Study Of Nanoscale Phase In Fe-Cr Based Alloys With Phase-field Simulation Under Multiaxial Strain

Fe-Cr based alloy has excellent mechanical properties,and good resistance to corrosion,oxidation and radiation.Therefore,Fe-Cr based alloy is widely applied in pressure pipelines of nuclear power plant,heat exchanger pipelines and marine engineering fields.Stress and strain change the composition distribution inside the alloy,also affect the micro structure and mechanical properties.Due to high temperature and high pressure,the alloy matrix separates the fine dispersed Cr-riched nano scale phase,which not only contributes to the precipitation strengthening but also thermal embrittlement phenomenon,threatening the service safety of the alloy.Therefore,the investigation of micro structure and kinetics evolution of nanoscale phase under strain can provide theoretical reference for the prediction of micro structure and properties of alloy.Based on the Cahn-Hilliard diffusion equation,a phase-field model coupled with applied stress is established to study the effects of multiaxial normal strain on the morphology and kinetics evolution of nanoscale phase in Fe-32at.%Cr and Fe-32at.%Cr-10at.%A1 alloy,as well as the micro structural evolution of the diffusion interface under the alternating strain in the multilayered alloy.The effects of uniaxial,biaxial and triaxial normal strains on the phase separation and micro structural evolution are revealed.Except that the triaxial compression strain delays the precipitation of Cr-riched nano scale phase,uniaxial,biaxial and triaxial strains promote phase separation,among which the biaxial tension with uniaxial compression strain results in the most obvious micro structural evolution on forming the thin stripe-slice phase.The particles under triaxial compression strain are more finely dispersed.The evolution of the boundary micro structure in the multilayered Fe-32at.%Cr alloy with alternating strain is investigated.The Cr-riched nano scale phase tends to precipitate at the boundary of strain relaxed region to form the band morphology parallel to the boundary,and the band is more regular at the boundary where tension and compression strain alternate.When the distance of each alloy layer is small enough,the neighbor bands in the tensile strain zone merge into a Cr-riched nanoscale band,and the compressive strain zone forms the matrix phase.The micro structure and kinetics evolution of Fe-32at.%Cr-10at.%Al ternary alloy under biaxial normal strains are studied.Biaxial normal strains promote the evolution of Cr-riched nanoscale phase,in which biaxial compression/tension normal strain results in the fastest variation,and secondly,and the evolution rate is faster under biaxial compression normal strain than that under biaxial tension normal strain.