添加Nb对Zr-4合金在500℃过热蒸汽中耐腐蚀性能的影响

EFFECT OF Nb ON THE CORROSION RESISTANCE OF Zr-4 ALLOY IN SUPERHEATED STEAM AT 500℃

用高压釜腐蚀实验研究了在Zr-4合金成分基础上添加0.1%-0.3%(质量分数)Nb的合金在500℃/10.3MPa过热蒸汽中的耐腐蚀性能,用TEM和SEM分别观察了合金的显微组织和氧化膜断口形貌,结果表明.合金在500℃/10.3 MPa过热蒸汽中腐蚀500 h均未出现疖状腐蚀.完全抑制了疖状腐蚀的产生,这与Nb在αZr中的固溶量较大有关.固溶在αZr中的Nb能抑制疖状腐蚀斑的形核,提高耐疖状腐蚀性能;合金耐均匀腐蚀性能随着Nb含量的增加而降低,这与Nb的添加降低了固溶在α-Zr中的(Fe+Cr)含量有关,也与Zr(Fe,Cr.Nb)_2第二相的析出有关.这2种因素都会加快氧化膜显微组织在腐蚀过程中的演化,促进孔隙和微裂纹的形成.

The corrosion resistance of Zr-4＋xNb alloys （x=0.1--0.3, mass fraction, %） was investigated in a superheated steam at 500℃ and 10.3 MPa by autoclave tests. The microstructure of the alloys and fracture surface morphology of the oxide film formed on the alloys were observed by TEM and SEM, respectively. Results show that no nodular corrosion appears on Zr-4＋xNb alloys in 500 ℃/10.3 MPa superheated steam even for 500 h, which is related to the higher Nb concentration dissolved in α-Zr matrix. The Nb dissolved in α-Zr matrix can restrain the nucleation of nodular corrosion, thus improve the nodular corrosion resistance. The uniform corrosion resistance of Zr-4＋xNb alloys is lowered with the increase of Nb content, which is related to the decrease of the solid solution concentration of （Fe＋Cr） in α-Zr matrix and the precipitation of the second phase particles of Zr（Fe, Cr, Nb）2, and the two aspects will accelerate the microstructural evolution of the oxide film during corrosion process to promote the formation of pores and micro-cracks. KEY WORDS zirconium alloy, Nb, nodular corrosion, microstructure