US2971838A - High temperature nickel base alloy - Google Patents

Description

United States PatentOflfice 2,971,838 Patented Feb. 14, 1931 HIGH TEMPERATURE NICKEL BASE ALLOY John C. Freche, Parma, Ohio, assignor to the United States of America as represented by the Administrator of National Aeronautics and Space Administration 'No Drawing. Filed Oct. 23, 1959, Ser. No. 848,482 4 Claims. (Cl. 75-171) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a nickel alloy capable of high load carrying capacity at temperatures'of 1800 F. and above.

In the operation of todays jet engine, it has been found that suitable turbine blades should preferably have high load carrying capacity at temperatures of 1800 F. and above in order that the thrustincreases possible through operation at higher inlet-gas temperatures may be realized. For such an application, a minimum stress rupture life of 190 hours at 15,000 p.s.i. stress, which is comparable to the blade root stresses in latter-day engine turbines, is required. Good impact resistance and good oxidation resistance are also important requirements for such an alloy. Materials currently capable of high load carrying capacity at temperatures of 1800 F. and above are ceramics, cermets, and refractory metals and their alloys. Each of these materials, however, has serious limitations for turbine blade applications; Most commercial alloys which are not subject to these limitations, such as nickel base and cobalt base alloys, do not have adequate strength at 1800 F. Only a very limited number of these alloys can be utilized under high loads at this temperature for a sufficient length of time to be considered for turbine blade application.

Several major disadvantages are found to exist in the previously used materials for high temperature, high stress applications. Ceramics, of course, are of a very brittle nature and lack heat shock and impact resistance, thus severely limiting their usefulness as turbine blade material. Cermets can be said to show a slight improvement over the ceramics but generally are subject to the similar hindrances. High melting point refractory metals can generally be said to have poor oxidation resistance at elevated temperatures. This can also be said to exist for the alloys of such high melting point refractory metals. Consequently, in order to permit their use at elevated temperatures for sufiiciently long periods of time, protective coatings are generally required for such metals or their alloys. However, the problem of providing strongly adherent coatings which give uniform coverage, as well as satisfactorily resisting errosion, is so great as to severely curtail the potential of these materials for turbine blade applications. The few commercial alloys available which can possibly be considered for high temperature turbine blade applications need closely controlled Vacuum melting techniques in order to achieve the required properues.

An object of the invention is an alloy series which demonstrates elevated temperature stress rupture properties greater than all commercial nickel or cobalt base alloys.

A further object of the invention is an alloy series with impact properties greater than all commercial alloys and most known high temperature materials.

An additional object of the invention is an alloy series which can be readily cast without the need for closely controlled vacuum techniques and still provide the desired high strength; high temperature properties.

A still further object of the invention is a nickel alloy series which has the combination of properties suitable for application to jet engine turbine blades operating at 1800 F.- without requiring protective coating to prevent oxidation and without the brittleness inherent in ceramic and cermet turbine blades.

This invention is embodied in alloys having the following intermediate composition range within the foregoing broad range:

Nickel From about 70% to about Molybdenum From about 5% to about 10%. Chromium From about 4% to about 8%. Aluminum From about 4% to about 8%. Zirconium From about 1% to about 3%.

A preferred alloy has the following composition:

Percent Nickel About 79 Molybdenum About 8 Chromium About 6 Alunnnum About 6 Zirconium About 1 Percent Nickel 77.375 Molybdenum 8 Chromium 6 Aluminum 6 Zirconium 1 Titanium 1.5 Carbon .125

The subject alloys were prepared with one of the simplest possible casting techniques. The melt was made in a refractory crucible which was placed in a high frequency induction coil. The alloy additions were made as the melting progressed in the following order: nickel, chromium, molybdenum, and aluminum. The zirconium can be picked up as a contaminant in the stabilized zircom'a crucible in the correct percentage during a 20-minute melting period. Argon gas was directed into the oven top crucible continuously during melting to provide an inert gas blanket over the melt. During pouring, which was done at 3150" F. :50 F., the inert gas coverage was removed. Melts were hand-poured into investment molds heated to 1600" F. and were permitted to come to equilibrium temperature naturally without speeding up the cooling process artifically. These alloys may also be prepared by more complex techniques such as closely controlled vacuum melting, which can result in further improvements in properties. In other instances, research has indicated that the improved cleanliness, plus the fact that the eitectiveness of such elements as titanium and aluminum is not reduced by the reaction with atmospheric gases, can also result in better strength, as well as improved ductility. Thus by introducing a higher degree of complexity in the casting process, an improved alloy is likely to result.

The novel alloys of the invention derive their strength 3 7 from the formation of a fine dispersion of aluminumnickel intermetallic compounds. The various modifications of the basic alloy compositions are further strengthened due to titanium additions wherein the formation of Ni;; (Al, Ti) inter-metallics transpires. Carbon plus titanium additions provides still further strengthening due to the formation of stable titanium carbides.

The major advantage of the invention lies in the properties of the instant alloys as demonstrated in various tests, results of which are shown and compared to exist- 10 TABLE I Nominal chemical composition in theseries never fell below 40 inch-pounds and in some instances was greater than 62.5 inch-pounds (unbreakable in a standard Izod test). Both the stress-rupture values and the impact values cited represent a considerable improvement over those values demonstrated by known commercial nickel and cobalt base alloys. Oxidation resistance of the alloy series was found to be excellent in the tests, even at temperatures of 1800" F. nd

Having thus described this invention in such full, clear, concise and exact terms as to enable any persons skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, it is stated that the subject matter which is regarded as being the invention is particularly pointed out and distinctly claimed in what is'claimed,

it being understood that equivalents or modifications of or New Alloy i 100 hr. Rupture Impact Resist- Strengths at once, in.-lb. 1,800 E, p.s.i.

New Alloy 19, 500

alloy of the invention is Inco 713 which has a 100-hour rupture strength at 1800 F. of 16,000 p.s.i. The alloy of this invention possessed a 19,500 p.s.i. rupture strength which was 3500 psi above the best strength of any of erties demonstrated by the subject alloys include a stress rupture life at 1800 F. and 15,000 psi. for'the as-cast alloys of from 19 hours for basic alloy composition to 380 hours for a preferred modification, which was the TABLE II substitutions for parts of the above specifically described embodiments of the invention may be made without departing from the scope of the invention as set forth in what is claimed.

What is claimed:

' 1. A nickel basealloy capable of high load carrying capacity at elevated temperatures consisting essentially of from'70% to 85% nickel, from 5% to 10% molybdenum from 4% to 8% chromium, from 4% to 8% aluminum, and from 1% to 3% zirconium.

2. The nickel base alloy of claim 1 additionally containing up to 2.5% titanium and up to .25 carbon, the nickel content of said alloy being adjusted to accom- 'modate the additions.

i 3. A nickel base alloy capable of high load carrying the Similar alloys Commercially available- Further P capacity at elevated temperatures consisting essentially of 79% nickel, 8% molybdenum, 6% chromium, 6%

aluminum, and 1% zirconium.

4. A nickel base alloy capable of high load carrying capacity at elevated temperatures consisting essentially of basic alloy plus 1.5% titanium and .125% carbon with nickel, 3% molybdgnumy chromium,

the nickel content being adjusted for these additives. After homogenization heat treatments, these rupture lives have been improved to 64 and 574 hours, respectively. Further indication of their remarkable strength is indicated in the various tests run on the disclosed alloys in which the impact resistance in the as-cast condition at 7 room temperature for all of the compositions considered References Cited in the file of this patent UNITED STATES PATENTS 859,608 Marsh July 9, 1907

Claims (1)

1. A NICKEL BASE ALLOY CABLE OF HIGH LOAD CARRYING CAPACITY AT ELEVATED TEMPERATURES CONSISTING ESSENTIALLY OF FROM 70% TO 85% NICKEL, FROM 5% TO 10% MOLYBDENUM FROM 4% TO 8% CHROMIUM, FROM 4% TO 8% ALUMINUM, AND FROM 1% TO 3% ZIRCONIUM.