(12) United States Patent
`Eaton et al.
`
`(10) Patent No.:
`
`(45) Date of Patent:
`
`US 7,060,360 B2
`Jun. 13, 2006
`
`US007060360B2
`
`(54) BOND COAT FOR SILICON BASED
`SUBSTRATES
`
`(75)
`
`Inventors: Harry E. Eaton, Woodstock, CT (US);
`Ellen Y. Sun, South Windsor, CT (US);
`Stephen Chin, Wallingford, CT (US)
`
`(73) Assignee: United Technologies Corporation,
`Hartford, CT (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 362 days.
`
`(21) Appl. No.: 10/443,342
`
`(22)
`
`Filed:
`
`May 22, 2003
`
`(65)
`
`(51)
`
`Prior Publication Data
`US 2004/0234784 A1 NOV. 25, 2004
`
`Int. Cl.
`B32B 9/00
`F03B 3/12
`
`(2006.01)
`(2006.01)
`
`(52) U.S. Cl.
`
`..................... .. 428/446; 428/450; 428/697;
`428/699; 428/701; 428/702; 416/241 B
`(58) Field of Classification Search ............... .. 428/446,
`428/697, 450, 698, 699, 700, 701, 702; 416/241 B,
`416/241 R
`
`........ .. 428/408
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,677,060 A * 10/1997 Terentieva et al.
`6,254,935 B1
`7/2001 Eaton et a1.
`6,284,325 B1
`9/2001 Eaton, Jr. et a1.
`6,296,942 B1
`10/2001 Eaton, Jr. et a1.
`6,299,988 B1
`10/2001 Wang et al.
`6,312,763 B1
`11/2001 Eaton, Jr. et a1.
`6,352,790 B1
`3/2002 Eaton et a1.
`6,365,288 B1
`4/2002 Eaton et a1.
`6,410,148 B1
`6/2002 Eaton, Jr. et a1.
`2002/0025454 A1
`2/2002 Wang et al.
`
`* cited by examiner
`
`Primary Examiner—Jennifer McNeil
`(74) Attorney, Agent, or Firm—Bachman & LaPointe, P.C.
`
`(57)
`
`ABSTRACT
`
`A bond layer for use on a silicon based substrate. The bond
`layer comprises an alloy comprising a refractory metal
`disilicide/silicon eutectic. The refractory metal disilicide is
`selected from the group consisting of disilicides of
`molybdenum, chromium, hafnium, niobium,
`tantalum,
`rhenium,
`titanium,
`tungsten, uranium, Vanadium, yttrium
`and mixtures thereof. The refractory metal disilicide/silicon
`eutectic has a melting point of greater than 1300° C.
`
`See application file for complete search history.
`
`14 Claims, 2 Drawing Sheets
`
`GE-1001.001
`
`GE-1001.001
`
`

`
`U.S. Patent
`
`Jun. 13,2006
`
`Sheet 1 of2
`
`US 7,060,360 B2
`
`/53»
`
`/fair 7
`
`GE-1001.002
`
`GE-1001.002
`
`

`
`U.S. Patent
`
`Jun. 13,2006
`
`Sheet 2 of 2
`
`US 7,060,360 B2
`
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`GE-1001.003
`
`GE-1001.003
`
`

`
`US 7,060,360 B2
`
`1
`BOND COAT FOR SILICON BASED
`SUBSTRATES
`
`BACKGROUND OF THE INVENTION
`
`invention is drawn to an environmental
`The present
`barrier coating and, more particularly, an environmental
`barrier coating applied to a silicon containing substrate.
`Silicon based ceramics exhibit accelerated oxidation rates
`
`in high temperature, aqueous environments such as for
`example, the combustor and turbine sections of gas turbine
`engines. In order to reduce the rate of oxidation on silicon
`based substrates used as ceramic components in such
`environments, significant effort has been given to providing
`environment barrier coating,
`i.e., barrier layer(s), for the
`silicon based substrates so as to increase the service life of
`
`such component parts.
`With reference to FIGS. 1a and 1b, prior art environmen-
`tal barrier coatings form a composite 10 comprising a silicon
`based substrate 12, a bond coat or layer 14 such as a dense
`continuous layer of silicon metal, a barrier layer 16 such as
`either an alkaline earth aluminosilicate based on barium and
`
`strontium, or yttrium silicate, and an optional top layer such
`as a refractory oxide and/or silicate layer 18 or other metal
`oxide such as for example zirconium oxide. In addition, an
`intermediate layer 20 may be provided between the 14 bond
`coat and the barrier 16 and/or between the barrier layer 16
`and the top layer 18. The intermediate layer comprises, for
`example, a mixture of the barrier layer material with an
`additional oxide such as mullite. These prior art environ-
`mental barrier systems have proved for many silicon based
`substrates to be protective with respect to oxidation of the
`silicon based substrate and,
`in addition, are adherent.
`However,
`it has now been found that certain mechanical
`properties of some silicon containing substrates especially
`those substrates having CTE’s less than silicon and those
`which are brittle, such as silicon nitride, suffer a significant
`reduction in 4-point bend strength at room temperature.
`Naturally, it would be highly desirable to provide envi-
`ronmental barrier coatings for silicon containing substrates
`such as silicon nitride which do not result in significant loss
`of mechanical properties.
`Accordingly,
`this is a principal object of the present
`invention to provide bond coats for silicon based substrates
`which does not have significant adverse affect with respect
`to mechanical properties.
`
`SUMMARY OF THE INVENTION
`
`The foregoing object is achieved by the present invention
`by providing an improved bond layer for use on a silicon
`based substrate. The bond layer comprises an alloy com-
`prising a refractory metal disilicide/silicon eutectic. The
`refractory metal disilicide is selected from the group con-
`sisting of disilicides of molybdenum, chromium, hafnium,
`niobium, tantalum, rhenium, titanium, tungsten, uranium,
`vanadium, yttrium and mixtures thereof. The refractory
`metal disilicide/silicon eutectic has a melting point of
`greater than l300° C.
`The particular advantage achieved by the present inven-
`tion is an increase in room temperature fracture touglmess
`when compared to silicon metal bond layers as discussed
`above. It has been found that the fracture touglmess of the
`bond coat is increased by more than 50% over that achiev-
`able with a simple phase silicon metal bond coat. This
`increase in fracture touglmess is attributable to the mecha-
`
`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`65
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`2
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`nism of the two phase microstructure of the present inven-
`tion which provides more resistance to crack propagation
`than that observed in a single phase, silicon layer.
`Further objects and advantages will appear hereinbelow.
`BRIEF DESCRIPTION OF DRAWINGS
`
`FIGS. 1a and 1b are schematic illustrations of composite
`articles in accordance with the prior art.
`DETAILED DESCRIPTION
`
`The present invention relates to an article comprising a
`silicon base substrate and a bond layer. The bond layer may
`be applied directly on the silicon base substrate or,
`alternatively, a silicon oxide intermediate layer or other
`intermediate layer may be provided between the bond layer
`and the silicon base substrate.
`
`The silicon containing substrate may be a silicon ceramic
`substrate or a silicon containing metal alloy. In a preferred
`embodiment, the silicon containing substrate is a silicon
`containing ceramic material as, for example, silicon carbide,
`silicon carbide composite, silicon nitride, silicon nitride
`composite, silicon oxynitride and silicon aluminum oxyni-
`tride.
`
`In accordance with the present invention, the bond layer
`comprises an alloy comprising a refractory metal disilicide/
`silicon eutectic. The bond layer may comprise 100% of the
`refractory metal disilicide/silicon eutectic or the bond layer
`may comprise a multiphase microstructure of the refractory
`metal disilicide/silicon eutectic alone or with either silicon
`
`or the refractory metal disilicide. In either case, the refrac-
`tory metal disilicide/silicon eutectic has a melting point of
`greater than l300° C. The silicon content of the bond layer
`is greater than or equal
`to 66.7 atomic percent silicon,
`preferably 80 atomic percent silicon, with the balance being
`the refractory metal.
`Preferred refractory metals used in the bond layer of the
`present invention are selected from the group consisting of
`molybdenum, chromium, hafnium, niobium,
`tantalum,
`rhenium,
`titanium,
`tungsten, uranium, vanadium, yttrium
`and mixtures thereof. Preferred refractory metals are molyb-
`denum and chromium and the most preferred refractory
`metal is molybdenum. The article of the present invention
`exhibits significant improvement in fracture toughness over
`silicon metal bond layers known in the prior art, that is, a
`fracture touglmess of greater than 1 MPa~m1/2.
`It is to be understood that the invention is not limited to
`the illustrations described and shown herein, which are
`deemed to be merely illustrative of the best modes of
`carrying out the invention, and which are susceptible of
`modification of form, size, arrangement of parts and details
`of operation. The invention rather is intended to encompass
`all such modifications which are within its spirit and scope
`as defined by the claims.
`What is claimed is:
`
`1. An article comprising a silicon based substrate, at least
`one environmental barrier layer selected from the group
`consisting essentially of an alkaline earth aluminosilicate
`based on barium and strontium, and yttrium silicate, and a
`bond layer between the substrate and the environmental
`barrier layer, the bond layer comprises an alloy comprising
`a refractory metal disilicide/silicon eutectic.
`2. An article according to claim 1, wherein the refractory
`metal disilicide is selected from the group consisting of
`disilicides of molybdenum, chromium, hafnium, niobium,
`rhenium, tantalum, titanium, tungsten, uranium, vanadium,
`yttrium and mixtures thereof.
`
`GE-1001.004
`
`GE-1001.004
`
`

`
`US 7,060,360 B2
`
`3
`3. An article according to claim 1, wherein the refractory
`metal disilicide is selected from the group consisting of
`disilicides of molybdenum, chromium, hafnium, niobium,
`rhenium, tantalum, titanium, tungsten, uranium, Vanadium,
`yttrium, molybdenum, chromium and mixtures thereof.
`4. An article according to claim 1, wherein the refractory
`metal disilicide/silicon eutectic has a melting point of
`greater than l300° C.
`5. An article according claim 1, wherein the bond layer
`comprises a multiphase microstructure of the refractory
`metal disilicide/silicon eutectic and silicon.
`
`6. An article according to claim 5, wherein the fracture
`toughness is of greater than 1 MPa~m1/2.
`7. An article according to claim 1, wherein the bond layer
`comprises a multiphase microstructure of the refractory
`metal disilicide/silicon eutectic and refractory metal disili-
`cide.
`
`8. An article according to claim 7, wherein the fracture
`toughness of greater than 1 MPa~m1/2.
`
`4
`
`9. An article according to claim 1, wherein the bond layer
`comprises a multiphase microstructure of the refractory
`metal disilicide/silicon eutectic and one of silicon and
`refractory metal disilicide.
`10. An article according to claim 9, wherein the fracture
`touglmess is of greater than 1 MPa~m1/2.
`11. An article according to claim 1, wherein silicon is
`present in an amount of greater than or equal to 66.7 atomic
`percent.
`12. An article according to claim 9, wherein silicon is
`present in an amount of greater than or equal to 66.7 atomic
`percent.
`13. An article according to claim 1, wherein silicon is
`present in an amount of greater than or equal to 80 atomic
`percent.
`14. An article according to claim 9, wherein silicon is
`present in an amount of greater than or equal to 80 atomic
`percent.
`
`5
`
`10
`
`15
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`GE-1001.005
`
`GE-1001.005
`
`

`
`UNITED STATES PATENT AND TRADEMARK OFFICE
`
`CERTIFICATE OF CORRECTION
`
`PATENT NO.
`APPLICATION NO.
`
`: 7,060,360 B2
`: 10/443342
`
`DATED
`INVENTOR(S)
`
`: June 13, 2006
`: Harry E. Eaton, Jr.
`
`It is certified that error appears in the above—identified patent and that said Letters Patent is
`hereby corrected as shown below:
`
`Col. 1, Line 4, please add the following paragraph on page 1 before the “Background of
`The Invention” in the Specification:
`
`--This Invention was made with Government support under Contract Number
`N00014-01-C-0032 awarded by the Navy. The Government has certain rights in this
`invention. --
`
`Signed and Sealed this
`
`Twenty—second Day of September, 2009
`
`David J. Kappos
`Director ofthe United States Patent and Trademark Oflice
`
`GE-1001.006
`
`GE-1001.006