Experimental And Numerical Simulation Study On Mechanical Properties Of Multiphase And Multiscale Metal Matrix Composites

During the experimental preparation of TiB₂ particles and TiB whisker reinforced Cu matrix composites,the ideal mechanical properties of the composites can be obtained by adjusting the type,morphology,size,distribution and hybrid proportion of the reinforcement generated by insitu synthesis.However,these parameters in the experiment interact and affect synergistically the mechanical properties of the composites,it is difficult to reveal the synergistic effect between the multiple phases by experimental verification.Meanwhile,in the experimental preparation of Y₂O₃ reinforced Mo matrix composites,the comprehensive mechanical properties of composites are further improved by rolling deformation.However,the influence mechanism of deformation and Y₂O₃ on mechanical properties of rolled Mo matrix composites remains unclear.Therefore,aiming at the problems existing in the experimental preparation of the above two composites,a numerical simulation method for multiphase cross-scale metal matrix composites is proposed in this paper.The quantitative relationship between macroscopic mechanical behavior and microstructure of composites is studied.For the hybrid reinforced Cu matrix composites,a 3D finite element model of as-cast(TiB_2p+TiB_w)/Cu matrix composites was constructed.The stress/strain distribution and damage evolution process of matrix,interface and reinforcement in the composite were analyzed to reveal the internal mechanism of synergistic strengthening of multiphase hybrid reinforced Cu matrix composites.Considering that the properties of the composites are not only dependent on the regulation of the characteristic parameters of the reinforcement in the preparation process,the subsequent plastic machining is also very important.Therefore,for the Mo matrix composites,a 3D finite element model of rolled Y₂O₃/Mo matrix composites prepared by powder metallurgy was constructed.The stress/strain distribution and damage evolution process of matrix,interface and reinforcement were analyzed.And combined with the experimental results,the influence mechanism of Y₂O₃ on the mechanical behavior of rolled Mo matrix composites was revealed.This work can provide useful guidance for optimal design and industrial application of metal matrix composites.The main conclusions are as follows:（1）Compared with TiB₂p/Cu composites,(TiB_2p+TiB_w)/Cu matrix composites have greater advantages in terms of strength,but the elongation is poor,which is still within the acceptable range.By evaluating the stress concentration factor,it can be found that whisker is the main bearer in hybrid reinforced Cu matrix composites.This makes the strength of hybrid composites much higher than that of TiB₂p/Cu composites.The matrix damage of hybrid reinforced Cu matrix composites is earlier than that of TiB₂p/Cu composites.The crack evolution in the Cu matrix shows that the existence of vertical whisker accelerates the propagation,connection and link up of microcracks in the matrix,resulting in poor plasticity of hybrid reinforced Cu matrix composites compared with TiB₂p/Cu composites.Whisker orientation has great influence on the mechanical properties of composites.Parallel whiskers contribute to the strength of the composite,while vertical whiskers contribute to crack propagation.Therefore,the service environment of the final composite component should be considered in the preparation and design of Cu matrix composites in the future.For example,based on the actual load characteristics of the material component,the direction of the whisker is designed and arranged according to the direction of the load of the composite component.（2）With the increase of the content of Y₂O₃,the tensile properties of Y₂O₃/Mo composites increase in strength and decrease in plasticity.From the experimental micro structure analysis,Y₂O₃ is the main reason for the increase of the strength of the composites.Moreover,it can be observed from the Mises stress of the composite that the Mo matrix is the main load bearer,and the second phase Y₂O₃ itself contributes little to the load bearing capacity.And by comparing two kinds of Y₂O₃/Mo composites,it is found that because the second phase Y₂O₃ causes different degree of grain refining to the matrix,the matrix has different level of load bearing capacity,and finally makes the yield strength and tensile strength of the two kinds of composite macroscopic mechanical properties are different.At the same time,it can be found from the damage evolution process of Mo matrix that the Mo matrix with high content of Y₂O₃ initiates cracks early in the position where the reinforcement exists,and rapidly expands and breaks,resulting in poor elongation.And this is consistent with experimental fracture observations.