US2698786A

US2698786A - Oxidation resistant refractory alloy

Info

Publication number: US2698786A
Application number: US226292A
Authority: US
Inventors: Lowis J Jones; Wainer Eugene
Original assignee: Thompson Products Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1951-05-14
Filing date: 1951-05-14
Publication date: 1955-01-04
Anticipated expiration: 1972-01-04

Description

OXIDATEQN RESESTANT REFRACTORY ALLOY Lewis .1. lanes and Eugene Viainer, Cleveland, Ohio, as signers to Thompson Products, Inc., Cleveland, Ohio, a corporation of Ohio No Tra ning. Application May 14, 1951,

Serial No. 226,292

*7 Claims. (61-755176) The present invention relates to an oxidation resistant refractory metal alloy, particularly suited for use in high temperature environments.

Recent developments in the field of aircraft engines, particularly in turbojet engines, have necessitated the provision of high temperature alloys which can retain their hot strength characteristics even in the presence of oxidizing and corrosive atmospheres.

One of the primary uses to which the alloys of the present invention can be put is the manufacture of turbine buckets for jet turbine engines. A turbine bucket will normally be exposed to temperatures in the range from about 1600 F. to 2000 F. in the operation of the turbine engine, and the bucket must have suflicient strength, toughness, creep resistance, and resistance to the oxidizing gases present in the turbine engine to enable the bucket to opcrate efficiently without deformation or corrosion.

In addition to turbine buckets, articles produced from the alloys of the present invention may be employed under conditions of higher temperature and lower stress than exist in a gas turbine bucket. One such application occurs in nozzle diaphragm vanes in gas turbines which must withstand very severe conditions of temperature and thermal shock but at a relatively low stress.

One metal which exhibits excellent properties of strength, toughness, and creep resistance'atelevated temperatures is molybdenum. This metal could be an extremely important raw material for jet engine manufacture, as deposits of molybdenum ores are plentiful in this country. The use of pure, metallic molybdenum, however, in high temperature oxidizing atmospheres is not feasible because the molybdenum metal oxidizes rather rapidly at temperatures even below the normal operating temperature of the gas turbine engine. At temperatures above 1,000 E, metallic molybdenum oxidizes to form the trioxide of molybdenum, and this trioxide sublirnes at a rapid rate as the temperature is increased.

We have now found that the hot strength characteristics of molybdenum can be retained while at the same time increasing the oxidation resistance of the metal by alloying the metal with nickel and aluminum. The alloys of the present invention are refractory base alloys,

that is, they contain at least 50% by weight of molybdenum.

An object of the present invention is to provide a refractory metal alloy having good hot strength characteristics even in the presence of oxidizing and corrosive atmospheres.

Another object of the present invention is to provide a molybdenum base alloy suitable for the manufacture of articles normally employed under conditions of high temperature and high stress.

Another object of the present invention is to provide a molybdenum base alloy whose forgeability characteristics can be varied by variation of its composition.

Still another object of the present invention is to provide molybdenum base alloys containing nickel and aluminum as primary components.

In general, the molybdenum alloys of the present invention contain nickel in amounts up to 25% by weight, and aluminum in amounts up to by weight, the weight ratio between the nickel and aluminum contents in the alloy preferably being between values of 6 to 1 and to 1.

We have also found that the oxidation resistance of such molybdenum base alloys can be increased by the addition of substantial amounts of chromium. The increase in oxidation resistance, however, through the addition of States Patent 50 2,698,786 P tented lent b,

chromium, decreases the forgeability of the alloy. 0nsequently, Where the alloymust be subjected to a subsequent forging operation, the chromium content is pref: erably held to a minimum, or completely eliminated. (in the other hand, substantial amounts of chromium, up to. 25 by weight can be included in the alloys where the forgeability of the alloy is unimportant. This is the case where the articles are fabricated from the alloy by powder metallurgy techniques.

In addition to the above components, the alloys of the present invention may contain minor percentages of ele: ments which stabilize and strengthen the alloy. Such elements include cobalt, manganese, silicon, titantium, zirconium, and boron. In the alloys of the present inven: tion, the total addition of such elements should not ex-, ceed about 3% by weight of the alloy.

The alloys of the present invention fall within the following ranges of composition, excepting the possible a'ddi, tion of minor amounts of stabilizing and strengthening 20 elements:

Table I Ni 8-25 by weight. Al l-5% by weight. 9 Cr -7--- og- Balance (et e. $t5Q%)- When relatively small amounts of chromium are added the nickel content should be comparatively high. The following table illustrates ranges for contents of the 0 various elements where relatively small amounts of chro:

miuin are used:

Table II Ni 10-25% by weight. Al 15% by weight. Cr 4-5% by weight. Mo Balance.

As larger amounts of chromium are added, to increase the oxidation resistance of the alloy, the average nickel 40 content is decreased from the range shown in the previous table, as illustrated in the following .table:'

Table Ill Ni 818% by weight. Al 1-3% by weight. Cr 20-25% by weight.

Mo Balance.

Where forgeability is an important consideration, the chromium content of the alloy is held to a minimum, or eliminated altogether. One specific alloy composition which has good oxidation resistance, while still having a fair degree of forgeability is the following:

Table IV Ni 17.3% by weight. ",5 Al 2.7% by weight.

Mo Balance.

Other typical alloys within the scope of the present invention, containing varying amounts of chromium and nickel are tabulated below:

Table V Ni 15 20 10 A1 2 3 1 3 2 20 Balance Balance Balance As previously mentioned, the alloys of the present invention may also contain small amounts, up to about 3%, of stabilizing and strengthening elements. For example the composition listed in Table IV can be modified by the addition of the stabilizing elements in the following The foregoing alloys are all characterized by good oxidation resistance, and good high temperature properties, while still retaining the refractory properties of the molybdenum base. One of the features of the alloys of the invention is the fact that their forgeability characteristics can be changed by the control of the chromium content, alloys of the present invention will find extensive use wherever a material having good hot strength characteristics and resistance to oxidation is required. The molybdenum alloys of the present invention can be used at temperatures far exceeding those of which molybdenum itself can be effectively utilized.

It will be appreciated that various modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

We claim as our invention:

1. An oxidation resistant alloy having the following composition:

Ni 8-25% by weight. Al 1-5% by weight. Cr 0-25% by weight. Mo Balance (at least 50%).

Ni 10-25% by weight. Al 1-5% by weight. Cr 4-5% by weight. Mo Balance.

the Mo, Ni, Al and Cr contents totalling at least 97% by weight of said alloy.

3. An oxidation resistant molybdenum base alloy having the following composition:

N 53-18% by weight. Al 13% by weight. Cr 20-25% by weight. Mo Balance.

the Mo, Ni, Al and Cr contents totalling at least 97% by weight of said alloy.

4. An oxidation resistant molybdenum base alloy having the following composition:

N 17.3% by weight.

4 A 2.7% by weight. Mo Balance.

5. An oxidation resistant alloy having the following composition:

Ni 8-25 weight per cent. Al 1-5 weight per cent. Mo Balance.

wherein the NizAl weight ratio is from 6:1 to 10:1, the Mo, Ni and Al contents totalling at least 97% by weight of said alloy.

6. An oxidation resistant alloy having the following composition:

Ni 8-18 weight per cent. Al 1-3 weight per cent. Cr 20-25 weight per cent. Mo Balance.

wherein the NizAl weight ratio is from 6:1 to 10:1, the Mo, Ni, Al and Cr contents totalling at least 97% by weight of said alloy.

7. An oxidation resistant alloy having the following composition:

OTHER REFERENCES Transactions of Amer. Soc. for Metals, vol. 43 (1951), pages 193-225.

Transactions of A. S. M. B, vol. 73 (1951), pages 723-732.

Claims

1. AN OXIDATION RESISTANT ALLOY HAVING THE FOLLOWING COMPOSITION: NI------------------------------- 8-25% BY WEIGHT. AL-------------------------1-5% BY WEIGHT. CR--------------------------0-25% BY WEIGHT. MO------------------------- BALANCE (AT LEAST 50%). THE MO, NI, AL AND CR CONTENTS TOTALLING AT LEAST 97% BY WEIGHT OF SAID ALLOY.