The Effect Of Reinforcements On The Microstructure And Mechanical Properties Of (TiC+TiB)/Ti Composites

At present,many scholars have studied the microstructures and mechanical properties of single reinforced titanium matrix composites,it is found that it is difficult to have good comprehensive mechanical properties.Existing studies have also showed that hybrid reinforced titanium matrix composites can take into account the mechanical properties of various reinforcements and improve some properties of single reinforced titanium matrix composites,which have higher strength,better plasticity and creep resistance.but the study of the coupling relationship between different reinforcements in hybrid reinforced titanium matrix composites is still insufficient.In order to further improve the mechanical properties of the hybrid reinforced titanium matrix composites,and to provide a basis for the composition design of the materials,it is necessary to study the influence of reinforcement on the mechanical properties of hybrid reinforced titanium matrix composites and establish a theoretical model of the coupling relationship between different reinforcement strengthening effects.In view of this,the project has studied the microstructure and room temperature tensile and compressive properties of?TiC+TiB?/Ti composites in casting and forging states.the coupling relationship between the strengthening effects of different reinforcements under different conditions was established by combining experimental and numerical analysis.The influence rules of different reinforcements on the tensile and compressive properties of titanium matrix composites were explored.The tensile properties at room temperature and high temperature of the forged titanium matrix composites were tested,and the fracture mechanism at room temperature and high temperature was studied.The main conclusions are as follows:?1?The matrix of cast titanium matrix composites is coarse cast microstructure and there are many casting defects.TiC reinforcement is equiaxed,short rod and dendrite,while TiB reinforcement is short fibre,the aspect ratio is high and the orientation is random.Compared with as-cast composites,the average particle size of TiC reinforcement in as-forged composites decreases and distributes symmetrically on the matrix in the form of equiaxed and slightly coarser ellipsoidal shape.The aspect ratio of TiB short fibers decreases,and most of TiB short fibers distribute along the forging direction.?2?In as-cast titanium matrix composites,the strengthening mechanism of TiC reinforcement is particle strengthening mechanism,and the strengthening mechanism of TiB short fiber mainly depends on its stress-bearing effect.According to the superposition relationship of strengthening effect,the following theoretical calculation models can be obtained:?_yc=?_ym(1+??_r/?_ym)and??_r=[(0.5?_ymV×l/d C₀)^q+(-?_ym)^q]^1/qComparing the theoretical calculation results with the experimental results,it is found that the theoretical yield strength calculated by q=1,1.5and 2 is higher than the experimental yield strength.?3?In the forged titanium matrix composites,the particle strengthening effect of TiC,the stress bearing effect of TiB short fibers and the fine grain strengthening effect are considered comprehensively.According to the superposition relationship of strengthening effect,the following theoretical models are established:?_yc=?_ym(1+??_r/?_ym)(1+??_HP/?_ym)and??_HP=k_md_m^-1/2??_r=[(0.5?_ymV×l/d C₀)^q+(-?_ym)^q]^1/qComparing the theoretical calculation results with the experimental results,it is found that the calculated values are in good agreement with the experimental values when q=1.5,which indicates that the three strengthening effects satisfy the superposition relationship of q=1.5 in as-forged composites.?4?In as-cast pure titanium and as-forged pure titanium,the absolute value of tensile yield strength and compressive yield strength at room temperature are similar,but in as-cast titanium matrix composites,the absolute value of the compressive yield strength at room temperature is higher than the absolute value of the tensile yield strength at room temperature.This difference is more pronounced in the forged titanium matrix composite.?5?Fracture failure of forged materials at room temperature is mainly caused by load-bearing fracture of TiC particles and TiB short fibers,while fracture failure at high temperature is caused by load-bearing fracture of reinforcements and debonding of some TiB reinforcements and matrix.