Research On Reaction Synthesis Of Intragranula Particles Reinforced Aluminum Matrix Composites In Al-TiO₂-B₂O₃ System

In this study,vacuum sintering was used to prepare in-situ aluminum matrix composites treating Al-TiO₂-B₂O₃ system as raw material.Finally synthesized composite structure,which is micron-sized particle Al₂O₃ packaging nano-sized TiB₂.Through DSC,SEM,FIB,TEM,XRD and EDS means to analysis reaction mechanism,and also tested mechanical properties and wear properties.The study found that the reaction process is divided into three stages.（1）Liquid aluminum reacted with TiO₂ to generate the active Ti atoms and the relatively stable Al₂O₃ particles,then aluminum exchanged with Ti atoms along the reaction layer pore to balance.（2）B₂O₃ particles reacted with Al and reaction products were Al₂O₃ particles,active B atoms,moreover Ti and Al combined rod-shaped particles Al3Ti.（3）Ti in Al3Ti particles was replaced by activated B to form small reinforcing particles TiB₂,then Ti and B generated TiB₂.Ultimately converted to（Al₂O₃+ TiB₂）/Al system.When the enhanced volume fraction is 30%,activation energy of the second and third reaction is 255.70kJ/mol and 211.68kJ/mol,respectively.When the enhanced volume fraction is 50%,activation energy of the second and third reaction is 328.59kJ/mol and 286.03kJ/mol,Respectively.Volume fraction,milling time and holding time would influence reaction process and microstructure.The reinforced particles are composed of light Al₂O₃ and gray TiB₂ particles,and evenly dispersed in the aluminum matrix.There are parts of nano-sized Al₂O₃ packaging TiB₂.in order to form in-situ particles.The formation of in-situ particles is that instantaneous exothermic melted particles,high melting point TiB₂ firstly solidified and then Al₂O₃ particles solidified as nucleation center TiB₂.Tensile properties test was that,ball mill time is 2h and 16h,the tensile strength and elongation were 196.22MPa,6.80%and 254.79MPa.3.96%,respectively.Tensile fracture of ball mill time 2h owned uneven dimples in different sizes and small cracks.while the 16h product owned even dimples in smaller sizes.no cracks were found in the microstructure.Wear test showed that 50%system is better than 30%in abrasion resistance properties.Material abrasion loss was increased with load and sliding distance increasing.When sliding speed was less than 0.8m/s,abrasion loss is proportional to the sliding speed.When sliding rate was more than 0.8m/s.abrasion loss was decreased as sliding speed increaing.