【作者】 逄锦程；

【导师】 耿林；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2013， 博士

【摘要】 为了满足我国航天、航空事业对于发动机轻质高强合金板材的迫切需求，TiAl板材的研制具有十分重要的理论和实际意义。本文利用Ti板材和SiC颗粒增强Al基复合材料板材为原材料，采用叠轧-反应退火合成工艺制备得到TiAl基复合材料板材。在制备板材过程中，利用SiC颗粒与Ti及Al高温下的化学反应，原位合成增强相，最终成功制备出同时具有微层（Ti₃AlC+Ti₈C₅）与弥散颗粒Ti₅Si₃两种形态增强体混杂增强的TiAl基复合材料板材。优势在于：一是利用叠轧-反应合成工艺制备TiAl基板材，成功避免了对于脆性TiAl材料进行直接轧制变形，降低了TiAl板材的制备难度；二是利用SiC颗粒与基体元素的高反应活性，制备出多种形态增强体混杂增强的TiAl基复合材料板材，为TiAl基复合材料板材的制备提供了一种新路径。本文系统地研究了叠轧-反应退火合成TiAl基复合材料板材的制备工艺，着重分析了叠轧变形过程和反应退火合成两阶段（低温反应退火+高温反应退火）过程中的物相组成，组织演化规律及反应产物的性能特点，并对具有（Ti₃AlC+Ti₈C₅）微层及弥散Ti₅Si₃颗粒混杂增强的TiAl基复合材料板材进行了片层化热处理，最终制备出具有细小全片层组织结构的TiAl基复合材料板材。对其进行了室温和高温力学性能测试，分析了增强体对TiAl基复合材料板材力学性能的影响。本文采用纯Ti板与SiC_p/Al板为原料通过叠轧制备得到Ti-（SiC_p/Al）多层复合板。Ti-（SiC_p/Al）多层复合板的轧制试验表明，在高温轧制过程中，SiC_p/Al复合材料板与纯Ti板具有良好的变形协调性。对轧制变形量为40%的Ti-（SiC_p/Al）多层复合板进行微观组织观察，发现在Ti层与SiC_p/Al层之间存在纳米级的TiAl₃界面反应层。力学性能测试表明该种具有纳米TiAl₃界面反应层的Ti-（SiC_p/Al）多层复合板有着优良的综合力学性能。利用制备出的Ti-（SiC_p/Al）多层复合板材反应退火合成TiAl基复合材料板材。本文通过DTA试验分析将反应退火合成工艺分为低温反应退火与高温反应退火两个阶段。在低温反应退火过程中，发现当温度为650℃时，在Ti-（SiC_p/Al）界面处有TiAl₃反应层生成。通过EDS/TEM分析发现，在TiAl₃晶粒中固溶了微量的Si元素。并利用纳米压痕与原子力显微技术表征了Si固溶对于TiAl₃相力学性能的影响。同时通过第一性原理计算从理论上分析了Si固溶对TiAl₃模量及电子结构产生的影响。650℃反应退火过程中，随着TiAl₃层的增长，TiAl₃层与SiC_p/Al层之间的应力不断增大，最终导致多层复合板材发生层间开裂。表明在此温度下无法顺利将Al基复合材料中的Al全部转化为TiAl₃相。当低温反应退火温度为700℃时，由于液相Al的参与导致Ti-Al间的反应剧烈，使得TiAl₃反应层的增长速率明显加快。经过700℃/10h低温反应退火后，可将Al基本转化为TiAl₃相。通过EDS及XRD分析发现低温反应退火后只有微量Al残余，这些Al可以有效地将松散的TiAl₃相连接在一起，避免低温反应退火后板材发生层间开裂，有利于进一步高温退火反应的顺利进行。在此过程中，液相Al与SiC颗粒间发生微弱反应，生成少量的Al₄C₃相。对经过700℃/10h低温反应退火后的复合材料板材进行高温反应退火，温度选定为1200℃。在高温反应退火过程中，低温反应退火后残余的纯Ti层全部转化为Ti₃Al金属间化合物相。同时在Ti₃Al层与TiAl₃层中间有连续TiAl反应层及非连续TiAl₂层生成。通过物相鉴定发现，增强体SiC颗粒及在低温反应退火阶段生成的Al₄C₃相全部消失，原位合成Ti₃AlC，Ti₈C₅及Ti₅Si₃增强体。通过组织观察发现，Ti₃AlC与Ti₈C₅被推挤到原始SiC_p/Al的中心线区域形成微层结构，而Ti₅Si₃颗粒分布在TiAl及TiAl₂反应层中。通过EDS/TEM分析发现Ti₅Si₃相中有微量Al元素固溶，并通过第一性原理分析了Al固溶导致的Ti₅Si₃形成能，模量及电子结构的变化情况。随着高温反应退火的进行，TiAl₃层及Ti₃Al层不断被消耗，TiAl₂层先增厚后减薄，最终形成具有TiAl，Ti₃Al层状分布结构的TiAl基复合材料板材。通过片层化热处理，使得TiAl基复合材料板材基体组织转化为全片层结构。由于Ti₅Si₃颗粒的分布特点，导致形成的全片层结构团簇尺寸细小。通过纳米压痕试验发现，微层（Ti₃AlC+Ti₈C₅）及颗粒Ti₅Si₃的引入使得TiAl板材的硬度及模量进一步提高。同时微层（Ti₃AlC+Ti₈C₅）使得TiAl复合材料板材的断裂韧性性存在方向性，与加载方向相关。高温拉伸试验表明，随着温度升高，TiAl复合材料板的抗拉强度不断增加。更多还原

【Abstract】 In order to satisfy the requirements of engines in the air field for high-strengthand low-density alloy sheets, it is of theoretical and practical significance fordevelopment and manufacture of TiAl-based alloy sheets. By roll bonding andreaction annealing, TiAl composite sheets with in situ reinforcements of（Ti₃AlC+Ti₈C₅） microlaminates and Ti₅Si₃particles have been successfullyfabricated of Ti sheets and SiC_p/Al composite sheets. On the one hand, thistechnique avoids the direct deformation of the brittle TiAl, decreasing thefabrication costs by using simplified techniques. On the other hand, by the highreactiveity between SiC and based element, the TiAl based composite sheet withdifferent reinforcements was successfully prepared, giving a new path to fabricateTiAl based composite sheet.This paper investigated the preparation technology of the TiAl basedcompostite sheet, excepecially researching the phases, microstructure evolution andproperties of the products in the roll bonding and reaction annealing. The fulllamellar structure with the fine lamellars was fabricated. Then the mechanicalproperties were tested and the influence of the reinforcements was studied。Due to the good strength of the SiC_p/Al composites at high temperature, thedeformation of the SiC_p/Al layers was uniform and coherent with the Ti layers atinitial rolling. The constituent dissimilar foils reduced gradually with the increasedcycles until a reduction of40%. The nano-sized TiAl₃interface layer was found bythe microstructure analysis. The multi-laminated Ti-（SiC_p/Al） composite with anano-sized TiAl₃was successfully fabricated by roll bonding. It shows good inmechanical properties by tests.By DTA tests, the reaction annealing was divided into Low-temperaturereaction annealing and High-temperature reaction annealing. In the present work,TiAl₃layers were synthesized by reaction annealing of a multi-laminatedTi-（SiCP/Al） composite sheet at650oC. It was found that Si dissolved in the TiAl₃layers during annealing. The effect of Si in the TiAl₃layers on mechanicalproperties was investigated both by experiment and theory. It was found that about6at.%Si was solved into TiAl₃, which leads to the lattice distortion of TiAl₃. Theelastic modulus and nanohardness of TiAl₃with Si increased and was verified byfirst-principles calculation of the theoretical elastic properties and can be explainedfrom the electronic structure. The interfacial debonding was brought by theincreaseing stress with the reaction annealing time between SiC_p/Al layer and TiAl₃layer. It prevents the reaction between Ti and Al. At700oC, liquid Al prefers to strongly react with Ti, which can prominently shorten the reaction time comparedwith the solid-solid reaction. After the reaction annealing at700oC/10h, Al matrixwas changed into TiAl₃. But a little of ‘Al was left and was found to connect TiAl₃phase. SiC can slightly react with liquid Al. Free [Si] and Al₄C₃are the two majorreaction products.The reaction annealing temperature was elevated to1200oC for the Hightemperature reaction annealing. In this processing, all SiC particles can beconsumed and transformed into new in-situ reinforcements. It can be seen the Ti andSiC_p/Al foils were completely consumed in reaction annealing at1200oC for2h, andthe peaks of the new reinforcements, i.e.: Ti₅Si₃, Ti₃AlC and Ti₈C₅phases can bedetected. By EDS/TEM analysis, some Al was solved in to Ti₅Si₃, the formationenergy, modulus and electronic structure were inveatigated by first-principlescalculation. With the high temperature, TiAl₃andTi₃Al consume, and the thicknessof TiAl₂was increased and then decressed. Finally the TiAl based composite sheetwas composed of TiAl and Ti₃Al layers.TiAl composite sheets containing fine lamellar structure were obtained bylamellar treatment at1400oC for20min after the High-temperature reactionannealing. The nanohardness and modulus were enhanced by the introduction of thein-situ reinforcements. Testing for fracture toughness shows that with addition ofceramic layers, the fracture toughness increases. Furthermore, the value of fracturetoughness depends on the loading direction. High temperature tensile testing showsthat with raising temperature, the strength of the TiAl composite sheets increases.更多还原