Research On Fabrication And Properties Of In-Situ TiB₂/Al Composite

In this papers, the TiB₂/Al composite fabricated by LSM (London Scandinavian Metallurgical) method was studied. The reaction thermodynamics of the Al- KBF₄ -K₂TiF₆ system was analyzed, and the fabrication processing of the in-situ TiB₂/Al composites was carried out though LSM technology. The effects of cooling rate, purification method and particulate deposition on the solidification microstructure have been investigated. The fluidity and thermal properties of TiB₂Al composite was analyzed based on theory, experiment is carried out in order to investigate the thermal expansion of TiB₂/Al composite. The tensile strength, friction and impact properties are experimentally test for TiB₂/Al composite.The main conclusions are:1. The reaction thermodynamics of the Al- KBF₄ - K₂TiF₆ system was analyzed. The result of thermodynamics analysis can determine processing parameters of TiB₂/Al composite. The experimental results showed that TiB₂ particulates distribute in the composite stably and homogeneously calculated by K₂TiF₆ + 2KBF₄ = TiB₂ + 4KF+ 5F₂. No phase as TiAl₃ has been found.2. The cooling rate has a markedly effect on the distribution of TiB₂ of TiB₂/Al composite. With the increasing of the cooling rate, solidification microstructures become finer, the distribution of TiB₂ particulates become more homogenous, and the agglomerated of TiB₂ particulates relieve.3. The purification method has a significant effect on the distribution of TiB₂ of TiB₂/Al composite. Flux refinement processes has no significant effect on the distribution of TiB₂ of TiB₂/Al composite and the content of TiB₂ particulates remains the same after refined. However, inert gas refinement processes has a strong effect and TiB₂ particulates has been not found.4. The deposition of TiB₂ particulate in composites has a strong effect on the solidification microstructure. With the position of molten aluminum alloy descent, the phenomena of TiB₂ Particulate coagulation become more obvious and the phenomena of TiB₂ particulate segregation become worse.5.As TiB₂ particulate content in the composites increase, the fluidity properties of TiB₂/Al composite will decrease. Composite has a good thermal conductibility. Coefficient of thermal expansion of TiB₂/Al composite is lower than that of Al matrix. Furthermore, TiB₂/Al composite has a good thermal-stability, especially in high-temperature.6.In comparison with the matrix the mechanical properties of TiB₂/Al com-posite has a great change. The ultimate tensile strength, hardness, friction performance and impact energy of TiB₂/Al composite are improved dramatically, however elongation has a slight decreases.7.Results show the fracture morphology of TiB₂/Al composite is characterized by brittle rupture.8.Heat-treatment have no obviously effects on the mechanical properties of TiB₂/Al composite.