钛合金等温锻用K403模具材料特性及失效研究

发布时间：2018-03-12 10:03

本文选题：钛合金大型复杂整体构件　切入点：局部加载等温锻造　出处：《西北工业大学》2015年博士论文　论文类型：学位论文

【摘要】：钛合金大型整体构件易于实现装备的轻量化、高性能、高可靠性、功能高效化而在航空航天领域得到广泛应用。局部加载等温锻造技术为解决该类构件的成形制造能力不足问题、成形成性一体化提供了新的途径。然而，在钛合金局部加载等温锻造过程中，模具长时间处于高温热暴露，其材料微观组织和性能将发生变化；同时模具受力复杂且不均匀，易引发模具产生局部变形甚至开裂失效，这严重制约着成形过程的实现和成形质量的保证。因此如何实现钛合金大型整体构件局部加载等温锻造模具的失效预测，提高模具使用可靠性和寿命成为迫切需要解决的关键问题。为此，本文采用理论分析、实验研究和有限元数值模拟相结合的方法，研究了镍基合金模具材料高温热暴露、高温变形及断裂行为，进而对钛合金大型整体构件局部加载等温锻造过程、模具的应力分析及失效预测、模具结构改进的问题进行了系统深入的研究。主要的研究内容和结果如下：采用热暴露试验、室温拉伸试验，研究揭示了热暴露温度、时间对用作钛合金局部加载等温锻造模具材料的K403镍基合金微观组织演变和性能的影响规律。发现K403合金在800~950℃温度下热暴露50~200h后，仍为典型的树枝晶组织，MC碳化物部分发生分解，强化相γ'相聚集长大，且随着热暴露温度的提高和热暴露时间的延长，γ'相粗化现象越显著；在850℃和900℃下热暴露后，有少量针状有害的TCP相（σ相）析出，且析出量随着热暴露时间的延长而增多；高温热暴露后合金的名义屈服强度和抗拉强度均下降，其主要原因是γ'强化相的聚集粗化和TCP相的析出。通过热模拟压缩和拉伸试验研究获得了变形温度、应变速率以及应力状态对K403镍基合金高温变形行为和微观组织的影响规律，探明了合金的高温断裂机制，建立了K403镍基合金高温断裂模型。结果表明：K403合金高温拉伸变形时，随着变形温度的升高、应变速率和应力三轴度的减小，，合金的峰值应力和断裂应力降低，而断面收缩率和断裂应变则随之而增大；温度低于900℃时，K403合金拉伸断口以准解理断裂为主，随着变形温度的升高，断裂类型由准解理断裂向沿晶断裂转变。研究提取了反映钛合金大型整体构件高筋薄腹板特点的两类筋板特征结构件，探明了特征结构件和具有代表性的大型整体隔框件局部加载等温锻造成形的变形行为和模具应力分布特征，确定了模具的危险区域，并揭示了模具几何参数对模具应力的影响规律。研究发现：大型整体隔框件局部加载等温锻造模具的危险区域为下模凸耳最外侧筋条的型腔外侧圆角区域，容易产生应力集中；增大模具型腔凹圆角半径和模锻斜度，可一定程度上降低模具应力；增大模具壁厚则可显著降低模具应力，但增大到一定程度后其效果减弱。基于所建立的K403合金高温断裂模型，结合有限元分析，实现了钛合金大型整体隔框件局部加载等温锻造模具的失效预测，并采用增加模具壁厚和预应力组合式下模两种方法改进模具结构，降低了模具应力和开裂失效的风险，其中采用预应力组合式下模更为有效。
[Abstract]:Titanium alloy large integral component is easy to realize equipment lightweight, high performance, high reliability, high efficiency and is widely used in the aerospace field. Local loading isothermal forging technology for solving the forming of this kind of member manufacturing capacity problems, the formation of integration provides a new way. However, in titanium alloy local loading isothermal forging process, die long time in high temperature heat exposure, and the performance of the material microstructure will be changed; at the same time the die stress is complex and uneven, easy to cause the mold to produce the local deformation or even cracking failure, which seriously restricts the forming process and forming quality assurance. So how to realize the failure prediction of titanium alloy large integral component isothermal local loading forging die, improve the mould life and reliability has become a key problem to be solved urgently. Therefore, this paper uses theory The analysis method of combining experimental research and finite element numerical simulation of thermal high temperature nickel base alloy die material exposure, high temperature deformation and fracture behavior of titanium alloy, and large integral component isothermal local loading forging process, and failure prediction analysis of mould, systematically studied the mould structure improvement the problem. The main research contents and results are as follows:
The heat exposure test, room temperature tensile test, the research reveals the thermal exposure temperature, effects of time on Microstructure of K403 nickel based alloy and titanium alloy used for the evolution performance of local loading isothermal forging die materials. K403 alloy under 800~950 DEG C after 50~200h heat exposure is still a typical dendritic structure, MC carbide partial decomposition, strengthen the Y "phase together with the set up, heat exposure with the increase of temperature and thermal exposure time prolonged, gamma 'phase coarsening phenomenon is more obvious; at 850 DEG C and 900 C after thermal exposure, there is a small amount of needle like harmful TCP phase (Xiang) precipitation, and precipitation with time. The increased exposure to heat; alloy after thermal exposure of the nominal yield strength and tensile strength decreased, the main reason is the gamma' Strengthening precipitates in the aggregation and coarsening and TCP phase.
Through thermal simulation compression and tensile test obtained the deformation temperature, strain rate and the effects of the stress state of K403 high temperature nickel base alloy deformation behavior and microstructure of the high temperature, the fracture mechanism of the alloy, a nickel based superalloy K403 fracture model. The results show that the K403 alloy with high temperature tensile deformation. The increase of deformation temperature, strain rate and the reduction of the stress axis three, alloy peak stress and fracture stress decreased, while the section shrinkage and fracture strain increases; the temperature lower than 900 DEG C, K403 alloy tensile fracture to quasi cleavage fracture, with the increase of deformation temperature, fracture type from the quasi cleavage fracture to intergranular fracture.
Study on the extraction of titanium alloy large integral component reflects the aerocraft characteristics of two kinds of characteristics of stiffened plate structure, proved the characteristics of structure and large representative frame pieces of local loading and deformation behavior of isothermal forging die stress distribution characteristics, identify areas of risk of the mould, and reveals the influence of geometric parameters of the die on die stress. The study found: dangerous area of large integral bulkhead pieces isothermal local loading forging die for lateral cavity die fillet region lug most lateral ribs, prone to stress concentration; increasing the mold cavity concave fillet radius and the draft, to a certain extent on the lower die stress; increasing the mold wall thickness can significantly reduce the die stress, but increased to weaken the effect of a certain extent.
K403 alloy high temperature fracture based on the model with finite element analysis, the overall frame of large titanium alloy parts failure prediction of isothermal local loading forging die, and by using the improved die structure increase the mold wall thickness and prestressed die two methods, reduce the risk of failure and cracking force should die, which the prestressed die is more effective.

【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.23;TG319

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