Phase Equilibria And Properties Of Zr-Sn-Mo-Nb-Fe Alloy Systems

Zirconium alloys serves as the structural materials in the nuclear reactor.Nb,Mo,Sn and Fe are the important alloying elements in the zirconium alloy.The effects of alloying elements on the properties of zirconium alloys depended on the interaction of alloying elements in the zirconium alloys.Multicomponent alloy phase diagram provided basic knowledge to understand the relationship of microstructure on the properties.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,and energy dispersive spectroscopy（EDS）were used to study the isothermal sections of Zr-Mo-Fe（O）at 1000°C and 900°C and the phase composition of Zr-Mo-Nb-Fe（O）system at 1000°C.The effects of Mo and Fe contents on mechanical properties and corrosion resistance of Zr-0.5Sn-x Mo-1.0Nb-0.3Fe（x=0,0.2,0.4,0.6,0.8 wt.（4））and Zr-0.5Sn-0.5Mo-0.5Nb-y Fe（y=0,0.1,0.3,0.5,0.7 wt.（4））alloys were studied by universal tensile testing machine,XRD,hardness tester,electrochemical workstation and SEM.It is expected to provide a scientific knowledge for the optimization and establishment of thermodynamic database of zirconium alloy.The results are as follows:（1）The phase diagram of Zr-Mo-Fe（O）Zr rich region（Zr>30 at.%）at 1000°C was studied.A new ternary compound stabilized by oxygen,labeled asγ-Zr₂（Mo,Fe）,with its approximate composition of Zr₆₃Mo₁₂Fe₂₅,was found.The compound has a cubic structure of Ti₂Ni type with a lattice parameter of 1.2213 nm.No Zr₉Mo₄Fe compound was found.It is found that there are three four-phase regions in the isothermal section of Zr-Mo-Fe（O）（Zr>30 at.%）system at 1000°C,which are[βZr+λ-Zr（Mo,Fe）₂+γ+Zr Mo₂],[βZr+λ-Zr（Mo,Fe）₂+γ+liquid]and[λ-Zr（Mo,Fe）₂+γ+liquid+Zr Fe₂].（2）The phase diagram of isothermal section of Zr-Mo-Fe（O）（Zr>30at.%）at 900°C is studied.It is further confirmed that theγ-Zr₂（Mo,Fe）phase belongs to the oxygen stabilized ternary compound.No Zr₉Mo₄Fe compound has been found at this temperature.It is also found that there are4 four-phase equilibria in the system,i.e.,[γ-Zr₂（Mo,Fe）+λ-Zr（Mo,Fe）₂+Zr Fe₂+Zr₂Fe],[γ-Zr₂（Mo,Fe）+λ-Zr（Mo,Fe）₂+βZr+Zr₂Fe],[γ-Zr₂（Mo,Fe）+λ-Zr（Mo,Fe）₂+βZr+Zr Mo₂],and[γ-Zr₂（Mo,Fe）+αZr+βZr+Zr Mo₂].（3）The phase transformation of Zr-Mo-Nb-Fe（O）（Zr>50 at.%）alloy at 1000°C was studied.It was found that there was liquid phase in the Zr rich region.βZr with two different compositions was found.Due to the existence of oxygen,αZr could also be observed.The co-existence of[γ-Zr₂（Mo,Fe）+β₁Zr+L]was found.Theγ-Zr₂（Mo,Fe）in Zr-Mo-Fe system is different to the Zr₂（Nb,Fe）in the Zr-Nb-Fe system.No continuous solid solution between them was formed.（4）The effects of Mo content on mechanical properties and corrosion resistance of Zr-0.5Sn-x Mo-1.0Nb-0.3Fe（x=0,0.2,0.4,0.6,0.8 wt.%）alloys were investigated.When Mo content is 0.8 wt.%,the maximum yield strength and tensile strength are 646.9 MPa and 694.6 MPa,respectively.When Mo content is 0.6 wt.%,the maximum plasticity is3.11%.The Rockwell hardness of the alloy increases with the increase of Mo content.When Mo content is 0.8 wt.%,the maximum Rockwell hardness is 99.5 HRB.In terms of corrosion performance,with the increase of Mo content,the corrosion current density first decreases and then increases.When the Mo content is 0.4 wt.%,the minimum corrosion current density of the alloy is 4.41×10^-5m A/cm²,and the corrosion potential is-337.1m V,indicating that the addition of Mo element can improve the corrosion resistance of the alloy to a certain extent.（5）The effects of Fe content on the mechanical properties and corrosion resistance of Zr-0.5Sn-0.5Mo-0.5Nb-y Fe（y=0,0.1,0.3,0.5,0.7wt.%）low tin zirconium alloys were studied.Fe can improve the tensile strength and yield strength of Zr-0.5Sn-0.5Mo-0.5Nb-y Fe alloys,but has no obvious effect on the elongation.With the increase of Fe element,the tensile strength and yield strength of the alloy increase.When y=0.7 wt.%,the yield strength,tensile strength and elongation of the alloy reach the maximum value,which are 398.3 MPa,459.9 MPa and 3.09%,respectively.With the increase of Fe element,the Rockwell hardness of the alloy can also be increased.The maximum Rockwell hardness of the alloy is 93 HRB.The addition of Fe can also improve the corrosion resistance of the alloy.When the minimum corrosion current density of the alloy is 9.12×10^-6m A/cm²,the corresponding of corrosion potential is-345.1 m V.