剧烈塑性变形制备微纳米材料的变形细化机理

对剧烈塑性变形法(SPD)制备微纳米材料变形细化机理进行了总结归纳,着重介绍了位错变形和热机械变形两种机制,详细论述了材料在剧烈塑性变形加工过程中的组织转变特点,同时给出了SPD变形细化机制等研究方向的个人见解。     

强变形Al-Cu合金的退火组织与性能

研究时效Al-Cu合金强塑性变形后退火过程中的显微组织与性能的变化.制备分别只含θ″、θ′和θ相的时效Al-Cu合金,在室温多向压缩变形(MAC)后进行低温退火,测试合金的拉伸性能,借助X射线衍射仪和透射电镜分析显微结构的变化.结果表明,合金中含θ″相和含θ′相试样分别在MAC变形8道次和12道次时,析出相完全回溶于基体,形成过饱和固溶体.在退火过程中,基体发生回复,并伴随粒子再次析出,产生析出强化,再析出速度比同温度下的常规时效快.在120 ℃退火时,析出相完全回溶的含θ″相试样和含θ′相试样的强度分别在前60和30 min上升,而析出相未回溶的含θ相试样的强度则下降;在150 ℃退火时,析出相完全回溶的含θ″相试样和含θ′相试样强度与退火前强度基本持平,而析出相未回溶的含θ相试样强度明显下降;在200 ℃退火时,析出相回溶的试样和未回溶的试样强度都出现明显下降.说明强变形Al-Cu合金退火时强度取决于析出强化与回复软化的综合作用.在所有试样中,MAC变形8道次的含θ″相试样在120 ℃下退火60 min,表现出最好的综合性能.     

Effect of pressure on the evolution of copper microstructure upon large plastic deformation

Copper of 99.99% purity has been deformed by shear under pressure of 2, 6, or 9 GPa at room temperature. The structural changes observed correspond to the temperature and strain-rate conditions of deformation and occur as a result of three processes, namely, dynamic recovery, dynamic recrystallization, and post-dynamic recrystallization, relationship between which depends on the pressure applied. At a pressure of 2 GPa, the dynamic recovery plays a significant role, showing up in the absence of deformation-induced hardening and in a low driving force for grain growth upon the post-dynamic recrystallization. As the pressure rises to 6 GPa, the recovery is hampered and the post-dynamic recrystallization leads to growth of some coarse grains. Grains of more uniform size are retained after deformation at a pressure of 9 GPa.     

Formation of boron solid solution in Fe-Ni invar upon severe plastic deformation

Mössbauer spectroscopy, X-ray diffraction, electron microscopy, and magnetic susceptibility measurements have been used to study the process of mechanical synthesis of the solid solution of boron in the matrix of an Fe-Ni alloy. The internal effective field, the Curie temperature, and the lattice parameter of the Fe-Ni austenite were found to increase after severe plastic deformation in Bridgman anvils, which is related to the incorporation of boron into the matrix and the formation of a crystalline supersaturated solid solution coexisting with metastable borides.     

On possible mechanisms of nanostructure evolution upon severe plastic deformation of metals and alloys

Nondislocation mechanisms of deformation-induced fragmentation of nanostructures in metals upon plastic deformation are discussed. Conditions under which the refinement of nanograins can effectively occur via deformation twinning and/or deformation-induced phase transformations of a martensitic type are considered. It is shown that for each metal system and each deformation method, there exists a limiting nanostructure with a minimum possible average size of nanocrystallites.     

剧烈塑性变形对AZ31镁合金显微组织和力学性能的影响(英文)

通过等通道转角挤压技术(ECAP)对镁合金进行剧烈塑性变形,使用有限元法实现对ECAP加工过程及相关工艺参数的数值模拟,分析成形过程中的网格的变化、应力应变分布规律及其加载载荷规律,确定主要工艺参数影响规律。通过分析,得出晶粒细化程度与力学性能的关系,为镁合金的晶粒细化方法提供更合理的理论指导和参考依据。     

Effect of two-step severe plastic deformation on the microstructure and mechanical properties of commercial purity titanium

The present work investigates the microstructural and mechanical properties of commercial purity titanium after processing by a two-step severe plastic deformation procedure entailing warm equal channel angular pressing (ECAP) followed by cold rolling at liquid nitrogen temperature (LNT). The effect of subsequent cold rolling at room temperature is also investigated for comparison. After 10 passes of ECAP, an ultrafine-grained structure with average grain size of 213 nm was achieved. Subsequent cold rolling at LNT led to further refinement and decreased the grain size to 114 nm. Under these conditions, the material displayed high tensile strength of 995 MPa and high elongation to failure of 23%. These promising mechanical properties were interpreted in terms of characteristics of the microstructure: grain refinement, increased dislocation density, and a high fraction of high angle grain boundaries.     

Specific features of the formation of the microstructure of titanium nickelide upon thermomechanical treatment including cold plastic deformation to degrees from moderate to severe

X-ray diffraction, electron microscopy, microhardness measurements, and differential scanning calorimetry have been used to investigate the formation of the dislocation substructure and nanocrystalline and amorphous structures in Ti-Ni shape-memory alloys depending on the degree of cold deformation by rolling and post-deformation annealing. The moderate deformation (e = 0.25) leads to the formation of a developed dislocation substructure; with an increase in the deformation to e = 2, the dislocation substructure is gradually substituted by a mixed nanocrystalline and amorphous structures. The residual martensite completely disappears as the deformation increases in the interval of e = 2−3 or upon annealing in the interval of 200–300°C. Annealing at 400°C after a moderate deformation leads to the formation of a polygonized (“nanosubgrain”) dislocation substructure in austenite. As the initial deformation increases to e = 2, this structure is gradually substituted by a nanocrystalline structure of austenite. Annealing after deformation to intermediate degrees (e = 0.75−1.0) results in the formation of a mixture of nanocrystalline and submicrocrystalline polygonized structures.     

Effect of severe plastic deformation on microstructure and mechanical properties of bulk AZ31 magnesium alloy

The equal channel angular pressing (ECAP) was used to make large plastic deformation of magnesium alloy, and ECAP processing and relevant process parameters were obtained by using finite element method. The strain distributions in the workpieces and the loads on the dies were studied. The mathematical model of accumulated deformation results, microstructure refinement and mechanical properties were established. Through the analysis, the relationships between grain refinement and mechanical properties were obtained. The refined grain size and the obtained mechanical properties are forecasted by using characterization of accumulation deformation.     

退火工艺对强塑性变形珠光体钢丝组织和性能的影响

用TEM、XRD研究了强塑性变形（ε=2．60）SWRH72A钢丝经不同温度（100—400℃）退火处理后的微观结构变化。XRD分析显示强塑性变形引起SWRH72A钢丝中渗碳体回溶,部分碳原子溶入铁素体形成过饱和铁素体,过饱和铁素体中含碳量约O．34at％。由TEM分析可知强塑性变形钢丝经200—300℃退火,由于渗碳体颗粒的弥散析出,钢丝强度升高到2400MPa。退火温度进一步升高到400℃,渗碳体片开始球化,钢丝强度大幅降低,但塑性显著增加。     

Effect of severe plastic deformation on the microstructure and tribological properties of a babbit B83

The effect of severe plastic deformation carried out at room temperature by the methods of equal-channel angular (ECA) pressing and surface friction treatment (SFT) on the microstructure, rate of wear, and friction coefficient of a babbit B83 (11.5% Sb, 5.5% Cu, Sn for balance) has been investigated. It has been shown that severe plastic deformation that leads to a drop in the grain size of the babbit to 100–300 nm and to a strong refinement of particles of intermetallic phases (SnSb, Cu₃Sn) causes a considerable (twofold-fourfold) reduction in the rate of wear and a decrease in the friction coefficient of a steel-babbit pair under test conditions with lubrication at small (0.07 m/s) and enhanced (4.5 m/s) sliding velocities. As was shown by structural investigations performed with the use of scanning electron microscopy, this positive influence of severe plastic deformation on the tribological properties of the babbit is connected with the formation on the deformed-babbit surface of a developed porosity, which improves conditions for lubrication of the babbit-steel friction pair due to the action of the self-lubrication effect and thereby favors the retention of a stable regime of boundary friction of this pair. The formation of porosity is a result of the accelerated spalling of hard brittle intermetallic particles of SnSb and Cu₃Sn from the friction surface of the deformed babbit, which is caused by weakening and loss of the bonding of these particles with the plastic matrix (α solid solution based on tin) in the course of severe plastic deformation of the babbit. At the same time, under the conditions of dry sliding friction of the babbit-steel 45 pair, when a fatigue mechanism of wear of the alloy under consideration predominantly develops, this plastic deformation yields an approximately 1.6-fold increase in the rate of wear of the babbit. This increase is mainly due to numerous defects (microcracks) that are introduced into the babbit structure upon its severe plastic deformation and reduce the resistance of the surface layer of this material to the fatigue mechanism of wear.     

Microstructure development of steel during severe plastic deformation

The microstructure development during plastic deformation was reviewed for iron and steel which were subjected to cold rolling or mechanical milling (MM) treatment, and the change in strengthening mechanism caused by the severe plastic deformation (SPD) was also discussed in terms of ultra grain refinement behavior. The microstructure of cold-rolled iron is characterized by a typical dislocation cell structure, where the strength can be explained by dislocation strengthening. It was confirmed that the increase in dislocation density by cold working is limited at 10¹⁶m⁻², which means the maximum hardness obtained by dislocation strengthening is HV3.7 GPa. However, the iron is abnormally work-hardened over the maximum dislocation strengthening by SPD of MM because of the ultra grain refinement caused by the SPD. In addition, impurity of carbon plays an important role in such grain refinement: the carbon addition leads to the formation of nano-crystallized structure in iron.     

Phase and structural transformations in the aluminum amts alloy upon severe plastic deformation using various techniques

The paper presents experimental data on the structure formation in the commercial aluminum alloy of grade AMts subjected to severe plastic deformation using dynamic channel-angular pressing and torsion under high quasi-hydrodynamic pressure in Bridgman anvils. The dependences of the structural characteristics and hardness on the degree, rate, and scheme of deformation have been analyzed.     

大体积超细晶金属材料的剧烈塑性变形法制备技术

介绍了大体积超细晶金属材料的各种常见剧烈塑性变形法制备技术,系统阐述了各种制备技术的基本原理,并分析比较了这些制备技术的优缺点和适用范围,指出了剧烈塑性变形法制备技术的发展方向。     

Influence of plastic deformation on recrystallized microstructure of Fe-base ods alloy

The ferritic oxide dispersion strengthened alloys (ODS) are manufactured using the mechanical alloying process. The development of a coarse grained microstructure during recrystallization has been noted and discussed by a number of authors, but the mechanism of grain control remains uncertain. Recent work has emphasized the large influence of non-uniformities on the development of the recrystallized microstructure. The purpose of the present work was to study, with the help of finite element modeling techniques, the effect of non-uniform plastic strain on recrystallization of Fe-base ODS alloy named MA 957.     

热塑性变形过程中钛合金微观组织演变的可视化仿真

热塑性加工过程中材料的微观组织一般经历晶粒长大、静及动态再结晶等微观组织的演变,而微观组织状态直接影响着被加工零件的使用性能.因此,了解材料在热变形过程中组织的演变规律具有很重要的工程应用价值.在大量试验的基础上,利用有限元软件Marc模拟TC4钛合金的热锻过程.通过有限元软件,对热成形工艺参数如等效应力、等效应变、等效应变速率和变形温度的分布进行求解,再利用人工神经网络建立微观组织演变和热成形工艺参数的本构关系.然后,基于Voronoi图用软件Visual C++6.0来实现微观组织演变的可视化模拟.初步实现了TC4钛合金热变形过程微观组织的长大、再结晶等组织演变的二维可视化模拟.研究结果表明通过计算机模拟仿真,可以有效地、直观地预测热成形过程的材料微观组织变化规律,从而为热成形加工参数的优化提供参考.但要更精确地模拟和仿真热塑性变形中材料的微观组织的演变,还需更多地掌握在热塑性变形过程中的演变机制.