US3843421A - Wrought nickel-base alloy and products thereof - Google Patents

Abstract

1. A WROUGHT NICKEL-BASE SUPERALLOY ARTICLE HAVING A NOMINAL CHENISTRY WHICH CONSISTS ESSENTIALLY OF, ABOUT BY WEIGHT, 12.4 PERCENT CHROMIUM, 18.5 PERCENT COBALT, 3.2 PERCENT MOLYBDENUM, 4.3 PERCENT TITANIUM, 5 PERCENT ALUMINUM, 0.8 PERCENT VANADIUM, 0.02 PERCENT VORON, 0.06 PERCENT ZIRCONIUM, 0.07 PERCENT CARBON, BALANCE ESSENTIALLY NICKEL, AND CHARACTERIZED BY V-NOTCH STRENGTHENING IN THE TEMPERATURE RANGE OF 1300* -1400* F.

Description

United States Patent O 3,843,421 WROUGHT NICKEL-BASE ALLOY AND PRODUCTS THEREOF Arthur R. Cox, Lake Park, Fla., Paul R. Holiday, Haverstraw, N.Y., and Gary K. Lewis, Riveria Beach, and Sven D. Soderquist, Palm Beach Gardens, Fla., assignors to United Aircraft Corporation, East Hartford, Conn. No Drawing. Filed Oct. 16, 1972, Ser. No. 298,068

Int. Cl C22c 19/00 US. Cl. 148-32 3 Claims ABSTRACT OF THE DISCLOSURE A strong nickel-base superalloy is provided which displays good high temperature mechanical properties, including notch ductility, in wrought form when formulated to a very precise composition.

This invention was made in the preformance of a contract with the Department of the Air Force.

BACKGROUND OF THE INVENTION This invention relates to the high strength nickel-base superalloy field.

In the patent to Bieber 3,061,426 there is disclosed a nickel-base alloy of the 7-7 type which has for some time been extensively used in cast form in gas turbine engine blade applications. In such form, this alloy has been typically formulated to the nominal chemistry consisting of, by weight, 9.5 percent chromium, 15 percent cobalt, 3 percent molybdenum, 4.8 percent titanium, 5.5 percent aluminum, 1 percent vanadium, 0.015 percent boron, 0.06 percent zirconium, 0.17 percent carbon, balance nickel.

As originally developed and utilized, the strength and ductility of the alloy were such that it was practically undeformable and, hence, found application only in precision cast form and found utility only in those applications, such as turbine blades, where cast properties were acceptable. With the generation of the forging process described in the patent to Moore et al. 3,519,503 means were provided whereby the alloy could, if desired, be readily forged, including forging to shapes such as engine discs as well as miscellaneous other forms such asshafts, rings and seals. Because the high temperature strength/low density characteristics are so favorable for aerospace applications, serious consideration was given to the expanded use of the alloy, particularly for engine discs. Unfortunately, the mechanical property criteria applicable to discs differ in some respects from those required in blades and, although satisfactory performance was attained with the conventional alloy in cast form as blading, it was unsatisfactory in wrought form in engine discs.

In a gas turbine engine, the blades are typically retained in fir tree notches machined in the periphery of the disc. The disc must, therefore, not display unacceptable notch sensitivity. For an acceptable disc alloy, the presence of a notch should not result in a decrease in strength at the notch, vis-a-vis the unnotched specimen of the same dimensions as the notch. Preferably, in fact, the distribution of forces and alloy characteristics should be such that notch strengthening is exhibited. Unfortunately, at the usual specification composition the notch strength of the conventional alloy was less than that of the smooth specimen, particularly in the critical 1300-1400 F. temperature range to which the periphery of the disc may become heated in operation.

Thus, although the alloy could be formed into disc form, the utility in such form was limited.

SUMMARY OF THE INVENTION The present invention is directed to a wrought nickelbase superalloy of critical composition and wrought products produced therefrom, which, upon suitable heat treatment, produces a specific volume of the strengthening 7' phase, typically Ni (Al,Ti) together with a carbide, including the M C -type carbide, which not only maintains acceptable levels of other mechanical and physical properties but also provides notch strengthening, particularly in the 13001400 F. temperature range.

The wrought alloy is provided at a nominal chemistry of, by weight, 12.4 percent chromium, 18.5 percent cobalt, 3.2 percent molybdenum, 4.3 percent titanium, 5.0 percent aluminum, 0.8 percent vanadium, 0.02 percent boron, 0.06 percent Zirconium, 0.07 percent carbon, balance essentially nickel. 1

Forged products produced to the foregoing chemistry display notch strengthening in the 1300-1400 F. temperature range with oxidation resistance to at least 1600" F. when heat treated as follows:

The fully heat treated article is characterized by a 7' volume percentage of about 50-60 percent, preferably about 56 volume percent, as compared to a more typical 70 volume percent in the usual cast alloy chemistry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As previously mentioned, the conventional alloy was developed for and used in the production of castings exhibiting high temperature strength and oxidation resist ance. The present invention contemplates wrought component applications and has been developed to produce, upo favorable heat treatment, a specific volume of intermetallic precipitates of the 'y' and M C types which provide the requisite mechanical properties, including in particular notch strengthening, in the general temperature range of 1300l400 F. This is distinct from the criteria and microstructure used for and present in the prior castings and in wrought components formulated to the same composition as such castings.

The composition, which was found to be critical in several essential respects, is as follows, by weight: 11.9- 12.9 percent chromium, 18-19 percent cobalt, 2.8-3.6 percent molybdenum, 4.1-4.5 percent titanium, 4.8-5.2 percent aluminum, 0.5-1 percent vanadium, 0.016-0.024 percent boron, 0.04-0.08 percent zirconium, 0.05-0.09 percent carbon, balance essentially nickel.

The full preferred heat treatment specified is as follows.

Property criteria minimums are typically as follows:

(a) tensile properties (fully heat treated forgings).

Room temperature 1300 F.

Tensile strength; p.s.i 220,000 170, 000 Yield strength at 0.2% offset, p.s.i 145, 000 145, 000 Elongation, percent in 4D 12 12 Reduction of area, percent 15 15 (b) hardnessBrinell 321-414.

(c) stress-rupture (combination smooth/material specimen)-forging held at 1350 F. under continuously applied axial load of 100,000 p.s.i. shall not rupture in less than 23 hours.

(d) creep rupture-with a smooth specimen at 1300" F. and continuously applied axial load of 85,000 p.s.i., time to 0.2% plastic deformation shall average not less than 150 hours with no value below 110 hours.

Table I provides a comparative distributional analysis of the present invention and the conventional composition in terms of their respective physical properties.

TABLE I.-PROPERTY DISTRIBUTION ANALYSIS RIP. tensile (k.s.i.)

Conventional composition This invention Percent Percent Percent Pereen YS UTS RA. YS UT el. 11.11.

1,300 F. tensile Conventional composition This invention Percent Percent Percent Percent YS UTS el. R. YS UTS e1. RA.

Stress rupture (smooth) (1350 F./100 k.s.i.)

Stress rupture (V -noteh) 0.2% creep (1300 F./88 Conventional (1350 F./100 k.s.i.) k.s.i.)

composition This invention Conventional This Conventional This Percent Percent composition, invention, composition, invention, Hrs. el. Hrs el. hrs. hrs. hrs. hrs.

1 Distribution appears abnormal. 9 Greater than smooth. 1 150 avg, 110 min.

From the foregoing Table, it will readily be seen that the alloy of the present invention provides the requisite notch strengthening for sensitive forged or extruded components whereas forgings made from the conventional alloy were unacceptably deficient in this regard. This factor alone is determinative of the utility of the alloy in components such as turbine engine discs. And it is only within the criticality limits of the present invention that the necessary properties have been achieved, providing an article having properties never before reproducibly attained.

In the cast alloy previously used, the 7' content has generally been about 70 volume percent or higher. The wrought alloy composition of the present invention provides a microstructure having about -60 volume percent of the strengthening '7' phase, with about 56 volume percent appearing optimum. Thus, in the composition of the present invention, the total aluminum plus titanium content of the alloy is especially critical insofar as these elements are the principal determinants of the amount of the 7 phase which is formed.

Further, in the alloy two carbide phases appear present, including a Cr C carbide distributed along grain boundaries and a TiC carbide distributed intragranularly. The Cr C carbide precipitated at the grain boundaries is the phase of importance to the present invention for it produces a region of localized plasticity which can undergo microstrain and provide the necessary delay to failures attributable to grain boundary efiects. Thus, the carbon content is especially critical in this alloy.

What is claimed is:

1. A wrought nickel-base superalloy article having a nominal chemistry which consists essentially of, about by weight, 12.4 percent chromium, 18.5 percent cobalt, 3.2 percent molybdenum, 4.3 percent titanium, 5 percent aluminum, 0.8 percent vanadium, 0.02 percent boron, 0.06 percent zirconium, 0.07 percent carbon, balance essentially nickel, and characterized by V-notch strengthening in the temperature range of 13001400 F.

2. An article according to claim 1 which is also characterized by a microstructure in the fully heat treated condition exhibiting 50-60 volume percent of a 'y' intermetallic phase.

3. An article according to claim 2 wheerin the article is a gas turbine engine component.

References Cited UNITED STATES PATENTS 3,061,426 10/1962 Bieber 75--17l 3,519,503 7/1970 Moore et a1 148-115 F 3,642,469 2/1972 Ross et a1. 75171 RICHARD O. DEAN, Primary Examiner US. Cl. X.R.

Claims (1)

1. A WROUGHT NICKEL-BASE SUPERALLOY ARTICLE HAVING A NOMINAL CHENISTRY WHICH CONSISTS ESSENTIALLY OF, ABOUT BY WEIGHT, 12.4 PERCENT CHROMIUM, 18.5 PERCENT COBALT, 3.2 PERCENT MOLYBDENUM, 4.3 PERCENT TITANIUM, 5 PERCENT ALUMINUM, 0.8 PERCENT VANADIUM, 0.02 PERCENT VORON, 0.06 PERCENT ZIRCONIUM, 0.07 PERCENT CARBON, BALANCE ESSENTIALLY NICKEL, AND CHARACTERIZED BY V-NOTCH STRENGTHENING IN THE TEMPERATURE RANGE OF 1300* -1400* F.