The Structurization and Phase Formation of Fe-Ti-Ni-B4C Alloys in Thermal Synthesis

The structurization and phase composition of the alloys produced by in situ thermal synthesis at 1200 degrees C 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 iron and nickel contents were varied and the content of thermally reacting components (titanium hydride and boron carbide) remained unchanged in all mixtures and was 64 and 16%. Microstructural and X-ray diffraction analyses were conducted for the sintered samples, 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 consisting of 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, TiCx, whose stoichiometry x varied from 0.43 to 0.54. The introduction of 5% Ni into the mixture somewhat increased the stoichiometry of titanium carbide, but 10% and higher nickel content decreased the stoichiometry. The alloys produced from nickel-containing mixtures had a finer microstructure than the nickel-free alloy did, 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.