Research On Mechanical And Tribological Properties Of Aluminium Matrix Composites Reinforced With Hybrid SiC Microparticles And TiB₂ Nanoparticles

The hybrid reinforced aluminum matrix composites have better mechanical properties and tribological properties compared with single phase reinforced aluminum matrix composites and have a broad prospect in the application of brake friction materials.In the present paper,aluminum matrix composites reinforced with hybrid micron SiC particles and nano TiB₂ particles were fabricated by powder metallurgy method and hot extrusion.The microstructures and interfacial bonding conditions of the composites were analyzed by SEM and TEM.The tensile properties were tested by tensile experiments.The friction and wear tests of the composites under different load and speed were investigated by pin-on-disk friction test.The wear surfaces were analyzed to determine the wear mechanism of the materials under different conditions.The conclusions are drawn as following:1.Both SiC microparticles and TiB₂ nanoparticles were relatively uniformly distributed after ultrasonic dispersion and ball milling.To the 10%SiC/Al-7Si,the relative density of the cold pressed perform after pre-sintering is 90.07%.Hot extrusion can further increase the composite density up to 95.24%,and can also improve the dispersion of particles.Futhermore,hot extrusion can facilitate the grain structural refinement,while no interface reaction occurred between matrix and reinforcement particles,a good metallurgical bonding the Al matrix and SiC particle were achieved in the hybrid composites.2.The content of TiB₂ nanoparticles has a greater influence on the mechanical properties of the hybrid composites.For the hybrid composite with 5 wt.%TiB₂ nanoparticles,the ultimate tensile strength and yield strength were reached 222.96MPa and 122MPa,increased by 64%and 23%,respectively.After SEM and TEM analysis of tensile fracture,the strengthening mechanism of SiC/TiB₂ hybrid reinforced aluminum matrix composites can be divided into direct strengthening and indirect strengthening.Direct reinforcement refers to the main bearing by the SiC particles,while indirect strengthening is due to the addition of TiB₂ particles.Indirect reinforcement in this experiment can be divided into fine grain strengthening,dislocation strengthening and Orowan strengthening.3.Dry friction and wear tests of hot extrusion composites were conducted respectively.It was found that the effect of the applied load on the wear rate is very significant.As the load increases,the wear rate of SiC/TiB₂ reinforced aluminum matrix composites increases.At low load?20N?,the wear rate of SiC/TiB₂ particle hybrid reinforced aluminum matrix composites is lower than that single SiC particles reinforced aluminum matrix composites.When the load is increased to 60N,the wear rate of?10%SiC+8%TiB₂?/Al-7Si composite increases rapidly and is larger than that of single SiC particle reinforced aluminum matrix composites.When the load is fixed,with the increase of the dry sliding speed,the wear rate of the SiC/TiB₂ reinforced aluminum matrix composites is slightly increased.Through the SEM analysis of the wear surface,we can see that under the normal temperature conditions,the wear mechanism is divided into the following three stages.The first stage is a slight wear stage,with abrasive wear as the main wear mechanism.The second stage is the formation stage of the mechanical mixing layer,with the wear and oxidation wear as the main wear mechanism.The third stage is the stage of peeling off after the formation of the mechanical mixing layer,and the wear mechanism is the main wear mechanism.