Application of Differential Thermal Calorimetry to Measurements of Stored-Energy Release in Metals

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Abstract
A differential calorimeter operating by the method of quantitative differential thermal analysis was developed to study stored‐energy release spectra in metals. The method involves the heating of a test specimen and a fully annealed reference specimen by heat transfer from a uniformly heated calorimeter block programmed to a reproducible increase in temperature with time. The initial stored‐energy release run is followed by a base‐line run under identical conditions to compensate for differences in thermal coupling of the specimens to the block. The most stable conditions of thermal coupling have been obtained by the use of cells to contain the specimens and by continuous purification of the helium used as a thermal‐exchange gas. Calibration experiments on the heat of fusion of lead were carried out to evaluate the thermal coupling between specimens and to confirm the calorimetric technique. Typical results for high purity copper deformed in compression are given to demonstrate the existence of an appreciable grain‐size effect on the stored‐energy release; the precision is approximately ±0.4 cal/g‐atom for total stored energies of the order of 5 cal/g‐atom.

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