【作者】 张慧芳；

【导师】 张治民；

【作者基本信息】 中北大学 ， 火炮、自动武器与弹药工程， 2011， 博士

【摘要】 本文选用一种新型近α高温钛合金，通过热模拟压缩试验、平面应变压缩试验，借助现代冶金分析技术，研究了BTi-62421S合金的高温变形力学行为、形变强化行为以及微观组织变化；采用数值模拟和试验研究等手段，系统分析了钛合金复杂结构件多向加载整体成形理论及可行性；丰富了钛合金塑性加工和挤压成形理论，对提高我国武器装备制造水平有着重要的意义。主要研究内容和结果如下：（1）利用Gleeble-3800型热模拟试验机进行了等温恒应变速率压缩试验。分析了变形程度为70%时，变形温度、应变速率对BTi-62421S合金高温流动行为及组织演变的影响，通过变形激活能的计算和组织观察，揭示了其动态变形机制，并建立了该合金在（α+β）两相区的热变形本构方程，为设备吨位选择及有限元数值模拟提供了理论依据。（2）采用平面应变压缩试验，研究了热加工工艺参数对BTi-62421S合金力学性能的影响，研究发现：在（α+β）两相区，采用等效应变大于等于0.80的变形可以明显提高合金的抗拉强度；在（α+β）两相区，等效应变小于0.8或者在β单相区变形都不利于提高抗拉强度。同时发现，变形后的合金硬度均比原始铸态提高。（3）观察了热模拟压缩试验和平面应变压缩试验变形后的微观组织，分析了高温变形工艺参数对微观组织演变的影响，为控制零件的内部组织进而提高其机械性能奠定了基础。研究发现：在（α+β）相区变形时，片层组织主要发生等轴化演变，对BTi-62421S合金而言，片层组织的弯曲推进了片层组织等轴化，同时发现片层组织的等轴化需要在一定的变形量和变形温度条件下才会发生。片层组织等轴化的临界温度为900℃，临界等效应变为0.8。若考虑获得细小均匀的等轴组织，应该选择在（α+β）相区较高温度，较大变形量。（4）结合热模拟压缩试样开裂状态，建立了“铸态BTi-62421S合金压缩变形-T-开裂关系图”。根据平面应变压缩试验结果，建立了“BTi-62421S合金变形温度-变形量-抗拉强度关系图”，为使合金在成形时，提高工件性能，保证工件质量。（5）针对某产品的端框件，设计了合理的毛坯形状与尺寸，提出了三种多向加载整体成形工艺方案，采用数值模拟技术对不同方案的成形过程进行对比，得出：先轴向挤压后侧向挤压方案较其它方案成形载荷少，最大载荷的持续时间短，对模具寿命影响小，金属变形比较均匀，挤压终了损伤值最小，出现裂纹可能性最低。（6）采用BTi-62421S合金，对钛合金端框件整体成形进行了模具设计和试验研究。试验样件内腔各凸台充填饱满，未产生折叠、撕裂等缺陷，形状尺寸精度满足技术要求，表明：钛合金复杂构件“预制铸坯—加热—多向等温加载整体成形”工艺方案是可行的。同时，由铸造坯料直接成形、材料利用率可达83.4%，成形力的减小，力学性能的提高，最大可能地降低了生产成本，解决了钛合金复杂端框件整体成形的关键技术问题，丰富了钛合金成形理论，为钛合金端框件工程化应用奠定基础。更多还原

【Abstract】 The high temperature mechanical behavior, strain hardening behavior andmicrostructures of a new near α high temperature titanium alloy BTi-62421S were studied byhot compression simulation, plane strain compression tests. For the titanium complexstructure, the theory of integral forming process with multi-direction loading was analyzedusing numerical simulation, moreover practical processing was performed to veitify thefeasibility. The research has important significances on both enriching the plastic processingtheory of titanium alloy and improving the manufacturing level of weapons equipment. Themain research contents and conclusions are the following:(1) In this investigation, isothermal compression tests were carried out on Gleeble-3800system at constant strain rate with the deformation of70%. The influences of deformationtemperature and strain rate on the high temperature flow stress and microstructure ofBTi-62421S alloy were analyzed. The dynamic deformation mechanisms were revealedthrough deformation activation energy calculation and microstructure observation. Theconstitutive equation of this alloy in (α+β) two-phase region during hot deformation wasestablished, which can provides a theoretical basis for equipment selection and finite elementsimulation.(2) The influences of thermal processing parameters on the mechanical properties ofBTi-62421S alloys were studied by plane strain compression tests. The results showed that, inthe (α+β) two phase region, the tensile strength can be significantly improved by thedeformation with equivalent strain greater than or equal to0.80; while the tensile strengthwas decreased in β single-phase region or in the (α+β) two phase region with the equivalentstrain less than0.8. At the same time, it was also found that the hardness of the deformedalloys was higher than the as-cast one.(3) The microstructures of specimens after hot compression simulation experiments andplane strain compression test were observed, and the influences of thermal processingparameters on the evolution of microstructure were also analyzed. The results can establishthe foundation for controlling the microstructures of the components for further improvementtheir mechanical properties. When deformed in the (α+β) phase region, the lamellarstructure were mainly equiaxed evolved, for BTi-62421S alloy, the kinking of lamellarstructure promoted equiaxed processes. Meanwhile it was found that the globularization oflamellar structure need a certain deformation degree and deformation temperature, the criticalequivalent strain was0.8and the critical temperature was900℃. For obtaining uniform fineequiaxed microstructures, the deformation process should be held at higher temperature in the(α+β) phase region with larger deformation degree.(4)“theε&-T-cracking figure of compress deformed BTi-62421S alloy” was establishtedwith the combination of the crack specimens after hot compression simulation. According tothe results of plane strain compression tests,“the relationship among the deformation temperature–deformation degree-tensile strength of BTi-62421S Alloy” was establishted,In order to improve the performance and ensure the quality of the formed workpiece.(5) For a kind of monolithic component, in this study, rational shape and size ofroughcast were designed and three schemes of integral forming process with multi-directionloading were proposed. With the help of numerical simulation, a conclusion was drawn that,compared with other schemes, the forming process with first axial compression then lateralextrusion was the best for less loading, short duration of maximum load, little influences ondie life, uniform deformation, smallest injury and least likely of crack.(6) The die was designed for the monolithic component, and the forming process wascarried out in this work. The monolithic component made by BTi-62421S alloy was full filledwith no folding, tearing and other defects, besides the accuracy of shape and size can meetthe technical requirements.more results indicate that the forming process of “precast-heating-isothermal integral forming process with multi-direction loading” was feasible for titaniumcomplex components. Furthermore, material utilization through direct forming is morethen80%, together the cost of production is reduced for the decreasing of forming load and theimprovement of mechanical properties.Through the research, the key technical issues oftitanium complex monolithic component were solved, the forming theory for the titaniumalloy was enriched, witch lay the foundation for the engineering applications of titaniummonolithic component.更多还原