US2575915A - Nickel base high-temperature alloy - Google Patents

Description

Patented Nov. 20, i951 Albert G. Guy, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York No Drawing. Application May 21, 1945, Serial No. 595,081

2 Claims.

The present invention is a nickel base alloy which is particularly adapted for use at elevated temperatures such as encountered in the operation of gas turbines and the like.

It is one of the object of the present invention to provide an alloy which is oxidation resistant and which has high rupture strength at temperatures in the neighborhood of 1500 F. Other objects will appear hereinafter.

Heretofore nickel base alloys having considerable oxidation resistance have been available although the high temperature strength of such alloys generally has not been as satisfactory as that of similar cobalt base alloys. On the other hand, while cobalt base alloys have desirable high temperature characteristics the high cost of cobalt makes such alloys unavoidably expensive. Although iron base alloys also have been available and are desirable from a cost standpoint such alloys generally are incapable of meeting present day requirements for oxidation resistance and strength.

The alloy fabricated in accordance with the present invention has desirable properties in the as-cast condition and does not require any heat treatment. The alloy generally contains about to 20% chromium, about 5 to molybdenum and about 4% to 6% aluminum with the remainder substantially all nickel. However, in addition to the above elements I may include in the alloy about 2% columbium and about 0.5% boron. Manganese and silicon each in quantities up to about 0.5% may be present in the alloy due to their use as deoxidizing agents in the alloy. The alloy also may contain as impurities a small amount of carbon for example about 0.1% and up to about 4.5% iron. These elements are usually present in the essential elements employed in the fabrication of the alloy and it is very difiicult to remove them completely.

A typical alloy composition may contain 5 to chromium, 5 to 15% molybdenum, about 6% aluminum, about 2% columbium, about 0.5% boron, 4.5% iron, 0.5% silicon, 0.5% manganese and 0.1% carbon with the balance nickel. In general, I prefer to employ a composition containing about 12% chromium, about 5% molybdenum, about 6% aluminum, about 2% columbium, and about 0.5% boron with the balance substantially all nickel.

While good results may be obtained when the alloy composition does not include columbium and boron, improved results are obtained when both elements are present in the alloy. For example, if both columbium and boron are omitted, it is possible to obtain a hundred hour rupture strength of about 30,000 pounds per square inch at a temperature of 1500 F. If the usual quantity of boron is present in the alloy and columbium omitted the one-hundred hour rupture strength at 1500 F. is about 40,000 pounds per square inch. However, if both columbium and boron are present in the alloy the one-hundred hour rupture strength at 1500" F. may vary from about 45,000 to 50,000 pounds per square inch. My preferred alloy composition, as indicated above, has a hundred hour rupture strength of 50,000 pounds per square inch and an elongation of 5% in 2" at 1500 F. If desired, I may substitute up to about 20% cobalt for a corresponding portion of the nickel content in the alloy. The use of cobalt in the quantity indicated improves the ductility of the alloy without any sacrifice of its rupture strength. I prefer to employ an aluminum content of 6% in the alloy and to maintain a definite relation between the chromium and molybdenum content of the alloy. For example, with a molybdenum content of about 5% I find that the optimum properties in the alloy are obtained with a chromium content of 12%. With a molybdenum content of about 10% I find that the optimum chromium content of the alloy is about 6%.

In addition to having high oxidation resistance and a high rupture strength my improved alloy also has a low creep rate. For example, under a stress of 35,000 to 40,000 pounds per square inch and at a temperature of about 1500 F. the elongation of the alloy in 2" in one hundred hours was about 1.3%. i

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A cast heat-resistant alloy havin a high rupture strength at elevated temperatures in the as-cast condition and essentially consisting of 5 to 20% chromium, 5 to 15% molybdenum, 4.5 to 6% aluminum, about 2% columbium, about 0.5% boron, and about 0.1% carbon, the remainder, except for minor impurities, being metal from the group consisting of cobalt and nickel, the cobalt content of the alloy being not greater than 20%.

'2. A cast heat-resistant alloy having a high rupture strength at elevated temperatures in the as-cast condition and essentially consisting of 5 to 10% chromium, 5 to 10% molybdenum, 6% aluminum, 2% columbium, 0.5% boron, 0.1% carbon, remainder nickel except for minor impurities.

ALBERT G. GUY.

' file of this patent:

:UNITED STATES PATENTS Number Number nb r 7 Name Date Chevenard Apr. 1, 1924 Wissler Feb. 11, 1936 Pilling et a1. Dec. 14, 1937 Becket et a1. Jan. 24, 1939 Rohn et a1 June 17, 1941 Cooper Feb. 2'7, 1945 Scott et a1 July 2, 1946 Parker July 16, 1946 FOREIGN PATENTS Country Date Great Britain 4 "Mar. 5, 1928

Claims (1)

1. A CAST HEAT-RESISTANT ALLOY HAVING A HIGH RUPTURE STRENGTH AT ELEVATED TEMPERATURES IN THE AS-CAST CONDITION AND ESSENTIALL CONSISTING OF 5 TO 20% CHROMIUM, 5 TO 15% MOLYBDENUM, 4.5 TO 6% ALUMINUM, ABOUT 2% COLUMBIUM, ABOUT 0.5% BORON, AND ABOUT 0.1% CARBON, THE REMAINDER, EXCEPT FOR MINOR IMPURITIES, BEING METAL FROM THE GROUP CONSISTING OF COBALT AND NICKEL, THE COBALT CONTENT OF THE ALLOY BEING NOT GREATER THAN 20%.