【作者】 庞秋；

【导师】 孙东立； 武高辉；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2013， 博士

【摘要】 本文以航空航天结构材料为研究背景，以3D开孔泡沫Ni为基体，采用固体粉末包埋高温固相扩散工艺，制备出一种开孔率高达90%以上的三维网状结构的Ni-Cr-Fe泡沫合金。同时，为了进一步提高Ni-Cr-Fe泡沫合金的抗氧化性能，采用两步固体粉末包埋法在Ni-Cr-Fe泡沫合金表面上制备Al/Cr（Ce）双层涂层。利用扫描电子显微镜（SEM）、X射线衍射仪（XRD）、能谱仪（EDS）、电子拉伸试验机和显微硬度计等分析测试手段，分别对Ni-Cr-Fe泡沫合金及Al/Cr（Ce）涂层泡沫合金的微观组织结构及性能进行了系统的研究，并探讨了Ni-Cr-Fe泡沫合金及涂层泡沫合金的高温氧化动力学及氧化机理。利用固体粉末包埋法对开孔泡沫Ni表面进行Cr、Fe共渗处理，研究了Cr-Fe共渗层的显微组织、相组成及成分分布。结果表明：Cr-Fe渗层的致密化程度以及渗层与基体的结合强度受到不同共渗温度的影响。随着共渗温度增加，渗层与基体的结合强度增加，但是，共渗层表面颗粒团聚严重。共渗温度在1050℃时，Cr-Fe渗层表面均匀、致密且渗层与基体之间结合紧密。并且，1050℃时，随着保温时间延长，共渗层中外层和扩散层增厚曲线都近似遵循一次函数规律。以Ni-Cr-Fe三元相图模型为理论依据，效仿Inconel690高温合金的成分组成，实验确定了1200℃时进行泡沫Ni-Cr-Fe高温固相扩散合金化可以获得组织稳定，抗氧化性和抗热疲劳性较好的单一奥氏体γ相。同时，在高温扩散过程中，随着均匀化时间的延长，网丝骨架中Cr、Fe、Ni元素浓度梯度明显平缓，1200℃/48h均匀化热处理后，网丝骨架中Cr、Fe、Ni三种元素发生了充分的互扩散，达到合金成分均匀化，表面层主要由γ-（Fe, Ni）和γ-（Ni, Cr, Fe）固溶体组成。并且， Ni-Cr-Fe泡沫合金保持着初始泡沫Ni基体的三维网状及骨架中空结构。对Ni-Cr-Fe泡沫合金常温及高温力学性能进行测试，揭示了不同组成成分Ni-Cr-Fe泡沫合金组织与性能之间的关系。结果表明：Ni-Cr-Fe泡沫合金的常温及高温准静态压缩曲线呈现出典型韧性泡沫金属形变特征。高温扩散均匀化工艺有效提高Ni-Cr-Fe泡沫合金的压缩强度，也使得塑性屈服平台段的长度明显增加。同时，随着泡沫合金中Cr、Fe元素含量的增加，Ni-Cr-Fe泡沫合金材料的屈服强度和单位体积吸能量增大。与Gibson-Ashby经验公式相比，均匀化后Ni-Cr-Fe泡沫合金的屈服强度和比强度比理想泡沫Ni明显提高，这主要是Cr、Fe元素起到较好的固溶强化作用。尤其，Ni-36Cr-24Fe泡沫合金表观出最高的屈服强度和单位体积吸能。对Ni-Cr-Fe泡沫合金在800-1000℃条件下的抗高温氧化性能进行了研究，揭示了开孔Ni-Cr-Fe泡沫合金高温氧化动力学、热力学及氧化机理。结果表明：Ni-Cr-Fe泡沫合金具有比泡沫Ni基体和Ni-25Cr泡沫合金更高的抗高温氧化性能，其氧化曲线符合抛物线规律。随着泡沫合金中Cr、Fe元素含量的增加，Ni-Cr-Fe泡沫合金抗氧化性能增加。同时，随着氧化温度从800℃升高至1000℃，Ni-Cr-Fe泡沫合金的氧化层由Cr₂O₃、NiFe₂O₄和NiCr2O4的混合氧化物转变成致密的单一Cr₂O₃层，有效增强Ni-Cr-Fe泡沫合金的抗氧化性能。通过两步固体粉末包埋法在Ni-Cr-Fe泡沫合金表面制备Al/Cr（Ce）双层涂层，揭示了Al/Cr（Ce）双层涂层对Ni-Cr-Fe泡沫合金高温氧化性能及力学性能的影响，给出了Al/Cr（Ce）涂层泡沫合金氧化机理以及氧化后变形行为。结果表明：Al/Cr（Ce）双层涂层结构连续、致密，大量的Ce原子富集在外层，有效阻碍了Al原子的向内扩散以及基体合金原子沿晶界向外扩散。氧化后，Al/Cr（Ce）涂层泡沫合金的氧化动力学曲线遵循抛物线规律，Al/Cr（Ce）涂层表面容易形成致密的Al₂O₃层，并且，少量的Ce有效提高氧化层与基体的附着力。同时，与Ce–Cr涂层和Al/Cr涂层相比，氧化后Al/Cr（Ce）涂层泡沫合金的准静态压缩曲线表现出相对较高的屈服强度，有效增强了开孔Ni-Cr-Fe泡沫合金的抗氧化性能和力学性能。更多还原

【Abstract】 With the research background that served as the foundation for aerospacestructural materials, the reticulated open-cell Ni foam was used as a substrate andwas alloyed with Cr and Fe by pack-cementation, resulting in open-cell Ni–Fe–Cralloy foams with opening ratio of more than90%. Simultaneously, in order tofurther improve the oxidation resistance of the Ni-Cr-Fe alloy foam, the dual-layerAl/Cr（Ce） coating was deposited onto the Ni-Cr-Fe alloy foam by a two-step packcementation process. Scanning electron microscopy （SEM）, the X-ray diffractiontechnique （XRD）, energy dispersive spectrum （EDS） analysis, the electronic tensiletesting machine and micro hardness test were used to investigate the microstructuresand the performance of the Ni–Fe–Cr alloy foams and Al/Cr（Ce） coated alloy foam.The oxidation kinetics and the oxidation mechanism of Ni-Cr-Fe alloy foam wereexplored.Solid powder embedding method was used to make Cr-Fe penetrations to theopen-cell Ni foam. The microstructure, phase and components of the Cr-Fepermeation layer were also researched. The results show that the degree ofdensification of Cr-Fe permeation layer and the bonding strength of the matrix andpermeation layer are affected by different permeation temperature. The bondingstrength of the matrix and permeation layer increases with permeation temperatureincreases, however, the agglomeration of the surface of Cr-Fe coating becomes moreobvious. When the temperature is1050℃, the outside surface of the strut is coatedwith a uniform Cr-Fe deposition layer and the substrate on the bonding strength ofthe coatings is strong. Simultaneously, when the holding time is increased at1050℃,the thickening of the outer layer and the diffusion layer of the permeation layer isapproximate to follow linear function.As the theoretical basis of the Ni-Cr-Fe ternary phase diagram, the compositionof Inconel690high temperature alloy was emulated. The experiment results showthat the stable microstructure, the better the oxidation resistance and thermal fatigueresistance of a single austenitic γ phase can be obtained by high temperature solidphase diffusion of the Ni-Cr-Fe foam. At the same time, the Cr, Fe and Ni elementconcentration gradient of the strut is significantly reduced with the extension of the homogenization time in the high-temperature diffusion process. When thehomogenization time is extended to48h at1200℃, the Cr and Fe elements cancompletely diffuse into the inner strut and ensures a homogeneous alloycomposition. The surface layer of the Ni-Cr-Fe alloy foam is mainly composed ofγ-（Fe, Ni） and γ-（Ni, Cr, Fe） solid solution. Moreover, the Ni-Cr-Fe alloy foam stillretains the three-dimensional network structure and hollow struts of open-cell Nifoam.The room temperature and high temperature mechanical properties testing wereapplied to the Ni-Cr-Fe alloy foam, and the relationship between the organizationand the performance of the different components of Ni-Cr-Fe alloy foam wasrevealed. The results show that the quasi-static stress–strain behaviors of Ni-Cr-Fealloy foams at room temperature show the characteristic of typical ductile metallicfoam. High temperature diffusion homogenization process can effectively improvethe compression strength of open-cell Ni-Cr-Fe alloy foam at room temperature andincrease the length of the plastic yielding platform. At the same time, the energyabsorbed per unit volume of the Ni–Fe–Cr foams exhibits a significant increase withincreasing the Cr and Fe content of the foams. Compared with the Gibson-Ashbyexperience formula, the yield strength and specific strength of the Ni-Cr-Fe alloyfoam after homogenization are significantly improved than ideal open-cell Ni foam,which is mainly solid solution strengthening effect of Cr and Fe elements. Inparticular, Ni-36Cr-24Fe alloy foam exhibits the highest yield strength and unitvolume energy absorption.The high temperature oxidation resistance of Ni-Cr-Fe alloy foam was studiedat800-1000℃. The high temperature oxidation kinetics, thermodynamics andoxidation mechanism were revealed. The results show that the Ni-Cr-Fe alloy foamshave a higher oxidation resistance than Ni foam substrate and Ni-25Cr alloy foam,whose oxidation kinetics curves obey the parabolic law. The oxidation resistance ofopen-cell Ni-Cr-Fe alloy foam increases with increasing the Cr and Fe content. Atthe same time, when the oxidation temperature is increased from800℃to1000℃,the oxide layer of Ni-Cr-Fe alloy foam shows the change of the mixed oxide ofCr₂O₃, NiFe₂O₄and NiCr2O4into a dense single-phase Cr₂O₃layer, which caneffectively enhance the oxidation resistance of the Ni-Cr-Fe alloy foam.The dual-layer Al/Cr（Ce） coatings were deposited onto the Ni-Cr-Fe alloy foam by a two-step pack cementation process. The impact of Al/Cr（Ce） coating onthe oxidation resistance and mechanical properties of open-cell Ni-Cr-Fe alloy foamwas revealed. The oxidation mechanism and deformation behavior after theoxidation were given. The results show that the dual-layer Al/Cr（Ce） coatings arecontinuous and compact. The Ce added can effectively restrain the interdiffusionbetween the Ce–Cr coating and Al coating during the oxidation process. Theoxidation kinetics curve of Al/Cr（Ce） coated foam follows a parabolic law. A denseAl₂O₃layer is formed on the surface of Al/Cr（Ce） coating, and a small amount of Cecan effectively improve the adhesion of the oxide layer and the substrate.Simultaneously, compared to the Ce–Cr and Al/Cr coated foams, the Al/Cr（Ce）coated foam still exhibits higher yield strength, which can further enhance theoxidation resistance and mechanical properties of Ni-Cr-Fe alloy foam.更多还原