Effect Of Heating Method On The Mechanism And Microstructure Of In-situ Synthesis Of Al₃Ti Particles

Due to the advantages of low density,high hardness,and high wear resistance,A13Ti particle reinforced aluminum matrix composites were widely used in wear-resistant parts.However,due to defects such as long reaction period,coarse particles,easy agglomeration,and uncontrollable distribution position,the currently applicable process cannot substantially improve the wear resistance of the material.In this study,Ti fiber and Ti mesh with a diameter of 200?m were used as the reaction source.In the stage of preparing the preform,in order to pre-adjust the generation position of the particles,the reaction sources were fixed in the matrix at equal intervals to achieve the role of ensuring the uniformity at the initial state.Subsequently,Al3Ti particles reinforced aluminum matrix composites were prepared by means of resistance furnace heating and electromagnetic induction heating.In order to explore the effect of different heating methods on the in-situ reaction mechanism,the Al-Ti reaction model was established by testing and analyzing the product phase and microstructure under different parameters.By studying of the hardness,wear rate and friction coefficient of the composites,the influence of the heating method on the wear resistance was explored.The main conclusions are as follows:(1)The initial temperature of the Al-Ti reaction is 660? under the resistance furnace heating,and Al3Ti is the only product obtained.When the temperature rises to 690?,the Al3Ti layer breaks and flakes.Because the Ti fiber was completely reacted and the particles were not agglomerated,the temperature of 720? was determined as the optimal reaction temperature.At 750?,due to Vander Waals force and thermal diffusion,the particles were agglomerated and fused,and the dispersion was poor.At the optimal reaction temperature of 720?,a small amount of Al3Ti was generated at 5minutes of heat preservation,Ti was completely reacted after 30 minutes,and Al3Ti reunited again at 60 minutes.Therefore,30 minutes could be determined as the best holding time.From a thermodynamic point of view:when Al and Ti sources were sufficient,Al3Ti was preferentially generated due to the lower free energy.From a dynamic point of view:through the proportion of Al-Ti interface elements,the model of the reaction system was established,from inside to outside were Ti,LAl/Ti diffusion layer,Al3Ti layer,LTi/Al diffusion layer,Al-based.The main diffusion phase was Ti,and the main diffusion process was the diffusion of Ti atoms into Al;according to the location of the cracks in the Al3Ti layer,the Al3Ti interlayer thermal stress was calculated to be highter than the particle breaking strength.Finally,it was judged that Al3Ti flaking was caused by thermal stress.(2)The in-situ reaction product of Al-Ti under electromagnetic induction heating mode is unique,which was Al3Ti.As the frequency was increased from 100Hz to 5KHz,the degree of reaction was increased,and the flaking distance between Al3Ti layers and the drift distance of Al3Ti particles were enhanced by the Lorentz force.At 5KHz,the Ti fiber completely reacts,the particle size was refined to 5-7?m,and the gap was increased to 3-5?m,which was the optimal frequency parameter.At 10KHz,Al3Ti was not generated due to excessive skin effect.Under the optimal frequency parameter 5KHz,as the current increases,the degree of response was increased.At 15 A,the Ti fiber was completely reacted,while initial temperature of the reaction was reduced to 601.9?.The particle size and gap were 1-2?m and 5?m respectively,and the coverage area was the peak value of 2.7×106?m2,which was the best value under all parameters.When the current was 20A,the transition of Al3Ti to a long strip was due to its own crystal structure and magnetic field,which leaded to an increase in Al3Ti size and a decrease in dispersion.From a thermodynamic point of view:the total entropy of the system and the energy of the system were increased under the action of the magnetic field,which accelerated the Al-Ti reaction;From a dynamic point of view:the magnetic field could increase the melt convection,promote the fragmentation of the Al3Ti layer,increase the particle drift distance,and play the role of improving the Al-Ti diffusion rate,refining the size,and improving the dispersibility.(3)In order to ensure the accuracy of the friction and wear test,the Ti mesh was used as the reaction source to increase the Al3Ti content of the cross section.The wear resistance of the composite material under resistance furnace heating is much lower than that of the composite material prepared by electromagnetic induction heating,which was attributed to its low hardness,poor dispersion,and weak binding force between the particles and the matrix.When the load is 10N:the wear rate and friction coefficient of the composite material at 750? and 60min are 5.932mg/mm2 and 0.292 respectively,which were higher than the wear rate(2.03 1mg/mm2)and friction coefficient(0.102)under the optimal parameters of induction heating.When the load was increased to 30N,the wear rate and friction coefficient of the composite increased to 29.745mg/mm2 and 0.767 under the optimal parameters of resistance furnace heating.The wear surface was damaged seriously,not only the wear scar was deep,but also the particles and the matrix were peeled off in a large area;However,under the optimal parameters of induction heating,the wear rate and friction coefficient of the composite were 16.392mg/mm2 and 0.497,and only the particles were broken and the edge was peeled off,which proves that the composite can resist the friction and wear under high load.