| The particle reinforced aluminum matrix composites have been extensively investigated due the easy fabrication and low cost.With the increase of the particle volume fraction,the defects such as cracks and holes are easy formed in the aluminum matrix composites.Therefore,the aluminum matrix composites with high volume fraction??30%?of reinforcement particles are less studied.In this paper,the?Al3Ti+B4C?p/Al composites and?TiC+TiB2?p/Al composites were fabricated by two different in situ combustion synthesis methods from the Al-Ti-B4 C system.The effects of process parameters on the microstructure,hardness and wear properties of?Al3Ti+B4C?p/Al composites,as well as the influence on the microstructure,physical properties and mechanical properties of?TiC+TiB2?p/Al composites were then analyzed.The evolution of the combustion process in Al-Ti-B4 C system was proposed.The study results are listed as follows:?1??Al3Ti+B4C?p/Al composite material with a good shape,low porosity was obtained as the preheating temperature of aluminum melt was between 800? and 1000? by heating the sample of xAl-2.7Ti-B4 C system in the mold with aluminum melt.The higher the preheating temperature,the less Ti particles in the product,when the temperature is 1000?,the product without Ti particles remained.The reason why this method can quickly get the dense product was illustrated,it was due to the presence of Al-Ti quaternary liquid phase,under the capillary action spread to B4 C around,filled the residual pores in the sample.The Al content would affect the size of Al3 Ti in the combustion reaction product was proposed,when T=900?,the higher the Al content in the system,the faster the aluminum melt absorbe the heat released by the reaction,the smaller the size of Al3 Ti in the product.When the Al content x=4,the Al3 Ti size in the product was more than 200?m,and when x=8,the size of Al3 Ti was less than 80?m.When the temperature T=1100?,the reaction product was converted to TiC and TiB2,but the material was porous,this method was not suitable for the preparation of composite materials.?2?The higher the preheating temperature of the Al liquid,the greater the hardness,the better the wear resistance of the?Al3Ti+B4C?p/Al composite.When T=1000?,the aluminum content x=4,the composite material had the highest hardness of 96.3HRB.Under the dry sliding friction condition,the speed was 150r/min,the load was between 3N and 12 N,the wear volume of the?Al3Ti+B4C?p/Al composites was within 60% of the A356 alloy.With the increase of the load,the wear surface of the wear surface increased,the wear marks width also became larger.When the load is 3N,the wear mechanism of the composite material was mainly sliding wear.When the load was 12 N,the wear mechanism of the composite material was mainly abrasive wear.When the load was 6N,the speed was 150r/min,the wear mechanism of this composite material was mainly reflected in the sliding wear.When the speed increased,the material contact surface rapid heated and dropped a lot of massive debris,and some sticky Attached to the wear surface,the speed of 350r/min,the wear mechanism of this composite material was adhesive wear.?3??TiC+TiB2?p/Al composites were prepared by the method of electromagnetic induction ignition and manual pressurization.As the pressure increased,the porosity of the composite decreased,when the pressure was 10 MPa with mold control,the minimum porosity of the composites was 1.3%.The increasd in Al content reduced the amount of heat released by the combustion reaction,and decreased the size of the particles in the product.When the Al content x=4,the TiC size in the product was about 1?m,and when x=8,the TiC size reduced to about 0.3?m.When x=4 and 6,the size of TiB2 was about 1?m,and when x=8,the size of TiB2 reduced to less than 0.5?m.When the B4 C particles were involved in the reaction,the smaller the size of B4 C particles,the smaller the size of the particles in the product.?4?When the size of B4 C particle was 10?m,the higher the Al content,the greater the thermal conductivity and thermal expansion coefficient of?TiC+TiB2?p/Al composites,and the better the hardness,the compressive performance,and the wear resistance.When x=8,the maximum hardness of the composites was 47.7HRC,the maximum compressive strength was 1050 MPa,the wear rate was 4.923×10-4mg/mm,the maximum thermal conductivity was 70.144W/m-1?-1.When x=4,the least coefficient of thermal expansion was 2.25×10-6?-1. |
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