Age hardening in Inconel 718 is investigated using Brinell hardness measurements. Formation of a precipitate causes an increase in hardness

Hensley, W. E.

Koepke, B. G.

Zeto, R. J.

English

NASA Technical Reports Server

June 1970	 Brief 70-10261 
NASA TECH BRIEF
-	 -: 
NASA Tech Briefs announce new technology derived from the U .S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
--	 - - 
Mechanism and Kinetics of Aging in Inconel 718 
Inconel 718 is a nickel-chromium-iron-molybdenum 
alloy, hardened by the addition of columbium, tan-
talum, aluminum, and titanium. It is an age-harden-
able superalloy with good high-temperature strength 
and a rather sluggish aging response. The low rate 
of precipitation hardening exhibited during aging is a 
major factor in giving this alloy good weldability. 
Its property of slow aging facilitates studies concerned 
with the precipitation process. 
Age hardening in Inconel 718 was investigated 
using Brinell hardness measurements. Aging isotherms 
were determined at temperatures of 1141°, 1252°, 
1314°, 1390°, and 1492°F. On aging at the three low-
est temperatures, the hardness increased to a maxi-
mum and then remained constant. The aging time to 
reach maximum hardness was over 1000 hr at 114 1°F, 
about 200 hr at 1252°F, and only 35 hr at 13 14°F. At 
1390° and 1492° F the hardness increased to a maxi-
mum within a few hours, then decreased. Maximum 
hardness was lower and aging time to reach maximum 
hardness was longer at 1492° F than at 1390'F. 
The formation of a precipitate, identified as colum-
bium-rich y', Ni 3
 (Cb, Al, Ti), causes an increase in 
hardness. The precipitate has a face-centered cubic 
structure, and forms coherently with the matrix during 
aging.
An aging mechanism was proposed whereby the 
observed changes in hardness below about 1340°F 
were associated with the formation and loss (by over-
aging) of the -y phase. An activation energy of 76,500 
calories per mole was determined for the growth of 'y'. 
There is an incubation period before Inconel 718 
increases in hardness. The shortest incubation period 
corresponds to the fastest nucleation rate of the co-
herent 'y' phase and occurs at approximately 1340°F. 
Notes: 
1. This information maybe of value in the formulation 
of new alloys using aging mechanisms. 
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: TSP70- 10261 
Patent status: 
No patent action is contemplated by NASA. 
Source: B. G. Koepke, R. J. Zeto, 
and W. E. Hensley of 
North American Rockwell Corporation 
under contract to 
Marshall Space Flight Center 
(MFS- 18775) 
Category 04 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19700000250 2020-03-17T00:13:47+00:00Z


Mechanism and kinetics of aging in Inconel 718

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server