【作者】 王庆伟；

【导师】 张杰；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2013， 博士

【摘要】 为满足航空涡轮发动机叶片以及导向叶片对轻质高强合金板材的需求，对NiAl基合金板材的研发与制备具有十分重要的理论和实际意义。本文以TiB₂颗粒增强Al基复合材料板材（TiB₂/Al）和纯Ni板材为原料，采用轧制连接及反应合成方法，通过Ni与TiB₂/Al中的Al反应生成NiAl基体，同时保留TiB₂颗粒作为增强相，成功制备出微层TiB₂-NiAl复合材料板材。一方面避免了对于脆性的NiAl基合金锭的直接轧制变形，大大降低了加工成本，另外还克服了传统的叠轧加反应合成制备NiAl基合金板材致密度低的缺陷，并且改善了增强体的强化效果和基体的韧化效果。研究了微层TiB₂-NiAl复合材料板的制备工艺，系统的研究了轧制变形和两种反应合成过程中产物的组成、织构演变和反应机理，对微层TiB₂-NiAl复合材料板的室温和高温力学性能进行了检测，分析了TiB₂颗粒和独特的层状结构对TiB₂-NiAl复合材料板的组织与性能影响，并对微层TiB₂-NiAl复合材料板的抗氧化行为进行了研究。多层Ni-（TiB₂/Al）复合板的轧制试验表明，TiB₂/Al复合材料板与纯Ni板有良好的变形协调性。通过对轧制变形后的多层Ni-（TiB₂/Al）复合板的微观组织观察，界面结合良好，没有界面反应发生，但在Ni/（TiB₂/Al）界面处的Al （Ni）固溶体层内发现了高密度层错。第一种反应合成方法包含了固相法两步退火处理。多层Ni-（TiB₂/Al）复合板在650℃反应退火时，有NiAl₃和Ni₂Al₃生成。采用了一个有效形成热模型成功的预测了第一个生成相是NiAl₃，和处在Ni/NiAl₃内界面的第二个生成相是Ni₂Al₃。由于Ni/（TiB₂/Al）界面高的浓度梯度，最初的NiAl₃晶粒呈现出平行的柱状晶结构。然而由于Ni/NiAl₃界面相对低的浓度梯度，大部分Ni₂Al₃晶粒呈现出等轴形貌。TiB₂颗粒的添加对NiAl₃和Ni₂Al₃形成和长大都没有显著影响。650℃反应退火时，NiAl₃层向TiB₂/Al层生长速率高于向Ni层生长速率，原因在于NiAl₃相在Al/NiAl₃界面形核率更高。NiAl₃层生长遵循抛物线生长动力学规律。多层Ni-（TiB₂/Al）复合板经过650℃/50h反应退火和再在950¹000℃高温反应退火时，各个中间相不断消耗，最终得到层状的TiB₂-NiAl复合板。在反应合成过程中TiB₂没有参与反应。950℃反应退火时，NiAl层生长遵循抛物线生长动力学模式。由于固相法两步退火处理获得的TiB₂-NiAl复合板中存在大量孔洞，难以进行应用。我们开发了新的固液法反应合成工艺。多层Ni-（TiB₂/Al）复合板经过1200℃/3h/50MPa的固液反应后，形成微层的TiB₂–NiAl复合板。所得复合板材具有独特的单一粗晶NiAl层和富TiB₂细晶NiAl层交替排列的结构。反应合成过程中TiB₂没有参与反应。粗晶单一NiAl层有明显的{111}<112>和{111}<110>织构组分。这个织构是通过扩散反应从Ni板中的织构遗传得到的。NiAl织构的产生能定性的基于Ni相和NiAl相的密排面位相关系（N–W和K–S）来解释。通过轧制变形及固液反应合成法制备了四种体系（颗粒含量分别为0.7vol.%，1.3vol.%，2vol.%，3.3vol.%）的TiB₂-NiAl复合材料板，Al含量控制在51at.%Al⁵2at.%Al之间，随着颗粒含量增加板材致密度略微降低，晶粒尺寸和层厚没有明显变化。纳米硬度分布在9.5⁹.6GPa，弹性模量分布在200²10GPa，颗粒含量没有太大影响。随TiB₂颗粒的引入，微层TiB₂-NiAl复合材料板材断裂韧性增加。且微层TiB₂-NiAl复合材料板的断裂韧性与加载方向相关，微层2vol.%TiB₂-NiAl复合材料板平行于板材轧制方向加载的断裂韧性为6.9±0.3MPa·m^1/2，平行于法线方向加载的断裂韧性达到7.5±0.5MPa·m^1/2。裂纹蔓延沿着特定的晶面，接近{110}^B2和{100}^B2晶面族。富TiB₂细晶NiAl层对裂纹扩展起到阻碍作用并使裂纹发生偏转是断裂韧性提高的主要原因。高温拉伸实验表明，随着温度升高，微层TiB₂-NiAl复合材料板的抗拉强度、屈服强度先增加后减少，延伸率增加。韧脆转变温度介于750℃和800℃之间。750℃的屈服强度达到最大值为435MPa，延伸率为4.7%。富TiB₂层的增强作用和单相NiAl层对裂纹的钝化作用是导致其高温性能高于纯NiAl材料的主要原因。揭示了微层TiB₂–NiAl复合材料板材的强化机理。更多还原

【Abstract】 In order to satisfy the requirements of gas turbine engines blades and guidevanes for high-strength low-density alloy sheets, it is of theoretical and practicalsignificance for development and manufacture of NiAl-based alloy sheets.Microlaminated TiB₂–NiAl composite sheets have been successfully fabricated byroll bonding and reaction annealing of Ni sheets and TiB₂/Al composite sheets. Onthe one hand, this technique avoids the direct deformation of the brittle NiAlcompared with the conventional rolling method, along with the decrease infabrication costs by using simplified techniques. On the other hand, the obstacle offorming dense NiAl sheets by conventional solid-solid methods can be overcome.The strenghening effect can be effectively improved by a densification processconsisting of a solid-liquid reaction.Preparation processes of microlaminated TiB₂–NiAl composite sheets wereinvestigated. Phase composition, transformation of texture and reaction mechanismof the reaction products in the process of roll bonding and reaction annealing weresystemically studied using SEM, XRD, EBSD and TEM. The mechanical propertiesof microlaminated TiB₂–NiAl composite sheets at room temperature and hightemperature were evaluated and effect of laminate structure and TiB₂onmicrostructures and properties of microlaminated TiB₂–NiAl composite sheets wereinvestigated. Moreover, the oxidation resistance of microlaminated NiAl-TiB₂sheetwas investigated.Roll bonding of multi-laminated Ni–（TiB₂/Al） sheet show the gooddeformation compatibility between Ni and TiB₂/Al sheets with no subsequentreactions. The presence of wide stacking faults is observed in the Al （Ni） layer nearthe interface in multi-laminated Ni–（TiB₂/Al） sheet after the roll bonding process.The first reactive synthesis method is called “two-steps solid-solid annealingtreatment”. NiAl₃and Ni₂Al₃phase was detected in the multi-laminated Ni–（TiB₂/Al）composite sheet during annealing at650oC. A modified effective heat of formationmodel was applied and it predicted correctly the appearance of NiAl₃as the firstphase as well as subsequent formation of Ni₂Al₃between the Ni and NiAl₃layers.The initial NiAl₃grains demonstrated parallel columnar structure because ofthe high concentration gradient at the Ni/Al interface. Most Ni₂Al₃grains showedequiaxed morphology, due to the low concentration gradients of Al and Ni at theNi/NiAl₃interface. Growth velocity of NiAl₃towards TiB₂/Al layer is much fasterthan that towards Ni layer, due to the higher nucleation rate at the Al/NiAl₃interface.The growth of NiAl₃layer is consistent with the parabolic growth law, while annealing at650℃. When the laminate is subsequently annealed at950¹000℃after annealing at650℃for50h, TiB₂still remains stable. Finally, multi-layeredTiB₂-NiAl composite sheets are obtained. The growth of NiAl layer is attributed tothe reaction diffusion process and in consistent with the parabolic growth law, whileannealing at950℃.Because there are too much holes in the TiB₂-NiAl composite sheets after“two-steps solid-solid annealing treatment”, a new reactive synthesis method named“solid-liquid annealing treatment” was investigated. The dense microlaminated（0.7vol.%，1.3vol.%，2vol.%，3.3vol.%）TiB₂–NiAl composite sheet with alternatingTiB₂-rich and NiAl layers was successfully produced by reaction diffusion frommulti-laminated roll bonded Ni–（TiB₂/Al） sheet at1200℃/3h/50MPa. NiAl phasehas strong {111}<112> and {111}<110> texture components in the microlaminatedTiB₂–NiAl composite sheet. The texture may be considered to be a transformationtexture inherited from initial rolling texture of Ni in the multi-laminatedNi–（TiB₂/Al） sheets via reaction diffusion. The texture formation of the NiAl phasecan be qualitatively explained on the basis of the orientation relationships onclose-packed planes （N–W and K–S） between Ni phase and NiAl phase in view ofcoherency with texture of Ni. The content of Al in the microlaminated TiB₂–NiAlcomposite sheet is between51at.%Al and52at.%Al. The nanohardness is between9.5GPa and9.6GPa, and the elastic modulus is between200GPa and210GPa. Theparticle content does not influence the hardness and elastic modulus of themicrolaminated TiB₂–NiAl composite sheet.Testing for fracture toughness shows that with addition of TiB₂, the fracturetoughness increases. Furthermore, the value of fracture toughness depends onloading direction, fracture toughness of micro-laminated2vol.%TiB₂-NiAlcomposite sheets with loading parallel to normal direction （ND） is7.5±0.5MPa·m^1/2,while the value with loading parallel to rolling direction （RD） is6.9±0.3MPa·m^1/2.It was found that the crack in the micro-laminated2vol.%TiB₂-NiAl compositesheets propagates along the particular crystallographic planes close to that of{110}B2and {100}B2. TiB₂-rich fine NiAl layer hinders propagation of cracks andinduces crack deflection. These factors contribute to increase in fracture toughnessof micro-laminated2vol.%TiB₂-NiAl composite sheets with loading parallel to ND.High temperature tensile testing shows that with raising temperature, strengthof microlaminated TiB₂-NiAl composite sheets increases firstly and then decreases,coupled with an increase in elongation. The brittle-to-ductile transition temperature（BDTT） for this material lies somewhere between700℃and750℃. Yield strengthat750℃reaches the highest value of435MPa and elongation reaches4.7%. Theimprovements in strength and elongation are attributed to the unique laminated structure: bimodal distribution of grain size and good interface bonding betweenboth layers.TiB₂-rich layers acts as the “reinforcement phase” in the microlaminatedcomposite, and the monolithic NiAl layer results in cracks blunting which efficientlyreleases the stress concentration. The relationship between microstructure andstrength of the microlaminated TiB₂-NiAl composite was analyzed.更多还原