GB2112812A

GB2112812A - High strength corrosion resistant nickel base single crystal article

Info

Publication number: GB2112812A
Application number: GB08236691A
Authority: GB
Inventors: David Noel Duhl; Maurice Louis Gell
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1981-12-30
Filing date: 1982-12-23
Publication date: 1983-07-27
Also published as: JPS58120758A; IT1155093B; DE3248134C2; IL67502A0; FR2519033A1; IT8225044A1; IT8225044A0; GB2112812B; DE3248134A1; CA1339811C; IL67502A

Abstract

The article is formed of an alloy containing in wt % <IMAGE> Such single crystals, display elevated temperature rupture lives which are least 10x of that displayed by conventionally cast alloys of similar compositions.

Description

SPECIFICATION High Strength corrosion resistant nickel base single crystal article This invention relates to the field of high strength nickel base superalloy articles such as gas turbine components which are both resistant to corrosion and are capable of operating at high temperatures. This invention also relates to the field of single crystal superalloy articles.

Increasing demands for efficiency in gas turbine engines have resulted in demands for materials capable of withstanding more severe operating conditions. In particular, increased temperature capabilities are required for certain applications along with resistance to corrosion.

U.S. patent 3 494 709 describes the fabrication of gas turbine components in single crystal form for improved performance. U.S. patent 4 11 6 723 describes a heat treatment applicable to single crystal superalloy articles for the purpose of enhanced properties. U.S. patent 3 619 182 assigned to International Nickel Corporation, describes a moderate strength superalloy having superior corrosion resistance.

According to the present invention alloys in the composition range 9.514% Cr, 7-11% Co, 12.5% Mo, 3-6% w, 3-6% Ta, 3% Al, 3-5% Ti, 0--1% Nb balance essentially nickel are provided with improved mechanical properties through fabrication of the alloy in single crystal form.

The resultant single crystal article is then preferably heat treated. Heat treated single crystal alloys of this composition display at least a lOX improvement in rupture life in comparison to alloys of similar composition which have been conventionally solidified to produce an equiaxed polycrystalline structure.

Other features and advantages will be apparent from the specification and claims which illustrate an embodiment of the invention.

This invention had its origin in a surprising and unexpected observation. A series of commercial superalloys were evaluated in three different forms. Samples were prepared in polycrystalline (conventionally cast) form, columnar grain (directionally solidified) form, and single crystal (directionally solidified) form. The alloys tested were MAR-M200, MAR-M247, IN 939 and IN 792. The first two alloys are proprietary alloys produced under license from the Martin Metals Corporation and the latter two alloys are proprietary alloys supplied by the International Nickel Corporation. The composition of these alloys as tested is given in Table 1. Through reference to Table 1 it can be seen that the conventionally cast materials contained the grain boundary strengtheners carbon, boron, and zirconium as did all the columnar grain materials.Most of the columnar grained samples also contained additions of hafnium for improved transverse ductility. Most of the single crystal samples did not contain any of the elements carbon, boron, zirconium or hafnium.

The cast alloy samples were heat treated as described in Table 2 and the heat treatment described therein are conventional heat treatments which are typical of those which would likely be selected by one skilled in the art.

These alloy samples were creep tested under different conditions of load and temperature with the results shown in Table 3. Table 3 shows the surprising and unexpected benefits which derive from the fabrication of the modified IN 792 alloy in single crystal form. For the MAR-M200, MAR-M247 and IN 939 alloys the ratio of rupture life of the single crystal samples to the conventional cast samples averaged 4.1 X, however for the case of the IN 792, the ratio of single crystal rupture life to conventionally cast rupture life was more than 1 7 X (average of 8700C/344.75 MPa and 9800C/186.16 MPa tests). This degree of improvement is surprising and unexpected.It thus appears that the improvement (in creep rupture life) obtained by fabricating (modified) IN 792 in single crystal form is about 370% greater than the benefit one would predict based on the evidence of other superalloys. For purposes of defining the invention results, it appears that a minimum 10 X improvement in creep rupture life will be obtained.

A similar conclusion is reached when one considers the time to 1% creep. In this case, based on the two MAR M alloys, one would expect an average improvement of 5.4 X by changing the test sample macrostructure from polycrystalline to single crystal (in concert with minor composition and heat treatment changes). In fact, making this change to the modified IN 792 alloy results in an average benefit of about 1 2.6 X. Again, this is a disproportionate and unexpected improvement and not predictable from the prior knowledge in the art.

The substantial improvement in creep properties is rendered more significant because the invention composition is slightly less dense than the other alloys evaluated. Further, the notable resistance to corrosion exhibited by alloy IN 792 is fully maintained in this invention.

A heat treatment as described in U.S. 4 11 6 723 is preferred in order to obtain the maximum increase in properties. Such a heat treatment involves solutioning of the gamma prime phase and homogenization of the cast structure at a temperature above the gamma prime solvus 1 2320C for the invention composition) followed by one or more aging treatments at a lower temperature. U.S. patent 4 11 6 723 is incorporated herein by reference.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but the various changes and modifications may be made without departing from the scope of this novel concept as defined by the following claims.

Table I Alloy composition (Weight percent) Solidification Alloy mode Cr W Mo Ta Nb Al Tl Co C B Zr Hf Ni MAR-M200 CC 9 12.5 -- -- 1 5 2 10 0.15 0.015 0.05 -- Balance CG 9 12 -- -- 1 5 2 10 0.15 0.015 0.05 1.5 Balance SC 9 12 -- -- 1 5 2 -- -- -- -- -- Balance MAR-M247 CC 8.4 10 0.65 3.1 -- 5.5 1.1 10 0.15 0.015 0.06 1.4 Balance CG 8.4 10 0.6 3 -- 5.5 1 10 0.15 0.015 0.06 1.4 Balance SC 9 10.5 1 3.3 -- 5.8 1.2 -- -- -- -- -- Balance IN-939 CC 22.5 2 -- 1.4 1 1.9 3.7 19 0.15 0.01 0.010 -- Balance CG 22.5 2 -- 1.4 1 1.9 3.7 19 0.15 0.01 0.010 -- Balance SC 22.5 2 -- 1.4 1 1.9 3.7 19 -- -- -- -- Balance IN-792 CC 12.2 3.8 1.9 3.9 -- 3.5 4.1 9 0.12 0.015 0.06 0.5 Balance CG 12.2 3.8 1.9 3.9 -- 3.5 4.1 9 0.12 0.015 0.07 1.2 Balance SC 12.5 3.8 1.9 4.0 -- 3.5 4.0 9 -- -- -- -- Balance CC-Conventionally Cast ; CG-Columnar Grained ; SC-Single Crystal Table II Alloy heat treatment Solidification Alloy mode Heat treatment MAR-M200 CC 1090 C/4 hrs+871 C/32 hrs CG 1204 C/12 hrs + 1080 C/4 hrs+871 C/32 hrs SC 1301 C/4 hrs+1080 C/4 hrs +871 C/32 hrs MAR-M247 CC 1080 C/4 hrs+871 C/20 hrs CG 1232 C/2 hrs+ 982 C/5 hrs+871 C/20 hrs SC 1316 C/2 hrs+1323 C/2 hrs+982 C/5 hrs+871 C/20 hrs IN-939 CC 1160 C/4 hrs+1000 C/6 hrs+900 C/24 hrs+700 C/16 hrs CG 1160 C/4 hrs+1000 C/6 hrs+900 C/24 hrs+700 C/16 hrs SC 1232 C/4 hrs+1080 C/4 hrs+871 C/32 hrs IN-792 CC 1121 C/2 hrs+816 C/24 hrs CG 1204 C/10 hrs+1220 C/2 hrs+1080 C/4 hrs+816 C/24 hrs SC 1246 C/4 hrs+1080 C/4 hrs+871 C/32 hrs CC-Conventionaly Cast : CG-Columnar Grained ; SC-Single Crystal Table III Effect of solidification mode on creep-rupture properties Time to 1% Life Rupture Solidification Tempera- Stress 1% creep Creep ratio life Rupture Life ratio Alloy mode* ture ( C) (MPa) (hrs) SC/CC SC/CG (hrs) SC/CC SC/CG MAR-M200 CC 871 413.7 19 60 CG 49 190 SC 114 6.0 2.3 385 6.4 2.0 CC 982 220.64 11 32 CG 20 60 SC 53 4.8 2.7 171 5.3 2.9 MAR-M247 CC 982 206.85 -- 75 CG -- 122 SC -- 210 2.8 1.7 IN-939 CC 871 262.01 -- 150 CG -- 230 SC -- 260 1.7 1.1 IN-792 CC 871 344.7 17 60 CG 47 304 SC 208 12.2 4.4 1192 19.9 3.9 CC 982 186.16 7 22 CG 17 121 SC 91 13.0 5.4 334 15.2 2.8 *CC-Conventionally Cast ; CG-Columnar Grained ; SC-Single Crystal

Claims

1. A high strength nickel base superalloy article characterized in consisting essentially of 9.514% Cr7-11% Co, 1-2.5% Mo, 3-6% W,3-6% Ta,3-4% Al3-5% Ti, O-1% Nb balance essentially nickel with the sum of Al+Ti being from about 6.5 to 8%, said alloy being in the form of a single crystal and thereby exhibiting a substantially enhanced rupture life at elevated temperatures relative to similar alloys in conventionally cast form.

2. An article according to claim 1, characterized in that it has been heat treated and which exhibits a rupture life improvement of at least 10 X relative to similar articles in conventionally cast form.