Solidification paths in the iron-rich part of the Fe–Ti–B ternary system

Abstract

Iron-rich alloys in the Fe–Ti–B system are being studied for their potential as a new generation of lightened steel-matrix composites reinforced by titanium diborides. In this work, the iron-rich corner of the Fe–Ti–B ternary system was investigated at temperatures between 1150 °C and 1400 °C. For this purpose, fourteen key alloys containing up to 5 mass % Ti and B were selected on the basis of preliminary thermodynamic calculations and processed in an induction furnace by melting the starting materials at 1630 °C for 1 h. Two types of experiments were performed: (i) long-duration annealing experiments, involving a liquid phase, performed by the electromagnetic phase separation technique at temperatures between 1175 °C and 1250 °C and (ii) differential thermal analysis of samples during heating up to 1400 °C and cooling with different cooling and heating rates (2, 5 and 10 °C min−1).Samples were characterized by X-ray diffraction, scanning electron microscopy, field electron gun scanning electron microscopy and complementary chemical analysis, combining electron microprobe analysis, inductively coupled plasma and secondary ion mass spectrometry, were performed. On the basis of an analysis of the solidification paths of the fourteen alloys as well as solid/liquid equilibria investigations, a partial liquidus projection in the investigated region was proposed. Moreover, the composition and melting temperature of the γFe–TiB2–Fe2B ternary eutectic alloy are determined with good accuracy. This study is a first step towards an extended experimental work on the iron-rich corner of the Fe–Ti–B ternary system.