【作者】 李宝增；

【导师】 董闯； 王清；

【作者基本信息】 大连理工大学 ， 材料物理与化学， 2012， 博士

【摘要】 Fe基合金是最重要的工程材料,为实现不同使役性能,往往需要在Fe基体中添加各种组元,然而合金化组元添加的种类与最佳含量通常需要经过大量试验探索,新合金的设计与开发历时较长。本工作从稳定固溶体合金的结构出发,采用团簇加连接原子结构模型设计并表征Fe基多元合金,一方面证实了该理论模型的有效性,另一方面获得了一批新合金,具有重要的理论价值和工程意义。该结构模型源自多元非晶和准晶的成分分析,它将结构分为团簇部分和连接原子部分,团簇为基体结构中的第一近邻配位多面体,其形成源于溶质与溶剂组元间的强交互作用,合金成分因此可以表达为团簇式形式：[团簇](连接原子)x,x表示连接原子相对于一个团簇的数目。本工作选取了两类合金体系开展研究,一是具有面心立方结构(FCC)的奥氏体合金,二是具有体心立方结构(BCC)的铁素体合金,具体合金体系分别为Fe-Ni-Cu和Fe-Cr-Mo.Al-Cu,对此进行了组织结构及性能表征,并建立了合金成分、微观组织与合金性能之间的联系。Fe-Ni因瓦合金是电子工业应用广泛的封接合金,采用Cu合金化可以提高其耐腐蚀性能,但过多Cu的添加会导致第二相析出,从而造成合金的耐腐蚀性能下降。为确定Fe-Ni合金中Cu的最佳含量,采用团簇加连接原子结构模型对Fe-Ni-Cu因瓦合金成分进行了理论探讨及实验研究。商业Fe-Ni因瓦合金如4j42和4j46等中Cu含量都低于4mass％,在高Cl-环境中耐腐蚀性能较差。Fe-Ni-Cu奥氏体区在20-700℃之间Cu含量为2.5-3.5at.%。根据元素间混合焓(△HFe-Ni=-2kJ/mol,△H Ni-Cu=4kJ/mol,△HCu-Fe=13kJ/mol)和稳定固溶体结构模型,提出了Fe-Ni-Cu三元稳定固溶体合金双团簇模型[CuNi12][NiFe12]m(团簇均以原子个数表达,全文同),该模型假设在合金中可以有Fe-Ni. Ni-Cu近邻,但Fe-Cu必须分开,难溶元素Cu是以团簇CuNi12形式溶于Fe的合金基体之中。试验结果表明由团簇设计的合金具有单相FCC结构,在3.5wt.％NaCl溶液中的耐腐蚀性能高于商业Fe-Ni因瓦合金,且与成分接近的因瓦合金具有相当的膨胀性能。铁素体不锈钢是应用广泛的耐腐蚀材料,一般需要添加Cr、Mo等元素,但是Mo含量过高引起成本增加,而Al和Cu虽然是高耐蚀性元素,其含量高则容易引发第二相析出。为确定Fe基合金中Cr、Mo、Al、Cu的含量,采用团簇加连接原子结构模型对其Cr、Mo、Al、Cu的添加含量进行了理论探讨及实验研究。首先考察了Fe-Al-Cu三元体系,确定稳定铁素体固溶体的结构模型,在20-600℃相图中,铁素体区边界为Al/Cu=8(at.比例)恒定区,根据元素间混合焓(△HFe-Al=-1kJ/mol,△HAl-Cu=-1kJ/mol,△HCu-Fe=13kJ/mol),基于稳定固溶体合金思想,提出了Fe/Al-Cu三元稳定铁素体固溶体合金的团簇模型[CuAl]Fex。进而,考虑Cr.Mo以近似元素替代部分Fe来实现五元合金,Cr含量符合Tammann n/8规则,而元素Mo位于CuAlg团簇的外围,构成Cu的次近邻和Al的第一近邻,即在BCC结构中构建了一个Cu-Al8-Mo6团簇,由此建立了Fe-Cr-Mo-Al-Cu五元铁素体不锈钢的稳定固溶体合金团簇模型,为[(CuAl8)Mo6](Fe,Cr)x实验结果表明由该团簇成分式设计的合金具有单相BCC结构；一系列性能测试表明由团簇模型设计获得的Cr24Mo7A13Cu合金(在表述合金成分时一般采用mass%,全文同)和Cr27Mo6A13Cu合金在高Cl-环境、高氧化环境中具有良好的耐腐蚀性能,优于常规高Cr、Mo铁素体不锈钢,且在高温1100℃空气环境中抗氧化能力优于Fe-23Cr-5Al合金；其力学性能与铁素体Fe-Cr-Mo不锈钢相当。在实现上述多元合金化基础上,结合难溶元素的固溶方法,还分析了大量的基础三元合金体系,建立了相应的稳定固溶体合金团簇结构模型,预测了潜在的新型固溶体合金成分。更多还原

【Abstract】 Fe-based alloys are the most important engineering materials, where a host of alloying elements need to be added to meet different behaviors in service. However, the kinds and the contents of alloying elements are commonly determined by lots of try-and-error experiments, which results in that it will experience a long time to develop a new alloy. Starting from the local structure of stable solid solution alloys, this work applies the cluster-plus-glue-atom model to design Fe-based multi-element alloys, and amounts of experimental results confirm the validity of this cluster model. More importantly, a series of new Fe-based multi-component solid solution alloys are obtained with guidance of the model. This work possesses significances both in theory research and in engineering applications.The cluster-plus-glue-atom model is originated from the structural analysis and composition design of multi-component metallic glasses and quasicrystals. It dissociates an alloy structure into two parts:the cluster part and the glue atom part, where the cluster is the nearest neighbor coordination polyhedron and generally formed in solute elements with negative enthalpies of mixing (△H<0) with the base element, and the glue atoms are those elements having weak△H. The alloy composition is then expressed with [cluster](glue)x, x denoting the number of glue atoms matching one cluster. Two types of alloy systems, Fe-Ni-Cu and Fe-Cr-Mo-Al-Cu, representing FCC and BCC strucuture respectively, are selected, where the relationships among composition, microstuctrue and properties have been established through structure and property characterizations.Fe-Ni Invar alloys have been extensively used as sealing alloys in electronic industry. Minor amount of Cu addition can improve their corrosion resistance, but excess Cu could induce phase precipitation and thus deteriorates the corrosion resistance. In order to determine the optimum content of Cu in Fe-Ni alloys, the composition of Fe-Ni-Cu Invar alloys are analized with the cluster model and series of cluster formula alloys are designed and experimented. Generally, the Cu contents in conventional Fe-Ni Invar alloys, such as4j42,4j46et al., are less than4mass%, and these alloys possess poor corrosion resistance in high Cl--containing environment. In schematic Fe-Ni-Cu ternary phase diagrams from20℃to700℃, Cu solubility limit maintains constant, from2.5at.％to3.5at.%. The double cluster model [CuNi12][NiFe12]m (expressed in atomic number in cluster model in this paper) for Cu-containing Fe-Ni ternary stable solid solutions is proposed based on the enthalpies between the element pairs (△HFe-Ni=-2kJ/mol,△HNi-cu=4kJ/mol,△Hcu-Fe=13kJ/mol) and the cluster-structural model for stable solid solution. This model assumes that Fe-Ni and Cu-Ni nearest neighbors are allowed but the Cu-Fe ones should be avoided and Cu is dissloved in the Fe matrix in the form of CuNi12. Experimental results affirm that series of alloys formulated by this model maintain monolithic FCC structure and possess excellent corrosion-resistance, superior to those commercial Fe-Ni Invar alloys in3.5wt.%NaCl. In addition, these new alloys have comparable expansion coefficients with those comercial Invar alloys of approximate compisitions.As good corrosion-resistant materials, Cr and Mo elements are generally added into ferrite stainless steels. But excess Mo will raise the cost of materials. And too much Al and Cu could induce the second phase precipitation although they are benifical for corrosion resistantance. In order to determine the optimum contents of these alloying elements, the composition analysis and experiments are carried on with the cluster-plus-glue-atom model. The cluster model is first established for Fe-Al-Cu stable BCC solid solution. In the schematic Fe-Al-Cu ternary phase diagrams, the atomic ratio of Al/Cu is almost maintains constant from20℃to600℃and its value is Al/Cu=8. So the cluster model [CuAl8]Fex is established according to the enthalpies between the elements (△Hfe-Ai=-11kJ/mol,△HAl-cu=-1kJ/mol,△Hcu-Fe=13kJ/mol). And then, Cr and Mo substitute for some Fe due to their similar essence, the Cr content is according to Tammann’s n/8law. The addition of Mo is supposed to be the second neighbour of Cu and the fisr neighbour of Al, and the Cu-Al8-Mo6cluster is then established. Finally, the cluster formula [(CuAl8)Mo6](Fe,Cr)x is proposed for Fe-Cr-Mo-Al-Cu quinary solid solution alloys. The experimental results show that the cluster formula alloys maintain single BCC structure. The obtained Cr24Mo7A13Cu and Cr27Mo6A13Cu alloys (mass%) posses better corrosion resistance than commercial ferrite stainless steels with high contents of Cr and Mo in high Cr-contained and strong oxidized environments. Moreover, they have much better oxidation resistance than conventional Fe-23Cr-5Al alloys at1100℃, their mechanical properties are comparalble with that of the Fe-Cr-Mo ferrite stainless steel.Based on the alloying principle of insoluble elements in above two typical systems, a lot of similar ternary phase diagrams are analyzed, and the corresponding stable cluster structure models are then established to forecast new solid solution alloys.更多还原