WO1993007302A1 - Alliages metalliques refractaires resistants a l'oxydation - Google Patents

Alliages metalliques refractaires resistants a l'oxydation Download PDF

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Publication number
WO1993007302A1
WO1993007302A1 PCT/US1992/008357 US9208357W WO9307302A1 WO 1993007302 A1 WO1993007302 A1 WO 1993007302A1 US 9208357 W US9208357 W US 9208357W WO 9307302 A1 WO9307302 A1 WO 9307302A1
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alloy
weight percent
chromium
silicon
alloys
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PCT/US1992/008357
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English (en)
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Vaidyanathan Nagarajan
Ian G. Wright
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Battelle Memorial Institute
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
    • C22C27/06—Alloys based on chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
    • C22C27/04—Alloys based on tungsten or molybdenum

Definitions

  • This invention relates to a process and compositions for protecting refractory metal alloys from oxidation and corrosion in high-temperature environments.
  • the invention has utility in protecting the refractory metal alloys from oxidation attack at high temperatures, especially those above 1000°C, such as that encountered in jet propulsion engines or thermal power plants.
  • high temperatures especially those above 1000°C, such as that encountered in jet propulsion engines or thermal power plants.
  • the higher temperatures that can be realized with the invention allow increased power and/or efficiency.
  • the focus of this invention is on the design of refractory metal alloys which would form an outer Cr 0 3 scale together with an inner protective Si0 2 , Al 0 3 , or Si0 2 /Al 2 0 3 scale at high temperatures.
  • Cr 2 0 3 scales alone are not suitable since (i) Cr 2 0 3 tends to excessively volatized at temperatures over 1000°C, especially in high velocity gas streams, and (ii) diffusion of oxygen and chromium through Cr 2 0 3 is rapid at temperatures over 1000°C.
  • One way to grow protective Si0 2 and/or Al 2 0 3 scales on refractory metals is to alloy them with sufficient silicon and/or aluminum.
  • this alloying approach requires additions of approximately 35 weight percent or greater of silicon or aluminum.
  • the refractory metal molybdenum, tungsten, niobium, tantalum, technetium, and rhenium
  • an intermetallic line compound having an extremely narrow range of compositional stoichiometry and stability
  • MSi 2 or MA1 3 where M is the refractory metal.
  • these line compounds will undergo oxidation which results in compositional changes that can have drastic and adverse effects on the physical and mechanical properties of the alloys.
  • A1 2 0 3 layer on copper Wagner also observed that he could use zinc as a secondary-getter and reduce the level of aluminum required to form a protective A1 2 0 3 layer. By adding approximately 20 weight percent of zinc to copper, the level of aluminum required to develop a protective A1 2 0 3 layer could be reduced to approximately 5 weight percent.
  • This concept has been used in recent years in the design of high-temperature alloys based on iron, nickel, and cobalt (eighth group of the Periodic Table) . Such alloys are discussed by Stott, F.H.
  • a typical general embodiment of the invention comprises an oxidation-resistant alloy comprising a refractory metal selected from the group consisting of molybdenum, tungsten, niobium, tantalum, technetium, rhenium, and mixtures thereof; chromium in an amount effective to provide a continuous solid Cr 2 0 3 layer at a surface of the alloy when the alloy is exposed to a high- temperature environment; silicon and/or aluminum in an amount effective to provide a continuous protective Si0 2 , A1 2 0 3 , or an Si0 2 /Al 2 0 3 layer between the continuous solid Cr 2 0 3 layer and the surface of the alloy, wherein the Si0 2 , A1 2 0 3 , or the Si0 2 /Al 2 0 3 layer imparts oxidation resistance to the alloy when exposed to the high- temperature environment; and wherein the sum of the refractory metal(s) selected is at least about 15 weight percent.
  • Another typical embodiment is obtained when the sum of the refractory metal(s) selected is at least about 15 weight percent, the chromium content is about 25 to about 83 weight percent, and the silicon and/or aluminum content is about 2 to about 20 weight percent. More preferably, in a yet further embodiment, the sum of the refractory metal(s) content is at least about 25 weight percent. In another typical embodiment, a silicon and/or aluminum content from about 5 to about 10 weight percent is also preferred.
  • an oxidation-resistant alloy comprising a refractory metal selected from the group consisting of molybdenum, tungsten, and mixtures thereof; chromium from about 25 to about 83 weight percent; silicon and/or aluminum from about 2 to about 20 weight percent; and wherein the refractory metal selected is present in an amount of at least 15 weight percent.
  • a refractory metal selected from the group consisting of molybdenum, tungsten, and mixtures thereof
  • chromium from about 25 to about 83 weight percent
  • silicon and/or aluminum from about 2 to about 20 weight percent
  • the refractory metal selected is present in an amount of at least 15 weight percent.
  • the typical sum of the refractory metal(s) content is at least about 25 weight percent. More preferably the typical chromium content is between about 35 to about 75 weight percent.
  • the typical alloy has a chromium content between about 40 to about 49 weight percent such that the chromium/refractory metal weight percent ratio is about 1:1.
  • an oxidation-resistant alloy comprising a refractory metal selected from the group consisting of niobium, tantalum, and mixtures thereof; chromium from about 25 to about 83 weight percent; silicon and/or aluminum from about 2 to about 20 weight percent; and wherein the sum of the refractory metal(s) selected is least about 15 weight percent.
  • a typical refractory metal content is at least 25 weight percent. More preferably a typical chromium content is between about 35 to about 75 weight percent.
  • a chromium content sufficient to obtain a beta ( ⁇ ) NbCr 2 intermetallic phase is most preferred, corresponding approximately to a .
  • chromium content between about 50 to about 55 weight percent.
  • a chromium content sufficient to obtain a beta ( ⁇ ) TaCr 2 intermetallic phase is most preferred, corresponding approximately to a chromium content between about 35 to about 38 weight percent.
  • an oxidation-resistant alloy comprising a refractory metal selected from the group consisting of technetium, rhenium, and mixtures thereof; chromium from about 25 to about 83 weight percent; silicon and/or aluminum from about 2 to about 20 weight percent; and wherein the refractory metal selected is present in an amount of at least about 15 weight percent.
  • a typical refractory metal content is at least about 25 weight percent. More preferably a typical chromium content is between about 35 to about 75 weight percent.
  • a typical alloy comprises a mixture of a solid solution alloy phase, rich in chromium, and also containing technetium and/or rhenium in solution, and a fine dispersion of an intermetallic sigma ( ⁇ ) phase.
  • ⁇ intermetallic sigma
  • the typical high-temperature environment contemplated for all of the embodiments is at about 1000°C or higher. At these temperatures an outer solid oxide layer of predominately Cr 2 0 3 , and a continuous Si0 2 , Al 2 0 3 , or Si0 2 /Al 2 0 3 layer between the outer solid oxide layer and the oxidation-resistant alloy is obtained. Most preferably the typical silicon and/or aluminum content is from about 5 to about 10 weight percent for all of the embodiments.
  • Figure 1 is a graph depicting oxidation behavior by weight change, ⁇ W, (ordinate Y) in mg/cm 2 versus time, t, (abscissa X) in hours due to oxidation at 1200°C in air for molybdenum-chromium alloys containing: 0 (Alloy 1) , 5 (Alloy 2) , or 10 (Alloy 3) weight percent aluminum; or 0 (Alloy 1) , 5 (Alloy 4) , or 10 (Alloy 5) weight percent silicon.
  • Figure 2 is a graph depicting weight change, ⁇ W, (ordinate Y) in mg/cm 2 versus time, t, (abscissa X) in hours due to oxidation at 1400°C in air for molybdenum- chromium alloys containing: 5 (Alloy 2) or 10 (Alloy 3) weight percent aluminum, or 5 (Alloy 4) or 10 (Alloy 5) weight percent silicon.
  • Figure 3 is a graph depicting weight change, ⁇ W,
  • Figure 4 is a graph depicting weight change, ⁇ W, (ordinate Y) in mg/cm 2 versus time, t, (abscissa X) in hours due to oxidation at 1400°C in air for tungsten- chromium alloys containing 5 (Alloy 9) or 10 (Alloy 10) weight percent silicon.
  • Figure 5 is a graph depicting the oxidation behavior in air at 1400°C of an alloy of molybdenum- chromium with 10 weight percent silicon prepared by powder metallurgy (P) (Alloy 21) and cast alloy (C) (Alloy 5) techniques. Oxidation behavior is plotted as weight change, ⁇ W, (ordinate Y) in mg/cm 2 versus time, t, (abscissa X) in hours.
  • Figure 6 is a graph depicting weight change, ⁇ W, (ordinate Y) in mg/cm 2 versus time, t, (abscissa X) in hours due to oxidation at 1200°C in air for NbCr 2 alloys containing: 0 (Alloy 11), 5 (Alloy 12), or 10 (Alloy 13) weight percent aluminum; or 0 (Alloy 11) , 5 (Alloy 14) , or 10 (Alloy 15) weight percent silicon.
  • Figure 7 is a graph depicting weight change, ⁇ W, (ordinate Y) in mg/cm 2 versus time, t, (abscissa X) in hours due to oxidation at 1400°C in air for NbCr 2 alloys containing: 5 (Alloy 14) or 10 (Alloy 15) weight percent silicon, or 10 (Alloy 13) weight percent aluminum.
  • Figure 8 is a graph depicting weight change, ⁇ W, (ordinate Y) in mg/cm 2 versus time, t, (abscissa X) in hours due to oxidation in air at 1200°C for TaCr 2 alloys containing: 0 (Alloy 16), 5 (Alloy 17), or 10 (Alloy 18) weight percent aluminum; or 0 (Alloy 16) , 5 (Alloy 19) , or 10 (Alloy 20) weight percent silicon.
  • Figure 9 is a graph depicting weight change, ⁇ W, (ordinate Y) in mg/cm 2 versus time, t, (abscissa X) in hours due to oxidation in air at 1400°C for TaCr 2 alloys containing 5 (Alloy 19) or 10 (Alloy 20) weight percent silicon.
  • Figures 10A-E show a metallographically prepared cross section of an molybdenum-chromium 10 weight percent silicon alloy oxidized at 1200°C for 72 hours.
  • Figure 10A shows a secondary electron image (SEI) of this cross section.
  • Figure 10B shows an x-ray map for silicon in the material of Figure 10A.
  • Figure 10C shows an x-ray map for chromium in the material of Figure 10A.
  • Figure 10D shows an x-ray map for oxygen in the material of Figure 10A.
  • Figure 10E shows an x-ray map for molybdenum in the material of Figure 10A.
  • Figures 11A-D show a metallographically prepared cross section of a molybdenum-chromium 10 weight percent silicon alloy oxidized at 1400°C for 72 hours.
  • Figure 11A shows a secondary electron image of this cross section.
  • Figure 11B shows an x-ray map for silicon in the material of Figure 11A.
  • Figure 11C shows an x-ray map for chromium in the material of Figure 11A.
  • Figure 11D shows an x-ray map for molybdenum in the material of Figure 11A.
  • Figures 12A-E show a metallographically prepared cross section of an NbCr 2 -10 weight percent silicon alloy oxidized at 1400°C for 72 hours.
  • Figure 12A shows a secondary electron image of this cross section.
  • Figure 12B shows an x-ray map for silicon in the material of Figure 12A.
  • Figure 12C shows an x-ray map for chromium in the material of Figure 12A.
  • Figure 12D shows an x-ray map for oxygen in the material of Figure 12 .
  • Figure 12E shows an x-ray map for niobium in the material of Figure 12A.
  • Figures 13A-E show a metallographically prepared cross section of a TaCr 2 -10 weight percent silicon alloy oxidized at 1400°C for 72 hours.
  • Figure 13A shows a secondary electron image of this cross section.
  • Figure 13B shows an x-ray map for silicon in the material of Figure 13A.
  • Figure 13C shows an x-ray map for chromium in the material of Figure 13A.
  • Figure 13D shows an x-ray map for oxygen in the material of Figure 13A.
  • Figure 13E shows an x-ray map for tantalum in the material of Figure 13A.
  • the secondary-gettering approach of the present invention relies on the addition to a refractory metal of sufficient, suitable "substitute" element for silicon and/or aluminum.
  • This substitute element is required to form a solid oxide which can provide temporary oxidation protection, but which is thermodynamically less stable than Si0 2 , A1 2 0 3 , or Si0 2 /Al 2 0 3 . If this substitute element is added in sufficiently large amounts to the refractory metal, then initially the refractory metal will develop a continuous layer comprised predominantly of this solid oxide when exposed to a high-temperature environment. To achieve this effect, this substitute element must have high solubility in the refractory metal.
  • this substitute element will form a continuous and solid oxide layer, this layer may not be fully protective by itself over the desired range of conditions.
  • this oxide layer will act as a barrier between oxygen in the environment and the refractory metal, and thus will reduce the effective partial pressure of oxygen at the metal/oxide interface.
  • This reduced, effective partial pressure will allow sufficient time for silicon and/or aluminum to diffuse to the oxide/metal interface and oxidize at that location to form, a continuous Si0 2 and/or A1 2 0 3 layer beneath the layer of oxide of the substitute element, even when the refractory metal contains very small amounts of silicon or aluminum.
  • this element substitutes for silicon or aluminum by acting as a "secondary getter" for oxygen.
  • chromium can be used as an effective secondary getter for growing Si0 2 and/or A1 2 0 3 protective layers on refractory metals such as molybdenum and tungsten from the sixth group, and niobium and tantalum from the fifth group in the Periodic Table. It is also expected that similar results can be obtained for the refractory metals technetium and rhenium from the seventh group of the Periodic Table.
  • Chromium forms an oxide, Cr 2 0 3 , which is less stable than Si0 2 and/or A1 2 0 3 ; however, Cr 2 0 3 has a very high melting point (about 2266°C) and will remain solid in the temperature ranges where these refractory metal alloys will be used, even though there will be some loss from its outer surface through further oxidation to the volatile oxide, Cr0 3 . Also, examination of the molybdenum-chromium and tungsten-chromium phase diagrams indicates that molybdenum and chromium, and tungsten and chromium form continuous solid solutions, which suggests that large additions of chromium can be made to molybdenum or tungsten.
  • phase diagrams for niobium- chromium and tantalum-chromium indicate that, in both of the systems, intermetallic compounds of composition NbCr 2 and TaCr 2 form, which contain large amounts of dissolved chromium. These intermetallic compounds are not line compounds and have a range of stoichiometry.
  • beta ( ⁇ ) and beta prime ( ⁇ l ) phases shown in the above phase diagrams for niobium-chromium and tantalum-chromium both of these phases are included herein and will be referred to only as the beta ( ⁇ ) phase.
  • intermetallic compounds are not suitable (unlike the NbCr 2 and TaCr 2 intermetallic compounds in the niobium-chromium and tantalum-chromium systems) for development since the chromium content is low.
  • a two-phase field appears in the phase diagrams.
  • These two- phase fields contain a mixture of chromium having technetium or rhenium (about 50 weight percent) in solid solution in the sigma phase. See the phase diagram for technetium-chromium in Venkatraman, M. and Neumann, J.P. "The Cr-Tc (Chromium-Technetium) System," Bull. Alloy Phase Diagrams; 2(6), 1986; pp.
  • the present invention deals with the development of molybdenum and tungsten oxidation-resistant alloys containing chromium in solid solution, and also containing relatively small additions of silicon and/or aluminum so that the alloys will form an outer, continuous Cr 2 0 3 layer, and continuous protective inner Si0 2 , A1 2 0 3 , or Si0 2 /Al 2 0 3 layers.
  • the alloys have molybdenum and/or tungsten present in an amount whereby the molybdenum and/or tungsten content is at least about 15 weight percent, chromium is present in an amount effective to provide a continuous outer solid Cr 0 3 layer, and silicon and/or aluminum are present in an amount effective to provide an Si0 2 , Al 2 0 3 , or an Si0 2 /Al 2 0 3 layer between the continuous outer solid Cr 2 0 3 layer and the alloy, when the alloy is exposed to a high-temperature environment.
  • the oxidation-resistant alloys have a molybdenum and/or tungsten content of at least 23 weight percent, chromium is present in an amount between about 35 to about 75 weight percent, and silicon and/or aluminum is present in an amount between about 2 and 20 weight percent. Most preferably the sum of the molybdenum and/or tungsten content is between about 40 to about 49 percent, the chromium content is also between about 40 to 49 percent such that the chromium/refractory metal weight percent ratio is about 1:1, and the silicon and/or aluminum content is from about 5 to about 10 weight percent.
  • the present invention also deals with (1) niobium and tantalum alloys containing chromium as an intermetallic compound of the form NbCr 2 and TaCr , (2) niobium and tantalum alloys containing chromium such that the alloy is a mixture of Nb or Ta solid solution containing a fine dispersion of NbCr 2 and TaCr 2 , or (3) niobium and tantalum alloys containing chromium such that the alloy is a mixture of a chromium solid solution containing a fine dispersion of NbCr 2 and TaCr 2 ; and also containing relatively small additions of silicon and/or aluminum so that the alloys will form a continuous outer layer of Cr 2 0 3 , and continuous, protective inner Si0 , A10 3 , or Si0 2 /Al 2 0 3 layers.
  • the alloys have a niobium and/or tantalum content of at least about 15 weight percent, chromium is present in an amount effective to provide a continuous outer solid Cr 2 0 3 layer, and silicon and/or aluminum are present in an amount effective to provide an Si0 2 , A1 2 0 3 , or an Si0 2 /Al 2 0 3 layer between the continuous outer solid Cr 2 0 3 layer and the alloy, when the alloy is exposed to a high-temperature environment.
  • the oxidation-resistant alloys have a niobium and/or tantalum content of at least 23 weight percent, chromium is present in an amount between about 35 to about 75 weight percent, and silicon and/or aluminum are present in an amount between about 2 and 15 weight percent.
  • the chromium content is sufficient to obtain a beta ( ⁇ ) NbCr 2 intermetallic phase. This corresponds approximately to a chromium content between about 50 to about 55 weight percent.
  • tantalum the chromium content is sufficient to obtain a beta (/S) TaCr 2 intermetallic phase. This corresponds approximately to a chromium content between about 36 to about 38 weight percent.
  • the chromium content is sufficient to obtain a beta (0) (Nb/Ta)Cr 2 intermetallic phase with a silicon and/or aluminum content from about 5 to about 10 weight percent.
  • This chromium content can easily be ascertained by those skilled in the art.
  • the present invention also deals with technetium and rhenium alloys containing large amounts of chromium such that the alloys are: (1) a chromium-rich solid solution, (2) mixtures of chromium-rich solution and the sigma phase, or (3) the sigma phase alone, and also containing relatively small amounts of silicon and/or aluminum so that the alloys will form a continuous outer Cr 2 0 3 layer, and continuous protective inner Si0 2 , A1 2 0 3 , or Si0 2 /Al 2 0 3 layers.
  • the alloys have technetium and/or rhenium contents of at least about 15 weight percent, chromium is present in an amount effective to provide a continuous outer solid Cr 2 0 3 layer, and silicon and/or aluminum are present in an amount effective to provide an Si0 2 , A10 3 , or an Si0 2 /Al 2 0 3 layer between the continuous outer solid Cr 2 0 3 layer and the alloy, when the alloy is exposed to a high-temperature environment.
  • the oxidation-resistant alloys have a technetium and/or rhenium content of at least 23 weight percent, chromium is present in an amount between about 35 to about 75 weight percent, and silicon and/or aluminum is present in an amount between about 2 and 20 weight percent.
  • the chromium content is such that the alloy consists of a mixture of a chromium solid solution containing technetium and/or rhenium and a fine dispersion of a sigma ( ⁇ ) phase. This corresponds approximately to a chromium content between about 30 to about 60 weight percent.
  • the silicon and/or aluminum content is about 5 to about 10 weight percent.
  • the present invention also deals generally with an alloy where the refractory metals are selected from the group consisting of molybdenum, tungsten, niobium, tantalum, technetium, and/or rhenium alloys containing relatively large amounts of chromium and also containing relatively small amounts of silicon or aluminum so that the alloys will form protective Si0 2 or A1 2 0 3 layers.
  • refractory metals are selected from the group consisting of molybdenum, tungsten, niobium, tantalum, technetium, and/or rhenium alloys containing relatively large amounts of chromium and also containing relatively small amounts of silicon or aluminum so that the alloys will form protective Si0 2 or A1 2 0 3 layers.
  • rhenium when added to molybdenum results in an alloy having improved ductility. This improved ductility when coupled with the teachings of the present invention results in an oxidation-resistant composition having very useful properties at high temperatures.
  • Samples of approximately 100 grams were prepared by vacuum arc melting for each of above the Alloys 1-20.
  • the alloys were prepared from high purity (99.9 weight percent or better) starting materials. Starting materials of appropriate composition were loaded in the hearth of a vacuum arc-melting furnace. An electric arc was initiated between an electrode and the material in the hearth of the furnace, and was maintained until the alloy was completely molten. The molten alloy was then allowed to cool to room temperature and solidify into a button. The solidified button was then flipped over and remelted; this procedure was repeated three times to achieve compositional uniformity. After the final remelting procedure, the molten alloy was drop-cast into a water-cooled copper mold. However, despite these homogenization treatments, metallographic examination showed that some segregation existed in some alloys.
  • EDM electric discharge machining
  • the specimens were ultrasonically cleaned, degreased in alcohol, measured, weighed, and exposed to air in a furnace maintained at the required temperature. The exposure time varied from a few hours up to 72 hours. The specimens were periodically withdrawn from the furnace and weighed. The weight change per unit area data for all the exposed specimens were computed as a function of time and plotted. The exposed specimens were mounted in epoxy and subjected to metallographic examination and electron microprobe analysis.
  • FIG. 5 shows the weight change data for the same alloys oxidized at 1400°C.
  • the 10 weight percent silicon alloy (Alloy 5) showed the best protective behavior.
  • the 5 weight percent silicon alloy (Alloy 4) initially lost weight, but after approximately 50 hours developed a protective oxide scale as indicated by the greatly reduced weight loss at longer times.
  • the aluminum-containing alloys (Alloys 2 and 3) both lost weight, but the rate of loss decreased with time indicating the development of an increasingly protective scale.
  • the aluminum-containing alloys did not show as strong a tendency to form a protective layer as did the silicon-containing alloys; one reason for this was the poor distribution of aluminum in the alloys due to segregation.
  • Figures 3 and 4 show corresponding results for the tungsten-chromium alloys (Alloys 6-10) containing 0, 5, or 10 weight percent silicon or aluminum.
  • Figure 3 shows that the aluminum-containing alloys (Alloys 7 and 8) and the binary alloy (Alloy 6) gained weight. This was surprising since tungsten forms an oxide (W0 3 ) which is volatile. Hence it was expected that the specimens would loose weight. However, the specimens can gain weight, if the weight loss of W0 3 is over compensated by the weight gain due to excessive oxidation of chromium (and formation of nonprotective Cr 2 0 3 ) .
  • the aluminum-containing alloys (Alloys 7-8) were not tested at 1400°C because their microstructures were so nonuniform. However, it is expected that uniform microstructures that can be obtained by powder metallurgy approaches, for instance, will provide a uniform distribution of aluminum, and protective scale formation is expected on these more homogeneous materials.
  • the alloys described (Alloys 1-20) were prepared by melting and casting. Despite repeated melting and heat treatment, the microstructures were not very homogeneous. However, if these alloys were prepared by powder metallurgical techniques, the microstructure could be considerably improved due to the fine grain size and uniformity of composition of the processed alloy powder. Hence, powder metallurgy will be a preferred route for preparation of alloys for practical use in high- temperature environments. As an example, an approximately 50 gram sample of molybdenum-chromium 10 weight percent silicon alloy (Alloy 21) was reprocessed by high-energy milling and vacuum-hot-pressing to demonstrate that alloy preparation by powder metallurgy would lead to an improved microstructure.
  • the alloy powders were first blended together and then loaded into a high-energy-impact ball mill. Milling was carried out at a ball-to-powder ratio of 10 to 1. The milling time was approximately 2 hours.
  • the milled powder mixture was compacted by vacuum-hot- pressing at 1300°C for 1 hour at a pressure of 13,000 psi, in a graphite die lined with tantalum foil.
  • Figure 5 shows the oxidation behavior at 1400°C of the cast alloy (Alloy 5, labelled "C") and the powder alloy (Alloy 21, labelled "P") . It appears that the powder alloy has similar oxidation resistance measured by weight change as a function of time. However, its more homogeneous microstructure resulted in improved uniformity of surface recession, and is expected to provide superior mechanical properties.
  • FIG. 6 shows the weight gain data for specimens of NbCr 2 containing: 0 (Alloy 11) , 5 (Alloy 14) , or 10 (Alloy 15) weight percent silicon, or 5 (Alloy 12) or 10 (Alloy 13) weight percent aluminum oxidized in air at 1200°C. Since niobium forms a solid oxide, all the specimens have gained weight. However, the specimens containing silicon and aluminum show slower weight gain than the NbCr 2 specimen.
  • Figure 7 shows the weight gain data for specimens of NbCr 2 containing 5 or 10 weight percent silicon (Alloys 14 and 15, respectively), or 10 weight percent aluminum (Alloy 13) oxidized at 1400°C.
  • the 10 weight percent silicon- and aluminum-containing specimens show apparent protective oxidation behavior.
  • Figure 8 shows the weight gain data for specimens of TaCr 2 containing: 0 (Alloy 16) , 5 (Alloy 19) , or 10 (Alloy 20) weight percent silicon, or 5 (Alloy 17) or 10 (Alloy 18) weight percent aluminum oxidized at 1200°C. Since tantalum also forms a solid oxide, all the specimens have gained weight.
  • the weight gain for the silicon-containing specimens is small, which indicates that these specimens have formed protective Si0 2 scales.
  • Figure 9 shows the weight gain data of the silicon-containing TaCr 2 specimens (Alloys 19 and 20) oxidized at 1400°C. Clearly, the weight gain data indicate that the alloys are forming protective Si0 2 scales even at 1400 ⁇ C.
  • the tantalum alloys showed better potential protective behavior than the niobium alloys.
  • the presence of 5 or 10 weight percent silicon in the tantalum alloys promoted protective scale formation. The presence of aluminum did not appear to be beneficial.
  • FIGS 10A-E and 11A-D show the microstructural features of 10 weight percent silicon-containing molybdenum-chromium alloy (Alloy 5) oxidized at 1200 and 1400°C respectively.
  • Figures 12A-E and 13A-E show the microstructural features of 10 weight percent silicon- containing NbCr 2 alloy (Alloy 15) and 10 weight percent silicon-containing TaCr alloy (Alloy 20) , respectively, oxidized at 1400°C.
  • Figures 10A, 11A, 12A and 13A show layers I, II, III, and IV that correspond to (I) a mounting material (bakelite containing quartz particles) layer, (II) a layer which is predominantly Cr 0 3 , (III) a continuous Si0 layer, and (IV) an unoxidized alloy layer.
  • the oxygen and silicon maps of Figures 10B and D, 11B, 12B and D, and 13B and D reveal the presence of Si0 2 particles in the bakelite mounting material (Layer I) above the oxide layer which is predominantly a Cr 2 0 3
  • the right hand side part of the silicon map does not show the presence of a silicon-rich layer in the inner oxide layer (Layer III) . This is due to the spallation of the Si0 2 layer (from the right hand side part of the silicon map) during metallographic preparation.
  • FIG 11A shows the secondary electron image
  • Figures 11B-D show the x-ray maps for silicon, chromium, and molybdenum, respectively, of a (molybdenum-chromium 10 weight percent silicon) specimen (Alloy 5) oxidized at 1400°C for 72 hours. It is quite apparent that the specimen has formed a duplex oxide layer containing an outer Cr 2 0 3 layer (Layer II) and an inner Si0 2 layer (Layer III) . The specimen exhibited protective oxidation behavior due to the formation of a continuous Si0 2 layer (Layer III) . Note that an oxygen map is not provided with Figures 11A-D.
  • Figure 12A shows the secondary electron image
  • Figures 12B-E show the x-ray maps for silicon, chromium, oxygen, and niobium, respectively, for a (NbCr 2 - 10 weight percent silicon) specimen (Alloy 15) oxidized at 1400°C for 72 hours. Again, a duplex Cr 2 0 3 /Si0 2 protective oxide layer is present. The specimen exhibited protective oxidation behavior due to the formation of a continuous Si0 2 layer (Layer III) beneath a Cr 2 0 3 layer (Layer II) .
  • Figure 13A shows the secondary electron image
  • Figures 13B-E show the x-ray maps for silicon, chromium, oxygen, and tantalum, respectively, for a (TaCr 2 -10 weight percent silicon) specimen (Alloy 20) oxidized at 1400°C for 72 hours. Again, a duplex Cr 2 0 3 /Si0 2 protective oxide layer is present. The specimen exhibited protective oxidation behavior due to the formation of a continuous Si0 2 layer (Layer III) beneath a Cr 2 0 3 layer (Layer II) . Note that micrographs were not provided for W-Cr-

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  • Manufacture And Refinement Of Metals (AREA)

Abstract

Alliage résistant à l'oxydation comprenant un métal réfractaire sélectionné dans le groupe composé de molybdène, tungstène, niobium, tantale, technétium, rhénium, et leur mélanges; du chrome en une quantité efficace pour former une couche solide continue de Cr2O3 sur une surface de l'alliage, lorsque cette surface est exposée à un environnement à haute température; du silicium et/ou de l'aluminium en une quantité efficace pour former une couche protectrice continue de SiO2, Al2O3 ou SiO2/Al2O3 entre la couche solide continue de Cr2O3 et l'alliage, la couche continue de SiO2, Al2O3 ou SiO2/Al2O3 conférant une résistance à l'oxydation à l'alliage lorsqu'il est exposé à un environnement à haute température. La somme du métal ou des métaux réfractaire(s) sélectionné(s) est égale à au moins 15 % en poids. L'environnement à haute température mentionné correspond à des températures égales ou supérieures à environ 1000 °C.
PCT/US1992/008357 1991-10-10 1992-09-30 Alliages metalliques refractaires resistants a l'oxydation WO1993007302A1 (fr)

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US775,658 1991-10-10

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0709478A1 (fr) * 1994-10-17 1996-05-01 ABB Management AG Alliage à base de siliciures, contenant du chrome et du molybdène
WO2003102255A1 (fr) * 2002-05-31 2003-12-11 Honeywell International Inc. Procede de metallurgie des poudres a temperature reduite et sous pression pour consolider les alliages de rhenium
US6821313B2 (en) 2002-05-31 2004-11-23 Honeywell International, Inc. Reduced temperature and pressure powder metallurgy process for consolidating rhenium alloys
DE10340132B4 (de) * 2003-08-28 2010-07-29 Eads Deutschland Gmbh Oxidationsbeständige, duktile CrRe-Legierung, insbesondere für Hochtemperaturanwendungen, sowie entsprechender CrRe-Werkstoff
CN105112915A (zh) * 2015-04-30 2015-12-02 宁夏东方钽业股份有限公司 抗氧化材料及用其制备钽钨合金抗氧化涂层的方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1196974A (fr) * 1956-12-04 1959-11-27 Union Carbide Corp Composition et éléments et revêtements faits de cette composition
US3595644A (en) * 1968-10-21 1971-07-27 Iit Res Inst Hafnium base alloy (cr-ai)
EP0348858A1 (fr) * 1988-07-01 1990-01-03 General Electric Company Revêtement métallique protecteur pour pièces en alliages réfractaires de moteurs à réaction
EP0425972B1 (fr) * 1989-11-03 1994-05-11 Asea Brown Boveri Ag Alliage réfractaire, résistant à l'oxydation et à la corrosion, à base d'un composé intermétallique

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1196974A (fr) * 1956-12-04 1959-11-27 Union Carbide Corp Composition et éléments et revêtements faits de cette composition
US3595644A (en) * 1968-10-21 1971-07-27 Iit Res Inst Hafnium base alloy (cr-ai)
EP0348858A1 (fr) * 1988-07-01 1990-01-03 General Electric Company Revêtement métallique protecteur pour pièces en alliages réfractaires de moteurs à réaction
EP0425972B1 (fr) * 1989-11-03 1994-05-11 Asea Brown Boveri Ag Alliage réfractaire, résistant à l'oxydation et à la corrosion, à base d'un composé intermétallique

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
JOURNAL OF THE ELECTROCHEMICAL SOCIETY vol. 113, no. 8, August 1966, pages 769 - 773 TEDMON 'The High-Temperature Oxydation of Ductile Cr-Re Alloys' *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0709478A1 (fr) * 1994-10-17 1996-05-01 ABB Management AG Alliage à base de siliciures, contenant du chrome et du molybdène
CN1044009C (zh) * 1994-10-17 1999-07-07 亚瑞亚勃朗勃威力有限公司 以至少一种铬和钼为基础的包含硅化物的合金
WO2003102255A1 (fr) * 2002-05-31 2003-12-11 Honeywell International Inc. Procede de metallurgie des poudres a temperature reduite et sous pression pour consolider les alliages de rhenium
US6821313B2 (en) 2002-05-31 2004-11-23 Honeywell International, Inc. Reduced temperature and pressure powder metallurgy process for consolidating rhenium alloys
DE10340132B4 (de) * 2003-08-28 2010-07-29 Eads Deutschland Gmbh Oxidationsbeständige, duktile CrRe-Legierung, insbesondere für Hochtemperaturanwendungen, sowie entsprechender CrRe-Werkstoff
CN105112915A (zh) * 2015-04-30 2015-12-02 宁夏东方钽业股份有限公司 抗氧化材料及用其制备钽钨合金抗氧化涂层的方法

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