【作者】 张杰；

【导师】 闻立时； 董闯；

【作者基本信息】 大连理工大学 ， 材料物理与化学， 2010， 博士

【摘要】 Cu-Ni合金以其良好的耐海水腐蚀和加工性能广泛地应用于电厂、化工和轮船中的冷凝器材料。在Cu-Ni中添加Fe、Mn等元素可以进一步提高合金的耐蚀和加工等性能,添加的元素含量通常源于大量经验探索,这就使得在开发和设计Cu-Ni多元合金材料时,难以实施最佳有效的成分设计与优化。为此,本论文围绕Cu-Ni合金中添加的改性元素类型及其含量这一关键问题,开展了一系列理论与实验研究,最终建立了Cu-Ni-M多元稳定固溶体合金的原子团簇结构模型-合金成分-微观组织-宏观性能之间的联系,该研究具有理论和实际应用双重意义。基于Fe元素在Cu-Ni合金中的固溶度与温度的关联分析,提出了Cu-Ni-Fe稳定固溶体合金的概念,特指在一定温度下容易获得的具有较大固溶度和较高稳定性的合金。Cu-Ni-Fe合金在高温时,由于热无序破坏了短程有序性结构使得Fe在Cu-Ni合金中的固溶度随温度升高而迅速增加,在低温时,由于Cu-Ni相分离使得Fe1Nil2团簇聚集使得Fe在Cu-Ni合金中的固溶度随温度降低而缓慢减小。基于与Cu具有正混合焓,与Ni具有负混合焓的过渡族金属元素M在Cu-Ni合金中的固溶度与Ni元素的关联分析(M元素包含Fe、Co、Cr、V、Nb、Mo、Ru、Ta、W、Mn等),建立了Cu-Ni-M稳定固溶体合金的原子团簇结构模型,在该模型中,Cu-Ni-M固溶体合金在局域上形成以M原子为中心,以Ni原子为第一近邻分布CN12的M1Ni12八面体原子团簇,M1Ni12原子团簇无序的分散到Cu基体中形成[M1Ni12]Cux稳定固溶体合金。最后,基于[M1Ni12]Cux稳定固溶体合金的原子团簇结构模型优化设计了添加Fe,Mn和Cr元素改性的Cu-Ni-M多元耐蚀合金成分,并应用XRD、SEM、TEM和电化学腐蚀测试方法得到了[M1Ni12]Cux稳定固溶体合金的微结构、耐腐蚀性能和硬度的变化。实验结果表明,添加Fe,Mn和Cr改性的Cu-(Ni,M)合金在800℃C保温5h后水淬,在M含量为M／Ni≤1／12时对应于单一固溶体相结构；在M含量为M／Ni>1／12时有M-Ni弥散析出相；在M含量为M／Ni=1／12的稳定固溶体合金附近成分具有最佳耐蚀性能；Cu-(Ni,M)固溶体合金的硬度随添加的M元素含量的增加而提高,在M／Ni≤1／12阶段对应于M元素的固溶强化,在M／Ni＞1／12阶段对应于M-Ni析出相弥散强化；基于Cu-Ni-M稳定固溶体合金的原子团簇结构模型设计的[(Fe0.75-xMn0.25Crx)Ni12]Cu30.3合金在3.5%(wt.%)NaCl水溶液中具有优异的耐蚀性能,浸泡240h后的平均腐蚀速率为0.0008μm／h。更多还原

【Abstract】 Cu-Ni alloys are widely employed as tube and vessel materials due to their excellent resistance to seawater corrosion. Minor Fe and Mn additions are necessary to enhance the corrosion resistance of commercial Cu-Ni alloys. The corrosion resistance decreases with further increasing Fe and Mn contents due to precipitation of a Ni-(Fe, Mn) phase. So the key issue is the optimum modification element contents in different Cu-Ni alloys with high temperature stability. Generally, single-phase homogeneous solid solution alloys are desirable for good corrosion resistance performance. Such a single phase state is easily retained by quenching when the solid solution alloy has the maximum thermal stability. Therefore, the amounts of modification element additions are determined by the stability issue of the parent Cu-Ni alloys. The aim of this investigation was two-fold, first to experimentally verify the optimum M (M=Fe, Ni and Cr) levels in different Cu-Ni based alloys from the view point of homogeneous solid solution and corrosion performances, and second to theoretically establish a cluster-based structural model for stable solid solutions that quantitatively explains the solid solubility. A series of studies were carried out focusing on the modification element contents of Cu-Ni alloys and the relationships among solid solution alloy composition-atomic cluster structure model-alloy heat treatment process-microstructure-macroeconomic performances have been established, which is important to theoretical research and practical applications.In this work, an atomic cluster-based structure model was presented to explain the stable solid solution solubility limit of M elements in Cu-Ni-based alloys, the M elements having negative enthalpies of mixing with Ni and positive enthalpies of mixing with Cu. By this model, it assumed that one M (M=Fe, Ni and Cr) atom and twelve Ni atoms formed a M-centered and Ni-surrounded cube-octahedron and these isolated M1Ni12 clusters are embedded in the Cu matrix conforming to a cluster formula [M1Ni12]Cux. The ratio of M and Ni is equal to 1/12, and the stable solid solution compositions of the M-modified Cu-Ni alloys is [M1/13Ni12/13]1/(1+x)Cux/(1+x), (M=Fe, Ni and Cr). The high stability of the resultant Cu-Ni-Fe alloys have been confirmed by first-principles calculations.XRD, SEM, TEM and electrochemical corrosion measurements were used to characterize the microstructure and corrosion-resistance performance of Cu-(Ni, M) alloys. Vickers hardness measurement revealed a two-stage hardening process as a function of Fe/Ni ratios. These two stages correspond to the Fe solution stage (Fe/Ni(?)1/12) presumably dominated by solute hardening, and to the precipitation stage (Fe/Ni>1/12) dominated by dispersion strengthening but also counter-balanced by softened Fe-Ni deprived Cu matrix. The alloy [(Fe0.6Mn0.25Cr0.15)1Ni12]Cu30.3 of Cu-Ni modified by Fe, Ni and Cr additions has the best corrosion resistance in 3.5% NaCl aqueous solution, the immersion corrosion rate being 0.0008μm/h after 240 hours.更多还原