| The thesis studied several kinds of Zirconium alloys with different componentswhich were N1, N2, N3, N4, N5, N18, T1and T7alloys by SEM-SE, SEM-ECC,EBSD, TEM and DSC. The microstructural evolution of Zr alloy sheets and tubesduring processes and the effects of alloy elements (Cu, Cr and Sn) on the second phasesand phases transformation of Zr alloys were researched. At the same time, the dynamicmechanism of second phases precipitation were discussed simply. Some conclusionswere obtained below:(1) The undeformed microstructure of T1and T7Zr alloy sheets and tubes withc//ND (normal direction) was formed during cooled rolling. The distribution of secondphases was transformed from streamline distribution to diffusion distribution duringcooled rolling and the changes of second phases sizes cannot be observed obviously.The process of second phase growth fits for the Ostwald during annealing after cooledrolling, which is in good agreement with the curve calculated for second order kinetics.(2) T1tube contains βNbwith BCC structure and small size and Zr-Nb-Fe withFCC and bigger sizes. Most of second particles distributed in grain boundaries areZr-Nb-Fe phase which have stacking faults. The second particles of T1tube decomposeduring process and formed cluster contained two or more second particles.(3) Zr(Fe, Cr, Nb)2Laves with HCP or FCC and tiny sizes were observed in N1,N3, N4, N5and N18alloys and stacking faults were found in these Laves phases. TheCu, Cr and Sn elements have significant effects on the second phases of Zr alloys. theZr2Fe and Zr3Fe were formed by adding Cu and the formation of Laves phases werepromoted by adding Cr. The types of second phases were not changed by adding Sn.Meanwhile, the alloys elements have important effects on the second particle sizes.(4) The αâ†'β transformed temperatures were measured by DSC, quenching andcalculated used equilibrium phase transformation model built by Zhu and Devletian.Compared the measuring dates and calculative results, the result measured byquenching is more agree with the temperature of equilibrium phase transformation. Thedate measured by DSC is slightly higher than that of quenching, which can refer toactual temperature of αâ†'β phase transformation. The equilibrium phase transformationmodel by Zhu and Devletian were used to calculate the temperature of phasetransformation of Zr alloys. The calculative results were accorded with the date of quenching, proving that the model can be used in calculation of phase transformationtemperature of Zr alloys successfully.(5) Alloy elements have significant effects on the temperatures of αâ†'βå'ŒÎ²â†'αtransformations. During the heating process, the Tαâ†'α+βdecreases and Tα+βâ†'βincreaseswith Cu of Cr addition, which increase the region of the β phase. The Tαâ†'α+βincreasesand Tα+βâ†'βdecreases with the increase of content of Sn, which increase the region of αphase. During the cooling process, the Tβâ†'α+βand Tα+βâ†'αare increased by Cu addition,while Tα+βâ†'αincrease more than that of Tβâ†'α+β, which increase the region of β. TheTβâ†'α+βincreases by Cr addition, while Tα+βâ†'αis affected differently for different alloysby Cr element. However, the region of β is enlarged. The Tβâ†'α+βand Tα+βâ†'αaredecreased and increase respectively, which enlarge the region of α. Above all, the Cuand Cr elements can steady the region of β and Sn can steady the region of α.(6) The ship of volume fraction of β phase and temperature relational grahp is ‘S’.The relationship of energy (E) and precipitation temperature is similar in differentalloys that the E is highest in starting precipitation temperature and the change of E isnot apparent when the precipitation contents is about10%-90%, while the E is decreasenear the finishing precipitation temperature. |
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