Fe3Al基合金用作结构材料的应用基础研究

研究了Fe-28Al-5Cr与Fe-28Al-5Cr-0.5Nb-0.1C合金的高温变形行为,发现温度在850℃左右,应变速率为8.33×10-4s-1时,呈现出大晶粒的超塑性变形行为,延伸率分别达到145%和254%.这意味着不需要获得细晶的特别工艺处理就可以直接进行超塑性成形.与传统细晶导致超塑性不同,其激活能分别为243kJ/mol和218kJ/mol,变形机理为位错运动而不是晶界滑动.在较低的应变速率及大约850℃下制备出壁厚为1.7～2mm,直径为50mm的薄壁管坯分别用电子束焊(EBW)及钨极氩弧焊(GTA)两种方法对厚度为2mm左右的Fe-Al基合金试样进行了可焊性及焊接工艺优化研究.电子束焊在真空中进行,集中的高能量输入使熔合区组织细化,可实现对Fe3Al基合金的焊接.采用钨极氩弧焊时,以中低碳铬钼钢为填充料,降低焊接电流和热输入,对焊件采用适当的预热、缓冷工艺,是焊接工艺优化的主要因素,应用可焊性及焊接工艺优化研究的结果,制备出相应尺寸的薄壁焊管.     

Effect of initial microstructure on superplastic deformation of AZ70 magnesium alloy

The mechanical properties and deformation mechanism of semi-continuously casting and as-extruded AZ70 magnesium alloys in a wide range of grain sizes(from 14 to 103μm)were investigated at 653 K and 1×10-3s -1.It is discovered that with reducing grain size,flow stress is weakened and plasticity is improved and even superplasticity exhibits.SEM and OM were used to clarify the deformation mechanism.It is suggested that dynamic recrystallization(DRX)is the coordination deformation mechanism of grain boundary sliding(GBS)for coarse grain,and cavity and intracrystalline slip are the coordination deformation mechanisms of GBS for fine grain.     

超塑性差温拉深与整形复合工艺数值模拟与试验

采用热一力耦合数值模拟与试验结合,研究超塑性差温拉深与整形复合工艺.计算大拉深比支架件初始毛坯;建立AA5083材料随温度变化的粘塑性本构关系,经子程序将其植入MARC软件模拟;依据模拟结果,制造2套模具并成形了合格零件.超塑性差温拉深的凹模温度为525℃,即此材料最佳超塑性温度,凸模内部通水冷却;整形过程温度亦为525℃.结果表明,成形支架厚度分布均匀,与模拟结果吻合良好.     

轧态Zn-5Al-RE合金的超塑性研究

用恒载荷法研究了轧态Zn-5Al-RE合金的组织超塑性和相变超塑性的蠕变特征,测定了轧态Zn-5Al-RE合金超塑变形的激活能Q值和应变速率敏感指数m值。试验结果表明：当载荷减小、温度降低和淬火保温时间延长时,组织超塑性变形中稳态蠕变阶段延长;粗晶粒可降低组织超塑性变形时的伸长率,但对相变超塑性变形的伸长率影响不大;组织超塑性变形的m值大于相变超塑性变形的m值;轧态Zn-5Al-RE合金的表观激活能略大于Zn-5Al-RE合金的激活能。     

Zn-5Al共晶合金的表面效应对超塑变形的影响

用光学显微镜，扫描电镜研究了Zn-5Al共晶合金超塑变形的表面效应及其影响因素。结果表明：超塑变形中的晶界滑移机制导致某些晶界由材料内部滑移至表面，从而使外表面增加；Zn-5Al合金的超塑性表面流动具有长程性，而且表面流动对超塑变形具有协调作用，表面镀层由于破坏了表面流动的协调性，对合金的超塑变形产生阻碍作用。空洞是材料的内自由表面，其形核长大与（2γs-γgb）有关，提高表面能，降低晶界能可增强材料的超塑性。     

Mesoscopic grain boundary sliding as the rate controlling process for high strain rate superplastic deformation

Important features observed during high strain rate superplastic deformation are enumerated. Starting from the premise that the phenomenon of structural superplasticity in different classes of materials results when grain boundary sliding that develops to a mesoscopic scale (defined to be of the order of a grain diameter or more) controls the rate of flow, the particular case of high strain rate superplasticity is explained. The rate equation developed is validated using experimental results concerning 5 alloy systems in which an ultra-fine grain size is developed by thermomechanical processing and retained in a similar condition during superplastic deformation by fine, grain boundary pinning particles and 3 alloy composites in which the volume fraction of the reinforcing constituent is significant (15–25%). It is demonstrated that the analysis results in estimates for the externally measured strain rates that are within a factor of two, in addition to providing a physically meaningful free energy of activation for the rate controlling process. This approach explains superplastic flow in different classes of materials in terms of a single rate controlling mechanism of deformation, viz., mesoscopic grain boundary sliding, with the help of a few constants that have the same values for all systems. The system-dependent variables of threshold stress needed for the onset of mesoscopic boundary sliding and free energy of activation are obtained directly from superplasticity stress–strain rate data, without external inputs.     

诱发钛合金塑性增强的分步超塑性成形法

介绍了分步超塑成形法,从成形方式上探索一种增强材料塑性的途径。分步超塑成形过程中,分别以恒速度与最大m值法,分两步先后作用于拉伸试样,通过控制初始变形方式的变形量以及各步间隙时间等,来促使材料内部产生晶粒细化、组织结构改善等,从而增强材料塑性。实验比较了单步拉伸成形与分步拉伸成形,以及分步成形中恒速法的预应变量对金属延伸率与组织的影响。结果表明:未经特殊细化处理的TC6钛合金分步拉伸,其恒速变形的工程应变为2.0时,可获得延伸率为2053%,而同温度下单步恒速与最大m值法拉伸的延伸率为753.9%与1347%;TC4钛合金在分步拉伸中恒速应变量为1.5时,可获得2147%的大延伸率。可见分步成形显著诱发了塑性增强。此外,预应变量决定着拉伸试样的晶粒组织大小。     

铸轧AZ31镁合金的高温拉伸性能

研究了铸轧AZ31镁合金的高温拉伸性能和变形机制.在300~450℃条件下,分别以恒定拉伸速率10^-3 s^-1和10^-2 s^-1进行拉伸至失效试验,在真实应变率为2×10^-4~2×10^-2 s^-1的范围内进行变应变率拉伸试验.当拉伸速率为10^-2s^-1时,试样在400℃和450℃的延伸率均超过100%;当拉伸速率为10^-3 s^-1时,试样在400℃和450℃的延伸率均超过200%,该条件下的应力指数ⁿ≈3,蠕变激活能^Q=148.77 kJ·mol^-1,变形机制为溶质牵制位错蠕变和晶界滑移的协调机制.通过光学金相显微镜和扫描电子显微镜观察显示试样断口处存在由于发生动态再结晶和晶粒长大而形成的粗大晶粒,断裂形式为空洞长大并连接导致的韧性断裂.     

西北有色金属研究院钛合金研究进展

概述了西北有色金属研究院（NIN）研发的部分高温、高强、低成本、超塑性及低温钛合金近年来的研究进展。指出：使用温度在550～650℃之间的高温钛合金中，550℃高温钛合金已获得应用，Ti-600合金因室温和600℃下综合性能优异，尤其是极佳的蠕变性能，可以用做高推重比发动机压气机轮盘和叶片，具有较好的应用前景；在强度级别为1000～1600MPa的高强钛合金中，Ti—B20合金和Ti-1300合金适宜制作高强或超高强钛合金弹簧；低成本钛合金、超塑性温度较低且应变速率较高的超塑性钛合金、低温钛合金的研究从未间断过，某些合金也已得到应用；NIN今后研究重点是建立已研发合金的规范体系，降低其制造成本，提高其使用性能，最终使其获得广泛应用。