Alumina-boride composite powders obtained by reactive milling

This study aimed to synthesize and characterize alumina-boride powders by reactive milling to obtain composite of mixtures of high hardness phases. The experiment involved aluminothermic reactions activated by high energy milling of WO₃ , TiO₂ , or Ti , B₂O₃ or B and aluminum powder, as precursors. Aluminum is the reducing agent to obtain a mixing of alumina with titanium and tungsten borides. The reactions were of the self - propagating type, with short milling times until the ignition (between 2-15 min). The ignition time of the reactions was monitored by infrared and the reaction products were kept under additional milling time to obtain nanometric particles. The powders were characterized by X-ray diffraction and measurement of density. Specimens pressed in form of discs and sintered at 1700 °C under high vacuum were characterized by apparent density, X-ray diffraction and scanning electron microscopy. The results showed complete conversion of the reactants forming multiphase powders of the system Al₂O₃ - (WB/W₂B/WB₂/W₂B₅) - TiB₂. Depending on the synthesis reaction, the powder presented different behavior during sintering: powders that densify to approximately zero porosity and powders that do not densify, with final apparent porosity of about 30%.

high energy ball milling; ceramic high hardness, borides, composite.