosed generally with regard to air data probe  10  of  FIG.  1   . Air data probe  100  includes heating element  102 , tube  104 , and braze  106 . Tube  104  includes inner surface  110 , which defines cavity  112 . In the depicted example, tube  104  has a hollow conical shape and extends generally along axis A-A. However, tube  104  can be formed into other suitable shapes or combinations of multiple shapes. For example, tube  104  can be formed as a hollow cylinder. In another example, tube  104  can include both cylindrical and conical sections. Inner surface  110  defines cavity  112  and forms a channel through which a fluid, such as air, can flow or accumulate. Similar to tube  14 , tube  104  has one or more openings or ports (not shown) such that air data probe  100  can take in air from a flow of air. One or more sensors can be coupled to and/or integrated with tube  104  for measuring air data. In operation, air data probe  100  is placed in a flow of air to measure air data of the flow of air. In some examples, air data probe  100  can be attached to an aircraft and used to determine one or more of pressure altitude, altitude rate (e.g., vertical speed), airspeed, Mach number, angle of attack, angle of sideslip, air speed, or another suitable air data parameter. 
     Heating element  102  is disposed within tube  104  adjacent to inner surface  110  and extends away from inner surface  110  into cavity  112 . Heating element  102  is a resistive heating element configured to heat inner surface  110  during operation of air data probe  100 . Heating element  102  is affixed to inner surface  110  by brazing, forming fillets of braze  106  between heating element  102  and inner surface  110 . The portion of heating element  102  extending away from inner surface  110  is exposed to air in cavity  112 . In  FIG.  2   , heating element  102  has a helical shape and wrap helically around inner surface  110  of tube  104 . The helical shape of heating element  102  depicted in  FIG.  2    improves uniformity of heating of inner surface  110 . However, in other examples, heating element  102  has other shapes. In some examples, tube  104  is formed of a nickel material. In further examples, braze  106  is comprises a mixture of metals. 
     In low temperature conditions, ice can form on inner surface  110  and clog tube  104 , impeding the flow of air through cavity  112  and thereby reducing the accuracy of air data collected with air data probe  100 . Heating element  102  reduces ice formation along inner surface  110  by applying heat to inner surface  110 . However, in corrosive environments, repeated heating and cooling of heating element  102  can cause corrosion of heating element  102  and/or tube  104 , potentially leading to failure of heating element  102 , tube  104 , or another component of air data probe  100 . The corrosive environment can be, for example, a saltwater air environment. 
       FIG.  3    is a cross-sectional diagram of air data probe  200 , which has a partial layer of anti-corrosive braze material as compared to prior art air data probe  100 , which lacks any layer of anti-corrosive braze material. Air data probe  200  includes heating element  202 , tube  204 , braze  206 , inner surface  210 , cavity  212 , and uncovered region  224 . Air data probe  200  is substantially similar to air data probe  100  and can perform substantially the same functions as air data probe  100 , but includes braze  206 , which covers more of heating element  102 . Heating element  202 , tube  204 , inner surface  210 , and cavity  212  are substantially similar to heating element  102 , tube  104 , inner surface  110 , and cavity  112 , respectively, as described with respect to  FIG.  2   . 
     Like braze  106 , braze  206  affixes heating element  202  to inner surface  210  and can be formed of a metal material or a mixture of metal materials. However, braze  206  is formed of more braze material than braze  206  and covers more of heating element  202  than braze  106  covers of heating element  102 . Notably, although braze  206  includes more braze material than braze  106 , braze  206  does not cover all heating element  202 . Specifically, uncovered region  224  of heating element  202  is not covered by braze  206 . 
     Braze  206  confers corrosion protection to heating element  202  where braze  206  covers heating element  202 . At uncovered region  224 , heating element  202  has degraded due to corrosion, reducing or eliminating the ability of heating element  202  to melt ice that has accumulated on inner surface  210  of tube  204 . To this extent, uncovered region  224  is a weak spot of heating element  202  that is not protected by a layer of braze  206  and that has increased susceptibility to corrosion as compared to the portions of heating element  102  that are covered by a layer of braze  206 . 
       FIG.  4 A  is a cross-sectional view of air data probe  300 , which has a complete anti-corrosive braze layer.  FIG.  4 B  is a cross-sectional view of heating element  302  of air data probe  300  showing braze coverage across heating element  302 .  FIGS.  4 A-B  will be discussed together. 
     Air data probe  300  includes heating element  302 , tube  304 , and braze  306 . Tube  304  includes inner surface  310 , which defines cavity  312 . Heating element  302 , tube  304 , inner surface  310 , and cavity  312 , are substantially similar to heating elements  102 / 202 , tubes  104 / 204 , inner surfaces  110 / 210 , and cavities  112 / 212  respectively, as described with respect to  FIGS.  2 - 3   . Like air data probes  100  and  200 , air data probe  300  can also include one or more sensors for sensing air data. 
     Braze  306  covers substantially all of heating element  302 , affixing heating element  302  to inner surface  310  and forming a barrier between heating element  302  and cavity  312 . Advantageously, the continuous barrier formed by braze  306  protects heating element  302  from corrosion-based failure and thereby also functions to prevent corrosion-based failure of heating wire  320 , increasing the operational lifespan of heating element  302 . 
     As shown more clearly in  FIG.  4 B , braze  306  forms a continuous layer that covers all of heating element  302  and at least a portion of inner surface  310  such that there are no uncovered regions of heating element  302 . As braze  306  forms a continuous layer that covers all of heating element  302 , heating element  302  does not have any uncovered regions or weak spots that have increased susceptibility to corrosion. To this extent, heating element  302  has reduced susceptibility to corrosion-based failure and an increased operational lifespan as compared to the uncovered heating element  102  shown in  FIG.  2    and the partially covered heating element shown in  FIG.  3   . In some examples, braze  306  forms a continuous layer that covers the entirety of inner surface  310  and the entirety of inner surface  310 , thereby conferring additional environmental protection to inner surface  310  of tube  304 . 
       FIG.  5    is a flow diagram of method  400 , which can be used to create a corrosion-resistant air data probe. Method  400  includes steps  402 - 408  of applying braze material (step  402 ), positioning the air data probe (step  404 ), drying the air data probe (step  406 ), and heating the air data probe (step  408 ). Method  400  optionally includes steps  410 - 412  of removing excess braze material (step  410 ) and masking the air data probe (step  412 ). 
     Prior to or as a preliminary step of method  400 , heating element  302  is arranged within tube  304  of air data probe  300 . In step  402  of method  400 , a braze material is applied to inner surface  310  and heating element  302  of air data probe  300 . To improve distribution of braze material along inner surface  310  and heating element  302 , the braze material is to be applied as a slurry containing a powdered metal and a solvent. The metal can be, for example, a mixture of multiple metal materials. Following heating in step  406 , the braze material applied in step  402  forms braze  306 . In some examples, the slurry can also include a viscous element, such as a cement, to increase the viscosity of the slurry. Advantageously, the viscosity of the slurry can be selected to improve coverage of the braze material following heating in step  408 , as will be explained in more detail subsequently. In some examples, tube  304  includes drain holes that are configured to allow for melted ice to flow out of tube  304  as during operation of air data probe  300 . In these examples, the drain holes of tube  304  can be plugged prior to application of braze material in step  402  to prevent the braze material slurry from flowing out of the drain holes during method  400 . 
     In step  404 , air data probe  300  is positioned prior to heating in step  406 . The position of air data probe  300  is selected to increase coverage and uniformity of braze  306  following heating in step  406 , which advantageously improves the anti-corrosion properties conferred by braze  306 . For example, air data probe  300  can be positioned substantially horizontally such that axis A′-A′ is perpendicular to the direction of gravity. Advantageously, positioning air data probe  300  substantially horizontally prevents the braze material applied in step  402  from accumulating at an end (i.e., an end along axis A′-A′) of tube  304  during drying of the braze material during step  406  prior to heating in step  408 . 
     In step  406 , the braze material applied in step  402  is dried to remove solvent from the braze material applied in step  402 . The duration of drying can be selected based on the volatility of the solvent and the atmospheric conditions in which drying is performed. Advantageously, drying the braze material in step  406  reduces the ability of the unbrazed braze material to flow out of tube  304  during subsequent steps of method  400 . As the braze material is in a slurry form until heating during step  408 , the braze material can flow out of air date probe  300  or flow into regions where it is undesirable for brazing to occur during step  408 . Air data probe can be cleaned following drying in step  406  to remove dried braze material from areas where brazing should not occur in step  408 . 
     In step  408 , air data probe  300  is heated to braze the powdered metal in the braze material applied in step  402 , thereby forming a coating of braze  306  on heating element  302  and inner surface  310  Air data probe  300  can be heated in, for example, a vacuum furnace to braze the metal powder. Advantageously, braze  306  formed in step  408  functions both to affix heating element  302  to inner surface  310  and to protect inner surface  310  from corrosion. 
     In some examples of method  400 , an excess of braze material is applied in step  402 . The excess of braze material can be applied by, for example, filling cavity  312  with braze material. Cavity  313  can be filled with braze material by, for example, placing a cap on an open end of tube  304  and filling cavity  312  by injecting braze material through the cap. Air data probe  300  can be oriented substantially vertically such that axis A′-A′ is substantially parallel with the direction of gravity as cavity  312  is filled with an excess of braze material. Advantageously, applying an excess of braze material increases the uniformity of braze material about inner surface  310  and heating element  302  prior to brazing in step  408 . In examples where an excess of braze material, method  400  can include step  410  of removing excess braze material after step  402  (applying braze material) and before step  404  (positioning air data probe  300 ). Excess braze material can be removed by draining or another suitable method. 
     In further examples, method  400  includes step  412  of masking air data probe  300  following step  406  (drying air data probe  300 ) and before step  408  (heating air data probe  300 ). In step  412 , a masking compound can be applied to one or more areas of air data probe  300  to prevent brazing and/or heat scale formation in those areas during step  408  of method  400 . The masking compound can be, for example, a mica-based masking compound. 
     Although positioning tube  304  substantially horizontally in step  404  reduces the propensity of braze material to accumulate at an end of tube  304 , gravity biases the distribution braze material slurry applied in step  402  to the gravitational bottom of tube  304 , reducing the uniformity of coverage of braze  306  following step  408 . Nonuniform coverage of braze  306  can result in uncovered regions of heating element  302 . Similar to uncovered region  224  of heating element  102  of air data probe  200  discussed previously with respect to  FIG.  3   , uncovered regions of heating element  302  are susceptible to corrosion. To reduce or eliminate uncovered regions of heating element  302 , method  400  can be repeated multiple times and tube  304  can be placed in a different position or orientation during step  404  of each subsequent iteration. Advantageously, changing the position of tube  304  during each subsequent iteration of method  400  can allow for regions that were previously at the gravitational top of tube  304  after step  404  to be placed closer to or at the gravitational bottom of tube  304  during a subsequent iteration. 
     The number of iterations can be selected to create a continuous covering of braze  306  over heating element  302  and at least a portion of inner surface  310  such that there are no uncovered regions of heating element  302 . In some examples, performing only one iteration of method  400  can create a discontinuous braze layer that does not cover all of heating element  302 , similar to braze  206  of air data probe  200 . In these examples, subsequent iterations of method  400  can be used to ensure braze  306  coverage of regions that are not covered by braze  306  after a single iteration of method  400 . 
     The number of iterations of method  400  can be further selected to ensure that the layer of braze  306  does not negatively impact performance of air data probe  300 . Excessive braze  306  coverage can reduce the accuracy of measurements made using air data probe  300 . Advantageously, a limited number of iterations of method  400  can be performed to apply a corrosion-resistant layer of braze  306  to heating element  302  without creating excessive braze  306  coverage that negatively impacts the performance of air data probe  300 . 
     Air data probe  300  can be positioned in step  404  in each subsequent iteration according to, for example, the desired number of iterations. For example, where two iterations of method  400  are performed, the orientation of air data probe  300  in the second iteration can be rotated 180° about axis A′-A′ relative to the orientation of air data probe  300  in the first iteration, such that braze material slurry is biased to different sides of air data probe  300  in different iterations of method  400 . As a further example, where three iterations of method  400  of performed, the positions of air data probe  300  in each iteration can be offset by 60° about axis A′-A′ relative to each other. Alternatively, air data probe can be rotated 180° about axis A′-A′ in each subsequent iteration of method  400 . 
     After the desired number of iterations of method  400  have been performed and an anti-corrosion layer of braze has been formed on inner surface  310  and heating element  302  of air data probe  300 , air data probe  300  can be further processed by, for example, installation of one or more air data sensors. 
     Other operational parameters of method  400  can be adjusted to improve uniformity of braze following heating in step  408  of method  400 . The viscosity of the slurry of braze material can affect flow characteristics of the braze material after it is applied to inner surface  310 , and can be optimized to reduce accumulation of braze material at the gravitational bottom of tube  304  between steps  404  and  408 . In examples where an excess of braze material is applied in step  402 , the rate at which braze material is applied can be selected to reduce settling of powdered metal at the bottom of tube  304  along axis A′-A′. Where method  400  includes step  410 , the rate at which excess braze material is removed can further be optimized to increase the uniformity of the distribution of unbrazed braze material along inner surface  310  and heating element  302 . Generally, increasing the rate at which excess braze material is removed can increase the uniformity of the unbrazed braze material. Further, temperature to which the air data probe is heated in step  408  can be selected to optimize brazing of the braze material. Similarly, the rate at which the air data probe is heated can be selected to minimize accumulation of braze material at the gravitational bottom of tube  304  and thereby improve distribution uniformity of braze  306  following step  408 . 
     Advantageously, method  400  allows for construction of air data probes with improved corrosion resistance as compared to existing methods. The improved corrosion resistance imparted by the inner braze layer created using method  400  reduces the susceptibility of an air data probe tube or heating element to corrosion-type failure modes. In addition to conferring corrosion-protection, the inner braze layer created using method  400  can further provide protection from other potential environmental effects that can lead to failure of one or more air data probe components. 
     Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     An embodiment of a corrosion-resistant air data probe includes a hollow tube having at least one opening, an inner surface of the hollow tube defining an interior cavity, a heating element, and a continuous layer of a braze material. The heating element is disposed adjacent to the inner surface, within the interior cavity. The continuous layer of the braze material completely covers the heating element and covers at least a portion of the inner surface. 
     The corrosion-resistant air data probe of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A corrosion-resistant air data probe according to an exemplary embodiment of this disclosure includes, among other possible things, a hollow tube having at least one opening, an inner surface of the hollow tube defining an interior cavity, a heating element, and a continuous layer of a braze material. The heating element is disposed adjacent to the inner surface, within the interior cavity. The continuous layer of the braze material completely covers the heating element and covers at least a portion of the inner surface. 
     A further embodiment of the foregoing corrosion-resistant air data probe, wherein the inner surface forms a hollow cylinder and the heating element has a helical shape. 
     A further embodiment of any of the foregoing corrosion-resistant air data probes, wherein the inner surface comprises a first material and the braze material comprises a second material. 
     A further embodiment of any of the foregoing corrosion-resistant air data probes, wherein the continuous layer of the braze material covers an entirety of the inner surface. 
     An embodiment of a method of fabricating an air data probe includes applying a braze material to an inner surface of an air data probe, positioning the air data probe in a first orientation relative to a direction of gravity, heating the air data probe while in the first orientation to braze a braze material to the inner surface and a heating coil disposed adjacent to the inner surface, applying additional braze material to the inner surface after heating the air data probe while in the first orientation, positioning the air data probe in a second orientation relative to the direction of gravity, and heating the air data probe while in the second orientation to braze the additional braze material to the inner surface and the heating coil. The air data probe comprises a hollow tube having at least one opening, an interior cavity of the hollow tube is defined by the inner surface, and the hollow tube is oriented along an axis. The second orientation is rotated about the axis relative to the first orientation. 
     The method of fabricating an air data probe preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A method of fabricating an air data probe according to an exemplary embodiment of this disclosure includes, among other possible things, applying a braze material to an inner surface of an air data probe, positioning the air data probe in a first orientation relative to a direction of gravity, heating the air data probe while in the first orientation to braze a braze material to the inner surface and a heating coil disposed adjacent to the inner surface, applying additional braze material to the inner surface after heating the air data probe while in the first orientation, positioning the air data probe in a second orientation relative to the direction of gravity, and heating the air data probe while in the second orientation to braze the additional braze material to the inner surface and the heating coil. The air data probe comprises a hollow tube having at least one opening, an interior cavity of the hollow tube is defined by the inner surface, and the hollow tube is oriented along an axis. The second orientation is rotated about the axis relative to the first orientation. 
     A further embodiment of the foregoing method of fabricating an air data probe, wherein the second orientation is rotated 180 degrees about the axis relative to the first orientation. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein the axis is orthogonal to the direction of gravity when the air data probe is positioned in the first orientation and in the second orientation. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein the axis is substantially parallel to the direction of gravity while the braze material is applied. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein the braze material comprises a slurry. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein the slurry further comprises a cement material. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein applying the braze material to the inner surface of the air data probe comprises applying an excess of the braze material to the inner surface and removing a portion of the braze material from the inner surface after applying the excess of the braze material. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, further comprising at least partially drying the braze material after positioning the air data probe in the first orientation and before heating the air data probe in the first orientation. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, further comprising at least partially drying the braze material after position the air data probe in the second orientation and before heating the air data probe in the second orientation. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein the inner surface is formed of a material that is different than the braze material. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, further comprising applying additional braze material to the interior cavity of the air data probe after heating the air data probe while in the second orientation, positioning the air data probe in a third orientation, and heating the air data probe while in the third orientation to braze the additional braze material to the inner surface and the heating coil. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein the third orientation is rotated about the axis relative to the second orientation. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein a continuous layer of the braze material covering the heating element and covering at least a portion of the inner surface is formed after heating the air data probe while in the second orientation. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein the continuous layer of the braze material covers an entirety of the inner surface. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, wherein the inner surface forms a hollow cylinder and the heating element has a helical shape. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, further comprising attaching a nose cap to one opening of the tube before applying the braze material to the inner surface, wherein applying the braze material comprises injecting the braze material into the interior cavity through the nose cap. 
     A further embodiment of any of the foregoing methods of fabricating an air data probe, further comprising applying a masking compound to a portion of the tube after applying a braze material and before heating the air data probe while in the first orientation. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.