Study On The Preparation,mechanical Property And Mechanism Of The High Strength And Toughness （B₄C+Gr）/Al Composite With Nacre-like Structure

The shell nacre realizes the perfect match of strength and toughness with its"brick-mud"laminated nanostructure,as well as crack deflection,bridging and passivation.In this paper,Using"Chemical adsorption dispersion-Laminated bonding-Accumulative roll bonding"method to prepare a nacre-like structure（B₄C+Gr）/Al composite（Gr:graphene）with controllable stack size and interface structure.With the help of OM,EDS,SEM,TEM,EBSD and other analysis and testing methods to study the influence of reinforcement content,accumulative roll-bonding process on the structure and mechanical properties of composites,and explore the strength and toughness mechanism of the nacre-like structure（B₄C+Gr）/Al composite.The main research work and conclusions are as follows:（1）The effect of chemisorption and dispersion on Gr shows that:GrO can be compounded on the B₄C surface closely and uniformly by"Chemical adsorption dispersion",and the relative content of GrO can be increased by"multiple-coated";RAM and SEM analysis show that the high temperature reduction effectively converts GrO to Gr with maintaining good structure,（B₄C/Gr）composite reinforcement is effectively prepared.（2）The effect of the Laminated bonding and Accumulative roll-bonding process on the composite’s structure and mechanical properties shows that:the high rolling temperature is beneficial to the lamination compound,but too high（>450℃）is easy to form reactant and"sticky rolls",The three-stage rolling process（450℃×20min+350℃×20min+250℃×20min）can ensure remarkable compactness and effectively avoid reactant forming.With ARB passes increasing at 250℃,the reinforcement distribution becomes more uniform,the structure of the composite become more denser,the mechanical properties are significantly improved,however,these becomes stable after 7th pass;The yield strength of 7th pass（3vol.%B₄C+0.05wt.%Gr）Al composite is 172 MPa,the hardness is 46.14 HV,the elongation is 13.76%,which is49.57%,118.07%,7.00%higher than 3rd pass respectively.（3）The effect of reinforcement content on the composite’s structure and mechanical properties shows that:As B₄C content increases,the distribution of the reinforcement becomes more uniform,the number of dimple in tensile fracture becomes more and size becomes smaller;as the Gr content increases,the tensile fracture surface becomes rougher,and the fiber shape becomes more obvious.When the B₄C content increases from 1 to 7 vol.%,Composite yield strength increases from159 to 182 MPa,the hardness increases from 35.92 to 55.69 HV,the CTE reduces from 18.65×10^-66 to 9.49×10^-6（1/K）,however,the elongation reduces from 15.68 to8.01%;When the Gr content increases from 0.01 to 0.5 wt.%,the yield strength increases from 161 to 187 MPa,the elongation increases from 11.53 to 15.71%,and the hardness increases from 45.67 to 48.53 HV.（4）The strength-toughening mechanism of the nacre-like structure（B₄C+Gr）/Al composite shows:The strength improvement of composite is mainly dependent on fine crystal strengthening,reinforced body dislocation and bearing strengthening,geometrically necessary dislocation strengthening;B₄C,Gr and Al achieve nanoscale level integration at nanoscale level in 7th pass composite matrix,which is conducive to the B₄C/Gr synergistic strength-toughening.There are three states of Gr:（1）Pulled out by tearing,（2）Coexisting with B₄C in the depth of dimple,（3）Existing between the laminated interface.With ARB pass increases,the matrix gradually forms a laminated structure,texture become more stronger,the dislocation cells of low-pass composite is gradually transformed into sub-grain boundaries and grain boundaries,the grains are greatly refined and tend to be equiaxed,the grain boundaries show a typical"bimodal"orientation distribution,which is conducive to improve the strength and toughness of the composit by matrix work hardening and dislocation glide.