Effect Of Zr On The Oxidation Resistance Of Fe-based Alloys And Related Phase Equilibrium

Iron-based superalloys are widely used in high-temperature service environments due to their excellent performance and low cost.The low oxidation resistance is one of the key factors affecting the service life of iron-base superalloys.The addition of alloying elements is an important method for improving the material properties in the world.Zr is a frequently alloying element in high-temperature alloys.Its main function is to increase the oxidation resistance and plasticity of the alloy.There has been a consensus Si can improve the high temperature oxidation resistance of the alloy.Rare earth element Y can not only purify the alloy but also improve its other properties such as oxidation resistance.In this dissertation,the effect of Zr on high-temperature oxidation resistance of Fe-based alloy and related phase equilibrium of Zr-Si-Y ternary system were studied.The isothermal section phase relationship of Zr-Si-Y ternary system at 900 ? was determined by experiment,and the effect of Zr on high-temperature oxidation resistance of Fe-based alloy.The research results provide relevant experimental data for the design and development of new iron-based alloys,it has strong guiding significance and a certain application value.The isothermal section phase relationship of the 900? Zr-Si-Y ternary system was determined by using the equilibrium alloy method.The isothermal section has 10 three-phase regions,nine three-phase regions were determined by experiment.They were:Zr+Y+Zr2Si,Y+Zr2Si+Y5Si3,Zr3Si2+Zr2Si+Y5Si3,Y5Si3+Y5Si4+Zr5Si4,ZrSi+Zr5Si4+Y5Si4,ZrSi+YSi+Y5Si4,YSi+Y3Si5+ZrSi,ZrSi+ZrSi2+Y3Sis and Si+Y3Si5+ZrSi2.The maximum solid solubility of Zr in Y,Y5Si3,Y5Si4,YSi and Y3Si5 were:2.2at.%,5.0at.%,4.1at.%,4.8at.%and 2.9at.%.The maximum solid solubility of Y in Zr,Si,Zr2Si,Zr3Si2,Zr5Si4 and ZrSi were:0.2at.%,1.9at.%,4.4at.%,5.1at.%,3.3at.%and 3.4at.%.The maximum solid solubility of Si in Y is 4.1at.%.Y has very limited solid solubility in ZrSi2.The effect of Zr on the oxidation resistance of iron-based alloys was investigated using constant temperature oxidation method.Four alloy of Fe-3Si-mZr(m=0,0.5,1,2)were designed.The results show that the addition of Zr can significantly improve the oxidation resistance of Fe-3Si alloy in air at 900?.The Fe-3Si-lZr alloy has the best high-temperature oxidation resistance.The order of the oxidation rates of the four alloys were:Fe-3Si>Fe-3Si-0.5Zr>Fe-3Si-2Zr>Fe-3Si-lZr.The addition of Zr element refines the crystalline grain of the Fe-3Si alloy and oxide,it can increase the grain boundaries in the alloy and the oxide,increases the diffusion rate of each element in the alloy,promote the formation of active elements oxide films such as SiO2 and ZrO2,thus it can improves high-temperature oxidation resistance of alloy.The oxidation kinetic curves of the four alloys conform to the parabolic law.