Temperature and age effects on the temporal stability of Invar

摘要

A testing program was conducted to determine the long term temporal stability properties of sheet Invar. The tests were conducted at the University of Arizona's Optical Sciences Center over a period of 9 months. Growth measurements were made using an interferometric optical technique at both ambient and elevated temperatures. Eleven specimen types, in groups of three, were included in the test. These data were combined with published historical data to establish an estimate to the long term behavior. It was found that Invar exhibits short term behavior with a rapid initial growth rate, 8 - 12 ppm/yr and time constant on the order of 100 days plus long term exponential growth at lower growth rates, 2 - 5 ppm/yr initial (end of year 1) with a three to eight year time constant. The parameters which most significantly effect Invar growth rate were found to be: time since final heat treatment; carbon content; heat treatment; and, ambient temperature.