Alloy Elements Cr,Mo On Strengthening And Toughening Mechanisim Of Iron Aluminide Intermetallic Compounds

Iron aluminide intermetallic compounds show excellent resistances to high-temperature oxidation,heat corrosion,and erosion.Further,they contain Fe and Al,two of the most commonly used metals in the industry and thus have the advantage of low cost.Therefore,iron aluminide intermetallic compounds have been studied as structural materials for decades.However,they are yet to find widespread use in industrial applications.Given that they exhibit many excellent properties,the basic research and development of iron aluminide intermetallic compounds is being given significant importance in China.Moreover,improving the room-temperature brittleness of the iron aluminide intermetallic compounds used as engineering materials remains an important issue.In this study,the effects of Cr and Mo on the strength and toughness of B2-FeAl and DO3-Fe₃ Al as well as the underlying mechanisms responsible are investigated based on density functional theory and the empirical electron theory of solids and molecules.In addition,it is determined whether the observed effects are related to solid-solution hardening,grain-boundary segregation,and phase-interface strengthening.The objectives and results of the study can be summarized as follows:?1?The effects of Cr and Mo on the structural stability and elastic properties of B2-FeAl and DO3-Fe₃ Al through replacement solution are studied using density functional theory.The underlying micromechanisms are also investigated.The results show that Cr and Mo preferentially replace Al in both FeAl and Fe₃ Al.Further,the addition of the alloying elements improves the strength and ductility of FeAl and Fe₃ Al,with the effect of Mo being more significant than that of Cr.The reason for the observed improvements is the fact that the addition of Cr or Mo improves the atomic bonding capacities of FeAl and Fe₃ Al,thereby enhancing their stability.?2?The effects of Cr and Mo solid-soluted in FeAl and Fe₃ Al on the valence electron structures and ductility of B2-FeAl and DO3-Fe₃ Al are studied using a developed system that involves calculating and analyzing the bond length difference based on the empirical electron theory of solids and molecules.Based on the increases in the lattice electronic number and the covalent bonds electronic logarithmic of the Cr-and Mo-ternary alloys of FeAl and Fe₃ Al,it is concluded that Cr and Mo improve the toughness and structure stability of FeAl and Fe₃ Al.?3?The effects on the grain-boundary stability and the segregation of Cr or Mo at the grain boundaries of FeAl?3?1 10?and Fe₃Al?5?012?are investigated.The results show that the grain boundaries of the FeAl and Fe₃ Al systems alloyed with Cr or Mo are stable,with both Cr and Mo replacing Al at the grain boundaries and increasing the grain-boundary strength.In addition,the strengthening effect of Mo is greater than that of Cr.Elucidation of the micromechanisms involved suggests that the Cr-d or Mo-d orbital electrons are involved in hybrid and that the charge densities of Cr-Fe,Cr-Al,Mo-Fe,and Mo-Al increase after the addition of Cr or Mo,which,in turn,increases the atomic binding capacities of the FeAl and Fe₃ Al grain boundaries.?4?The effects of the cohesive capacity and electronic structures of Cr2 Al and Mo on the FeAl and Fe₃ Al phase interfaces are studied.In addition,the stable structures of the FeAl/Cr2 Al,FeAl/Mo,Fe₃Al/Cr2 Al,and Fe₃Al/Mo phase interfaces are determined.The results also show that both Cr2 Al and Mo strengthen the FeAl phase interface and that the strengthening effect of Cr2 Al is stronger.The strengthening effect of Cr2 Al on the FeAl phase interface can be attributed to the fact that the configuration of the electrons around the Cr,Fe,and Al atoms changes and the directionality of the electron atmosphere decreases.The strengthening effect of the Mo phase on the FeAl phase interface can be attributed to the fact that the directionality of the electron atmosphere between Mo-Fe and Mo-Al is decreased.On the other hand,Mo strengthens the Fe₃ Al phase interface while Cr2 Al weakens it.The effect of Cr2 Al on the Fe₃ Al phase interface can be attributed to the fact that the width of the Fe₃Al/Cr2 Al interface is greater than that of the Fe₃Al/Fe₃ Al interface,even though the charge densities of Fe₃Al/Cr2 Al and Fe₃Al/Fe₃ Al are nearly identical.Finally,the effect of the Mo phase on the Fe₃ Al phase interface can be attributed to the fact that the charge density of Mo-Fe at the Fe₃Al/Mo interface is greater than that of Al-Fe at the Fe₃Al/Fe₃ Al interface,even though the widths of the Fe₃Al/Mo and Fe₃Al/Fe₃ Al interfaces are similar.?5?The preferred substitutional positions of Cr and Mo as alloying elements at the FeAl/Fe₃ Al phase interface are investigated,and the effects of Cr and Mo on the electronic structure of the FeAl/Fe₃ Al phase interface are analyzed.It is found that Cr and Mo preferentially replace Al at the FeAl/Fe₃ Al phase interface.Based on an analysis of the electronic structure and electronic densities,the observed increase in the Griffith rupture work,W,of the FeAl/Fe₃ Al phase interface can be attributed to the substituted elements Cr and Mo increasing the number of bonding peaks of the density of states of the FeAl/Fe₃ Al phase interface as well as the numbers of density of states of the Al and Fe atoms at the FeAl/Fe₃ Al phase interface and the charge densities of Cr-Fe,Cr-Al,Mo-Fe,and Mo-Al at the FeAl/Fe₃ Al phase interface.