α－钛／低碳钢爆炸复合界面结合层内的绝热剪切现象

利用光学显微镜（ＯＭ）、扫描电镜（ＳＥＭ）和透射电镜（ＴＥＭ）研究了α－钛／低碳钢爆炸复合界面结合层内α－钛侧产生的绝热剪切带（ＡＳＢ）内的微观组织结构。结果表明，ＡＳＢ内的晶粒得到显著细化，已转变为～０．１μｍ　的等轴细晶组织且晶粒内位错密度低。ＡＳＢ　内未发生ｈｃｐ→ｂｃｃ转变，亦无熔化迹象。依据ＡＳＢ　内的形变温度条件，利用动态再结晶理论进行了分析讨论：动态再结晶所产生的细晶组织可能导致高应变率下超塑性的发生，致使ＡＳＢ内发生大剪切应变。还对仅在界面层内α－钛侧产生ＡＳＢｓ　而钢侧却从未观察到ＡＳＢｓ这一现象首次从材料热粘塑性本构失稳理论，就材料物理－力学－热学三方面性能进行了综合分析，并表明：绝热剪切是一个速率相关过程。     

α—钛／低碳钢爆炸复合界面结合层内的绝热剪切现象

利用光学显微镜、扫描电镜和透射电镜研究了α－钛／低碳钢爆炸复合界面结合层内α－钛侧产生的绝热剪切带内的微观组织结构。结果表明，ＡＳＢ内的晶粒得显著细化，已转变为－０．１μｍ的等轴细晶组织且晶粒内位错密度低。ＡＳＢ内未发生ｈｃｐ→ｂｃｃ转变，亦无熔化迹象。     

时效处理对QBe2/Q235复合板力学性能影响

研究了时效处理对QBe2/Q235爆炸复合板的QBe2侧硬度的影响,得出复合板的较佳时效处理工艺为310～320℃时效3 h;并研究了在该时效处理工艺前、后,复合板的剪切、粘结和弯曲性能,以及界面显微硬度的变化.结果表明:时效处理后复合板的剪切强度没有明显变化,而粘结强度明显降低,冷弯性能有一定程度的降低,并且在QBe2侧产生了沉淀硬化.     

中温变形下TC4合金绝热剪切带研究（英文）

研究了TC4合金在中温变形过程中形成的绝热剪切带,应变速率为50 s-1,变形温度为560~660 oC。结果表明变形温度对绝热剪切带的形成有很大影响。剪切带宽度随着变形温度的升高从85μm增加至140μm。因为发生了加工硬化和绝热剪切带中产生的细晶强化作用,绝热剪切带对应的维氏显微硬度比基体高。讨论了绝热剪切带中微观组织演变规律,大应变以及高温使得绝热剪切带中发生了动态再结晶,形成了等轴的再结晶晶粒,再结晶晶粒尺寸为200 nm左右。本研究中形成的绝热剪切带具有形变剪切带和相变剪切的特点。     

Adiabatic Shear Band of TC4 Alloy during Warm Comp- ression

研究了TC4合金在中温变形过程中形成的绝热剪切带,应变速率为50 s-1,变形温度为560~660 oC。结果表明变形温度对绝热剪切带的形成有很大影响。剪切带宽度随着变形温度的升高从85μm增加至140μm。因为发生了加工硬化和绝热剪切带中产生的细晶强化作用,绝热剪切带对应的维氏显微硬度比基体高。讨论了绝热剪切带中微观组织演变规律,大应变以及高温使得绝热剪切带中发生了动态再结晶,形成了等轴的再结晶晶粒,再结晶晶粒尺寸为200 nm左右。本研究中形成的绝热剪切带具有形变剪切带和相变剪切的特点。     

Monel合金/Cu爆炸复合棒界面的微观组织和力学性能

利用爆炸复合的方法成功制备了Monel合金/Cu双金属复合棒材.借助金相显微镜(OM)、扫描电子显微镜(SEM)、能谱分析(EDS)和压剪分离测试,探讨了不同工艺条件下Monel/Cu爆炸复合界面的微观组织和力学性能.结果表明,随着爆炸比的增加,结合界面逐渐由平直状过渡到波状;在铜基体晶粒内的形变孪晶数量随爆炸比的增加而增加;界面局部存在少量熔区,熔区内存在细小的柱状晶;复合界面中没有发生扩散,但经过热处理后其界面观察到了扩散.剪切断裂发生在铜侧而非界面处,表明界面结合强度高于铜基体.     

一种典型近α型钛合金绝热剪切带组织特征研究

本文采用帽形试样对一种典型近α型Ti-6Al-2Zr-1Mo-1V钛合金在不同应变率条件下的绝热剪切特征开展了研究,结果表明：合金的动态应力应变曲线呈现典型的三阶段特征,分别对应于应变硬化、热软化和剪切局部化阶段,最终形成绝热剪切带(ASB)。在近剪切带处,初生α相和次生α相在过渡区内发生扭曲变形,甚至断裂,出现孪晶变形特征,近剪切带区域微观取向差增大,利于位错滑移/孪晶取向的α相优先发生塑性变形,形成亚结构,晶粒碎化,发生动态再结晶;随着应变率的提高,剪切带宽度呈增大趋势,且出现旋涡结构以协调和适应变形;通过纳米压痕试验,分析了ASB及其附近与基体α相、β相的弹性模量和显微硬度,表明该合金的绝热剪切带为一条软化带,影响区的宽度在ASB附近30μm以内。     

高速弹丸冲击诱发TC32钛合金中绝热剪切带的组织演化行为

采用光学显微镜(OM),扫描电子显微镜(SEM)和透射电子显微镜(TEM)研究了Ti-5Al-3Mo-3Cr-1Zr钛合金在高速弹丸冲击后的组织特征和演变行为。在弹坑周围,绝热剪切带(ASB)和剪切应力一直呈半圆状分布。观察到绝热剪切带中尺寸较大等轴晶粒和细长板条亚晶粒的旋转细化过程。采用聚焦离子束(FIB)技术准确地从ASB中的裂纹尖端取样制备TEM样品,在裂纹尖端区域周围发现非晶区、非晶-纳米晶过渡区域、细小纳米晶区共存。计算结果表明,绝热剪切带内温度升高可导致微观组织熔化,快速淬火后形成非晶区和细小的纳米晶。由于绝热剪切带中的显微组织是细小的等轴晶和非晶,具有较高的强度,使形变带与基体之间成为相对较弱的区域,绝热剪切带中的裂纹也主要在该区域萌生,裂纹通过微孔洞旋转联结的方式扩展。     

Ti-5Al-2.5Sn合金绝热剪切带的形成机制

利用分离式Hopkinson Bar技术,采用帽形试样,对Ti-5Al-2.5Sn合金进行动态剪切实验,通过光学显微镜、透射电镜研究了其绝热剪切带的形成机制。结果表明：孪晶在Ti-5Al-2.5Sn合金绝热剪切带的形成过程中起到了非常关键的作用;Ti-5Al-2.5Sn合金绝热剪切带的形成过程可分为3个阶段：第1阶段,在冲击载荷作用下,强迫剪切区的塑性变形由位错滑移与孪生切变共同完成,并形成大量孪晶;第2阶段,由于孪晶的形成,调整了局部晶体的位向,原来不动的位错启动,形成长条状的亚晶结构;第3阶段,在外加动态载荷下,运动位错与孪晶作用,使孪晶片发生断裂,形成细小等轴晶粒;同时,剪切带中心区域局部形成了等轴、畸变小、位错少的细小动态再结晶晶粒。Ti-5Al-2.5Sn合金绝热剪切带内的细小等轴晶粒尺寸为0.1~0.3 μm     

Ti-15Mo-3Al-2.7Nb-0.2Si钛合金绝热剪切带的微观结构演化

采用分离式Hopkinson压杆技术对Ti-15Mo-3Al-2.7Nb-0.2Si钛合金的帽形试样进行了强迫剪切试验,通过扫描电镜(SEM)及透射电镜(TEM)研究了Ti-15Mo-3Al-2.7Nb-0.2Si钛合金在动态加载下绝热剪切带的微观结构演化.结果表明:Ti-15Mo-3Al-2.7Nb-0.2Si钛合金由于其组织以bee晶格的a相为主,具有较好的变形能力,因此其绝热剪切带的形成是位错运动的结果;剪切带的微观结构演化过程为:晶粒在外加切应力作用下拉长变形一拉长晶粒的破碎-形成呈一定方向排列的细小等轴晶:带内形成的细小等轴晶尺寸为O.2～0.4ìm.     

预变形TA2剪切带中微观组织的演变

采用HOPKINSON压杆装置和帽形试样对工业纯钛TA2进行高速冲击，利用扫描电镜（SEM）、透射电镜（TEM）、和高分辨透射电镜（HREM）研究剪切带内部微观组织的演化过程。结果表明：剪切带内没发生相变，剪切带组织由细小的等轴晶组成，剪切带内的动态再结晶过程是通过晶粒机械碎化及晶界迁移、亚晶粗化的混合机制和渐进式亚晶位向差的再结晶机制共同作用完成。     

高应变率下铀铌合金的断裂组织特征

对经过内部爆破加载后产生的U-Nb合金破片进行了断口形貌、金相组织等微观分析。结果表明：U-Nb合金在爆炸加载下的断裂方式为剪切断裂；破片组织内部发现因高速应变引起的大量的绝热剪切带，靠近绝热剪切带的基体晶粒发生明显的拉长变形：破片中存在大量的微裂纹，裂纹沿着绝热剪切带扩展，当与沿壳体环向的拉应力形成的纵向主裂纹相交汇时，形成破片。     

Structure of titanium subjected to dynamic channel-angular pressing in copper shells

It has been established using metallography and electron microscopy that the dynamic channel-angular pressing of titanium in cylindrical copper shells of a sufficient thickness removes the effects of localized deformation in the form of cracks and adiabatic shear bands, which were observed upon deformation without shells. This mode of deformation is effected via the formation of numerous twins; as a result, the initial grains become divided into small regions. Together with twins of ordinary morphology in the form of plates, there are observed wavy bent “noncrystallographic” twins, whose appearance is caused by the rotational deformation modes. Twins in the form of rods have been revealed, which sometimes are grouped into lamellar packets arranged perpendicularly to the longitudinal axis of the sample. The formation of numerous twins in titanium during dynamic channel-angular pressing leads to an increase in the microhardness by 15–35%. Twinning can be used to increase the strength characteristics of titanium, additionally to the creation of nanocrystalline and submicrocrystalline structures.     

取样方向对冷轧Cu板动态强迫剪切变形行为的影响

分别沿与冷轧Cu板轧向成0°(RD-0°),45°(RD-45°)和90°(RD-90°)方向取帽形试样,利用Split-Hopkinson压杆实验装置,研究了强迫剪切条件下冷轧Cu板的动态变形特征.结果表明:冷轧Cu板强迫剪切动态力学行为呈现出明显的各向异性,RD-90°方向屈服强度和峰值应力最大,RD-45°其次,RD-0°方向最小.不同方向的绝热剪切变形行为也表现出较大的差异,RD-0°方向的绝热剪切带内的变形相比其它2个方向均匀,绝热剪切敏感性最弱.基于剪切应力-剪切应变曲线和绝热剪切扩展所需能量,定性解释了不同方向绝热剪切敏感性的差异.EBSD的实验观察表明,3个方向上的剪切带内均有超细晶存在.基于亚晶旋转动态再结晶机制,理论计算结果证实了剪切带内发生再结晶的动力学可行性.     

LOCALIZED SUPERPLASTIC BEHAVIOUR INα-TITANIUM AT HIGH STRAIN RATE

The microstructure ofx-Ti/mild steel composite fabricated by using constant stand-off cladding technique was observed with optical microscopy, SEM and TEM analvses. Veryfine equiaxed grains (<0.1μm) with a low dislocation density were observed in the adiabatic shear bands (.4SB);this enables a thermomechanical response that may lead to a superPlastic de formation.     

Deformation behavior ofAZ31 magnesium alloy at different strain rates and temperatures

The deformation behavior of AZ31 was examined by compression and tension testes over a wide strain rate and temperature range, strain rate from 10^-3 to 10^3 s^-1, temperature from 300 to 623 K. Analysis of flow behavior and microstructural observations indicate that in tension tests dislocation glide is the most important deformation mechanism in the test strain rate and temperature range, while in compression tests twinning deformation mechanism is important at lower temperature when the strain rate ranges from 10^-3 to 10 s^-1. At 10^3 s^-1 strain rate, dislocation glide and twinning are present at the same time. At the strain rate of 2 964 s^-1, adiabatic shear band can be found easily, even at the strain rate of 1 537 s^-1 adiabatic shear localization zone can be found. In adiabatic shear localization zone, there are fine recrystallization grains. But in adiabatic shear band, the grains cannot be identified by optical microscopy.     

Microstructure evolution mechanism in adiabatic shear band in TA2

The microstructure evolution mechanism in adiabatic shear band in commercial pure titanium (TA2) at high strain rates(γ≈l0^5 - 10^6/s) were studied. The nanosized recrystallized grains (about 50 nm in diameter) within the center of adiabatic shear band (ASB) were observed by means of transmission electronic microscope (TEM). A Rotational Dynamic Recrystallization (RDR) mechanism can explain the microstructure evolution (i. e. nanosized grains were formed within 5 - 10μs) in ASB. Kinetics calculations indicate that the recrystallized small grains are formed during the deformation and don‘t undergo significant growth by grain boundary migration after deformation.     

Ti5Mo5V2Cr3Al合金中绝热剪切带的微观结构演化

利用分离式Hopkinson压杆,对Ti5Mo5V2Cr3Al(TB10)合金帽形试样进行强迫剪切试验,通过光学显微镜和透射电镜技术观测其绝热剪切带(ASB)内的微观结构。结果表明,ASB的过渡区由具有高位错密度的沿着剪切方向的宽度为20～50nm的拉长组织构成;剪切带中心由大量低位错密度(相对ASB的过渡区)的直径为50～100nm的晶粒组成,具有典型的再结晶组织特征。在绝热剪切变形过程中ASB内的平均绝热温升约为784℃。ASB内发生了动态再结晶,晶粒尺寸为50～100nm。     

Microstructure and Mechanical Properties of Laser Solid Formed Ti-6Al-4V Alloy Under Dynamic Shear Loading

To investigate the mechanical properties of the Ti-6Al-4V alloy fabricated by laser solid forming technology, both static and dynamic shear tests were conducted on hat-shaped specimens by a servohydraulic testing machine and an enhanced split Hopkinson pressure bar system, over a temperature range of 173-573 K. The microstructure of both the original and deformed specimens was characterized by optical microscopy and scanning electron microscopy. The results show that: (1) the anisotropy of shear properties is not significant regardless of the visible stratification and the prior-β grains that grow epitaxially along the depositing direction; (2) the ultimate shear strength of this material is lower than that of those Ti-6Al-4V alloys fabricated by forging and extrusion; (3) the adiabatic shear bands of approximately 25.6-36.4 μm in width can develop at all selected temperatures during the dynamic shear deformation; and (4) the observed microstructure and measured microhardness indicate that the grains become refined in adiabatic shear band. Estimation of the temperature rise shows that the temperature in shear band exceeds the recrystallization temperature. The process of rotational dynamic recrystallization is considered to be the cause of the grain refinement in shear band.     

Effect of spherically converging shock waves on phase and structural state of quenched Al-4 wt % Cu alloy

Optical metallography, scanning and transmission electron microscopy, and microhardness measurements have been used to perform a layer-by-layer study of the structure of a quenched Al-4 wt % Cu alloy subjected to loading by spherically converging shock waves. It has been established that, when using this mode of loading, the high-strain-rate plastic deformation of this alloy occurs via intragranular dislocation slip. No bands of localized deformation at the grain boundaries, twins, and adiabatic shear bands are formed. Highstrain-rate plastic deformation leads to the dissolution of Guinier-Preston zones.