The Study On Microstructure And Properties Of Iron-Based Metal-Intermetallic-Laminated Composites

Scientists have designed laminated composites that are inspired by the toughening mechanism of the structure of the shell nacre.Metal/intermetallic laminated composites have been widely studied,especially in Ti-Al and Ni-Al material systems,but investigated less in the corresponding Fe-Al.At most,the reaction phases of Fe-Al material system are studied,and its mechanical properties are hardly involved.In this subject,carbon steel,430SS and304SS reacted with Al to form distinct interfaces severed as the interfacial reaction system of Fe/Al,Fe-Cr/Al and Fe-Cr-Ni/Al,respectively.Further study of their microstructure and reaction phases,simple study of physical properties,significant study of mechanical properties were performed.Specimens have been synthesized by a hot-pressure diffusion forming process.At a vacuum of 1×10^-1 Pa,they were heated at an actual temperature of655°C for different times.The phases of the intermetallics in laminated composites were analyzed by metallographic optical microscopy,SEM+EDS and XRD,respectively,and the growth kinetics of the intermetallics was calculated.Two physical properties for density and microhardness were measured by drainage method and microhardness tester,respectively.Compressive and flexural strength were obtained by quasi-static compression and room temperature three-point bending test,respectively.The dynamic compression performance was tested using a split-Hopkinson pressure bar?SHPB?test system.The main results of this research are as follows.?1?After carbon steel/Al reaction,the formation phases are FeAl₂ and Fe₃Al phase.after430SS/Al reaction,the microstructure is a uniform layer composed of Fe₂Al₅ phase and a two-phase layer composed of Al_5.5Cr_1.95Fe_2.5 precipitate as well as Cr₂Al₁₃ and Fe₄Al₁₃3 phases.The products of the 304SS/Al reaction were similar to 430SS/Al,but the Fe_0.7Ni_1.3Al₉ phase was added to the uniform layer.?2?The FeAl₂ and Fe₃Al phases of carbon steel/Al reaction satisfy the parabolic relationship with time,and it was known that both growth was controlled by bulk diffusion.The overall intermetallic compound layer after 430SS/Al reaction growed according to the“mixed kinetic growth mechanism”,which was between bulk diffusion and interfacial diffusion.The overall intermetallic compound layer after 304SS/Al reaction is also grown according to“mixed kinetics growth mechanism”,which is between the grain boundary diffusion and the body diffusion.?3?The study of the physical properties of the materials showed that the density of the carbon steel/Al reaction sample is good,but the sample prepared by 430SS/Al is not dense enough,and the density of the sample prepared by 304SS/Al is between carbon steel/Al and304SS/Al.The microhardness at the interface of the three materials is in line with reality.Thin toughness DO3 layer of Fe₃Al phase between carbon steel and FeAl₂ uniform layer can reduce stress concentration and delamination at the interface of the materials,but the interfaces between each two stainless steels and intermetallic layers are more stress-concentrated,which may also lead to Layer phenomenon.?4?The study of the mechanical properties of the materials showed that the samples prepared by 304SS/Al have the highest compressive strength by quasi-static compression test.The flexural strength of the samples prepared by 304SS/Al was much stronger than that of430SS/Al.After the dynamic compression performance test,the tensile strength of the samples with 304SS/Al reaction for 6h was found to be between 750-1200MPa.