Microstructure And Mechanical Properties Of NiTi Fiber Reinforced NiTi/?Al₃Ti+Al₃Ni? Laminated Composite

In recent years,Ti/Al₃Ti laminated composite has attracted extensive attention due to its high specific strength,impact resistance and low density.The Ni Ti/?Al₃Ti+Al₃Ni?laminated composite?MIL?developed on this basis improves the overall mechanical properties of the composite by virtue of the superelasticity of the Ni Ti layer.On this background,the same Ni Ti fibers were used to strengthen Ni Ti/?Al₃Ti+Al₃Ni?laminated composites,and the microstructure characterization and mechanical properties of the as-fabricated Ni Ti fiber reinforced Ni Ti/?Al₃Ti+Al₃Ni?laminated composites?SFR-MIL?were tested.Firstly,SFR-MIL composite was successfully prepared by vacuum hot pressing sintering process,and the reasonable preparation parameters?the temperature was kept under vacuum at 645?for 4 hours and the initial pressure was 3MPa?were determined,and the influence of various process parameters on the material structure was discussed.Secondly,the microstructure of this novel material was characterized.The XRD and EDS results show that the 1060Al plate,as one of the original materials,is fully consumed and only two intermetallic compounds,Al₃Ti and Al₃Ni,are formed.The long-term periodic symmetrical structure of SFR-MIL composites can be clearly observed by the scanning electron microscope?SEM?.A complete period in SFR-MIL composite is"Ni Ti plate-reaction band-intermetallic compound layer-reaction band-Ni Ti fiber-reaction band-intermetallic compound layer-reaction band-Ni Ti plate".From the reaction band to the intermetallic compound layer,the size of the two intermetallic compounds,Al₃Ti and Al₃Ni,keeps increasing,showing the feature of size gradient.The centerline layer in the MIL composite is deflected into a cellular structure surrounding the fiber due to the presence of Ni Ti fibers in the SFR-MIL composite.Thirdly,the basic physical properties of SFR-MIL composite material were measured.Its density was 5.52?5.85g/cm³,and its elastic modulus was 130.94GPa.The distribution of microhardness follows the periodic symmetry characteristics of the structure,with the highest hardness at the reaction band?about 750HV?,high hardness at the intermetallic compound layer?580?620HV?,and the lowest hardness at the center line?about 250HV?and Ni Ti plate?about 200HV?.Finally,the mechanical properties of SFR-MIL composites were tested and the failure mechanism was analyzed.The static tensile test showed that the introduction of Ni Ti fiber effectively improved the overall strength of the material,making the ultimate tensile strength of the material reach 360.74MPa.The static compression test indicates that the material has excellent orientation,and the compressive strength in the parallel direction is 1140.67MPa,22.97%higher than that in the perpendicular direction.Three-point bending experiments showed that the fracture absorption energy of SFR-MIL composite was higher than that of MIL composite,and Ni Ti fiber enhanced the energy absorption characteristics of the whole material.In the fracture toughness test,SFR-MIL composite showed better toughness characteristics,with an average K_IC value of 65.99MPa·m^1/2,reflecting the strong toughening effect of Ni Ti fiber.Interface delamination,fiber debonding and pull-out,metal layer deformation and intergranular fracture occurred in intermetallic layer are the main failure mechanisms of SFR-MIL composites.The reason why SFR-MIL composites have good toughness and energy absorption characteristics is that the fibers bear the load directly and form the new interface to transfer the load.The above results indicate that Ni Ti fiber-reinforced Ni Ti/?Al₃Ti+Al₃Ni?laminated composite?SFR-MIL?is a promising material with high strength and toughness.