A Study of the Metal Carbide-Carbon Peritectic Phase Transition for the Cr-C System

The authors recently reported the very first radiometric plateau observation of high-temperature fixed points of metal-carbide carbon peritectics. These act in a similar way to the metal (carbide)-carbon eutectic points in the sense that they can be used at high temperature without being contaminated by their graphite crucibles. The performance seems similar in terms of repeatability and plateau shape. The peritectic transition temperatures are close to the transition temperatures of some of the metal (carbide)-carbon eutectics. In this article, results of further study to understand the melting and freezing involved in these fixed points are reported, with the focus on the Cr3C2-C peritectic point. Difficulty in producing an ingot without voids was encouIntered. To overcome this, a filling technique that takes advantage of the capillary effect was devised. Plateau shapes and microstructures observed with electron-probe microanalysis (EPMA) and back-scattered electron imaging (BSE) for various filling methods were compared. The observation of two fixed-point plateaux, one at the Cr3C2-C peritectic point and the other at a lower temperature of the Cr7C3-Cr3C2 eutectic point, correlates to the presence of two kinds of domains in the observed microstructure. The graphite crucible is shown to play an essential role in realizing peritectic plateaux of good quality.