Preparation And Characterization Of Fe₃Si Type IMC Layer On Stainless Steel

In very harsh Oxidation conditions,the weight gain of a0Cr18Ni9 austenitic stainless steel, is very slow ,But at some point the growth rate become largely ,lead to Large Oxide loss. For this reason 0Cr18Ni9 stainless steel is hard to use in Such occasions that have Strict requirements.Fe₃Si as a metal silicide has excellent oxidation resistance,the formation of SiO₂ play an imporant role in the oxidation resistance , but the room temperature brittleness limite silicide Fe₃Si as a structural material. But Fe₃Si used as a coating in the field of surface modification of materials which can avoid the brittleness of Fe₃Si and to expand the applications of Fe₃Si. Diffusion Coatings on 0Cr18Ni9 austenitic stainless steel in one hand can significantly increase strength, hardness, wear resistance on the surface of the 0Cr18Ni9 austenitic stainless steel and in the other hand can also increase High temperature oxidation resistance.Based on the above thoughts,Fe₃Si type silicide layer containing Cr and Ni alloying elements with different Si concent deposited on 0Cr18Ni9 austenitic stainless steel stainless steel were formed in molten salts. phase composition of silicon layer Analysis by x-ray diffraction By scanning electron microscopy (SEM) and energy dispersive spectrometer attached (EDS) of the diffusion layer cross-section of the morphology and composition.By means of Adjustment Molten Salt System, Temperature, and time.To improve the structure and performance of silicon coating and thus increase Mechanical properties and high temperature oxidation resistance of 0Cr18Ni9 austenitic stainless steel. Some useful conclusions are drawed :(1) using molten mixture of Na₂SiF₆:Si=8:2 as siliconizing agent and the molten halogenide of alkali metals of NaCl:KCl:NaF=2:2:1 as siliconizing agent carrier,can get different quality silicide coating. XRD analysis shows that: the surface of the sample after siliconized for 10h at 800℃in Silicon infiltration system 1 and 2 is Fe₃Si multivariate transition metal silicide.SEM image of cross-section of the silicide layer indicate that : combition betwween silicide coating and substrate. Is very tight but Kekendae Porosity zone exist betwween silicide coating and substrate dispite different Experimental parameters ,EDS analysis on cross–section showed that:in proceed of the experment Fe Cr Ni element spread from substrate to Silicide coating In contrast with the Si element,in junction between substrate and Silicide coating Occurred Sudden change of Si element concent.(2) Analysis showed that the axial tensile mechanical properties Proportional limit that siliconized for 10h and 5h larger than 0Cr18Ni9 austenitic stainless steel, siliconized for 10h and 5h have little effect on the tensile strength of stainless steel, silicide coating in addition to step-like fracture surface of the sample was outside, but also with a break along the Kekendaer pores, leading to the cross section of coating area decreases,and the reason for different elastic modulus of the sample.(3) The study concern influence of siliconized Temperature, siliconized time and siliconized System on Growth rate and quality of the Silicide coating. Analysis shows that: Growth rate Increase With siliconized Temperature up , When the silicide coating reaches a certain thickness, holding time is not very effective to increase the thickness of coating, In the same holding time and temperature , the infiltration system 2 obtained significantly greater than the thickness of system 1, but there is more penetrating layer defects infiltration system 2 than infiltration system 1.(4) Aspects of high temperatur oxidation Fe₃Si Silicide coating have good High-temperature oxidation resistance than bare 0Cr18Ni9 austenitic stainless steel . Cyclic oxidation kinetics of Fe₃Si Silicide coating at 800℃,900℃Performance Parabolic law In the high temperature oxidation process. As quickly form a continuous SiO₂ protective film,making the 900℃for better oxidation resistance. Experimental analysis shows that the composition of the Oxide layer is mixed with Fe₂O₃, SiO₂ and Cr₂O₃. In the high temperature oxidation process,at 800℃Silicide combine well with the 0Cr18Ni9 Stainless steel substrate In the high temperature oxidation process at 900℃Si ,Cr atom diffusion Strengthening the combine of the coating with the substrate. Oxide film on Silicide coating at 900℃is dense than at 800℃, Fe₂O₃ phase and small amount of SiO₂ was found in the Oxide layer ,the Peaks of SiO₂ at 900℃enhance greatly .