Zr-xNb-0.15Fe-0.05Cu-0.05Ge合金在400℃/10.3 MPa过热蒸汽中的耐腐蚀性能
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摘要
利用高压釜腐蚀试验研究了Zr-x Nb-0. 15Fe-0. 05Cu-0. 05Ge(x=0. 7,1,1. 3,1. 6,质量分数,%)合金在400℃/10. 3 MPa过热蒸汽中的耐腐蚀性能。使用SEM和TEM分别观察了合金和氧化膜的显微组织。结果表明:随着Nb的质量分数从0. 7%增加至1. 6%,试验合金的耐腐蚀性能逐渐下降。合金中的第二相为体心立方结构的β-Nb(bcc-β-Nb)相与含有Cu和Ge的密排六方结构的Zr(Nb,Fe)_2(hcp-Zr(Nb,Fe)_2)相,随着Nb含量的增加,主要第二相由Zr(Nb,Fe)_2相逐渐转变为β-Nb相,且呈条带状。Zr(Nb,Fe)_2和β-Nb第二相相对含量的变化对合金的耐腐蚀性能有较大影响。具有较大P. B.比、且呈条带状分布的β-Nb相促进了氧化膜中微裂纹的扩展,而且大量的β-Nb相氧化所产生的体积膨胀会影响氧化膜柱状晶的生长,增加了氧化膜中的内应力,促进孔隙和微裂纹形成,从而降低了合金的耐腐蚀性能。
Corrosion resistance of Zr-x Nb-0. 15 Fe-0. 05 Cu-0. 05 Ge( x =0. 7,1. 0,1. 3,1. 6,mass fraction,%) alloys exposed to superheated steam at temperature of 400 ℃ and under pressure of10. 3 MPa was studied by autoclave test. The microstructures of alloy and oxide film were observed by SEM and TEM. The results showed that as the mass fraction of Nb increasing from 0. 7% to 1. 6%,the corrosion resistance of the tested alloys decreased gradually. The second phase particles in the tested alloys were β-Nb( bcc-β-Nb) phase of the bcc structure and Zr( Nb,Fe)_2( hcp-Zr( Nb,Fe)_2)phase of the hcp structure which contained Cu and Ge. With the increase in Nb content,the main second phase changed from Zr( Nb,Fe)_2 into β-Nb asuuming banded distribution. The change in relative amount of the Zr( Nb,Fe)_2 and β-Nb second phases had greater influence on corrosion resistance of the alloy. The β-Nb phase with larger P. B. ratio and asuuming banded distribution promoted the propagation of cracks in oxide film. The volume expansion resulting from large amounts of β-Nb phase oxidation disturbed the growth of columnar grains and increased the internal stress in the oxide film,promoted the formation of pores and micro-cracks in oxide film,thereby reducing the corrosion resistance of the alloy.
Corrosion resistance of Zr-x Nb-0. 15 Fe-0. 05 Cu-0. 05 Ge( x =0. 7,1. 0,1. 3,1. 6,mass fraction,%) alloys exposed to superheated steam at temperature of 400 ℃ and under pressure of10. 3 MPa was studied by autoclave test. The microstructures of alloy and oxide film were observed by SEM and TEM. The results showed that as the mass fraction of Nb increasing from 0. 7% to 1. 6%,the corrosion resistance of the tested alloys decreased gradually. The second phase particles in the tested alloys were β-Nb( bcc-β-Nb) phase of the bcc structure and Zr( Nb,Fe)_2( hcp-Zr( Nb,Fe)_2)phase of the hcp structure which contained Cu and Ge. With the increase in Nb content,the main second phase changed from Zr( Nb,Fe)_2 into β-Nb asuuming banded distribution. The change in relative amount of the Zr( Nb,Fe)_2 and β-Nb second phases had greater influence on corrosion resistance of the alloy. The β-Nb phase with larger P. B. ratio and asuuming banded distribution promoted the propagation of cracks in oxide film. The volume expansion resulting from large amounts of β-Nb phase oxidation disturbed the growth of columnar grains and increased the internal stress in the oxide film,promoted the formation of pores and micro-cracks in oxide film,thereby reducing the corrosion resistance of the alloy.
引文
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[3]MARDON J P,CHARQUET D,SENEVANT J,Influence of composition and fabrication process on out-of-pile and in-pile properties of M5 alloy[C]//Zirconium in the Nuclear Industry:Twelfth International Symposium.West Conshohocken:ASTMSTP 1354,2000:505-524.
[4]PARK J Y,CHOI B K,YOUN H J,et al.Corrosion behavior of Zr alloys with a high Nb content[J].Journal of Nuclear Materials,2005,340(2/3):237-246.
[5]张金龙,谢兴飞,姚美意,等.Ge含量对Zr-4合金在Li OH水溶液中耐腐蚀性能的影响[J].中国有色金属学报,2013,23(6):1542-1548.
[6]GONG W J,ZHANG H L,QIAO Y,et al.Grain morphology and crystal structure of pre-transition oxides formed on Zircaloy-4[J].Corrosion Science,2013,74(6):323-331.
[7]OKAMOTO H.Sn-Zr(Tin-Titanium)[J].Phase Equilibria and Diffusion,2010,31(2):202-203.
[8]BARBERIS P,CHARQUET D,REEYROLLE V.Ternery ZrNb-Fe(O)system:phase diagram at 853 K and corrosion behavior in the domain Nb<0.8%[J].Nuclear Materials,2004,326(2/3):163-174.
[9]KIM H G,SANG Y P,LEE M H,et al.Corrosion and microstructural characteristics of Zr-Nb alloys with different Nb contents[J].Nuclear Materials,2008,373(1-3):429-432.
[10]LI S L,YAO M Y,ZHANG X,et al.Effect of adding Cu on the corrosion resistance of M5 alloy in superheated steam at 500℃[J].Acta Metallurgica Sinica,2011,47(2):163-168.
[11]YAO M Y,ZOU L H,XIE X F,et al.Effect of Bi addition on the corrosion resistance of Zr-4 in superheated steam at 400℃/10.3 MPa[J].Acta Metallurgica Sinica,2012,48(9):1097-1102.
[12]EUCKEN C M,FINDEN P T,TRAPP-PRITSCHING S,et al.Influence of chemical composition on uniform corrosion of zirconium-base alloys in autoclave tests[C]//Zirconium in the Nuclear Industry:Eighth International Symposium.West Conshohocken:ASTM STP 1023,1989:113-127.
[13]KIM H G,JEONGYH,KIM T H,Effect of isothermal annealing on the corrosion behavior of Zr-x Nb alloys[J].Journal of Nuclear Materials,2004,326(2/3):125-131.
[14]YILMAZBAYBAN A,BREVAL E,MOTTA A T,et al.Transmission electron microscopy examination of oxide layers formed on Zr alloys[J].Journal of Nuclear Materials,2006,349(3):265-281.
[15]曹潇潇.锆合金中第二相合金的腐蚀行为研究[D].上海:上海大学,2010.
[16]JEONG Y H,LEE K O,KIM H G.Correlation between microstructure and corrosion behavior of Zr-Nb binary alloy[J].Journal of Nuclear Materials,2002,202(1):9-19.
[17]屠礼明,张金龙,徐启迪,等.Zr-0.7Sn-1Nb-0.03Fe-x Cux Ge合金在400℃/10.3 MPa过热蒸汽中的耐腐蚀性能研究[J].稀有金属工程,2015,44(6):1391-1396.
[18]QIN W,NAM C,LI H L,et al.Tetragonal phase stability in Zr O2film formed on zirconium alloys and its effects on corrosion resistance[J].Acta materialia,2007,55(5):1695-1701.
[19]YAO M Y,GAO C Y,HUANG J,et al.Oxidation behavior ofβ-Nb precipitates in Zr-1Nb-0.2Bi alloy corroded in lithiated water at 360℃[J].Corrosion Science,2015,100:169-176.
[20]LIN Y P,WOO O T.Oxidation ofβ-Zr and related phases in Zr-Nb alloys:an electron microscopy investigation[J].Journal of Nuclear Materials,2000,277(1):11-27.
[21]HUANG J,YAO M Y,GAO C Y,et al.The influence of second phase particles on the crack formation in oxide films formed on zirconium alloys[J].Corrosion Science,2015,99(6):172-177.