FR2517329A1 - NICKEL-BASED SUPERALLIAGE HAVING OXIDATION RESISTANCE AND HIGH TEMPERATURE MECHANICAL PROPERTIES - Google Patents

Abstract

THE PRESENT INVENTION RELATES TO A NICKEL-BASED SUPERALLY WITH OXIDATION RESISTANCE AND HIGH MECHANICAL RESISTANCE AT HIGH TEMPERATURES. ALLOYS CONTAINING NI, AL, MO AND W ARE MADE INCLUDING IN ADDITION COORDINATED QUANTITIES OF CR, TA AND Y. THE INVENTION IS FOR EXAMPLE USE IN AEROSPACE, IN GAS TURBINE ENGINES.

Description

The present invention relates to a superalloy

  nickel base having exceptional oxidation resistance

  and the exceptional mechanical properties at high temperatures. So far researchers have worked with alloys belonging to the Ni-Al-Mo system. This work is, for example, described in US Patent Nos. 2,542,962 and

3,933,483.

  In US Pat. No. 3,904,403, the addition of 0.1 -3 atomic% (total) of one or more elements selected from the group consisting of Cr, Ta and W to alloys is suggested.

of the Ni-Al-Mo type.

  According to the present invention, a class of nickel-based superalloys having a resistance

  improved oxidation by the addition of coordinated amounts

  The improved oxidation behavior is achieved without significantly impairing the mechanical properties. The broad range of composition is 5.8-7.8% Al, 8-12% Mo, 4-8% W, 2-4% Cr, 1-2% Ta, 0-0.3% Hf, 0. , 01-0.1% Y, the balance being essentially nickel A preferred range is 6.3-7.3% Al, 8.5-11.5% Mo, 5-7% W, 2.5-3 , 5% Cr, 1-2% Ta, 0.05-0.2% Hf, 0.01-0.07% Y.

  Alloys having compositions in these inter-

  valles can be made of articles usable by the use of powder metallurgy or

  can be cast to size and then subjected to

thermal energy.

  Therefore, it is an object of the present invention to provide nickel-based superalloys having high oxidation resistance and mechanical strengths. For the invention to be better understood, reference is made to the following figures: FIG. 1 represents the effect of the variation of

  the amount of yttrium on the oxidation behavior.

  Figures 2A, 2B and 2C are scanning electron micrographs showing the morphology

  oxides obtained with different amounts of yttrium.

  Figure 3 shows the effect of varying the amount of chromium on the oxidation behavior at

10930 C.

  Figure 4 shows the effect of varying the amount of chromium on the oxidation behavior

at 11490 C

  Figure 5 shows the breaking behavior by

creep of several alloys.

  The present invention relates to a nickel-based superlite comprising a specific compound range.

  and narrow which gives an exceptional combination of resistance

  oxidation and mechanical properties at tempera-

high level.

  The broad and preferred composition ranges are shown in Tables 1 and 2. The tables are expressed in percent by weight as well as all other percentages in the present application unless otherwise specified. Table 1 contains

  equal values in atomic percents.

  The particular combination of Ni-Al-Mo components is similar in some respects to that described in US Patent Nos. 2,542,962, 3,655,462, 3,904,403 and 3,933,483. The Ni-Al-Mo alloys are recognized as

  having exceptional mechanical properties, but

  Until now, their surface stability and oxidation resistance have been unpredictable and marginal for long-term applications. The essence of the present

  invention is the addition of carefully coordinated amounts

  from Cr, Ta, Y and optionally Hf to these Ni-Al-Mo alloys to dramatically improve oxidation resistance while simultaneously maintaining or improving

the mechanical properties.

  Cr is added for oxidation resistance by 3-promoting the formation of an oxide of A 1203 rather than an oxide based on Ni O. For these purposes, at least about 2% Cr appears to be necessary by increasing the value. of Cr above 4%, substantial improvements are not

  compared to those obtained with 3% Cr.

  Since Cr simultaneously reduces the mechanical properties, Cr additions exceeding about 4% are undesirable. Ta is added to stabilize the microstructure and Ta in the amounts indicated overcomes the deficit.

  of mechanical properties which results from the additions of Cr.

  Therefore, the amounts of Cr and Ta are to a certain extent bound and optimum performance of the alloy will be obtained by coordinating the Ta and Cr values such that for high amounts of Cr, high amounts of TA are obtained. are used and for small quantities

  Cr, small amounts of Ta are used.

Table 1

LARGE COMPOSITION

  Lower limit Upper limit (% by weight) (% at) (% by weight) (% at) Ni (compl) (78,20) (78,65) (66,1) (66,15) Al 5.8 12.8 7.8 17.3 MB 8.0 4.7 12.0 7.8

W 4.0 1.2 8.0 2.4

  Cr 2.0 2.3 4.0 4.8 Ta 1.0 0.35 2.0 1.2

Y 0.01 0.01 0.1 0.05

Hf 0.0 0.0 0.0 0.3 -4-

Table 2

  PREFERRED COMPOSITION (% by weight) Lower Limit Upper Limit

Neither Compl Compl.

Ai 6.3 7.3 MB 8.3 11.5

W 5.0 7.0

Cr 2.5 3.5 Ta 1.0 2.0 Hf 0.0 0.2

Y 0.01 0.7

  At least one subject selected from the group comprises

  Y and Hf must also be added.

  improve the adhesion of the surface oxide to the super-

  al 1 Eges, thus reducing flaking and limiting the weight loss due to oxidation It seems that 0.1 to 0.3% by weight (total) of these elements will perform the desired function, the preferred composition being 0, 02-0.2% (total) and Yde preferably, being present in an amount of from

less 0.01 to 0.07%.

  Figures 1, 2 and 3 will help to understand the

  effects of the elements explained above The figures shown in

  the alloy compositions tested and show the change in weight during the oxidation test It will be understood that when an alloy oxidizes, initially it

  gaining weight due to the formation of a layer of oxy-

  Then, if this oxide layer falls, a weight loss will result and a new layer of oxide will reform The loss (peeling) of the oxide and the loss of

  resultant weights are undesirable since this is

  results in a loss of the elements forming the oxide in the

  Underlying substrate Peeling of the oxide may be

  to a time when the alloy is unable to reform the desired protective oxide layer and forms a non-protective oxide layer at this point, oxidation becomes faster and faster.

  uncontrolled and possibly the sample will be destroyed.

  Since most alloys derive their resistance to oxidation of the formation of a layer

  protective oxide, the desirable behavior of

  weight gain is a slight initial increase in

  weight indicating the formation of a protective oxide layer

  followed by essentially no change in weight (or a very slight increase) The critical and unexpected result of yttrium additions is shown in Figure 1 This figure shows the weight loss experienced by various alloys with different amounts of yttrium, after cyclic tests at 1204 OC of 50 cycles of one hour It is apparent that for the base alloy tested (10% Mo, 6.7% Ai, 6% W, 3% Cr, 1.5 % Ta, 1% Hf, the complement being Ni) additions of about 0.01 to

  about 0.06% yttrium produces a remarkable improvement

  Although it has been previously observed that yttrium can improve the oxidation performance of coatings (U.S. Patent Nos. 3,754,903 and 3,754,903) and alloys (U.S. Patent No. 3 754 903) we have so far, to our knowledge, shown that yttrium quantities exceeding

about 0.1% was harmful.

  The results shown in FIG. 1 can be explained with reference to FIGS. 2A, 2B and 2C which are

  pictures with a scanning electron microscope (gross

  3000 X) of the oxidized surface of three samples.

  The nominal composition of the sample is that

  Figure 2 A is a sample containing 0.1% Hf and less than 0.002% Y Figure 2B is a sample containing 0.1% Hf and 0.029% Y Figure 2C is a sample containing sample containing 0.1% Hf and 0.073% Y.

  Figures 2A and 2C both show a morpho-

  Coarse irregular oxide log and show evidence of flaking of the oxide whereas Figure 2 B 6 - shows evidence of adherent oxide morphology So, Figures 1, 2 A, 2 B and 2 C clearly demonstrate that a limited critical amount of Y produces a substantial improvement in oxidation behavior. Figures 3 and 4 show that a critical value of chromium is required for optimum oxidation resistance. Figure 3 shows the effect of varying amounts of Cr on the oxidation behavior of a base alloy containing 10. % Mo, 7.4% at 1, 6% W, 1.5% Ta, 0.1% Y, the balance being Ni It can be seen that under the conditions of the test (500 cycles of one hour of oxidation in the oven at 1093 C) the desired minimum weight change is

  obtained with amounts of Cr of about 3%.

  FIG. 4 allows to make the same point by using the cyclic oxidation values obtained at 1149 C. The figure shows the change of weight as a function of the test duration Four curves are represented for a base alloy containing 10% Mo, 6 , 6% A 1, 1.5% Ta, 0.1% Y, the balance being Ni (with varying amounts of Cr) The effect of increasing Cr is to turn the curves upwards towards the 'horizontal (or change

from zero to zero).

  Figures 3 and 4 demonstrate that a necessary amount of about 3% is required to obtain a good

  oxidation behavior in this type of alloys.

  The mechanical properties of Al-Mo alloys

  have been demonstrated in the art to be superior

  in most cases, to those of conventional superalloys. The present invention balances the additions

  of Cr, Ta, Y and / or Hf for oxigen behavior.

  significantly improved in combination with

  mechanical parts have at least equivalent and in some

  cases superior to the properties of Al-Mo-Ni base alloys.

  This constitutes a contras 1 marked with respect to alloying

  typical where the improvement of a property is accompanied by

  variably by the decrease of the other properties.

  FIG. 5 is a graph of rupture by

  creep for different alloys, including the alloy previously

  MAR-M 200, a well-known superalloy, and an alloy falling within the scope of the present invention. The data in Figure 5 are for the creep rupture properties of various compositions tested in a single crystal with an (111) orientation. As can be seen in the figure, the modified composition of Ni-Al-Mo has a duration up to improved fracture compared to other tested alloys It appears that the modified alloy has a temperature improvement of about 1050 C compared to usual superalloys. This means that under equivalent stress conditions, the alloy can be processed at higher temperatures of 1050 C while achieving the same service life This high temperature may be a result of higher engine operating temperature or reduced flow of cooling air if the engine temperature was higher. unchanged Any of these possibilities allows substantial savings Another possibility is to maintain the operating conditions Including the temperature at the same value and get a significantly increased life Finally, we can maintain the same temperature, but increasing the stress, get increased performance for the same fuel consumption and the same life These compositions previously described can be used in the form of cast monocrystal or, alternatively, can be manufactured in

  partly using the techniques of metallurgy of the

  Then, by a directed recrystallization to obtain an aligned grain structure which is at the limit, can be a single crystal. In the case where the molded / leaded crystalline pathway is used, it is necessary that the molded element be homogenized and subjected to heat treatment as described in US Patent Application No. 177,047. If the element is to be manufactured by the powder metallurgy approach, the composition can be formed into a powder by various techniques although The resulting rapid solidification rate is desirable because of the resulting increased homogeneity.

  in US Patent Nos. 4,025,249, 4,053,264 and 4,078,873.

  The resulting powder is then consolidated and subjected to directed recrystallization to produce the desired structure. Oriented recrystallization is described in US Patent No. 3,975,219 and specific approaches for obtaining various crystallographic alignments in the final structure are described in the patent application. US 325,248

  The resulting products find particular utility

  In the case of gas turbine engines If the molding technique is used, a molded part can be produced directly of the desired size. However, if the track is used by the powder metallurgy, the blade manufacturing technique described in the patent US No. 3,872,563 may be followed with advantage in order to arrive

  to a blade having the maximum cooling capacity.

  Although the compositions described here are exceptional-

  oxidation-resistant, they will undoubtedly be used as coatings and coatings.

  may include a coating of alumixEure o coatings

  external elements of the M Cr Al Y type Of course, various modifications can be made by those skilled in the art to the alloys which have just been described solely as non-limiting examples.

  without departing from the scope of the invention.

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Claims (2)

claims:   1 Nickel-based alloy with mechanical strength   that elevated and improved resistance to oxidation characterized in that it essentially comprises: , 8 7.8% A 1 8 -12% MB 4 -8% W 2 -4% Cr 1 -2% Ta 0 0.3% Hf 0.01 0.1% Y   Complement Ni 2 Nickel-based superalloy having high mechanical strength and improved oxidation resistance according to claim 1, characterized in that it essentially comprises: 6.3 7.3% A 1 8.5 -11.5% MB 5 7% W 2.5 3.5% Cr 1 2% Ta 0 0.2% Hf 0.01 0.07% Y Complement Ni.