Microstructure Characterization And Properties Of NiTi Fiber-Fe/Al Metal-intermetallic-Laminate Composite

With the progress and development of modern national defense,aerospace,machinery and other industries,single metal or non-metallic materials can not meet the growing demand in above fields,so composite materials are more and more widely used.Composite materials have many characteristics,which can improve or overcome the weakness of single material,make full use of the advantages of each material,and give new properties to components.Metal-Intermetallic-Laminate composite is a new type of composite materials based on bionics principle of shell multilayer structure,which has low density and good comprehensive mechanical properties.Fe/Al based MIL composite has attracted more and more attention due to its low cost.However,there are some problems during fabrication process,such as slow interfacial reaction speed,prefer to form brittle intermetallic compounds and so on.In order to solve these problems,Traditional Thick Foils(TTF)method was used to introduce Ni Ti fibers into Fe/Al based MIL composite by vacuum hot pressing sintering method.Ni Ti fibers were introduced to react with Al rapidly to accelerate sintering speed.Meanwhile,Multi Thin Foils(MTF)structure was designed to further shorten the reaction time,Ni Ti_f-Fe/Al based MIL micro laminate composite(MTF Ni Ti_f Fe/Al),which is composed of ductile Fe rich phases,was prepared and compared with Fe/Al based MIL micro laminate composite(MTF Fe/Al)without fibers introduction.Microstructure of three different MIL composite was characterized by SEM,EDS and XRD.The physical and mechanical properties of composite were studied by density test,hardness test,compression test and tensile test.In aspect of microstructure,TTFNiTi_f Fe/Al MIL composite is consists of metal layer,transition layer and intermetallic layer.The intermetallic layer is composed of Fe-Al intermetallic region,fiber and fiber reaction region.Ni Ti fiber is at the center position of intermetallic layer.Fe-Al intermetallic region is composed of Fe Al and Fe Al-Fe Al₂ eutectoid layers.The composition of fiber reaction region is a complex mixture of Al-Ti phase and Al-Ni phase with Al₃Ti as main component.MTF Fe/Al MIL composite is consists of metal layer,transition layer and Fe-Al intermetallic layer.The main component of Fe-Al intermetallic layer is Fe Al.The microstructure of MTF Ni Ti_f Fe/Al MIL composite is similar to that of TTFNiTi_fFe/Al MIL composite,but the main component of Fe-Al intermetallic region is Fe Al phase.In aspect of physical property,the average densities of TTFNiTi_f-Fe/Al,MTF Fe/Al and MTF Ni Ti_f-Fe/Al MIL composites are 6.038 g/cm³,6.107 g/cm³ and 6.248 g/cm³,respectively.In aspect of hardness,the hardness values perpendicular to the stacking direction of Ni Ti_f-Fe/Al MIL composites fabricated by different methods change periodically.The hardness test of TTFNiTi_f Fe/Al MIL composite showing hard-brittleness of composite,and cracks appear around the indentation.There is no crack distributes around the indentation of intermetallic layer prepared by multi thin foil method,which indicates that Fe rich intermetallic layer has a certain toughness.In aspect of compressive properties,MTF Fe/Al MIL composite has the best compressive properties,with the average compressive strength of 2278.4 MPa and the average failure strain of 0.423 in the direction perpendicular to layers,2455.2 MPa and 0.524 in the direction parallel to layers.The introduction of fibers reduces the compressive properties of MIL composites,which results in stress concentration caused by Ni Ti fibers and acceleration of crack propagation during compression process.In aspect of tensile properties,the average tensile strengths of TTFNiTi_f-Fe/Al,MTF Fe/Al and MTF Ni Ti_f-Fe/Al MIL composites are337.4 MPa,380.6 MPa and 410.4 MPa,respectively.After introducing 1.5%Ni Ti fibers into Fe/Al system MIL micro laminated composite,the tensile strength of composite is increased by7.8%attribute to fibers pulling out.