Torpakov A. Electric discharge dispersion and synthesis of high modulus fillers for obtainment of wear-resistant metal-matrix composites

The thesis is devoted to investigation of the regularities of phase- and structure formation of high modulus fillers during high voltage electric discharge treatment of Fe, Ti, Al powders and their mixtures in kerosene as well as to the obtainment of metal-matrix composites with increased mechanical and performance characteristics. Performed experimental and theoretical studies allowed selection and justification of regimes of powders high voltage electric discharge treatment and the development of physical and technological basics of controlling the process of dispersion and synthesis of high modulus fillers, aimed at the creation of multifunctional metal-matrix composites. Parameters of high voltage electric discharge treatment for obtainment of highly disperse (35 % of particles have size from 10 to 600 nm) homogeneous powder mixtures for metal-matrix composites and for carbidization of Ti powder (up to 98 %) are found. In order to achieve this, high voltage electric discharge treatment has to be performed with the current rise rate (di/dt) from 16 to 29 GA/s, current density in discharge channel (jk) from 0.6 to 0.8 kА/mm2, and the specific treatment energy (Ws) must be in range from 25 to 40 MJ/kg. In the work it is found out for the first time, that high voltage electric discharge preparation of powders with their subsequent spark-plasma sintering allows obtainment of metal-matrix composites of Fe – Ti – C system with Vickers hardness up to 14.7 GPa and metal-matrix composites of Al–Ti–C system with Vickers hardness up to 8.3 GPa. Specimens of Ti–TiC and Al–Ti–C after HVED treatment and SPS were used at gas turbine research and development complex “Zorya” – “Mashproekt” for the modification of the structure of SM88U heat-resistant alloy in quantity of 0.01 %. This allowed decreasing of grain size in alloy specimens from 1…2 mm to 0.2…0.3 mm. Long-time strength of modified alloy at the stress of 280 MPa and the temperature of 900 ˚С have increased by 10…15 %, tensile strength at the temperature of 600 ˚С was 110…113 MPa and tensile strength at the temperature of 900 ˚С was 65…69 MPa.