Preparation Process And Mechanical Behavior Of Fe/Al-based Metal-intermetallic Laminated Composites

Metal-intermetallic layered（MIL）composites are a new class of composite materials based on shell structure.Due to its high toughness,high specific strength,high specific stiffness and excellent impact resistance,this kind of composite material has broad application prospects in important fields such as aerospace and weaponry.In recent years,Fe Al-based MIL composites have gradually become the focus of development and research due to their flexibility in structural element adjustment and low cost.However,the interfacial reaction rate of such MIL composites is slow,the preparation efficiency is not high,and the intermetallic compounds generated by the reaction are relatively brittle and prone to cracking.Based on the above problems,three Fe/Al MIL composites of FHP-1000-30,FHP-1000-50 and VHP-880-50were prepared by using fast hot press sintering（FHP）and ordinary vacuum hot pressing sintering（VHP）technology combined with“multi-thin foil stacking”+“two-stage sintering”.For Fe Al MIL composites prepared by FHP technology,the effect of thin foil thickness on reaction rate and metallurgical bonding quality was explored by adjusting the initial foil thickness.At the same time,Fe Al MIL composites were prepared by ordinary VHP technology and corresponding process methods.By comparing with the FHP process,the effects of different preparation processes on the microstructure and mechanical properties of the materials were analyzed.Finally,the potential microscopic fracture mechanism of MIL composites is analyzed and discussed.In terms of microstructure:by comparison,each unit layer of the three Fe/Al MIL composites is composed of metal layer,transition layer and intermetallic compound layer,and there are a large number of dispersed precipitated phases(Ni Al,Al₅Fe Ni,Al₁₃Fe₄)in the transition layer.Both the transition layer and the intermetallic compound layer consist of aαphase and a B2-Fe Al phase,and the metal layer consists of aγphase.The difference is that the metal layer in the sample prepared by VHP has a partial martensitic phase transition,and the grain size of each layer in the sample is more fine,which is closely related to the selection of sintering temperature.In addition,the intermetallic layer of each sample,that is,the grain of the B2-Fe Al phase,has obvious silk texture in the?111?direction.This is because the formation and growth process of the B2-Fe Al phase is driven by the unidirectional diffusion of atoms,so a sintered texture appears in the?111?direction.In terms of performance:The VHP-880-50 composite material is the most dense,with an average density of 5.963 g/cm³;FHP-1000-30 composite hardness distribution is relatively dispersed,FHP-1000-50 composite hardness distribution shows a certain regularity,that is,the hardness distribution of the intermetallic compound layer is relatively uniform,and the hardness peak occurs in the transition layer on both sides,the hardness of each layer of VHP-880-50composite material shows a certain periodic distribution,the hardness of the transition layer is between the hardness value of the metal layer and the intermetallic compound layer,combined with the corresponding nanoindentation analysis.The transition layer plays a fine hardness transition role;In terms of tensile properties,The VHP-880-50 composite material has the best tensile performance,with a 32.2%increase in tensile strength compared to the composite material prepared by the FHP method;In terms of quasi-static compression performance,Among the three types of Fe/Al MIL composites,VHP-880-50 composite had the best compressive performance,with the average compressive strength parallel to the laminate reaching 3688.6 MPa and the average compressive strength perpendicular to the laminate reaching 3238.9 MPa.In terms of dynamic compression performance,the average compressive strength of FHP-1000-30 composite parallel to the stack reached 1015.8 MPa,and the average compressive strength perpendicular to the stack reached 2165.1 MPa.The average compressive strength of FHP-1000-50 composite parallel to the laminate is 2435.5 MPa,and the average compressive strength perpendicular to the laminate reaches 1990.8 MPa.The average compressive strength of VHP-880-50 composite parallel to the laminate reached 1981.7 MPa,and the average compressive strength perpendicular to the laminate reached 2054.3 MPa.In terms of material deformation and fracture mechanism:for stage compression parallel to the stack,a new“multi-microcrack”energy dissipation mechanism is found in the intermetallic compound layer,which can promote the uniform distribution of stress during the deformation process by releasing the stress concentration.For stage compression perpendicular to the stack,the reinforced metal layer and hard transition layer deflect and prevent the propagation of the crack tip.The stress distribution characteristics inside MIL composites were analyzed by finite element simulation.Under the compressive strain parallel to the stack,the HDI stress of each unit layer is positive,which is the main reason for microcrack initiation and propagation.When the compressive strain is perpendicular to the lamination,the HDI stress is negative in the metal layer,positive in the intermetallic layer,and close to zero in the transition layer.Due to the presence of the transition layer,delamination between the metal layer and the intermetallic compound layer is avoided.Under dynamic loading,each layer of the material exhibits different strain response states.The grains of the metal layer are broken,and dense small-angle grain boundaries are formed between the grains.Compared to other layers,the dislocation density and distribution of the metal layer are significantly higher,which is closely related to the large plastic deformation that occurs.In addition,there was a significant change in the crystal orientation of local grains in the intermetallic compound layer after dynamic loading,which is related to the large angle deflection of some grains during the dynamic loading process.