Study On Microstructure And Mechanical Properties Of Iron-aluminide Intermetallics Prepared By Microwave-assisted Combustion Synthesis

Iron-aluminide intermetallics were prepared by microwave-assisted combustion synthesis technology,based on raw materials of Al and Fe₂O₃ powders.A series of iron-aluminide intermetallics(the contents of Al at.%:21%,25%,28%,32%,36%) were prepared by adjusting the proportion of mixture.The effect of Al content on microstructure and properties was investigated.The microstructure and properties of Fe-28Al alloy were also studied after addition of 3 at.%Cr.The adiabatic temperature(T_ad) of reaction system was calculated by using thermodynamics theory.From the point of view of thermodynamics,the cause of reaction generation was analyzed,and the variation of T_ad with different content of Al,as well as the effect of T_ad on microstructure formation was investigated.In addition,the mechanism of microstructure formation was discussed.The results indicate that bulk nanocrystalline Fe-Al intermetallics are successfully prepared by microwave-assisted combustion synthesis.The microstructure of products is nanocrystalline Fe₃Al matrix with the grain size of 30nm～50nm dispersed with acicular and granular phase of Fe₃Al with several hundred micrometres order of magnitude.In the range of stoichiometric composition of Fe₃Al,microstructure with nanocrystalline is obtained when Al content is altered.The acicular phase in non-stoichiometric composition is coarser than that of Fe-25Al alloy with stoichiometric composition.The solidification microstructure is characterized with dendrites when Al at.%reaches 36%.Acicular phases in the microstructure of Fe-28Al disappear after addition of chromium,and a large number of granules appear in Fe-28Al-3Cr.Compared with conventional casting Fe-25Al,the microhardness and wear resistance of iron aluminides prepared by microwave-assisted combustion synthesis increase obviously. The microhardness of Fe-Al alloys with different compositions is about 420HV～650HV,and the casting Fe-25Al is 250HV on average.And the wear rate is one order of magnitude lower than that of casting.The wear resistance increases with the increase of Al content.Compared with Fe-28Al alloy,microhardness of Fe-28Al-3Cr alloy is little affected by chromium addition,while the wear rate is decreased.