| B4C ceramics have high strength,high hardness and poor toughness,Al has good plasticity,high toughness and low hardness.Their special physical properties are regarded as ideal elastomers and plasticizers in the field of ceramics and metals.The combination of B4C and Al can effectively"take its long and make up for its short".B4C/Al composites are considered to be an ideal structural material.However,the mechanical properties of B4C/Al composites are far from the expectation of material workers due to the huge difference of physical properties between the two materials and the influence of phase reaction products in the process of heating preparation.In this experiment,different components of homogeneous B4C/Al composites were used to fabricate"hard-soft-hard"composites with high strength,high hardness and good plasticity.Compared with the homogeneous B4C/Al composites,the layered B4C/Al composites have great advantages in quasi-static and dynamic mechanical properties.It breaks through the key bottleneck of poor mechanical properties of the traditional layered cermet composite due to the mismatching of thermodynamic properties,and solves the science that impurities in the interface reaction products are unfavorable to the mechanical properties of B4C/Al composites.The specific research contents are as follows:The interfacial reaction products of B4C/Al composites were discussed.The element diffusion between B4C and Al was studied by means of SEM,EDS,EPMA characterization.In order to verify the interface diffusion type between B4C and Al powders,the phase composition of B4C and Al powder in the sintering temperature range was systematically studied and analyzed by high temperature in-situ XRD technology.It is confirmed that the type of diffusion between them is chemical reaction diffusion.The microstructure of B4C/Al composites was analyzed by TEM and SAED.The results show that the products of B4C/Al interface reaction are AlB12,AlB2 and Al3BC.At the same time,the stress-strain in the Al grain during the phase transformation reaction was analyzed and calculated.The mechanical properties of 5-30vol.%B4C/Al composites were tested and analyzed.The best plasticity?56.43%?,maximum compressive strength?292.15MPa?and bending strength?585.70MPa?were obtained at 5vol.%B4C/Al composites,15vol.%B4C/Al composites and 25vol.%B4C/Al composites,respectively.The layered B4C/Al composites were prepared by using the above three groups of homogeneous B4C/Al composites powders in a"hard-soft-hard"symmetrical structure.The mechanical properties of layered B4C/Al composites were tested and analyzed.The Vickers hardness,bending strength and fracture toughness of the laminated B4C/Al composites reached 116.23HV,780.45MPa and12.21MPa·m1/2,which greatly improved the mechanical properties of the homogeneous B4C/Al composites.The deformation behavior and strengthening and toughening mechanism of the laminated B4C/Al composites were analyzed and discussed.The dynamic mechanical properties of the laminated B4C/Al composites under high strain rate are studied and analyzed by means of Split Hopkinson Bar?SHPB?test and Bullet impact test.The results of SHPB test show that the dynamic compressive strength of layered B4C/Al composites is much higher than that of homogeneous B4C/Al composites with the same content of B4C,and the layered materials can still maintain good structural integrity after high-speed impact.Ceramic materials show higher strength under high speed impact.The bullet impact test shows that the external high B4C content layer can effectively dissipate and disperse the stress wave,and the internal high Al content layer can absorb the stress wave.TEM microscopic characterization was carried out on the damaged layered B4C/Al composite near the crack,and it was found that during the process of high speed impact,a large number of dislocation appeared in the grain,accompanied by twin crystals and stacking dislocation,etc.,proving that B4C also has certain plastic deformation ability under high strain rate. |
PDF Full Text Request