FR2478128A1 - Nickel alloy for single crystal casting - contg. chromium, cobalt, titanium, aluminium, tungsten, niobium, tantalum, and carbon - Google Patents

Abstract

An alloy for use in the form of a single crystal casting comprises 7-13% Cr, 2-15% Co, 0.2-5% Ti, 4.5-6.7% Al, 7-12% W, 0-1% Nb, 0-1% Mo, 1.5-5% Ta, 0-2% Hf, 0.015-0.05% C, 0-0.01% B, 0-0.05% Zr, balance Ni. Prefd. alloys contain 8-10% Cr, 2-11(3-7)% Co, 1.25-1.75% Ti, 5.25-5.75% Al, 9-11% W, 2.25-5% Ta, 0-1.7% Hf, 0.015-0.05% C, 0-0.01% B, 0-0.01% Zr, balance Ni. The alloy may be soln. heat treated at 1300-1320 deg.C for 1 hr. followed by cooling to room temp. and ageing at 870 deg.C for 16 hrs. Typically, the alloy has a stress life at 730 MPa at 760 deg.C of 435 hrs. cf. 187 hrs. for a similar superalloy. The alloy is used to cast gas turbine rotor blades and other turbine components. Life of components cast from alloy is increased.

Description

The present invention relates to an alloy suitable for producing monocrystalline moldings; it also relates to a molding-made with such an alloy.

In cases where objects made of nickel-based alloys are intended to be used at elevated temperatures under severe mechanical stress and corrosive attack conditions, single-crystal moldings have been found to provide virtual benefits by combining their service life and their resistance to high temperatures. The most important area in which these properties are useful is the hottest parts of gas turbine engines such as vane vanes and turbine blades. But nickel-based special alloys commonly used, the realization of which has been very advanced for the usual isoaxial moldings, have combinations of constituent materials which are possibly unfavorable to the properties of a monocrystalline molding.
Starting from a modern special alloy, the inventors have developed a combination of alloy compositions giving excellent properties when used as a microcrystalline molding.

The alloy according to the present invention, usable in the form of monocrystalline molding, has the following composition, expressed in ss by weight
Chrome 7 to 13% Molyedene 0 to 1%
Cobalt 2 to 15% Tantalum 1.5 to 5%
Titanium 0 to 2.5 ss Hafnium o to 2 ss
Aluminum 4.5 to 6.7% Carbon 0.015 to 0.05%
Tungsten 7 to 12% More o to 0.01 ss
Niobium 0 to 1% Zirconium O to 0.05 d
The complement being made of nickel, plus any impurities
Preferably, this alloy will comprise the following compounds, expressed in: by weight
Chrome 8 to 10% Tantalum 2.25 to 5%
Cobalt 2 to 11% Hafnium O to 1.7%
Titanium 1.25 to 1.75% Carbon 0.015 to 0.05
Aluminum 5.25 to 5.75% Boron 0 to 0.01%
Tungsten 9 to 11% Zirconium O at 0.05%
The complement being made of nickel, plus any impurities
Experience has shown that 3 to 7% of cobalt has special advantages
if it is adequate,
The alloy may be heat treated in solution to a temperature of about 1300 C; in some specific cases for example, this heat treatment was at a temperature of 1300 to 1320 C for one hour, followed by cooling at room temperature and heating at 870 C for 16 hours
The invention also relates to a monocrystalline molded object, made of the alloy according to the invention, and in particular a molded mobile auot for a gas turbine engine, made of this alloy cast in monocrystalline form.
Tests have been carried out with a view to obtaining confirmation of the properties of the alloys according to the invention
These tests are described below with reference to the accompanying drawings in which - Figure 1 is a columnar diagram showing
the service life of specimens of various alloys
under mechanical stress and at a first tempe
low erection; and - Figure 2 is a diagram similar to that of
Figure 1 represents the service life of the
same test pieces at a second temperature more
higher than the first
For the tests of the alloys according to the invention, specimens of the various alloys in monocrystalline cast form have been produced. There are two known methods of producing monocrystalline moldings, consisting of either using a crystalline seed or using solidification. directional followed by use of a labyrinthine passageway to select a single crystal of the alloy, growing to form the specimen
Although one or the other method may be used, the second has proved to the inventors more convenient and they have realized, for each of the alloys tested, a specimen made of a single crystal. To allow the comparison, they have also produced a similar test piece cast in the form of a directionally solidified material, the latter material being constituted, as we know, by a plurality of individual grains, all parallel, and generally having better properties than those of a conventional molding. or isoaxic of the same alloy the appended drawings make it possible to compare the ability to withstand the stress before breaking, at a low temperature (760 C) and to use the higher temperature (1040 C) of ten monocrystalline specimens with that of a test specimen directionally solidified
The theoretical compositions of each test piece are shown in Table I below, but it will be noted that the actual analysis might give somewhat different figures.
TABLE I (first part)

<tb> Specimen <SEP> Chrome <SEP> Cobalt <SEP> Titanium <SEP> Aluminum <SEP> Fungsten
<tb> Control <SEP> 9 <SEP> 10 <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb> test <SEP> 1 <SEP> 9 <SEP> 10 <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb><SEP> - <SEP> 2 <SEP>#<SEP> 9 <SEP><SEP> 10 <SEP> 1.5 <SEP> 5.5 - <SEP> 10
<tb><SEP> - <SEP> 3. <SEP> 9 <SEP> 10 <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb><SEP> - <SEP> 4 <SEP> 9 <SEP> 10 <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb><SEP> - <SEP> 5 <SEP> 9 <SEP> 10 <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb><SEP> - <SEP> 6 <SEP> 9 <SEP> 10 <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb><SEP> - <SEP> 7 <SEP> 9 <SEP> 10 <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb><SEP> - <SEP> 8 <SEP> 9 <SEP> 5 <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb><SEP> - <SEP> 9 <SEP> 9 <SEP> 0+ <SEP> 1.5 <SEP> 5.5 <SEP> 10
<tb><SEP> - <SEP> 10 <SEP> 9 <SEP> 10 <SEP> 1.5 <SEP> 5.5 <SEP> t0 <SEP>
<Tb>
TABELEAU I (End)

<tb> Specimen <SEP> Tantalum <SEP> Hafnium <SEP> Carbon <SEP> Boron <SEP> Zirconium
<tb> Control <SEP> 2.5 <SEP> 1.2 <SEP> 0.15 <SEP> 0.015 <SEP> 0.05
<tb><SEP>'test<SEP> 7 <SEP> 2,5 <SEP> 1,2 <SEP> 0,15 <SEP> 0,015 <SEP> 0,05
<tb><SEP> - <SEP> 2 <SEP> 2.5 <SEP> 0.5 <SEP> 0.015 <SEP> 0+ <SEP> 0+
<tb><SEP> - <SEP> 3 <SEP> 2.5 <SEP> 1.0 <SEP> 0.015 <SEP> 0+ <SEP> 0+
<tb><SEP> - <SEP> 4 <SEP> 2.5 <SEP> 1.2 <SEP> 0.015 <SEP> 0+ <SEP> 0+ <SEP>
<tb><SEP> - <SEP> 5 <SEP> 2.5 <SEP> 1.2 <SEP> 0.015 <SEP> 0+ <SEP> 0.05
<tb><SEP> - <SEP> 6 <SEP> 2.5 <SEP> 1.2 <SEP> 0.15 <SEP> 0+ <SEP> 0+
<tb><SEP> - <SEP> 7 <SEP> 2.5 <SEP> 1.2 <SEP> 0.015 <SEP> 0.015 <SEP> 0+
<tb><SEP> - <SEP> 8 <SEP><SEP> 2.5 <SEP> 0+ <SEP> 0.015 <SEP> 0+ <SEP> 0+
<tb><SEP> - <SEP> 9 <SEP> 2.5 <SEP> 0+ <SEP> 0.015 <SEP> 0+ <SEP> 0+
<tb><SEP> - <SEP> 10 <SEP> 2.5 <SEP> 0+ <SEP> 0.015 <SEP> 0+ <SEP> 0+
<tb> 0+: Note that it is impossible to eliminate any
trace of these elements; the alloy will therefore contain
unwanted residual traces of these elements
ments
This Table I shows that the alloy 1 is identical to the control alloy; any difference between their respective properties is therefore due to the structural difference existing between a monocrystalline molding (alloy 1) and a directionally solid molded molding (alliabe.temoin). Each of the other alloys demonstrates the effect of a change in the composition of the constituent material. We see that the alloys 2 to 5, 8 and 10 fall within the scope of the present invention while the alloys 1, 6, 7 and 9 are outside this area
In all the cases represented in FIGS. 1 and 2, the alloys were treated thereafter in solution at a temperature of 870 ° C. for 16 hours.
Referring to the diagrams, Figure 1 shows the longevity of the samples of the various alloys when they are held under a mechanical stress of 730 megapascal at a temperature of 760 C.

This clastic test method is used to determine the tensile strength properties before breaking of the alloy and will not be described in more detail here. It is found that the control alloy has a longevity of less than 80 hours while the same alloy in monocrystalline form (alloy 1) has a longevity almost double 145 hours. The first alloy according to the invention (alloy 2) has a longevity close to 260 hours, which indicates a considerable improvement. The alloys 3, 4 and 5, although not reaching this maximum value, also reveal a marked improvement with longevities greater than 200 hours (alloys 3 and 4) and 230 hours (alloy 5)
Alloys 6 and 7 are within the scope of the invention because of the low carbon content for alloy 6 and the low boron content for alloy 7. None of these alloys is worth the alloy 1 and, with regard to the alloy 7, its longevity is almost as reduced as that of the alloy tint. With the alloys 8 and 10, one returns to the values met for the alloys 3 and 4 (greater than 200 hours), while the alloy 9, outside the scope of the invention because of its very low cobalt content, is also less advantageous than the control alloy. It is interesting to note that this alloy was found to be unstable after being soaked for 500 hours at elevated temperatures of the order of 850 to 1050 C.
Figure 2, which is referred to now, shows the results obtained by a test method similar to the previous one but at a higher temperature (1040 C) and are constrained proportionally lower (128 magapascals). The behavior of the specimens at a lower temperature is repeated to a great extent. Monocrystalline alloy 1, for example, is similar to the control alloy, and alloys 2 to 5 show considerable improvement over these first two alloys.
Alloy 6 is much less effective, as well as alloy 9, while alloy 8 is very promising under these conditions and actually has a better balance of all its properties, especially when heat-treated. (to see further) . The alloy 7 is similar to the alloy 5 under these temperature conditions but it is obviously undervalued by its very poor behavior at the lower temperature.
It is thus seen that the alloys according to the invention show a marked improvement in their properties quite out of proportion with the rather reduced modifications of their constituents. Although longevity before rupture, under stress, is very important for the utility of an alloy, it is not the only parameter to be considered; the modifications coriorm.es the invention do not seem to go with nefast ter the significant parameters of an alloy and it is found that they improve some
The original melting point is thus high by the low levels of boron and zirconium, these two bodies having the property of lowering the melting point.

This feature is advantageous for two reasons because it gives an immediate opportunity to raise the working temperature of the alloy, and because it allows to use a heat treatment in solution at a higher temperature. Raising the temperature of the heat treatment causes a rise in the degree to which the hardening phase
enters into solution, and the durability before rupture under stress is increased
Table II below shows the increase of the original melting point and the improvement of the durability under stress, obtained by means of the heat treatment at higher temperature thus made possible. It is seen that the longevity before Rup ture is indicated for the conditions applied to obtain the results shown in Figures 1 and 2, which allows the results to be compared.

The modified heat treatment consists of cooling from the solution treatment temperature to room temperature and then applying a curing heat treatment at a lower temperature.

Obviously, the heat treatment temperature must be lower than the melting point which, for certain alloys according to the invention, may be lower or preferred melting point of 1300 - 1320 C.

TABLE II

<tb><SEP><SEP> Point of <SEP> Treatment <SEP> Longevity <SEP> Longevity
<tb> Alloy <SEP> Fusion <SEP> Thermal <SEP> (730 <SEP> MPa, <SEP> (128 <SEP> MPa,
<tb><SEP> of origin <SEP> 760 C) <SEP> 1040 C
<tb> All. <SEP> 1 <SEP> 1180 C <SEP> 16h <SEP> to <SEP> 870C <SEP> 145 <SEP> h <SEP> 109 <SEP> h
<tb> All. <SEP> 9 <SEP> 1320 C <SEP> 16h <SEP> to <SEP> 870C <SEP> 75 <SEP> h <SEP> 109 <SEP> h
<tb><SEP> 1h <SEP> to <SEP> 1320C <SEP> 187 <SEP> h <SEP> 284 <SEP> hr
<tb> + 16h <SEP> to <SEP> 870 C
<tb> All. <SEP> 8 <SEP> 13200 <SEP> C <SEP> 16 <SEP> h <SEP> to <SEP> 8700 <SEP> C <SEP> 216 <SEP> h <SEP> 203 <SEP> h
<tb><SEP> 1 <SEP> h <SEP> to <SEP> 1320 C
<tb><SEP> +16 <SEP> h <SEP> to <SEP> 870 C <SEP> 435 <SEP> h <SEP> 325 <SEP> hr
<tb> All. <SEP> 10 <SEP> 13000 <SEP> C <SEP> 16 <SEP> h <SEP> to <SEP> 8700 <SEP> C <SEP> 210 <SEP> h <SEP> h <SEP> 177 <SEP > h
<tb><SEP> 1 <SEP> h <SEP> to <SEP> 1300 C <SEP> 335 <SEP> h <SEP> 291 <SEP> hr
<tb><SEP> +16 <SEP> h <SEP> to <SEP> d <SEP> 8700 <SEP> C
<Tb>
It will be noted that between the initial heat treatment in high temperature solution and the subsequent lower temperature ripening treatment the test piece was cooled to room temperature. The inventors have found that this cooling phase and the speed with which it was carried out could cause significant differences in the final properties. Thus, a cooling rate of 70 to 100 ° C. per minute at the time of this phase can It is clear from Table II above that it is possible to obtain a considerable increase in the durability before breaking, under stress, by means of a heat treatment in solution at high temperature. This is mainly the case of alloying 8 which is a preferred alloy
Other parameters are also improved
The inventors have found, for example, that using tantalum instead of tungsten and molybdenum as solid solution hardeners can improve the resistance to corrosion and oxidation.
They demonstrated the importance of this addition of tantalum by comparative tests of alloys with or without tantalum. For alloy 10, for example, this durability under a stress of 730 MPa and a temperature of 7602C was 210 hours while it was 177 hours under 128 MPa and 1040 C (see Table II). For specimens made of an identical alloy but without tantalum, the corresponding longevities were 67 and 51 hours, respectively. At the contents used for the test specimens, tantalum is clearly essential and the inventors believe that in fact additions up to 3% and even slightly above this figure may be beneficial. Subsequent tests on the resistance of the alloy to corrosion confirmed the importance of the addition of tantalum. Thus, three samples, one made of the control alloy, a second one of 8 alloy but without tantalum, and a third of the alloy 8 in which the tantalum had been replaced by tungsten, were placed for 90 hours at 1050 C in an air atmosphere supplemented with 4 parts per million of salt. At the end of this time, the control sample revealed an attack of 140 P while the other two samples revealed a more severe attack of 200%.
In addition, the low carbon content causes the appearance of relatively small carbide particles and thus eliminates the appearance of carbides of large soriptic morphology which could reduce the oxidation resistance of special alloys based on carbon. aluminides coated with aluminides (as well as for directionally solidified alloys). Thus, corrosion tests were carried out on isotropic compounds coated with aluminues. similar, for the rest, to the aforementioned control alloy, and it was found that with fine carbide particles longevity was twice that of normal alloy
It was also found that the impact resistance of the compounds according to the invention was considerably improved compared with that of the unmodified, directionally solidified compound. The inventors believe that this effect is due to the absence of soriptic carbides.
The stability of the alloy, which is determined by the contents of aluminum, titanium, chromium, tuingsten and cobalt, is not seriously affected by the modifications proposed by the invention, but it will be understood that by taking alloys The contents of constituents are located at the extreme values of the proportions indicated it is possible to produce alloys with reduced stability although still useful co = i -.e alloys It is clear from the description above that the connections according to the invention provide properties suitable for parts working under very severe stress conditions at high temperatures such as, for example, the blades of gas turbine engines. However, the growth of these alloys makes them suitable for many other uses such as for other parts of gas turbines.

Claims (10)

1. Usable alloy in the form of mono molding  crystalline, characterized by the composition sui  vante, expressed in% by weight  Chrome 7 to 13% Nolybdenum 0 to 1%  Cobalt 2 to 15 i Tantalum 1.5 to 5%  Titanium 0 to 2.5% Hafnium 0 to 2%  Aluminum 4.5 to 6.7% Carbon 0.015 to 0.05%  Tungsten 7 to 12% Bore 0 to 0.01%  Niobium 0 to 1 f Zirconium. 0 to 0.05  The complement consisting of nickel, more  possible impurities 2.Alloy according to claim 1, characterized by  the following composition, expressed in% by weight  Chrome 8 to 10% Tantalum 2.25 to 5%  Cobalt 2 to 11% Hafnium 0 to 1.7%  Titanium 1.25 to 1.75% Carbon 0.015 to 0.05%  Aluminum 5.25 to 5.75% Pore 0 to 0.01%  Tungsten 9 to 11% Zirconium 0 to 0.05%  the complement consisting of nickel, plus  possible impurities 3. Alloy according to Claim 2, characterized by  the following composition, expressed in% by weight  Chrome 8 to 10% Tungsten 8 to 10%  Cobalt 3 to 7% Tantalum 2.25 to 5%  Titanium 1.25 to 1.75% Hafnium O at 0.5%  Aluminum 5.25 to 5.75% Carbon 0.015 to 0.05%  Bore 0 to 0.01%  Zirconium 0 to 0.05%  the complement consisting of nickel, plus  possible impurities 4.Alloy according to Claim 3, characterized by  the following composition, expressed by weight  Chrome 9% Aluminum 5.5% Carbon 0.015%  Cobalt 9% Tungatene 10%  Titanium 1.5% Tantalum 2.5%  the co-ple..ent being constituted by nickcl, plus  possible impurities 5. Alloy according to Claim 3, characterized by  the following composition, expressed in% by weight  Chrome 8.5 d Aluminum 3.5 S Carbon 0.02 r  Cobalt 5 i Tungsten 9.5%  Titanium 1.5% Tantalum 3.25 r  the complement consisting of nickel, plus  possible impurities 6.Heat treatment in solution for an alloy  according to any one of Claims 1, 2, 3,  4 or 5, characterized in that it consists of heating  iron said alloy up to a temperature included  between 1300 and 1320 C 7. Heat treatment in solution according to the Claim  cation 6, characterized in that it consists of re  to cool the alloy since said temperature jus  only at room temperature at a speed of 70  at 100 C per minute 8. Heat treatment in solution according to the invention  cation 7, characterized in that after cooling  at room temperature said alloy is  reheated to a temperature of about 870 C  9. Heat treatment in solution according to the  cation 8, characterized in that it consists of heating  iron said alloy at a temperature of about 1320  degrees centigrade for an hour, to cool it  to room temperature and then to warming  iron at a temperature of about 870 C and to the rain  hold at this temperature for 16 hours 10. As a new industrial product, molding  monocrystalline made from an alloy according to  any one of Claims 1, 2 or 3