Synthesis of Ti–Fe intermetallic compounds from elemental powders mixtures

Abstract

Introduction. Intermetallic compounds Fe2Ti and FeTi are of practical application as hydrogen accumulators (FeTi) or as magnetic materials (Fe2Ti). Due to the peculiarities of the double equilibrium diagram, the production of these intermetallic compounds by casting is difficult. Therefore, powder metallurgy methods are widely used combined with preliminary mechanical activation of the powder mixtures. The aim of the work is to investigate the possibility of obtaining single-phase compounds from powder mixtures of titanium and iron of target compositions. Research methods. Mechanically activated powder mixtures, products of combustion and subsequent annealing were studied by X-ray phase analysis, optical metallography, and scanning electron microscopy using elemental composition determination by energy-dispersive X-ray spectroscopy. Research methodology. Powder mixtures were mechanically activated for 20 minutes in an Activator 2S planetary ball mill with an intensity of 40 g and a ball/mixture ratio of 20. The mechanically activated mixtures were heated in a sealed reactor in argon media at an average rate of 85 C°/min. Results and discussion. At a temperature of about 500 °C, thermographs of thermocouples placed in a mechanically activated mixture showed a sharp rise (thermal explosion), indicating an exothermic reaction in the mixture. The rise for the 2Fe + Ti composition turned out to be more pronounced than that for the Fe + Ti composition. X-ray diffraction analysis showed that the main reaction product is the Fe2Ti compound for both mixtures. The predominant formation of Fe2Ti is explained by the greater negative enthalpy of Fe2Ti formation of compared to FeTi (−87.45 and −40.58 kcal/mol, respectively). Conclusion. High-temperature annealing of thermal explosion products did not make it possible to obtain single-phase target products. The content of secondary phases and unreacted reagents changed little after annealing. Based on the obtained results, it was concluded that the thermodynamic factor (the enthalpy of formation of the intermetallic compound) is the main one that determines the phase composition of the synthesis products in powder mixtures of titanium and iron.