Effect Of Temperature、Cr Concentration And Dislocation On The Precipitation Of α’ Phase In Fe-Cr Alloy By Phase Field Method

Fe-Cr alloy has become been the key material for nuclear reactors and aerospace pipelines owing to its excellent high temperature mechanical properties and good decay resistance.When Fe-Cr alloy is used in the temperature range of 573~823K,spinodal decomposition of Fe-Cr alloy will produce Cr-rich Nanoscale α’ phase,which will lead to a sharp decrease in decay resistance and high temperature mechanical properties of Fe-Cr alloy.Isothermal aging of FeCr alloys at different Cr concentrations and different temperatures will cause different size,morphology and density of the α’ phase produced by the spinodal decomposition of the Fe-Cr alloy.The dislocation and the spatial location of dislocation also will affect the nucleation location,diffusion form,particle size and micro-morphology of the α’ phase.Phase decomposition mechanism,micro-morphology and growth and coarsening process of Fe-Cr alloy will produce important impact in the evolution of thermal aging structure,improvement of mechanical properties and risk avoidance of the alloy.In the initial stage of isothermal aging,fine α’ phase particles are gradually separated from Fe-Cr alloy.With the ageing going on,fine particles of α’ phase gradually change into spherical.Non-spherical particles of α’ phase will gradually disappear in the matrix and eventually reach equilibrium state.With the increase of temperature,the average particle radius and equilibrium volume fraction of spherical α’ phase are increased gradually,while the number of particles are reduced gradually.The results show that the temperature is higher,the coarsening degree of the growth of the alpha phase is greater,and the mechanical properties of the alloy are lower.The spinodal decomposition of Fe-35 at.% Cr alloy,Fe-40 at.% Cr alloy and Fe-45 at.% Cr alloy aged at 700 K was studied.As aging time goes on,some of the fine alpha-phase particles in Fe-40 at.%Cr alloy turn into spherical fine α’ phase independently,while some of the alphaphase particles connect with each other and gradually become ellipsoidal or rod-like α’ phase.With the aging time prolonging,the fine particles of Fe-45 at.% Cr alloy were transformed into rod-like phases.The dislocations form α’ phase,and there is a clear phase boundary between the dislocations and the matrix phase.With the prolongation of aging,the phase boundaries continue to diffuse outward,and the phase boundaries continue to form a’ phase.With the increase of the concentration of Cr,the phase boundaries will gradually connect and form a ring to diffuse outward,and the average particle radius of the a’ phase will be equal,and the volume fraction will increase compared with the dislocation-free effect.