DE2043053A1 - Superalloys contain separated, layered, densely packed phases - Google Patents

Description

UIiITED AIRCRAFT CORPORATION, East Hartford, Connecticut 06108 (United States of North America)

Superalloys containing precipitated, layered, densely packed phases M

This invention relates generally to nickel and cobalt superalloys, in particular those essential application possibilities in gas turbine construction.

Superalloys are generally understood to be those alloys which develop high resistance forces at the temperatures generated in gas turbines. These alloys typically contain a solid solution of hard nickel or cobalt-rich base material with a precipitated carbide phase to strengthen the core boundary. The harder nickel alloys usually contain additional precipitates such as the intermetallic compound represented by the normal Ni, (Al, Ti), usually referred to as the " ή phase". This "v 'phase" can consist of a fine, evenly distributed, strong excretion or a globular, kidney-shaped structure, which was created by a solid phase reaction. Due to its size and distribution, the aforementioned type of γ precipitation is generally the most effective for increasing the strength of alloys.

The determination of the strength of nickel superalloys gave consists of three different mechanical processes:

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1) solid solution to harden; 2) carbide precipitation and 3) y Phase elimination.

The solid solution for hardening the alloy is created by adding refractory material with a very high melting point, such as 3. Tungsten, molybdenum, tantalum, niobium and chromium. These hardness generators are originally found in the matrix of the alloys examined. The carbide precipitation takes place by adding carbide-generating elements and carbon, these additions May contain alloy components, which also contribute to solid solution hardening.

The addition of titanium, zirconium and hafnium promotes carbide formation. The γ phase is eliminated by adding those elements which develop this phase. These are mainly aluminum and titanium, although limited amounts of other elements are often found in this phase by chemical analysis.

In addition to the carbide and a ^c phases of the various superalloys, it is also possible in some cases even excretions to gain further phases. One of these further phases is the one which is referred to as a topologically or layered close-packed phase, ie phase (TCP). The phase named sigma is a particularly well known precipitate of this general type of phase and many commercially available superalloys are specially labeled to avoid the formation of sigma. A reduction in physical properties usually occurs with the elimination of Sigma and therefore the material specifications for superalloys often contain control standards to avoid formulations which result in the elimination of these unpleasant phases.

The undesirability of the TCP phases results from the fact that they typically form lamellae or needles, which are considered natural The result is mechanical weakness and also fights against the base material with the strengthening elements. A detailed one The publication contains a discussion of the Sigma-Phnse by E.C. Hall et al in "The Institute for Metals" Volume 11 (1961) page 61.

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In to develop-

Thus, it is now advantageous superalloy formulas no, which, adapted to the above technical explanations, result in additional consolidation, or other useful property improvements by utilizing copious amounts of dispersed TCP precipitations of an essentially rectified phase structure.

The present invention relates generally to superalloys in the nickel and cobalt range, characterized by a fine one Scattering of the layered, densely packed phases, such as Sigma, in a rectified phase structure, as well as compositions and Process for obtaining such superalloys.

The possibility of retiring the TCP phases of a given binding depends on a number of factors. In a special * nickel 1-3 super alloy (of, by weight, 15% chromium, 15% cobalt, 4.4% molybdenum, 3-4% titanium, 4.3% aluminum, 0.02% boron, 0.07% carbon, remainder nickel) was previously determined that 4.66 (atomic% Cr + atomic% Mo) + I.71 (atomic % Co) + 0.61 (atomic% remaining Ni) - as applied for the remaining matrix - are used to determine the initial value of the sigma phase precipitation can.

In this way, and although the weight% of the alloy constituents are very carefully controlled, one must also take into account the control of the mutual interaction of the constituents. In those alloys which were intended to avoid sigma-phase M precipitation, which is harmful during the working process, the numerical value of the above formula remains below 2.32.

The TCP phases are intermediate phases without a precise quantitative ratio. In general, the formation of such phases in the nickel super alloys is ensured by the procurement of sufficient components, in particular those transition elements which contain chromium, cobalt and molybdenum and which actively participate in the formation of the TCP phases. At the same time, the depletion of the nickel bases will increase the tendency towards the formation of TCP phases. This is done in a suitable way by enriching the alloy with aluminum or titanium, which generate more nickel reinforcement in the - <■ phase and thereby the basic mass of ^J 109817/1205

Let the nickel take off. It was also found that adding of silicon in the super-alloys the formation of the TCP phases promotes. The cobalt superalloys contain tungsten, tantalum, Chromium and molybdenum are particularly effective in forming the TCP phase precipitations.

When using this invention ula. in gas turbine construction the nickel superalloys in general, by weight, 10-25% Chromium, 10-25% cobalt, 0-7% molybdenum, 2-5% titanium, 1.5-6% aluminum, 0.01-0.1% carbon and 0.005-0.02% boron. The determination of the amount of the individual alloy components of the above series takes place together with those of the other ingredients, so that the Elimination of sufficient quantities of TCP phases is encouraged.

It is not enough to just pay attention to how the alloy stocks come together in such a way to cause the separation of the TCP phase Achieve: The metallurgical properties of the alloy must also allow that the precipitation does not occur in the usual disadvantageous, a needle-like structure takes place, but in a rectified phase structure.

The thermo-mechanical process preferred for nickel superalloys includes: 1) heating the alloy to dissolve the precipitates; 2) Refinement of the alloy to a separation of the -f phase of at least 25% by volume in a homogeneous distribution, their effective interparticle spacing is not 5 microns exceeds, at a high enough temperature to avoid a substantial retirement of the TCP phases; 3) poor machining of the alloy to achieve a reduction in the area of at least 15% i while preserving mainly the same Volume% and distribution of the finishing process, V · phase usually set at the refining temperature: A-) Heat treatment of the alloy to achieve the TCP phase precipitation in a thermally and mechanically stable order of microcrystalline defects.

Sb, the TCP phases do not only have to be excreted in abundant quantities be in order to produce effective strength or softening, but it would have to eliminate these phases with Preferably take place within a range of temperatures in which

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rather the f phase is stable without any of the TCP phases in elimination. This is achieved by a Pormelierung principle in which the ■ $ ■ solution temperature of the alloy is above, preferably significantly above the precipitation temperature of the TCP Fhasen.

In any case, the precipitation process in the nickel superalloy process must be such that the excretion of the

- $ Fhase, if not before, yet more rapidly than that of the TCP phase occurs, v / eil the f-phase morphology and-distribution, the method according serves as a control factor to achieve the desired TCP-phase morphology. Based on a basic weight of 16.5% chromium, 16.5% cobalt, 5 · 2% molybdenum, 5.0% aluminum, 4.6% titanium, 0.005% boron, 0.025% carbon, otherwise nickel, a high γ solution temperature should arise which gives a high content of aluminum plus titanium in the alloy, of about 9%. It is usually recommended to keep the component from aluminum to titanium equally close to the unit.

example

Two bars were chemically examined as follows: CrTiMoCoAlB Zr C Ni BarA 16.5 4.6 5-2 16.5 5-0 .005 .001 .025 remainder BarB 16.5 4.6 5.2 16.5 5 · 1 .ΟΟ5 .001 .025 remainder

The alloys consisted of arcs that were melted under the action of a vacuum, formed like electrodes and consequently combustible, which were melted under vacuum into two bars, each one inch in diameter. The bars were ^{annealed to 1177 °} C. for 4 hours and quickly air-cooled. Ingot A was then heated again for 4 hours at 1080 ° C. to precipitate the Jf phase and it was brought to 60% reduction in volume at 1080 ° C., ie with 6% reduction per 10 minutes of heating. Ingot B received the precipitation heat at 1024 ^° C., but without any change in shape and it was used as a standard. Ingot A received final heat exposure of 4 and 24 hours at temperatures of 1024 ⁰ C - 649 ⁰ C.

The hardness of the heat worked material was significant higher than that of the conventional nickel super alloy

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struggles. Hardness values of Rc 50 were obtained after finishing at temperatures reached below 92? ° C. The hardness serves as a comparison of highly heated alloy of the Udimet trademark 7OO approximately Rc is 39. In addition, the compressive strength of pre-processed samples was significantly higher than that of conventional ones Superalloys. The extensibility was at room temperature of the most processed pattern is higher than that of sheet steel, although the yield strength is around 7030 kg / cm was lower.

As yet, at 539 ⁰ C, the strength was reduced from äusserr.t steel sheet, the hot processed alloy with the TCP phases lost very little of Uiederstandskraft. In this way it was clearly proven that not only the harmful effects of lamellar Sir-iaa precipitation in the superalloys are reduced, but that significant property improvements are also achieved by using the TCP phase precipitation in a substantially unidirectional phase structure.

Here are some examples of additional compositions Obtain copious amounts of TCP precipitates and which are drawn into the process by thermomechanical means, to generate the rectified TCP phase structure:

description
Alloy 1

Alloy 2
Alloy 3
Alloy 4
Alloy 5
6th

Alloy 7

Composition; (in weight%)

10% Cr, 15% Co, 4.0% Ti, 6% Al, 6.0% W, 4.0% Ta, "

3.0% Mo, 1.0% Cb, 0.1% C, 0.015% B, 0.05% Zr, remainder

Ni.

12% Cr, 15% Co, 5.5% Ti, 5.5% Al, 2.04% Mo, 3.0% Ta

2.0% Cb, o.l% C, O.ol5% B, 0.08% Zr, balance Ni.

20% Cr, 20% Co, 3 «5% Ti, 3 · 5% Al ₁ 3.5% Mo, 1.5% Cb,

0.05% C, 0.015% B, 0.08% Zr, balance Ni.

20% Cr, 10% Co, 2.0% Ti, 1.5% Al, 3-5% Mo, 7-0% Cb,

2.0% W. 20% Fe, o.005% B, 0.05% C, balance Ni.

16.5% Cr, 16.5% Co, 4.5% Al, 4.6% Ti, 0.5% Si, 5.2% Mo, 0.025% C, 0.005% B, balance Ni. 16.5% Cr, 16.5% Co, 5% Al, 4.6% Ti, 6.5% Mo, 0.005% B, remainder Ni.

25% Gr, 10% W, 10% Mi, 7.5% Ta, 5% Fe, 0.6% C, 0.01% B, 0.01% Zr, balance Co.

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Name Zusrmreensetzunp; (in % by weight) Alloy 8 25% Cr, 10% Ni, 15% W ₁ 1.5% Mn, 0.5% Si, 0.08% C,

Rest Co.

As can be seen from the above examples, the formulations of the nickel superalloys, which are particularly sensitive to improvement of strength and hardness through utilization of the TCP phase precipitation, contain in general, in weights: 10-25% Chrcn for resistance to oxidation, 10-25 _a % Cobalt, 0-7% molybdenum, 15-7% aluminum., 0.01-5% carbon and O.OO3-0.02% boron.

These alloys can include various other refractory metals can be added, such as tungsten, niobium or tantalum to increase strength and silicon to promote TCP phase precipitation. With this basic formulation, there are a number of those alloys that meet the main requirement for TCP phase strengthening, namely a plentiful amount of TCP phase precipitates, thermomechanically accessible to the process, so that these Phase corresponds to a substantially rectified phase structure.

The cobalt superalloy systems generally have a higher level Chromium content. With 20-30% chromium, 5-20% nickel, 10-20% tungsten or molybdenum, C-15% tantalum, 0.25-1% silicon and 0.05-1% carbon they effect copious amounts of the TCP phases and so are likely to that correspond to existing methods of increasing strength.

The above are particularly in the area of nickel alloys Formulations, in connection with the strengthening and hardening effect of the sigma in the same direction, are fundamental Significance for the gas turbine engine industry. Since the TCP phases Precipitation is usually associated with higher aluminum and titanium content than conventional superalloys, Low alloy densities result.

Although the present invention has been described in detail with reference to specific examples for better understanding, It does not limit itself, in further view, to the specified particular details and it is here with unmistakable ones Variants to be calculated

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Claims (8)

PATIiNTANSPRUEGH E; 1) Alloy with high strength and hardness at high temperature, made from an alloy of nickel and cobalt superalloys, characterized by the uniformly distributed content of a layered close-packed phase in one essential rectified phase structure. 2) Nickel superalloy according to claim 1) characterized by high strength and hardness at high temperature, mainly Consists of a nickel alloy matrix with a high melting point, a uniformly distributed ■ ** phase, as well as a distributed, layered, densely packed phase substantial rectified phase structure. 3) Object according to claim 2), characterized by a Alloy whose microstructure is a polygonal substructure, consisting of dislocations to form a regular arrangement of To give mistakes. 4) Object according to claim 2), characterized in that the alloy microstructure is random, non-oriented Has dislocation distribution. 5) Material according to claim 2), characterized in that the alloy, in weight, 10-25% chromium, 10-25% cobalt, 0 -?% Molybdenum, 1.5-7% titanium, 1.5-7% aluminum, 0.01-0.05% carbon and contains 0.003-0.02% boron. 6) Material according to claim 5) ι characterized in that the alloy by weight, 16-17% chromium, 16-18% cobalt, 5-6% molybdenum, 4-5% titanium, 4.5-5.5% aluminum, 0.01-0.08% carbon and contains 0.004-0.01% boron. 7) cobalt superalloy according to claim l), characterized due to high strength and hardness at high temperature, containing mainly 20-30% chromium, 5-20% nickel, 10-20% tungsten or molybdenum, 0-15% tantalum, 0-1% silicon and 0.05-1% carbon, with the excretion of a scattered, stratified 109817/1205 close-packed phase in a substantially rectified phase structure. 8) Material according to claim 7j characterized by the content of the following alloy components, in weights:
23-27% chromium, 8-12% nickel, 15-17% tungsten, molybdenum or tantalum, 25-0.75%, silicon, 0.05-0.1% carbon and 1-2% manganese. 109817/1205