【作者】 周晓明；

【导师】 颜鸣皋； 唐定中； 汪武祥；

【作者基本信息】 北京航空材料研究院 ， 材料学， 2006， 博士

【摘要】 本文研究了三种典型非金属夹杂物（Al₂O₃、SiO₂及两者的混合物）在两种广泛应用的粉末高温合金（FGH95和FGH96）中的遗传特征,并从实验和计算机模拟两方面研究了非金属夹杂物对基体材料损伤力学行为的影响,并提出了改善合金中非金属夹杂物的措施。研究结果表明,三种夹杂物在FGH96合金中经不同工艺状态后,表现出了不同的行为特征:Al₂O₃由于其较高的硬度和热稳定性,在整个工艺过程中,形状、尺寸和成分等都没发生变化;而SiO₂经热等静压后,与合金中的Al和Ti等元素发生了反应,改变了基体/夹杂物之间的界面结合方式,影响了SiO₂周围基体中γ′相的数量和尺寸,形成贫γ′相区;Al₂O₃和SiO₂与合金粉末混合后,在热等静压（HIP）过程中,在高温、高压同时作用下,两种非金属夹杂物之间发生了化学反应,生成另外一种非金属夹杂物—莫来石。莫来石在高温下可能发生软化,在周围球形粉末颗粒的挤压下变形,界面呈圆弧状,形成尖锐的棱角。该种夹杂物也与基体之间发生了化学作用,表现出了与SiO₂相似的行为特征,但反应区的作用范围较窄。由于三种夹杂物与基本材料在热膨胀系数方面的差异,经淬火（油淬或盐淬）处理后,界面处易于萌生微裂纹。时效处理对两种反应型夹杂的影响不大。在等温锻造过程中,由于以上行为特征的差异性,使Al₂O₃完全被破碎,呈“链状”分布于基体中;SiO₂在其周围塑性区的缓冲下,发生局部断裂;而莫来石因其在高温时的软化,呈“薄膜状”分布。尽管FGH95和FGH96合金在成分及热工艺制度方面存在着一定的差异,三种夹杂物在合金处理的各工艺过程中表现出了相同的行为特征。基于镍基粉末高温合金在成分种类方面的相似性,可将三种夹杂物在上述两种合金中的遗传特性推广应用到所有镍基粉末高温合金中。在原位拉伸和原位疲劳实验中,夹杂物处是裂纹萌生的择优位置。裂纹萌生方式分为两种:夹杂物本身开裂和基体/夹杂界面开裂,通常为基体/界面开裂。扩展初期,裂纹在夹杂物尖角应力集中处沿与主应力成45o向基体中扩展,之后沿与最大正应力垂直的方向扩展至断裂。由于SiO₂和莫来石与基体之间的化学作用,改变了其周围基体的塑性,使断口表现出了特定的行为特征。夹杂物对基体力学性能的影响是很复杂的,主要取决于其位置和尺寸。在同一位置,夹杂物的尺寸越小,或同一尺寸,夹杂物距表面的距离越远,都会降低夹杂物对基体材料的危害性。用计算机模拟了夹杂物对基体材料损伤力学行为的影响。当夹杂物的形状,位置及取向等发生变化时,夹杂周围的应力场分布情况会发生相应的变化,尤其在疲劳过程中,夹杂物周围的应力场会随加载历程的不同而出现周期性变化。为提高模拟结果的准确性,应引入夹杂物的特性参数,除形状和位置外,还应考虑夹杂物在不同温度时的变形性及自身相变引起的体积变化等。合金中的实际夹杂物主要来源于母合金及其熔炼与雾化制粉过程,主要为Al、Si、Ti、Mg和Ca的氧化物。人工加入的三种非金属陶瓷夹杂物与合金中的实际夹杂物相比,具有一定的代表性,所表现出的遗传特征涵盖了合金中各夹杂物的基本特性。针对夹杂物的来源及与合金粉末的不同特点,提出了粉末高温合金盘件制备各工艺环节中夹杂物的控制措施及鉴别方法。根据各夹杂物在合金中的遗传特性,结合计算机数值模拟技术,并对模拟结果进行验证,以指导合金中夹杂类损伤容限的确定。更多还原

【Abstract】 The genetic characteristic of three kinds of typical non-metallic inclusions—Al₂O₃, SiO₂ and their mixture—mullite, in two widely used superalloy—FGH95 and FGH96, was investigated. The effect of non-metallic inclusions on damage mechanical behavior of the matrix materials was studied by experimental tesing and computer simulation. Simultaneously, the methods of removing the non-metallic inclusion from the superalloys were advanced.The results indicate that the three kinds of non-metallic inclusions show different behavior characteristic in FGH96 superalloy after hot-working processes. The morphology, size and composition of Al₂O₃ are not changed due to its hardness and thermal stability. While, SiO₂ reacts with Al and Ti elements in FGH96 superalloy, and the thinγ′phases zone is formed in the matrix around the inclusion. Theγ′phases around SiO₂ particles become smaller in size, and few in amount. Because of the synchronous effect of high temperature and pressure during HIP, the mixed inclusions––Al₂O₃ and SiO₂––are turned into mullite. The mullite is apt to be soften at high temperature to form arc boundary. The mullite also reacts with the matrix and has the same thing with SiO₂, but the width of reaction zone is narrower than that of SiO₂’s. The micro-cracks usually initiate at interface between the matrix and the inclusion after being quenched—oil quenched or salt quenched, because of their difference in thermal expanding modulus. The effect of aging treatment on the characteristic of the tow kinds of reacting inclusions—SiO₂ and mullite, is not evident. As the high hardness, low ductility and coefficient of thermal expansion, the three kinds of non-metallic inclusions could not be deformed with the matrix during HIF simultaneously, and tend to be broken into pieces. Al₂O₃ particle is completely broken as a chain along deforming direction; SiO₂ particle is partly broken due to the protection of reaction zone. And the mullite becomes narrow like film. The characteristic of the three kinds of inclusions in the two kinds of superalloys—FGH95 and FGH96, is the same although the difference in compositions and processes between them. Thus, the above characteristic could be applied in all PM superalloys because of their similarity in compositions. The cracks tend to be initiated at inclusions during in-situ tension and in-situ fatigue experiments. The cracks are usually initiated at the interface between inclusion and the matrix, and seldom at the inclusion itself. At the beginning, the crack propagates into the matrix from the corner of the inclusion about 45°with the main stress axis, and then, normally until the matrix is ruptured. The fracture surface shows special characteristic because of the reaction zone generated by SiO₂ and mullite. The effect of non-metallic inclusions on the mechanical properties is rather complicated, and lies on the location and size of the inclusion. The smaller in size and the further from the surface, the less effect of non-metallic inclusion on the mechanical properties of the matrix is.The influence of non-metallic inclusion on damage mechanical behavior of the matrix was studied by computer simulation. The distribution of stress field around a non-metallic inclusion will be changed accordingly when the shape , location and orientation of the inclusion are varied. Especially, during LCF. The diagnostic parameter of the inclusion—deformable capability at different temperature, the size variety due to phase transformation other than shape and location, should be introduced to improve the veracity of the simulation results.The actual non-metallic inclusions in superalloys are oxides of Al, Si, Ti, Mg and Ca those come from original alloy melting and argon atomization. The three kinds of artificial non-metallic inclusions may be on behalf of the actual inclusions in PM superalloys. And the characteristic shown by them could be applied in all the inclusions in PM superalloys. Remove and discriminate methods for the inclusions are advanced for respective process according to the source and different characteristic with the metal powders. The criterion of damage tolerance can be established based on the characteristic of the non-metallic inclusions in PM superalloy applied with computer simulation technology.更多还原