Study of phase transformation in U-2.5Zr-7.5-7.5Zr and U-3.0Zr-9.0Nb system by Rietveld method

The Rietveld refinement has been employed for study of phase transformation of alloys U-2.5Nb-7.5Zr (wt%) and U-3Zr-9Nb (wt%). The ingots were produced in vacuum induction furnace at temperature of about 1500 degree C followed by cooling to room temperature. The ingots were cut into coin-shaped samples with 2.5 cm in diameter and 0.3 cm of thickness. The samples of both alloys were homogenized at 1000 degree C/16 hours e aged at 600 degree C for 0.5, 3 and 24 hours. At the end of each treatment the samples were quenched in water. Data from X-ray diffraction were collected at room temperature using a Rigaku diffractometer D Max-RAPID radiation Cukα using steps of 0.02 degree (2θ) with scan angle in the range of 10-80 degree (2θ). The full diffraction pattern was analyzed by the Rietveld method using the GSAS program. The results showed that the refinement to this type of alloys is a challenging task. The difficulty can be attributed to microstructural imperfections such as planar defects. In the conditions employed in this work both U-3Zr-9Nb and U-2.5Zr-7.5Nb alloys aged for 0.5 and 3.0 hours presented the same composition of phases with majority presence of γS phase (93%wt) followed by minority presence of γ0 phase (7%wt). For the aging time of 24 hours both alloys experienced phase transformation with of presence of α and γS phases where the alloy U-3Zr-9Nb stabilized more strongly the γS phase. The alloy U-2.5Zr-7.5Nb is constituted of 69.5%wt of α phase and 30.5%w of γS phase and the alloy U-3.0Zr-9.0Nb constituted by 60%wt of α and 40%wt of γS phase. (author)