Effects Of Cu And Quenching Rate On The Precipitation Behavior Of The Precipitates In Zr-Sn-Nb Alloy

In present study,the microstructure and properties of Zr-1.0Sn-0.3Nb-0.3Fe and Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cu,noted as Nland N2 respectively,were investigated using multiple characterization and analysis techniques including optical microscopy(OM),scanning electron microscope(SEM),electron channeling contrast(ECC),electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).A systematic work was conducted on the microstructure characterization and the kinds of secondary phases in different cooling rate and the secondary phase evolution in isothermal aging followed water quenching of N1,N2 alloy,meanwhile the effect of Cu element on the microstructure and secondary phase were discussed tentatively in N2 alloy.Extensive work has been done to investigate the effect of cooling rate on SPPs in Zirconium alloy in terms of types,morphologies,sizes and distributions.Main conclusions attained by present study are as following:? Following ? solution treatment,cooling process was conducted in different media consisting of water,liquid nitrogen,air and furnace for both N1 and N2.Four distinct microstructures were obtained after cooling,which are tiny intersecting needle-like martensites,basket-weave widmanstatten structure,parallel-plate widmanstatten structure and lenticular structure.It was found that the microstructure of N2 alloy was refined considerably due to cu element addition,and leading to a higher microhardness.Furthermore.With decreasing in cooling rate,the average width of a laths increases,while the micro-hardness of alloys goes down.? Retained ? phase accompanied with ? phase was observed at a lath boundaries and triangular grain boundaries in water-quenched specimens.The orientation relationship(OR)between ? and a matrix corresponds with the well-known Burgers OR,is {0002}?//{110}p,<1120>?//<111>?.While the retained ? and ? phase were determined to be obeying two ORs as followed:(0001)?//(111)?,[2110]?//[101]? or(1010)?//(121)?,[1012]?//[012]p.Moreover,the addition of Cu led to evident refinement of retained ?+? phase.For the evolution of Secondary phase,Zr3Fe,Zr2Fe,(Zr,Nb)2Fe with orthorhombic,tetragonal and face-centered cubic crystal structures respectively were found at boundaries of a laths for both air and liquid nitrogen cooling specimens,an OR of {111}zr2Fe//{0001}??<110>zr2Fe//<1120>awas detected between Zr2Fe and a matrix.The retained ? phase riched in Nb and Zr(Fe,Nb)2 with hcp structure were explored in specimens with furnace cooling.? The following conclusions of precipitation sequence for the two novel alloys during isothermal aging can be drawn:1)N1 alloy:Zr3Fe(Orthorhombic)?Zr3Fe(Orthorhombic),Zr(Fe,Nb)2(HCP)?Zr3Fe(Orthorhombic),Zr(Fe,Nb)2(HCP),(Zr,Nb)2Fe(FCC).2)N2 alloy included a little amount of Cu element:Zr3(Fe,Cu)(Orthorhombic)?Zr3(Fe,Cu)(Orthorhombic),Zr(Fe,Nb,Cu)2(HCP)?Zr3(Fe,Cu)(Orthorhombic),Zr2(Fe,Cu)(Tetragonal),Zr(Fe,Nb,Cu)2(HCP).