The Research Of B₄C/Al Composite Fabrication And Its Fatigue Performance And Fracture Mechanism

With the advantages of low density, high strength and wear resistance and etc, the aluminum matrix composite reinforced by ceramic particles has became a new material which integrates structure with function and widely used in transportation,aerospace,electronic thermal control,nuclear power and many other fields. The current research of B4C/Al composite is just limited to small trials on the laboratory, however,the research of industrial production is rarely reported.By the method of powder metallurgy to prepare extrusion blank,then through the processes of extrusion and rolling,we finally have successfully manufactured largr size of B4C/Al composite sheet with good integrity and excellent mechanical properties,particles evenly distuibuted.what’s more,The composite sheet can realize industrialized batch production.Finally,the microstructure, mechanical properties and fatigue performance of the B4C/Al composite sheet is studied.Through the observation the microstructure of B4C/Al composite,we can conclude that the enhanced particle B4C distribute uniformly in the matrix alloy and no obvious macroscopic defects is discovered in the metallograph.The density contrast of B4C/Al composite furtherly verify the uniform distribution of B4C particles.The mechanical properties of B4C/Al composite show that the rolling sheet has anisotropic performance,and the mechanical properties of the longitudinal is better than the transverse.combining the result of tensile fracture SEM and analysing the EDS of fracture,we put forward two patterns of fracture mechanisms:the B4C particle ruptured and extracted.The crack expanding furtherly by thses two ways,eventually leading to the fracture of B4C/Al composite.The fatigue test is conducted according to the fatigue test standard,Through the fatigue experiment we draw the S-N cueve of B4C/Al composite and learn that the fatigue limit of B4C/Al composite is110MPa under1×107fatigue cycles. The SEM and EDS are used to observe the fatigue fracture and analyze the feature points. The fractography of fatigue fracture also can clearly observe the characteristics of crack initiation, crack propagation, unstability to breakdown..The results indicate that different kinds of fatigue source exist in the B4C/Al composite;The fatigue crack extension path of B4C-Aluminium composites with high content of boron carbide depends on the particle interval of B4C and dimension of the crack tip plastic zone. When the radius of crack tip is more than the the interval between B4C particle,the fatigue crack extends mainly along the grain interface of particles and fracture surface of B4C particles;otherwise, the passivating of the crack tip leads to slowing down the propagation of the crack and changing the crack propagation direction.