Patent Application
20110064963
The present invention relates generally to metallurgy, and more particularly, some embodiments relate to coating technology.
Thermal spray processing is a technique used to apply a coating onto a substrate material. Often, the coating material is used to give the substrate enhanced surface properties. Also, the technique can be used to repair the substrate after damage or improper machining. Techniques for thermal spray processing involve using a spray gun to impart the coating material with a sufficient amount of energy such that it impacts and sticks via a mechanical bond. In these processes, molten or semi-molten droplets or particles of the coating material are impacted with the substrate material. Once deposited, these droplets or particles are often called “splats” owing to the plate-like appearance of the deposited particles. In many cases, the surface of the substrate is prepared by sandblasting to create asperities on the surface for the coating material to attach to. Some porosity in the coating is inevitable, and is a function of the material, spray parameters, and technique used (HVOF, plasma, combustion, TWAS, etc.).
Although mechanical bonding is the primary technique for coating adhesion to the surface, some materials are said to be self-bonding and form a limited metallurgical bond between the substrate/coating and between the individual splat particles that impact the surface during the spray process. The amount of coating that may be deposited in one application is typically limited by the residual stress caused by particle shrinkage upon cooling. If this residual stress exceeds the bond strength of the coating, the coating may peel off the substrate. To improve coating adhesion for a variety of coating types, a primary layer of an improved bonding material is often layered down before the desired coating material is applied.
Some embodiments of the invention provide The present invention provides a method for coating an article comprising applying a thermal spray coating to the article; applying a brazing material to the article; and heating the brazing material to at least a brazing temperature of the brazing material to form a resultant coating on the article, wherein the resultant coating is characterized by at least partial metallurgical bonding or at least partial alloying between the thermal spray coating and the brazing material.
In further embodiments, the brazing material comprises a nickel-based braze alloy or a Fe and Ni based braze alloy, and the thermal spray coating comprising an amorphous or partially amorphous metallic compound. In some embodiments, the brazing material or thermal spray coating material comprises a metal formed according to at least one of the formulae Fe54-75Cr9-15 Ni0-4.8(Mo,Nb)7.9-13C1.6-3B1.3-4.6W0-11Ti0-7Si0-1.1Mn0-1.1; (Fe61-75Cr9-14.4 Ni0-4.8(Mo,Nb)6-11.7C1.6-2.1B1.3-4.6W0-9.98Ti0-7S0-1.1Mn0-1.1)100-xAlx where x ranges from 0.5-10; Fe62-66Cr13-25(Mo,Nb)4-12(C,B)2.2-4.4Ni0-4.8Si0-1.5Mn0-1.2W0-3.8; Fe61-76Cr9-14.4 Ni0-5(Mo,Nb)7.9-11.7C1-6-2.1B1.3-5W0-9.98Si0-1.5Mn0-1.1; and Fe62-66Cr13-25(Mo,Nb)4-12(C,B)0-4.4Ni0-5Si0-1.5Mn0-1.2W0-3.8.
In still further embodiments, an article such as a substrate is coated with a brazing material and heated such that the brazing material diffuses into the substrate, thereby creating a compositional gradient from the surface of the material into the bulk of the material.
The present invention, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments of the invention. These drawings are provided to facilitate the reader's understanding of the invention and shall not be considered limiting of the breadth, scope, or applicability of the invention. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.
The figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the invention be limited only by the claims and the equivalents thereof.
Some embodiments of the invention provide methods for forming coatings and compounds that may be used in these methods. In some embodiments of the invention, a coated article is created by coating an article with a thermal spray coating and a brazing material. In some embodiments, this may comprise coating the article with the brazing material and then applying the thermal spray coating to the braze coated article. In other embodiments, this may comprise coating the article with the thermal spray coating and then applying the brazing material to the thermal spray coated article. In still further embodiments, the thermal spray coating material and brazing material may be combined prior to application, and the combination may be applied to the article. The heat present during the coating application, or a subsequent heat treatment, may be used to cause the brazing material to infiltrate interstitial spaces that occur within the thermal spray coating. Additionally, the brazing material may be caused to at least partially alloy with the thermal spray coating. In the embodiments described herein, many methods of applying the thermal spray coating material and brazing material may be used, such as, for example, high velocity oxygen fuel coating (HVOF), plasma spray coating, plasma, combustion spraying, twin wire arc spray coating (TWAS), etc.
In further embodiments, amorphous, nanocrystalline, or other fine grained metals may be used as the thermal spray coating materials or as the brazing materials. For example, in addition to the materials described herein, the various compounds described in Provisional U.S. Application Ser. No. 61/243,498 filed Sep. 17, 2009. Such compounds might comprise, for example, compounds formed according to one or more of the following formulae: Fe54-75Cr9-15 Ni0-4.8(Mo,Nb)7.9-13C1.6-3B1.3-4.6W0-11Ti0-7Si0-1.1Mn0-1.1; (Fe61-75Cr9-14.4 Ni0-4.8(Mo,Nb)6-11.7C1.6-2.1B1.3-4.6W0-9.98Ti0-7Si0-1.1Mn0-1.1)100-xAlx where x ranges from 0.5-10; Fe62-66Cr13-25(Mo,Nb)4-12(C,B)2.2-4.4Ni0-4.8Si0-1.5Mn0-1.2W0-3.8; Fe61-76Cr9-14.4 Ni0-5(Mo,Nb)7.9-11.7C1.6-2.1B1.3-5W0-9.98Ti0-7Si0.1.1Mn0-1.1; and Fe62-66Cr13-25(Mo,Nb)4-12(C,B)0-4.4Ni0-5Si0-1.5Mn0-1.2W0-3.8. In other embodiments, the brazing material may comprise a solder or other infiltrating material that is capable of infiltrating the thermal spray coating under proper process conditions.
Coating 160 illustrates an embodiment where the brazing material 167 is caused to infiltrate the thermal spray coating 166 without alloying to form a composite material. In this embodiment, the application of heat to the coating or coated article results in the brazing material 167 penetrating through a predetermined depth of the coating 167 to at least partially fill at least some of the interstitial spaces 165 that occur within the coating 166. As illustrated by infiltrated spaces 168, among other effects, this infiltration may increase the bond strength within the coating and may reduce the porosity of the coating. In particular embodiments, the reduction of the porosity of the coating increases the corrosion resistance of the resultant coating 160.
Coating 161 illustrates an embodiment where the brazing material 167 is caused to infiltrate the thermal spray coating 166 and to partially alloy with the thermal spray coating 166. In this embodiment, the process is configured such that, in addition to creating infiltrated spaces 168, the brazing material 167 is caused to alloy with the thermal spray coating 166 at locations 169. In various embodiments, this configuration may comprise modifying the temperature, length, or other characteristics of the heat treatment, or selecting different brazing or thermal spray coating materials, or modifying other characteristics of the coating process. In these embodiments, the amount of alloying, or the alloys formed in the coating may spatially vary or may vary according to coating types, relative proportions of the coatings, or other process parameters. In further embodiments, this partial alloying may comprise almost complete alloying. Coating 162 illustrates such an embodiment where the brazing material 167 is caused to alloy with the thermal spray coating to form a new alloy material 170. In these embodiments as well, in complete alloying may still result in a plurality of different alloys within the resultant coating.
In typical HVOF coatings, porosity in the coating remains sufficient to act as a pathway for electrolytic fluids. In both the as sprayed and heat treated coatings, the brazing material reduces this porosity to prevent corrosion of the substrate and damage to the substrate/coating interface. Furthermore, in the heat-treated resultant coating, porosity is further reduced throughout the coating itself, thereby prevent at least some encroachment by corrosive fluids.
The compositions used in various embodiments of the invention can have a significant effect on the electrical potential of resultant coatings.
Further embodiments of the invention provide materials that may be used in applications of the invention. In addition to other uses, (Fe,Ni)-based brazing materials may increase the corrosion resistance in applications of some methods of the invention. In particular, the increased amount of Fe in these materials lowers the cost of the brazing material and gives the brazing material a more similar electrochemical potential to the Fe-base materials that typically make up substrates and thermal spray coatings.
In further embodiments, other thermal spray coatings may serve as what has been termed brazing materials herein. For example,
In further embodiments, the resultant coating formed can made to diffuse into the substrate to create a functional composition gradient in the bulk of the article. In these embodiments, a base thermal spray coating is not used. In some applications, these embodiments may be employed in situations where thermal cycling might result in coating failure in most thermal spray or weld overlays.
In further embodiments, aluminum or aluminum alloys may be used as brazing materials, either in place of or in addition to the other brazing materials described herein.
In still further embodiments, the use of aluminum can be added to braze and thermal spray coating techniques. In these embodiments, in addition to creating a mechanically stronger coating, the brazing material also acts as a sacrificial anode to the coating in highly corrosive conditions.
As used herein, the term article may refer to an unprocessed article to be coated and to the article during any intermediate processing steps. As used herein, the term coating may refer to a material that is layered upon an article such as a substrate having a distinct interface between the coating material into the article; the term coating may also refer to a material that has at least partially diffused into or alloyed with the article.
Although the invention is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations, to one or more of the other embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments. Additionally, with regard to flow diagrams, operational descriptions and method claims, the order in which the steps are presented herein shall not mandate that various embodiments be implemented to perform the recited functionality in the same order unless the context dictates otherwise.
Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as meaning “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; the terms “a” or “an” should be read as meaning “at least one,” “one or more” or the like; and adjectives such as “conventional,” “traditional,” “normal,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future.
As used herein, the term “article” may refer to an unprocessed article to be coated and to the article during any intermediate processing steps. As used herein, the term “coating” may refer to a material that is layered upon an article such as a substrate having a distinct interface between the coating material into the article; the term coating may also refer to a material that has at least partially diffused into or alloyed with the article. In the formulae for compounds described herein, the notation (X,Y)a means that the element X, or the element Y, or a combination thereof are present in the compound in weight percentage a. Unless otherwise indicated, compound formulae are presented in weight percentage. The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent.
Additionally, the various embodiments set forth herein are described in terms of exemplary block diagrams, flow charts and other illustrations. As will become apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives can be implemented without confinement to the illustrated examples. For example, block diagrams and their accompanying description should not be construed as mandating a particular architecture or configuration.
This application claims priority from Provisional U.S. Application Ser. No. 61/243,498 filed Sep. 17, 2009, which is hereby incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61243498 | Sep 2009 | US |
