THE STRUCTURIZATION AND PHASE FORMATION OF Fe–Ti–Ni–B₄C ALLOYS IN THERMAL SYNTHESIS 

Abstract

The structurization and phase composition of the composites produced by in situ thermal synthesis at 1200 °С from TiH₂–Fe–Ni–B₄C powder mixtures were studied. To assess how the mixture composition influenced the structure and properties of the synthesized alloys, five different mixture compositions were prepared. The weight content of thermally reacting titanium hydride and boron carbide components was unchanged in all mixture compositions and was 64 and 16%, and the iron and nickel contents were varied. Data from microstructural analysis and X-ray diffraction of the sintered samples were obtained, and the microhardness and particle size distribution were determined for each composition. The resultant composite alloys had a substantially heterophase structure as a basic skeleton based on titanium carbide and diboride compounds and a cementing layer consisting of intermetallics and iron and nickel solid solutions. The main alloy phase was titanium carbide, TiC_x, whose stoichiometry x varied from 0.43 to 0.54. introduction of 5% Ni into the mixture somewhat increased the stoichiometry of titanium carbide, but 10% Ni and more decreased the stoichiometry. The alloys produced from nickel-containing mixtures had a finer microstructure than the nickel-free alloy, and all composites in the Fe–Ti–Ni–B₄C system were characterized by a significantly finer structure than the boron-free Fe–Ti–Ni–C alloys. The introduction of nickel to the composition also somewhat increased the average microhardness of the synthesized composite.