Preparation Of Fe₃Si Based Intermetallic Compounds And Investigation Of Their Oxidation Resistance

Fe₃Si based intermetallic compound is the research hotspot in the functional materials field due to its excellent magnetic properties and electrical properties. Besides,Fe3Si based intermetallic compounds have many excellent properties,such as, excellent corrosion resistance,oxidation resistance and wear resistance,etc.Moreover, they are easy to fabricate and the cost of the raw material is low,so the Fe₃Si based intermetallics can be a good candidate of structural material,unfortunately people didn't pay more attention to the relative research.Multi-component and multi-phase is one tendency of development of high performance intermetllics,but the researches about multi-component DO3-type Fe3Si intermetallics are very limited.However,these works can further improve the mechanical properties of Fe3Si and accelerate the applications of Fe₃Si as structural materials.Two kinds of Fe₃Si based intermetallic compounds(i.e.Fe₃(Si_1-x,Al_x)and Fe-Si-Cr-Al intermetallics)were prepared by using vacuum arc melting.In the present work,Al or Al,Cr was used as alloying elements to modify the mechanical properties of Fe₃Si by adjusting the long-rang-order parameter(LRO).Meanwhile,the as fabricated materials were characterized by XRD,SEM,EPMA,etc,and their LRO were calculated quantificationally.Besides,the hardness,compressive strength, bending strength of Fe₃Si based intermetallics were comprehensive evaluated.In addition,the excellent oxidation resistance of Fe3Si based intermetallics is one predominance for using as the structural material,so the high temperature oxidation behavior of Fe₃Si based intermetallics were studied at 800℃,900℃for 120h with the mode of circle oxidation in present work.Austenitic stainless steel AISI 304 was chose as a reference.Besides,the combination of effective diffusion coefficient D_effand oxidation rate constant was used to analyze the relative materials' oxidation kinetic process theoretically.The result showed that,The LRO value of Fe-3(Si_1-x,Al_x)intermetallics decreased with the increase of Al content.In the Fe-Si-Cr-Al system,the LRO decreased with the decrease of Si content markedly.The decreasing tendency of the LRO was promoted by the alloying of Al,Cr.The as fabricated Fe₃Si based intermetallics presented lower micro-hardness than that of Fe₃Si,but the compressive and bending strengths were improved.And the Fe₃Si based intermetallics alloyed by Al,Cr exhibited higher compressive and bending strengths than that of materials alloyed by Al.comprehensive evaluation showed that,appropriate LRO and a certain extent work hardening is the main course that the strength and strain of Fe₃Si were improved in the deformation.In the high temperature oxidation experiment,Fe₃Si intermetallics exhibited more excellent oxidation resistance than that of AISI 304 stainless steel,and the oxidation resistance of Fe₃Si based intermetallics was improved remarkably due to the exist of protective scale Al₂O₃.By using theoretical analysis about the oxidation kinetics of Fe₃(Si_1-x,Al_x),Al sub-boundaries diffusion was perhaps the mechanism for the scale growth of Fe₃(Si_0.67,Al_0.33)å’ŒFe₃(Si_0.80,Al_0.20),and the O grain boundary diffusion is also the possible mechanism.The mechanism for the scale growth of Fe₃(Si_0.33,Al_0.67) changed at 900℃,and the oxidation rate constant decreased due to the significant phase transformation of metastable Al₂O₃ to a-Al₂O₃.ln addition,in Fe-Si-Cr-Al,the element Cr accelerated the transformation of metalstable Al₂O₃ to a-Al₂O₃,especially at 900℃.But at 800℃,the addition of Cr induced the appearance of cankerous hole and grain boundary cracking.This special morphology is the result of collapse of the diffusion vacancies in the Cr₂O₃ due to the effect of internal stress in the scales. Besides,the composite alloying made the diffusion process of oxidation more complicated.