Effect of Heating Rate on the Formation of Intermetallics during SHS Process

Abstract

Self-propagating high-temperature synthesis is a simple and ecient method for the synthesis of various compounds including ceramics and intermetallics. In this process, the compressed mixture of elemental or master alloy powders is ignited or heated to initiate the exothermic reactions leading to the formation of desired compounds. In order to control the process eciently, the eect of several important parameters has to be determined in each applied alloy system. Previous results showed that those parameters are: initiation temperature, process duration, pressure used for compression and heating rate. This paper is devoted to the description and explanation of the eect of the heating rate on the formation of intermetallics during self-propagating high-temperature synthesis in FeAl and NiTi systems. Dierential thermal analysis of compressed powder mixtures under various heating conditions and microstructure observation of samples prepared by various heating rates using electric resistance heating and spark plasma sintering were carried out. The eect of heating rates on the formations of intermetallics in studied systems is discussed in this paper.

Formation of Ti-Al Phases during SHS Process

“…These results are totally different from tabulated values [3]. However, it can be seen that with increasing rates the peak area is larger hence enthalpies, maxima of exothermic reaction, T onset , T offset are moved to higher temperatures which was proved in study [5] and proceeding reactions are more distinct.…”

“…There are four exothermic peaks and the strongest peak appears at 1048 • C which is lower than the adiabatic temperature [3]. Reaction is initiated already at 823 • C and heating curve has the same trend as in the case of heating of Ni-Ti mixture in study [5]. Microstructures of the products are shown in Fig.…”

“…Subsequently, SHS reaction was performed at two various heating rates in electric resistance furnace which were previously applied for synthesis of intermetallics -20 and 300 • C/min [5]. This furnace enables to apply the highest heating rate in sintering of intermetallics.…”

“…Moreover, it was revealed that heating rate has significant effect on the synthesis of intermetallics, initiation and peak temperatures, and also on the amount of unreacted particles and the porosity [3,5]. In paper [6], it was revealed that intermetallic formation was shifted to higher temperatures with increasing heating rate in Fe-Al system.…”