In situ observation of phase transformation in an Fe-Zn system at high temperatures using an image plate

A unique system has been developed for in situ observation of phase transformation at high temperatures. Changes in powder-diffraction patterns from a heated specimen can be measured continuously by scanning an image plate located behind a slit. A heating system has been designed for a sheet specimen ( approximately 5 x 6 mm) using Joule heating, and it can heat the specimen up to 1100 K at a rate of up to 160 K s(-1), where effects of thermal expansion are minimized by a mechanism releasing stress. This system was applied to Zn-coated ( approximately 8 micro m in thickness) steel. At temperatures higher than the melting point of Zn, different types of Fe-Zn intermetallics formed sequentially through rapid interdiffusion. Changes in phase and crystallographic structure were monitored with a time resolution of less than a few seconds. It has been found that an addition of a small amount of an element, such as P, into Fe changes the incubation time before the alloying reaction starts. This system has been shown to have the potential for application to in situ observation of other reactions at high temperatures.