Kinetics of the peritectic phase transformation: In-situ measurements and phase field modeling
- PDF / 447,323 Bytes
- 10 Pages / 576 x 792 pts Page_size
- 5 Downloads / 243 Views
I. INTRODUCTION
THE peritectic transition in iron-carbon alloys, where L : , is an extremely complex and challenging phase transformation to study either experimentally or mathematically. Kerr et al.[1] have defined the peritectic transition into two separate components: the peritectic reaction and the peritectic transformation. The peritectic reaction occurs under the conditions where all three phases (L, , and ) are in contact, and the liquid and delta-ferrite phases react to form austenite. This reaction is rapid, currently accepted to be controlled by diffusion of solute in liquid, so that a film of austenite quickly separates the liquid and delta-ferrite phases. From this point onward, further formation of austenite is defined as the peritectic transformation, and it is this aspect of the phase transition that is the focus of the current study. Experimental difficulties in studying the peritectic transformation are related to the elevated temperatures at which this phase transformation occurs in Fe-C alloys, and hence the difficulty in making quality in-situ observations. Therefore, experimental studies have mostly relied upon quench experiments combined with post-transformation metallography. For example, Matsuura et al.[2] used a solid/liquid diffusion couple to study the kinetics of this transformation in ironcarbon alloys. The volume fractions of liquid, austenite, and delta-ferrite phases were analyzed following quenching of the diffusion couple, and the segregation of carbon was determined using an electron probe mass analyzer. The reliance upon post transformation metallography in Fe-C alloys is hampered by subsequent austenite decomposition that masks the higher DOMINIC PHELAN, APD Fellow, MARK REID, Research Associate, and RIAN DIPPENAAR, Professor, are with the Faculty of Engineering, BHP Steel Institute, University of Wollongong, NSW, Australia. Contact e-mail: [email protected] Manuscript submitted September 5, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
temperature transformation, rendering it impossible to determine precisely the spatial history of the L/ and / interfaces. In an alternative approach, El-Bealy and Fredriksson[3] used a chill apparatus to measure heat flow as a means to benchmark their model of the peritectic reaction, but also in this case the use of techniques to measure bulk thermal response cannot separate the spatial history of the L/ and / interfaces during the peritectic transformation. Recently, an experimental technique has been developed that enables high-resolution in-situ observation at elevated temperatures of phase transitions, including the peritectic transformation. High-temperature laser-scanning confocal microscopy (HTLSCM) was developed by Emi and his colleagues and has been used to study solidification, delta-ferrite to austenite transformations, and austenite decomposition phase transformations.[4–9] Shibata et al.[9] have used the HTLSCM experimental technique to make the first reported in-situ observations of the peritectic reaction and trans
Data Loading...
