A Rapid Heating Device for Measurement of the Activation Energy for Transient Creep, and Some Experimental Results

Abstract

The activation energy for transient creep by a differential test has been measured as follows. The temperature of the specimen is raised to the testing temperature in advance by a furnace placed outside a vacuum vessel. The heat necessary for raising the temperature of the specimen is instantly given by applying half a cycle of a very large alternating current (1400 A) of 50 Hz to the specimen, and a small current is applied so as to keep the temperature constant. This procedure makes it possible to raise the temperature of specimens with a cross section of 2×10 mm² by about 5°C for 10 ms. The activation energy for transient creep of alpha iron obtained at 700°C shows a higher value than that for self-diffusion when the creep strain is nearly zero and decreases rapidly to a minimum value (first region). Then the value increases to a peak value (second region) and decreases again gradually to that for steady-state creep (third region) as the creep strain increases. The first and second regions are observed below the creep strain of about 3%. The phenomenon is also observed in Fe–19Cr alloy. Accordingly, it is thought that the rate controlling process of the transient creep is not such a simple one as those proposed so far but a complex one which is composed of several stages.