7039铝合金靶板侵彻过程中的组织特征及数值模拟

采用光学显微镜(OM)分析子弹斜侵彻7039铝合金后弹坑周围的组织特征,并对侵彻过程进行数值模拟.结果表明:子弹侵彻7039铝合金靶材后,弹坑周围的显微组织呈现有规律的特征;当绝热软化作用较弱时,弹坑周围出现绝热剪切带和裂纹;且随着热软化的加强,绝热剪切带聚合成较宽的层叠剪切变形带,紧邻的晶粒严重变形产生扭曲带,侵彻末期组织中形成大量的变形显微带.采用Largrange描述的Johnson-Cook本构模型能够有效地模拟子弹斜冲击侵彻7039铝合金靶材的过程.     

Mg-Gd-Y系合金中绝热剪切带的特征

通过弹道冲击试验和高温Hopkinson Bar压缩试验研究了Mg-Gd-Y系合金的绝热剪切行为.利用光学显微镜对试验后试样的组织进行观察.结果发现,该合金在两种试验条件下形成两种绝热剪切带.弹道冲击过程中形成的剪切带在光学显微镜下呈白亮色,平均宽度约为10 μm,属于白亮带,带内组织的显微硬度明显高于周围基体.白亮带只能在稳定塑性侵彻阶段形成:整个高温Hopkinson Bar压缩过程中只在T=735 K时形成较明显的塑性变形带.远离绝热剪切带源点的裂纹的形成主要是由平行于剪切方向的孪晶引起的.     

冶金因素影响绝热剪切带形成的金相观察

对在相同爆炸复合条件下几种不同状态的金属所产生的绝热剪切带(ASB)的显微组织进行了观察及显微硬度测定，探讨了不同的相组成、预变形程度和晶体结构对绝热剪切带形成的影响。结果表明：ASB的形态、大小和数量受材料的预冷变形程度、成分、晶体结构、相组成等因素的影响；ASB的硬度值均高于基体。     

装甲钢板中绝热剪切带的特征

测量了碳含量（质量分数,％）分别为０．２４,０．２８,０．３０,０．３９和０．４４的Ｃｒ－Ｎｉ－Ｍｏ装甲钢板基体、变形区及绝热剪切带的显微硬度,观察绝热剪切带形貌的微观组织结构,结果表明：随硬度升高,绝热剪发带的数量增多,绝热剪切带的硬度远高于基体及淬火态试样的硬度,其硬度随碳含量变化的规律与淬火态试样随碳含量变化的规律一致,绝热剪切带微观组织是非常细小的马氏体板条构成的,未观察到绝热剪切带内部析     

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。     

快速凝固过共晶铝硅合金粉末的形貌与显微组织

采用快速凝固气体雾化工艺制备Al-27%Si合金粉末,研究合金粉末形貌和热处理对组织的影响,利用X射线衍射仪和显微硬度计等对Al-27%Si合金粉末中硅相的析出与长大进行表征。结果表明:快速凝固Al-27%Si合金粉末由基体α(Al)相、块状β-Si相和枝晶状共晶硅相组成;经热处理后,β-Si相发生粗化,共晶硅相逐渐转变为块状相且发生粗化;在500℃下加热保温后,α(Al)相和β-Si相的衍射峰强度随时间延长而增大,α(Al)相衍射峰向低角度偏移;合金粉末显微硬度在500℃下加热,初期有下降趋势,但随时间延长,不再下降,而是维持相对稳定。     

高应变速率下TC11钛合金动态剪切行为与性能

采用分离式霍普金森压杆（Hopkinson Bar）装置系统,对TC11钛合金进行室温高应变速率（700-2100s^-1）动态剪切试验,通过光学显微镜、显微硬度分析仪、扫描电镜研究了TC11钛合金动态剪切行为、绝热剪切带微观组织与性能。结果表明：TC11钛合金随应变速率的提高绝热剪切敏感性增加;绝热剪切带由过渡区域的变形拉长组织和中间部位的细小晶粒组织组成,具有清晰的剪切变形流线,宽度约为10μm;绝热剪切带内的显微硬度值高于基体组织,是,由应变速率强化和应变强化与热软化相互作用的结果。     

Fe83Ga17Tby合金组织结构及磁致伸缩性能

采用Φ7.62 mm装甲钢平头子弹对Ti-6Al-4V合金进行侵彻,分析了Ti-6Al-4V合金弹着点及其弹着点周围宏观与微观组织变化与损伤.结果表明,Ti-6Al-4V合金弹着点微观组织变化与损伤与侵彻不同阶段所受应力、应变、应变硬化、热软化和弹头形状等因素密切相关.在高应变率下,Ti-6Al-4V合金绝热剪切带的形成是一个由萌生、扩展、完全发展组成的过程.Ti-6Al-4V合金弹着点在不同发展阶段的组织变化与损伤不同,各个阶段靶板受力状态在其微观组织变化与损伤中起到非常重要的作用.     

Ti-6Al-4V合金弹着点及其周围组织变化与损伤

采用Φ7.62 mm装甲钢平头子弹对Ti-6Al-4V合金进行侵彻,分析了Ti-6Al-4V合金弹着点及其弹着点周围宏观与微观组织变化与损伤。结果表明,Ti-6Al-4V合金弹着点微观组织变化与损伤与侵彻不同阶段所受应力、应变、应变硬化、热软化和弹头形状等因素密切相关。在高应变率下,Ti-6Al-4V合金绝热剪切带的形成是一个由萌生、扩展、完全发展组成的过程。Ti-6Al-4V合金弹着点在不同发展阶段的组织变化与损伤不同,各个阶段靶板受力状态在其微观组织变化与损伤中起到非常重要的作用。     

单级时效对7050铝合金力学性能及晶间腐蚀性能的影响

采用硬度测试、恒温浸泡方法、金相和透射电镜技术研究不同温度不同时间的单级时效处理对7050铝合金的力学性能和晶间腐蚀性能的影响.结果表明:当时效温度由120℃升高至180℃时,合金时效硬化响应速度明显加快,合金进入过时效状态所需的时间缩短.合金在120℃峰时效时,随时效时间的延长,析出相的粗化、晶界的宽化和无沉淀析出带出现缓慢,合金的硬度能长时间维持在较高水平.合金的晶间腐蚀敏感性与晶界析出相和无沉淀析出带(PFZ)的特征有关;晶界析出相呈链状分布时合金的腐蚀敏感性强,晶界析出相大,分布不连续,PFZ的宽化,则合金的腐蚀敏感性低.     

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。     

热处理条件对搅拌摩擦镁合金接头各区域抗弹行为的影响

采用搅拌摩擦焊(FSW)工艺制备AZ31B镁合金焊接接头,并在不同条件下进行热处理。研究AZ31B镁合金焊后热处理(PWHT)不同区域的抗弹行为,使用7.62 mm×39 mm穿甲弹,冲击速度为(430±20)m/s。分析热处理前后搅拌摩擦焊接头的显微硬度。结果表明,PWHT工艺(250°C,1 h)能提高热处理后搅拌摩擦焊接头的显微硬度。扫描电镜(SEM)结果显示,热处理使α-Mg晶粒细化,形成细小的析出相,使β-Mg17Al12相溶解到Mg基体中。通过穿深(DOP)试验评估PWHT不同区域的抗弹行为。热处理后接头母材区(BMZ)的DOP值较小。抗弹试验后对弹坑周边3个区域的横截面进行SEM表征,观察到绝热剪切带(ASB)的形成。     

Experimental and finite element simulation study of the adiabatic shear band phenomenon in cold heading process

This paper presents the outcomes of a comprehensive experimental, metallurgical and finite element (FE) simulation study to characterize the development of adiabatic shear band (ASB) phenomenon in steel cold heading (CH) process. The main objective of this work is to investigate the complex interplay of different process and material parameters on the ASB development stages inside the cold headed parts.In this work, the drop weight compression test (DWCT) was selected to simulate the CH process impact loads on specimens machined from 1038 steel and 1018 steel. Series of DWCTs were performed under different impact loading conditions. The goal of these tests is to achieve different deformation levels and introduce ASBs at different stages.To reach a full understanding of this complex phenomenon, the FE simulation analysis was used to support the metallurgical examination of the DWCT specimens. The FE analysis provided important details about the changes of different material and process parameters at the critical zones inside the ASBs.This study confirmed that the ASB is mainly a thermo-mechanically controlled phenomenon. The ASBs develop in three stages: homogeneous plastic strain, inhomogeneous plastic strain, and strain localization. The ASB development stage depends mainly on the status of the competition between the work hardening and the thermal and geometrical softening mechanisms inside the bands. The domination of the softening mechanisms at advanced levels of deformation triggers a self-catalytic strain localization and material strength degradation process that leads to failure inside the band.In general, the metallurgical and finite element analysis investigation revealed that under impact loads, three ASBs can develop simultaneously inside the cold headed parts; lower, upper and central ASBs. As the deformation continues; the development of the lower and upper bands slows down and contributes in the rapid development of the adjacent central ASB. This study confirmed that the ASB has a canonical structure which leads to an ASB that can experience different development stages along the same band simultaneously.This study proved that the shape and the type of ASBs in cold headed parts depend highly on material's properties. The metallurgical and finite element analysis revealed that the higher the strength of the tested steel, the easier to form a narrow ASB that reaches the localization stage at low deformation levels. In contrast, ductile steels experience wider ASBs when subjected to the same deformation levels. These bands require higher levels of deformation to reach the localization stage in comparison to higher strength steels.     

纳米SiC_P/AZ61镁基复合材料的时效行为研究

采用箱式热处理炉、显微硬度计、SEM电镜、能谱分析仪,对纳米SiCP/AZ61镁基复合材料的时效行为进行分析,结果表明,复合材料在时效初期,未观察到不连续析出相在晶界析出,却观察到Mg17Al12比较分散的从基体中析出;随着时效温度的提高,SiCP/AZ61复合材料或AZ61合金到达时效峰值所需的时间减少;在同一温度下,SiCP/AZ61复合材料要比基体合金的时效速度快,但时效的效果比基体合金差;且在同一温度下,SiCP/AZ61复合材料的硬度值要比基体合金的硬度值高,主要是因为采用了高能超声法,使纳米SiC颗粒均匀地分布在基体中。     

Effect of size and distribution of titanium carbide on microstructure and mechanical properties of Ti-25V-15Cr-2Al-0.2C-0.2Si alloy

The effect of size and distribution of titanium carbide on the microstructure and mechanical properties of non-burning β titanium alloy Ti-25V-15Cr-2Al-0.2C-0. 2Si （mass fraction, %） was investigated. The microstructure of the heat-treated and exposed alloy was studied using optical microscopy（OM）, scanning electron microscopy （SEM） and transmission electron microscopy（TEM）. It is found that carbides with finer size and more uniform distribution can suppress the formation of α precipitates more effectively, and can especially decrease the amount of grain boundary α precipitates after long-term exposure at 540 ℃ （the expected application temperature）. Thus, significant improvement in thermal stability can be achieved by refining carbide particles in the matrix of the alloy.     

Microstructure evolution in the weld metal region of a Ni-based Inconel 718 superalloy produced by tungsten inert gas welding

The microstructure evolution of the weld metal (WM) region in a Ni-based 718 superalloy is discussed. The superalloy sheets were welded using the tungsten inert gas process at different heat inputs. The precipitates and dendrites in the WM of each joint were analyzed by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy (EDS). Statistics on the dendrite arm spacing and precipitates were obtained from the metallographs. Using the alloy composition determined by EDS and the phase diagram obtained using ThermoCalc, the equilibrium distribution coefficient of Nb, the temperature range of solid/liquid coexistence, and the distribution and morphology of Laves phase in different subregion of the WM were analyzed. There is lamellar segregation, regional segregation, and microsegregation in the WM. As the heat input increases, the arm spacing and the microsegregation increase. At a fixed heat input, the microsegregation rate is smallest in the crater, but with the macrosegregation seriously.     

Effect of post-weld heat treatment on microstructure and mechanical properties of welded joints of 6061-T6 aluminum alloy

6061 aluminum alloy T-joints were welded by double-pulsed MIG welding process. Then, the post-weld heat treatment was performed on the welded T-joints. The weld microstructure under different aging temperature and time was investigated by transmission electron microscopy and scanning electron microscopy. The mechanical properties were examined by hardness test and tensile test. The results showed that the micro-hardness was sensitive to heat treatment temperature and time. Increasing temperature was beneficial to the shortening of peak aging time. There were a large number of dislocations and few precipitates in the welded joints. With the increase of post-weld heat treatment temperature and time, the density of dislocation decreased. Meanwhile, the strengthening phase precipitated and grew up gradually. When the post-weld heat treatment temperature increased up to 200 °C, large Q' phases were observed. And they were responsible for the peak value of the micro-hardness in the welded joints.     

Shear localization behavior in hat-shaped specimen of near-α Ti−6Al−2Zr−1Mo−1V titanium alloy loaded at high strain rate

The microstructure characteristics in early stage shear localization of near-α Ti?6Al?2Zr?1Mo?1V titanium alloy were investigated by split Hopkinson pressure bar (SHPB) tests using hat-shaped specimens. The microstructural evolution and deformation mechanisms of hat-shaped specimens were revealed by electron backscattered diffraction (EBSD) method. It is found that the nucleation and expansion of adiabatic shear band (ASB) are affected by both geometric and structural factors. The increase of dislocation density, structure fragment and temperature rise in the deformation-affected regions provide basic microstructural conditions. In addition to the dislocation slips, the extension twins detected in shear region also play a critical role in microstructural fragmentation due to twin-boundaries effect. Interestingly, the sandwich structure imposes a crucial influence on ASB, which finally becomes a mature wide ASB in the dynamic deformation. However, due to much larger width, the sandwich structure in the middle of shear region is also possible to serve as favorable nucleation sites for crack initiation.     

TC6钛合金绝热剪切带不同发展阶段的精细结构

采用分离式Hopkinson Bar技术对TC6钛合金进行动态剪切试验,通过光学显微镜、扫描电镜及透射电镜研究Tc6钛合金绝热剪切带不同发展阶段的精细结构及其形成机制.结果表明:在高应变率下,材料绝热剪切带的形成是一个由萌生、扩展、完全发展组成的过程,Tc6钛合金绝热剪切带在不同发展阶段的精细结构有很大的不同,从萌生到完全发展,塑性变形剧烈程度逐渐增大,位错在TC6钛合金绝热剪切带的形成中起到非常重要的作用.