Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Zirconium alloys with low alloying content are mainly used in the nuclear industry as structural materials because of their superior properties in terms of thermal neutron transparency, mechanical strength and corrosion resistance. They are used for fuel cladding tubes and channels. The reaction between zirconium and water at high temperature forms oxide film on the surfaces. In order to further improve the corrosion resistance of Zrbased cladding tubes, research has continued on developing new zirconium alloys. The corrosion resistance of Zr-0.72Sn-0.32Fe-0.14Cr-xNb alloys (x=0, 0.12, 0.28, 0.48, 0.97, mass fraction, %) was investigated in a superheated steam at 500 ℃ and 10.3 MPa by autoclave tests. All the plate specimens of zirconium alloys with thickness of 2.8 mm have a similar texture. The microstructure of alloys and oxide films on the corroded specimens were observed by TEM and SEM. The results showed that no nodular corrosion appeared on these alloys for 500 h exposure. The thickness of oxide layers developed on the rolling surface (SN), the surface perpendicular to the rolling direction (SR) and the surface perpendicular to the transversal direction (ST) after 500 h exposure was close to each other. There was no anisotropic corrosion resistance for these alloys. The corrosion rate of the alloys increased with the increase of Nb content after 250 h exposure when the Nb content exceeded 0.28%. In the alloy with low Nb content, the fcc-Zr(Fe, Cr)2 or fcc-Zr(Fe, Cr, Nb)2 precipitate was mainly formed, while the hcp-Zr(Fe, Cr, Nb)2 precipitate was frequently observed in the alloy with high Nb content. The corrosion resistance of Zr- 0.72Sn- 0.32Fe-0.14Cr-xNb alloys was improved by decreasing the Nb/Fe ratio. From a point of view for the improving corrosion resistance, the addition of Nb no more than 0.3% is recommended.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-12 Cooperative journals: 《中国腐蚀与防护学报》
Abstract：摘 要:利用高压釜腐蚀实验研究了Zr-1Nb-xGe(x=0, 0.05, 0.1, 0.2，质量分数，%)合金在400℃/10.3MPa过热蒸汽中的耐腐蚀性能；利用SEM和TEM分别观察了合金和氧化膜的显微组织。结果表明：添加Ge可以改善Zr-1Nb合金的耐腐蚀性能，当Ge含量为0.05%时效果最佳. 在Zr-1Nb-xGe合金中存在4种第二相，分别是β-Nb，Zr(Nb,Fe,Cr)2，Zr(Nb,Fe,Cr,Ge)2第二相，和尺寸较大的Zr3Ge第二相. Zr-1Nb-xGe合金α-Zr基体中的最大固溶含量在0.05%---0.1%之间，固溶在α-Zr基体中的Ge可以有效延缓氧化膜中显微组织的演化，从而改善合金的耐腐蚀性能，当添加Ge含量超过合金的固溶含量，会形成Zr(Nb,Fe,Cr,Ge)2以及尺寸较大的Zr3Ge第二相，Zr3Ge会使耐腐蚀性能降低。
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Zr-4 coarse-grained specimens were corroded in static autoclave at 360 ℃, 18.6 MPa in 0.01 mol/L LiOH aqueous solution for 70 and 160 d exposure. EBSD, SEM and HRTEM were used to investigate the microstructures and crystal structures of oxide layers, and the relationships between the oxide thickness and the grain orientation of the metal matrix. The results showed that the oxide layers formed on the grain surfaces with the orientations nearby basal plane (0001) were thicker, and exhibited a prominent anisotropic for the oxide growth when Zr-4 specimens were corroded in LiOH aqueous solution for 160 d, but this was not the case for 70 d. The grains with the surface orientation nearby (0001), (1010) and (1120) were selected from the specimens corroded for 70 d to investigate the effect of metal grain orientation on the microstructure of oxide layers. The results showed that the crystal structure and microstructure of oxide layers formed on different metal grains were obviously different, and the scattering of m-ZrO2 columnar grain orientations in the oxide layers formed on near basal plane (0001) was wider than that on near prismatic plane (1010) and (1120). Besides the majority of m-ZrO2, c-ZrO2, t-ZrO2 and sub- oxide phase Zr3O were also detected at the oxide/metal interface, and it showed that the microstructure and crystal structure of oxide layers were very complex. The microstructural evolution of oxide layers will affect the diffusion of oxygen and subsequently the growth of oxide. Therefore, the microstructural evolution of oxide layers, which was affected by the different microstructure of oxide layers formed initially on grains and the water chemistry of corrosion tests, resulted in the anisotropic growth of oxide layers when Zr- 4 specimens were corroded in LiOH aqueous solution in subsequent corrosion tests.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：用高压釜腐蚀实验研究了Zr-1Nb-xBi（x =0.05%---0.3%, 质量分数）系列合金在360 ℃/18.6 MPa去离子水中的耐腐蚀性能, 结果表明在Zr-1Nb合金的基础上添加Bi对其耐腐蚀性能有明显的改善作用, 且随着Bi含量的增加改善作用愈明显. 合金显微组织的TEM和EDS分析表明, 合金中存在ZrNbFe型和β-Nb第二相, Bi含量对第二相的种类, 尺寸和数量没有明显的影响; 0.3%的Bi可全部固溶在α-Zr基体中, 且不影响Nb的固溶含量. 氧化膜断口和内表面形貌的SEM观察表明, 固溶在?-Zr基体中的Bi能够明显延缓氧化膜显微组织结构的演化, 包括孔隙发展成为微裂纹的过程和柱状晶向等轴晶的转变. 可见, 增加α-Zr基体中Bi的固溶含量可以改善合金的耐腐蚀性能.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：选用无织构的Zr-0.72Sn-0.32Fe-0.14Cr和 Zr-0.85Sn-0.16Nb-0.37Fe-0.18Cr合金大晶粒片状样品，利用静态高压釜在500 ℃，10.3 MPa过热蒸汽中进行500 h的腐蚀试验，采用EBSD，SEM和TEM等方法研究了合金的显微组织，以及氧化膜的厚度与金属晶粒表面取向的关系。结果表明，Nb对第二相的晶体结构产生影响，Zr-0.72Sn-0.32Fe-0.14Cr合金中的第二相主要为面心立方的Zr(Fe,Cr)2，Zr-0.85Sn-0.16Nb-0.37Fe-0.18Cr合金中的第二相为面心立方和密排六方的Zr(Nb,Fe,Cr)2；两种合金均未出现疖状腐蚀，并且不同金属晶粒取向上的氧化膜厚度没有明显差别，即没有表现出腐蚀各向异性特征。
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