Crystallography Of Ge Containing Zircaloy-4 Alloy

The performance of Zircaloy-4?Zr-4,Zr-1.30wt%Sn-0.20wt%Fe-0.10wt%Cr?alloy has become a vital factor for reactor operations as it governs nuclear reactor safety,service life and operating costs.Metallurgical optimization by Germanium?Ge?addition can improve the corrosion resistance of Zr-4 alloy,and crystallography of the Ge containing Zr-4 alloys would be crucial to alloy design and modifications.This thesis is mainly divided into three parts:crystallographic features of Zr-4 alloy;precipitates and their evolution in the as-solidified Ge containing Zr-4 alloys?Zr-4+0.01,0.05,0.10,0.25 and 0.50wt.%Ge?;and unusual characteristics of precipitates as observed in the hot-deformed Ge containing alloy.As the main body of the thesis,the second part would be systematically and comprehensively discussed.The rest two parts are supplements to the main body,and would be selectively introduced.The C14 structured Zr?Fe,Cr?2 Laves phase precipitates in Zr-4 alloy contained?0001?stacking faults,which were resulted from the synchroshear phase transformation.The driving force came from the interaction between precipitates and grain boundaries.The a?FCC phase transition induced by intergranular thermal residual stress?ITRS?in the as-solidified Zr-4 alloy was observed.The FCC phase and the a phase matrix obeyed the 'B-type'orientation relation:<2???0>a//<110>FCC and{0001}?//{111}FCC.All of the as-solidified Ge containing Zr-4 alloys exhibited lamellar microstructure,which contained a phase matrix and precipitates.Among these precipitates,Cr and Fe always accumulated simultaneously,whereas Ge independently.Thus,two kinds of precipitates could be classified:Cr-Fe containing precipitates and Ge containing precipitates.Cr-Fe containing precipitates included Fe-Cr containing a phase and Zr?Fe,Cr?2 Laves phase,and they were observed in 0.01wt.%-0.50wt.%Ge alloys.Ge containing precipitates involved the Ge containing a phase,Ge containing FCC phase,Ge containing ? phase,ordered Ge containing a phase,Zr5Ge4 phase and Zr₃Ge phase,and they were observed in 0.05wt.%-0.50wt.%Ge alloys.These precipitates displayed parallel cellular,parallel rod-shaped,triangular distributed needle-shaped,crossed rod-shaped,discrete granular and band-distributed granular morphologies,respectively.The Ge containing a phase was observed in 0.05wt.%?0.25wt.%Ge alloys,as a result of Ge segregation.The Ge containing FCC phase was observed in 0.25wt.%Ge alloy,and obeyed orientation relationship with the matrix:<2???0>a//<110>Fcc and {0001}?//{111}FCC.The Ge containing ? phase was observed in 0.50wt.%Ge alloy,obeying the orientation relationship with the matrix:{0001}?//{11???0}? and<11???0>?//<0001>?.The Ge atoms owned planar periodicity in their distribution where the planes were parallel to?21 1 0??,?11???0?? and?1210??,respectively,resulting in the unique triangular distribution of ? phase.The ordered Ge containing a phase was observed in 0.50wt.%Ge alloy,and Ge atoms were ordered at every 5?11???0?? and?10????? planes.Zr5Ge4 phase was observed in 0.25wt.%Ge alloy,as a result of Ge segregation.Zr₃Ge phase was observed in 0.50wt.%Ge alloy,which was led by L??+Zr₃Ge eutectic reaction.As the content of Ge increased,the distribution of Ge atoms gradually transformed from disordered into ordered forms.The ordered distribution of Ge atoms would play detrimental role in corrosion resistance.During the hot deformation,the morphology,size,distribution and structure of Zr₃Ge phase altered.While the loading was nearly parallel to the major axis of Zr₃Ge phase as well as the?0001?? basal plane in the matrix,core-shell structured Zr₃Ge precipitates would be observed.The 'core'was Zr₃Ge phase,and the'shell,structure was FCC-Zr phase,which obeyed the'B-type'orientation relationship with the matrix:<2???0>?//<110>FCC and {0001}?//{111}_FCC.The region with?0001?_? stacking faults was located between the matrix and the FCC shell structure,and acted as the transition zone during ??FCC transformation.