JP3506734B2 - Precipitation hardenable nickel-base superalloys and methods of using the alloys as materials in the manufacture of directional solidified structural members - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a precipitation hardenable nickel superalloy containing, in addition to nickel, at least chromium, cobalt, tungsten, aluminum, titanium and tantalum as other alloy components. The invention also relates to the preferred use of the above alloys.

[0002]

2. Description of the Prior Art In the present invention, for example, a chromium content of> 10 wt.% As required to ensure sufficient corrosion resistance in contact with combustion gases containing sulfur in stationary gas turbines. Reference is made to the prior art as is substantially apparent from U.S. Pat. Nos. 3,459,545, 3,619,182 or 4,957,703 for alloys having.

Alloys such as those described in US Pat. No. 3,459,545 are often used as materials for the rotating blades of gas turbines. This alloy excels in having very good corrosion resistance at high temperatures. This is due, inter alia, to the relatively high chromium content of this alloy of about 16% by weight. However, a high chromium content also reduces the creep strength at the same time. At a load of 150 MPa / 50,000 h, which is typical for stationary gas turbines, the metal temperature that this alloy can withstand is limited to about 820 ° C.

Nickel super alloys described in US Pat. Nos. 3,619,182 and 4,957,703 and also used as materials for rotating blades of gas turbines.
The alloy exhibits creep resistance that allows the use of this rotating vane material at temperatures of about 850 ° C. due to its relatively low chromium content. Chromium content about 10% by weight
Further increases in heat resistance by further reduction below are not possible when used in corrosive media. This is because there must be sufficient chromium accumulation to form a protective chromium oxide coating.

However, the operating temperature of members made of nickel superalloys depends on the directional solidification (gerichtetes Erstarren).
Can be raised even further by. In doing so, the expanded particle limit (Korngrenzen) contrary to the preferred direction brought about by the above-mentioned directional solidification is removed, and the solidification conditions are chosen such that this preferred direction corresponds to the main loading direction of the component. To be done. However, when producing particularly hollow components, such as possibly coolable gas turbine rotor blades, from the usual types of materials, cracks often occur along the longitudinal grain boundaries (Laengskorngrenzen) during the process of solidification. Occurs, rendering this material unusable. The cause is caused by the various expansion coefficients of nickel superalloys , and by the ceramic particles needed to produce hollow members, and thermal strain that is not sufficiently removed from the material by plastic deformation. Is.

Journal of Metals
Metals) July 1971, pp. 38-40, DN Duhl and CP Sullivan.
"Some effects of hf addition on the mechanical properties of columnar nickel superalloys ".
afnium additions on the mechanical properties of a
columnar-grained nickel-base superalloy) ", the addition of haunium can improve the transverse ductility of nickel-based superalloys, which correspondingly reduces their tendency to crack. As long as the complete dissolution of the γ'-precipitate is no longer possible during the solution heat treatment, the melting point of the nickel superalloy is lowered, which leads to a reduction in creep resistance and the directional solidification The beneficial effects are at least partially offset again. Another problem is that hafnium
It is apt to react with the material of the outer shell of the receiving mold when producing the nickel-based superalloy. Particularly in the case of large parts, the hafnium becomes depleted during the process of solidification, so that a sufficient improvement in lateral ductility is no longer guaranteed.

[0007]

The problem to be solved by the present invention is that it is essentially better suited for the production of directionally solidified parts, and that it has a higher temperature than prior art nickel superalloys. To provide a nickel-based superalloy having improved creep life in comparison with the former superalloy.

The nickel superalloys according to the invention are distinguished by improved castability and higher creep life compared to comparable nickel superalloys according to the prior art. The improved castability surprisingly emerges without the addition of hafnium, and in this case even components which were not conventionally produced in the directionally solidified mold can now be directionally solidified or It can be exploited that a more effective cooling concept can be realized, which leads to an improved creep life in both cases. Therefore, components made from nickel-based superalloys according to the present invention and exposed to high temperatures, in particular components such as rotary blades of gas turbines, will be of conventional size with corresponding dimensions under the same mechanical load and temperature conditions. Nickel by technology
It has a life several times longer than that of superalloy members.

[0009]

Nickel according to the invention
These unexpected beneficial effects of superalloys are probably due to the particularly good stability of the alloy structure manifested by the reduced titanium content and the increased tantalum content. This is also a result of the complete solubility of the γ'-precipitates in the surrounding γ-matrix during solution annealing. This possibility of complete dissolution surprisingly appears immediately when the weight ratio of tantalum to titanium exceeds a value of 1.5. By increasing the tantalum content and possibly also the tungsten content, the structural stability and creep strength are further improved.
However, by making the titanium content relatively low, the appearance of brittle Ni ₃ Ti containing eta phases is also largely avoided. Thereby the longitudinal grain boundary surface
The appearance of nuclei for the formation of cracks along (Laengskorngrenzen) is avoided, which substantially improves the castability.

Further, the improvement in castability is due to the directivity in manufacturing .
It is also evident by the fact that the solidified parts can no longer form freckles. Such "speckles" are equiaxed particles juxtaposed in the shape of pearls. They occur in the unstable liquid layer (lower light layer, upper heavy layer) associated with the enrichment of titanium in the dendritic melt. With increased tantalum content (tantalum is heavier and also dendritic enriched) as well as reduced titanium content, the formation of "speckle" is significantly reduced, and thereby castability is significantly improved. .

The alloy according to the prior art has a high positive fitting defect (Fehlpassun) between the lattice constant a of the matrix lattice and the lattice constant of the γ'-precipitates contained in the matrix.
g) δa = (a'-a) / a is shown. This is a result of the relatively high content of titanium and tantalum which expands the lattice of the γ'-phase, and also of the relatively small content of tungsten which expands the lattice of the γ-matrix. Due to the decrease in the titanium content, the high fitting defect δa is significantly reduced. This gives the alloy according to the invention two quite essential advantages. That is, on the one hand, the tendency of the alloy according to the invention to crack during directional solidification is thereby reduced and ductility is improved. This is because the induced stress can be reduced by plastic deformation. On the other hand, at a slight misfit, the expanding motion of the γ'-precipitates slows down, which leads to an improved long-term stability of the structure, ie improved long-term robustness at elevated temperatures. Get burned.

[0012]

Embodiments of the invention will be described in more detail below with reference to the accompanying drawings. FIG. 1 shows alloy C according to the invention.
Resonance (Wa) measured by differential thermal analysis (DTA) of
It is a figure which shows the correlation of ermetoenung) W [relative unit] and temperature T [degreeC].

FIG. 2 is a graph measured for prior art Alloy I corresponding to FIG. FIG. 3 is a graph measured for alloy H according to the present invention, corresponding to FIGS. 1 and 2.

Alloys having the compositions shown below in weight percent were melted in a vacuum induction furnace. Alloy A B C D E F G H I Ni <------------------- Substrate ----------------- -------> Cr 12.0 12.0 12.0 12.0 12.0 12.5 12.5 12.0 12.4 Co <---------------------- 9.0 ------- --------------> Mo-----1.85 1.85-1.87 W 9.0 9.0 6.0 5.7 5.0 4.1 4.1 6.0 4.0 Al 3.5 3.7 4.2 4.0 5.0 3.4 3.4 4.1 3.4 Ti 3.0 2.0 2.0 1.9 1.5 3.8 3.8 3.3 3.9 Ta 5.0 5.8 6.8 6.5 5.0 4.1 4.1 5.0 4.1 Zr <---------------------- 0.02 ---------- ------> 0.01 Hf------0.45-0.87 B <---------------------- 0.015 ------- -------> 0.013 C <---------------------- 0.07 ---> 0.08 0.07 0.08 After melting in a vacuum induction furnace, Directionally solidified rods, each having a diameter of approximately 14 mm and a length of 250 mm, respectively, as well as approximately 250 mm from the above alloys
The length of a gas turbine hollow rotor blade was cast. At that time, the following casting parameters were adjusted for all alloys: Drawing speed: 8 mm / min Casting temperature: 1550 ° C. Shell temperature: 1550 ° C. Alloys F, G and I were used as comparison alloys and almost New York City The International Nickel Company, Inc. New
It corresponds to a prior art alloy similar to the alloy sold under the model number IN792 by (York).

The rods according to alloys A and F were subjected to the heat treatment process customary in prior art alloys: 120
0-1250 ° C / 4h (solution treatment) + 1080-11
20 ° C / 2-4h (precipitation hardening) + 850 ° C / 24h (precipitation hardening). A sample with a total length of 46 mm and a diameter of 5 mm in the measuring section was prepared from a directional solidified rod. These samples were subjected to a stress at a temperature of 950 ° C., which was pre-determined and constant, and the time to failure of each sample was recorded. At that time, the following numerical values were confirmed: alloy temperature [° C.] stress [MPa] time to failure [h] A 950 250 153 A 950 225 243 A 950 200 636 F 950 250 250 83 F 950 225 126 F 950 200 204 From the above, it can be seen that parts made of alloys according to the invention according to composition A exhibit 2-3 times improved creep properties and thus corresponding higher lifetimes compared to parts made of alloys according to the prior art. It should be taken care of.

2 from alloys C and G using the same process parameters at about 1400 to 1500 ° C.
A single rotary vane for a stationary gas turbine was cast that had the same dimensions and was directionally solidified, formed hollow for cooling purposes. It was confirmed that the rotating blade manufactured from Alloy G formed cracks along the grain boundary surface in the longitudinal direction. On the contrary, in the case of a rotary blade cast from alloy C, no cracks were found even when using extremely sensitive test methods, such as a penetration test with a liquid which emits fluorescence. Compared to the alloy G according to the prior art, alloy C is therefore used as a material, in particular in the production of hollow-formed, directionally solidified components, such as possibly coolable rotor blades for gas turbines. It exhibits castability that makes it possible. In this case, it is of particular advantage that good castability is achieved without the addition of hafnium, which improves the castability of nickel superalloys , i.e. the addition of hafnium, on the one hand,
It significantly lowers the melting temperature of nickel superalloys . This makes it difficult or even impossible to dissolve the γ'-phase during the solution heat treatment. On the other hand, hafnium
It tends to react with the melt-receiving mold shell, which can adversely affect the manufacture of large components.

Other casting experiments have shown that, in addition to alloy C, other precipitation hardenable nickel containing at least chromium, cobalt, tungsten, aluminum, titanium and tantalum as other alloying components in addition to nickel.
The le superalloy also exhibits excellent castability as long as the tantalum content is at least 1.5 times the titanium content, expressed in weight percent.

In order to obtain excellent mechanical properties, in addition to the castability, in particular, the γ'-phase is used in the solution treatment process performed during the heat treatment of the nickel superalloy according to the present invention. Can be dissolved. Only then can a uniform distribution of the γ′-particles in the matrix material juxtaposed around the γ-phase be ensured during the subsequent precipitation heat treatment as an additional step. On the contrary, if the γ'-phase cannot be completely dissolved, it results in mainly coarsely formed γ'-particles which are non-uniformly distributed in the γ-matrix. This affects on the one hand creep strength and on the other hand accelerates corrosion and oxidation.

It has now been found by differential thermal analysis that in the alloy according to the invention there is a wide temperature interval between the melting of the γ'-phase and the melting of the sample of the analyzed alloy. In this temperature interval, a complete, but at least almost complete dissolution of the γ'-phase is generally possible.

This is clear from FIG. 1, for example. In this figure, the thermal resonance of the comparative sample without the phase runs as a substantially straight line. On the contrary, alloy C
The thermal resonance of γ ′ deviates from these straight lines in the direction of the endothermic thermal resonance because the dissolution of the γ′-phase begins at temperatures above about 900 to 950 ° C. At a temperature Tg of about 1240 ° C., the γ′-phase has completely melted, and the thermal resonance of alloy C again matches the thermal resonance of the comparative sample up to a temperature Ti of about 1280 ° C. Thanks to the endothermic thermal resonance again, alloy C
Starts to melt above the temperature Ti. This melting process only begins a long time after the complete dissolution of the γ'-phase, with a slight increase in the heating rate. Due to the relatively wide width of the temperature range limited by the temperatures Tg and Ti, the γ′-phase is
Even in industrial heat treatment processes where exact temperature stabilization cannot be achieved, it can be completely melted without risking localized melting of the alloy.

Other nickel superalloys according to the invention, such as alloys A, B, D and E, also show corresponding properties. These alloys exhibit a temperature range between about 1200 ° C. and 1300 ° C. in which heat treatment steps, such as solution heat treatments, can be carried out without initiation of alloy melting.

All these nickel superalloys are distinguished by their tantalum content, expressed in% by weight, which exceeds their titanium content several times.
As soon as the weight percentages of tantalum and titanium are comparable to each other, the above temperature range is obtained, and complete melting of the γ'-phase is not possible without melting of the nickel superalloy in question. Is. This belongs to the prior art with a Ta / Ti weight ratio of about 1.05 according to FIG.
This is apparent from the DTA-chart of Nickel Superalloy I. In the case of this alloy, the temperature Ti at which melting starts is lower than the temperature at which melting of the γ'-phase ends. Therefore, in the case of this alloy, complete dissolution of the γ'-phase is not possible, and upon precipitation hardening only coarsely formed and non-uniformly distributed γ'-particles result. become. According to alloy F, a directionally solidified component from this alloy may have a castability of 2 to 3 with poorer castability compared to the alloy according to the invention.
It is clear that it shows a creep life that is twice as low.

In the case of nickel-based superalloys in which the content of tantalum, expressed in% by weight, reaches 1.5 times the content of titanium, almost all the γ'-phase is dissolved before melting. As can be seen from the DTA-chart of alloy H shown in FIG. 3, this is comparable for Ta / Ti ratios around 1.5.
Nickel superalloys no longer exhibit a temperature range that results in complete dissolution, but thermal resonance approaches the baseline of the comparative sample significantly before the onset of melting and after almost complete dissolution of the γ'-phase.

Since titanium contributes to a certain strength improvement of the γ'-phase, the content of titanium is at least 0.8% by weight.
Should be. Correspondingly, the tantalum content should be at most 10 times the titanium content, expressed in% by weight.

Particularly suitable for the production of directionally solidified components such as rotary blades of gas turbines, in addition to nickel, in wt% the following composition: Chromium 11.0 to 15.0 Cobalt 2.0 ~ 11.0 Tungsten 3.5-10.0 Aluminum 3.0-5.5 Titanium up to 3.5 Tantalum 4.0-9.0 Up to molybdenum 3 Up to zirconium 0.05 Up to boron 0.05 and carbon 0. Nickel super alloy having 01 to 0.15, where Ta / Ti ≧ 1.5
It's money .

At least 5% by weight of tungsten
By increasing the temperature to γ′-phase, the stability against grain coarsening and thus the long-term strain resistance and creep strength of the nickel superalloy according to the invention is further improved. The preferred alloy is therefore, in addition to nickel, wt%
The following components should be included in: Chromium 11.5 to 14.0 Cobalt 3.0 to 11.0 Tungsten 5.0 to 9.5 Aluminum 3.0 to 5.0 Titanium up to 3.5 Tantalum 4 .0～8.0 carbon 0.01 to 0.15 where Ta / Ti ≧ 1.5 to boron 0.05 to zirconium 0.05 to molybdenum 2.

Based on Ni the following composition: Chromium 11.5 to 14.0 Cobalt 3.0 to 11.0 Tungsten 7.5 to 9.6 Aluminum 3.1 to 4.0 Titanium 2.2 to 3 .3 tantalum 4.4 to 5.8 molybdenum up to 2 zirconium up to 0.05 zirconium up to 0.05 carbon up to 0.01 to 0.15 where Ta / Ti ≧ 1.5, and in particular Ni based Composition: Chromium 11.8 to 12.5 Cobalt 5.0 to 10.0 Tungsten 8.5 to 9.5 Aluminum 3.3 to 3.7 Titanium 2.7 to 3.2 Tantalum 4.8 to 5. 3 up to 2 molybdenum up to 0.03 zirconium boron 0.005-0.03 carbon 0.02-0.10 nickel superalloys according to the invention show particularly good creep strength.

% By weight in addition to nickel as the base metal
Described below in: Chromium 11.5 to 14.0 Cobalt 3.0 to 11.0 Tungsten 5.0 to 7.0 Aluminum 3.6 to 4.8 Titanium 1.4 to 2.4 Tantalum 5 .6 to 7.3 molybdenum up to 2 zirconium up to 0.05 boron up to 0.05 carbon 0.01 to 0.15 and further chromium 11.8 to 13.0 cobalt 5.0 to 10.0 tungsten 5.5. 6.3 Aluminum 3.9-4.4 Titanium 1.7-2.2 Tantalum 6.4-7.0 Up to molybdenum 2 Zirconium up to 0.03 Boron 0.005-0.03 Carbon 0.02-0. The nickel superalloy according to the present invention having 10 exhibits excellent creep strength and excellent castability.

[Brief description of drawings]

1 is a thermal resonance W [relative unit] and temperature T [° C.] measured by differential analysis (DTA) of alloy C according to the invention.
It is a graph which shows the correlation with.

FIG. 2 is a graph corresponding to FIG. 1 for Alloy I according to the prior art.

FIG. 3 is a graph prepared for alloy H according to the present invention, corresponding to FIGS. 1 and 2.

Continuation of the front page (56) References JP-A-53-35620 (JP, A) JP-A-57-2853 (JP, A) JP-A-4-56742 (JP, A) JP-A-57-210942 (JP , A) JP-B 37-18607 (JP, B1) JP-B 46-939 (JP, B1) JP-B 51-28564 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) C22C 19/05 F01D 5/28 C22F 1/10

Claims (9)

(57) [Claims] 1. Chromium 11.5-14.0 by weight,
Cobalt 3.0 to 11.0, Tungsten 5.0 to 9.
5, aluminum 3.0 to 5.0, titanium up to 3.5,
Tantalum 4.0-8.0, molybdenum up to 2, zirconium
Um up to 0.05, Boron up to 0.05, Carbon 0.01
~ 0.15 and balance nickel and tantalum
At least the titanium content expressed in wt%
Precipitation hardenable nickel, characterized by being 1.5 times
Super alloy. 2. A titanium content of at least 0.8% by weight.
The alloy according to claim 1, characterized in that 3. Alloy according to claim 1 or 2, characterized in that the content of tantalum is at most 10 times the content of titanium expressed in% by weight. 4. Chromium 11.5-14.0, by weight,
Cobalt 3.0 to 11.0, tungsten 7.5 to 9.
5, aluminum 3.1-4.0, titanium 2.2-3.
3, tantalum 4.4 to 5.8, molybdenum up to 2, zircon
Conium up to 0.05, boron up to 0.05, carbon 0.
A nickel content of 0.1 to 0.15 and the balance nickel.
Alloy described in. 5. Chromium 11.8 to 12.5, in weight%,
Cobalt 5.0-10.0, Tungsten 8.5-9.
5, aluminum 3.3 to 3.7, titanium 2.7 to 3.
2, tantalum 4.8-4.3, molybdenum up to 2, zircon
Conium up to 0.03, boron 0.005-0.03,
Consists of 0.02-0.10 carbon and the balance nickel
The alloy according to claim 4 . 6. Chromium 11.5-14.0, by weight,
Cobalt 3.0 to 11.0, tungsten 5.0 to 7.
0, aluminum 3.6 to 4.8, titanium 1.4 to 2.
4, tantalum 5.6 to 7.3, molybdenum up to 2, zircon
Conium up to 0.05, boron up to 0.05, carbon 0.
6. A nickel alloy containing 0 to 0.15 and the balance nickel.
Alloy described in . 7. By weight% chromium 11.8-13.0,
Cobalt 5.0-10.0, tungsten 5.5-6.
3, aluminum 3.9-4.4, titanium 1.7-2.
2, tantalum 6.4 to 7.0, molybdenum up to 2, zirconium
Conium up to 0.03, boron 0.005-0.03,
Consists of 0.02-0.10 carbon and the balance nickel
The alloy according to claim 6 . 8. An alloy obtained by precipitation hardening, γ-
8. A structure comprising a matrix lattice and .gamma .'- precipitates contained therein, the precipitates being dissolved in the matrix by solution treatment before precipitation hardening. Alloys with any of: 9. A precipitation hardenable nickel superalloy for a rotating blade of a gas turbine, which is made of the alloy according to any one of claims 1 to 8.