EFFECT OF THE INTERMEDIATE HEAT TREATMENT PROCESSES ON THE OXIDATION CHARACTERIS- TICS OF Zr-1Nb-0.2Y ALLOY IN 420 ℃ AIR
Changji LI1,2,Liangyin XIONG1,2,Shi LIU1,2()
1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
Changji LI,Liangyin XIONG,Shi LIU. EFFECT OF THE INTERMEDIATE HEAT TREATMENT PROCESSES ON THE OXIDATION CHARACTERIS- TICS OF Zr-1Nb-0.2Y ALLOY IN 420 ℃ AIR. Acta Metall Sin, 2016, 52(1): 85-92.
Zr-based alloys have been used as cladding tubes in nuclear reactors for several decades due to their superior mechanical properties, good corrosion resistance and low neutron absorption cross-section. Zr alloys consist of hcp-structured a-Zr matrix and dispersed precipitate particles. These precipitate particles play a key role in improving the service performance of the alloy. In general, the manufacturing of Zr-based alloy tubes or sheets involves a series of deformation and annealing processes, which lead to a modification of the precipitate particles in size and distribution and an improvement of comprehensive properties of the alloys. In this work, the effect of intermediate heat treatment processes on precipitate particles and air oxidation characteristics of Zr-1Nb-0.2Y (mass fraction, %) alloy was studied. With increase of rolling and annealing times, the oxidation resistance of Zr-1Nb-0.2Y alloy was improved. The final product from manufacturing route II with intermediate annealing process of 640 ℃, 3 h+570 ℃, 3 h was proved to be most resistant to oxidation in 420 ℃ air. TEM images and EDS results showed that relevant parameters such as precipitate particle volume fraction, precipitate particle mean diameter, Nb+Y content (including mean content and total content) in precipitate particles were modified by intermediate annealing processes, which essentially influenced the oxidation characteristics of Zr-1Nb-0.2Y alloy. The smaller the mean size of precipitate particle and the higher the Nb+Y content in the precipitate particle are, the better the resistance to air oxidation of Zr-1Nb-0.2Y alloy.
Fig.1 Four intermediate annealing processes for Zr-1Nb-0.2Y alloy
Fig.2 Oxidation weight gain curves for Zr-1Nb-0.2Y alloy in 420 ℃ air with manufacturing routes of I (a), II (b), III (c) and IV (d)
Fig.3 Comparisons of the weight gain curves for Zr-1Nb-0.2Y alloy with same deformation but different heat treatment processes for samples S4~S7 (a) and S8~S11 (b)
Fig.4 TEM images of samples S1 (a) and S1′ (b), and S1′ in 420 ℃ air for 400 h (c)
Fig.5 Oxidation weight gain curves of samples S1 and S1′ in 420 ℃ air for 472 h
Fig.6 TEM images of Zr-1Nb-0.2Y alloy of samples S1~S11 (a~k)
Fig.7 EDS analysis of the Y-containing precipitate in Zr-1Nb-0.2Y alloy (a) and TEM image of the square precipitates in Zr-0.2Y alloy (b)
Fig.8 Relationships of the weight gain of Zr-1Nb-0.2Y alloy at different manufacturing stages in 420 ℃ air for 532 h with second phase particle (SPP) volume fraction (a), SPP mean size (b), Nb+Y mean content in SPP (c), Nb+Y total content in SPP (d) and Nb+Y total content in matrix (e)
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