原始组织对304L超低碳奥氏体不锈钢等径角挤压变形的影响

304L超低碳奥氏体不锈钢由25kg真空感应炉冶炼,用透射电镜(TEM)研究了该钢铸态组织200℃等径角挤压变形(ECAP)后组织演变和铸态组织1道次ECAP+1150℃1.5 h,AC处理(固溶组织)再进行ECAP后的组织。结果表明,304L钢铸态组织1道次ECAP变形过程中主要的变形机制为滑移变形,同时出现少量的孪晶变形;304L钢固溶组织在ECAP变形过程中孪晶变形数量急剧增加,孪晶和滑移共同进行,细化原始晶粒组织演变。     

钛及钛合金形变孪晶的研究进展

钛及钛合金变形机制主要有滑移和孪生。形变孪晶的生成分为形核和长大两个阶段。形变孪晶在钛合金变形中的作用:(1)多种塑性变形过程,当位错滑移困难时,形变孪晶起到协调变形的作用,例如,纯钛中的■等形变孪晶可协调c轴塑性变形,在高速压缩和等通道转角挤压等特殊工艺条件下孪晶仍起到协调变形的作用;(2)在压缩、等通道转角挤压和轧制等工艺条件下,形变孪晶引起大量晶粒发生转动,促进新织构的生成;(3)形变孪晶激活后钛合金产生明显的应变硬化效应,这是由于多孪晶的交叉作用;(4)形变孪晶还能产生孪晶诱发塑性效应。形变孪晶对钛合金再结晶也有促进作用,这是由于孪晶界是局部高能区,可提供合适的再结晶形核位置。室温激活孪晶诱发静态再结晶细化晶粒;热加工过程激活的孪晶同时诱发动态再结晶过程;液氮温度激活孪晶诱发之后的动态再结晶细晶效果明显,通过液氮温度多向压缩激活高密度均匀孪晶,再进行热压缩诱发动态再结晶,可获得细小均匀的等轴晶组织。     

等通道转角挤压组织演变规律的研究进展

综述了金属结构材料和功能材料基体相晶体结构、层错能、Hollomon参数lnZ对等通道转角挤压ECAP变形组织演变规律影响的研究进展,试样基体相的晶体结构对变形组织的演变起重要的影响作用。随着应变量的增大,密排六方结构金属先形成形变孪晶、再启动优先存在的但被阻塞的滑移系统;面心立方结构金属的位错滑移主导着组织演变与晶粒细化过程,先形成亚晶界,再增大组织取向差,最终形成大角度晶界。在高层错能材料中,随着Hollomon参数lnZ增大,位错运动受到抑制,驱使变形机制从位错滑移逐渐转变成形变孪晶;当Z参数减小时,在ECAP高层错能材料中会形成微尺度的剪切带。在低层错能材料中形成丰富的孪晶,极低层错能的材料形成宏观剪切带。而中等层错能材料的变形机制则取决于Z值的高低。分析了ECAP过程动态再结晶的影响因素,认为γm·ln2Z30不宜作为ECAP过程是否发生动态再结晶的判据,ECAP过程动态再结晶的影响因素还有待进一步研究,如弄清ECAP过程温升规律、分析淬火保存ECAP变形组织将有助于研究ECAP动态再结晶。     

等通道热挤压变形制备奥氏体不锈钢纳米级组织

 通过采用700 ℃等通道挤压法(ECAP法)对00Cr19Ni10奥氏体不锈钢实施变形,制备出晶粒尺寸在200~300 nm的超细晶组织,由此可使其抗拉强度与屈服强度显著增加。同时探讨了ECAP细化机理,对试验钢在等通道挤压变形中的微观组织演变过程进行了分析,发现其组织演变与滑移、孪晶以及动态再结晶有关。     

7075铝合金等通道挤压过程工艺优化

文章探求7075铝合金一道次ECAP成型过程的最佳变形温度,利用DEFORM-3D有限元分析软件对7075铝合金方形坯料进行了不同挤压温度有限元数值模拟实验,利用元胞机模拟不同温度下变形晶粒尺寸,并加以实物观察验证。结果表明,500℃是7075铝合金最佳挤压温度;当7075铝合金处于较低挤压温度时,随着挤压温度升高,变形后的晶粒逐渐细化;当挤压温度大于500℃时,ECAP变形坯料由于再结晶后晶粒生长,晶粒异常粗大不符合生产要求。     

双级形变时效对铝合金电工圆杆组织及性能的影响

采用抗拉强度、导电率性能测试和X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等分析方法研究双级形变时效对Al-B电工圆杆组织和性能的影响。结果表明:经双级形变时效处理后,合金的导电率和抗拉强度随预时效温度的升高呈先升后降趋势,且预变形量越小,材料的抗拉强度峰值出现越缓慢,预变形量过大时材料的导电率和抗拉强度指标下降;析出相与基体保持共格关系,呈弥散分布,在STEM模式下结合傅里叶交换(FFT)衍射花样可确定为强化相θ'相。通过预变形32%+预时效110℃×2 h+终变形83%+终时效190℃×6 h处理,合金的抗拉强度达到181 MPa,导电率为58. 5%IACS,延伸率为8%,与单级形变时效(变形量83%+时效190℃×6 h)对比,其导电率和抗拉强度都有较大提升,综合性能较佳。     

形变时效处理对铝合金电工圆杆抗拉强度和导电率的影响

探究不同变形量形变热处理对铝电工圆杆导电率及抗拉强度的影响。结果表明,随着轧制变形量的增加,试样的导电率先增加后降低,其抗拉强度得到较大的提升。形变时效后,试样的晶界薄化,组织更加均匀,基体中第二相粒子的含量增加,且出现新相SiB_6、Al_(3.21)Si_(0.47)、Cu_3Fe_(17)、Al_2FeSi。通过"535℃×5h固溶处理+83%轧制+190℃×10h时效"的形变热处理后,试样抗拉强度达到234MPa的峰值,导电率为53.45%IACS。     

30Mn20Al3无磁钢加工硬化行为和组织变化

研究了30Mn20Al3无磁钢冷轧板经1000和800℃固溶处理10 min后的拉伸变形加工硬化行为和组织结构变化.结果表明:该钢的加工硬化速率在不同变形阶段随真应变的变化呈现不同的规律,加工硬化指数随真应变增加而增加.OM和TEM观察显示,变形量小时,滑移为主要变形机制;变形量增大,变形机制以形变孪晶与位错及形变孪晶之间的交互作用为主;1 000℃固溶处理的晶粒尺寸较800℃大,变形过程中产生的形变孪晶较多,且随着变形量增加,形变孪晶可持续形成,增大了TWIP效应;晶粒尺寸减小使变形过程中的形变孪晶产生的临界应力增大,抑制形变孪晶的产生,从而减小了TWIP效应.     

超细晶钛铝基合金的高温压缩性能研究

采用高能球磨及真空热压烧结的方法制备超细晶/纳米晶双相γ-TiAl基合金,将名义成分为Ti-45Al-7Nb(%,原子分数)的混合粉末经40 h高能球磨后,粉末达到纳米级。球磨后的混合粉末经真空热压烧结(烧结温度1200℃,压力30 MPa,保温保压1 h)。研究该合金在温度为1000,1050和1100℃,应变速率为1×10^-4,1×10^-3和1×10^-2s^-1 3个变形速率条件下的高温压缩组织、流变行为和本构关系。研究结果表明：经过高能球磨及真空热压烧结原位合成的组织为超细晶α₂-Ti₃Al及γ-TiAl双相等轴状合金组织,晶粒尺寸小于5μm。合金为热敏感型和应变速率敏感型合金,合金压缩流变应力随应变速率的降低和温度的升高而下降。高温热压缩时,合金组织由规整等轴状被压变形为长条形,形变主要发生在γ-TiAl相中,晶界和γ相晶内可见位错及孪晶,孪晶及位错为主要的形变机制。在1000,1050和1100℃,1×10^-4,1×10     

铸态304L奥氏体不锈钢等径角挤压变形的力学性能

 研究了经1~4道次等径角挤压变形(ECAP)后,铸态304L奥氏体不锈钢微观结构的演变,同时测定了ECAP变形后的力学性能。结果表明,经4道次变形后,铸态粗大晶粒破碎形成细小的大角度晶粒,平均晶粒尺寸约202 nm;抗拉强度和屈服强度大大提高(Rp02=1 002 MPa,Rm=1 100 MPa),但均匀塑性变形能力(A＜3%)和加工硬化指数(n=0060)却显著下降。     

Fe-Mn-Si-Al系和Fe-Mn-C系TWIP钢加工硬化行为

研究了在不同应变量下Fe-Mn-Si-Al系和Fe-Mn-C系孪晶诱导塑性(TWIP)钢的力学性能以及微观组织,分析了TWIP效应在两种不同系列TWIP钢中发挥的作用,阐明了TWIP钢的强化机制.两种系列的TWIP钢都具有高加工硬化能力,但层错能较低的Fe-Mn-C系TWIP钢加工硬化能力更强.两种系列的TWIP钢加工硬化表现为多加工硬化指数行为,这是由多种强化机理在不同阶段起主导作用的结果.微观组织形态与加工硬化强度之间存在着较强的关联性.位错的增殖和形变孪晶的产生对两个系列TWIP钢硬化曲线形态有着明显的影响.在高应变阶段,Fe-Mn-C系TWIP钢大量的第一位向形变孪晶T1和第二位向形变孪晶T2,以及附着在孪晶界旁的高密度位错区域是造成其具有高加工硬化能力的原因,而Fe-Mn-Si-Al系TWIP钢细密的第一位向形变条纹和孪晶片层间的位错是其高加工硬化原因,且其微观组织更为均匀细致.      

ECAP过程中TWIP钢的组织演变

 研究了 TWIP钢（30Mn-3Si-3Al）在等径角挤压冷变形过程中的组织演变。试验结果表明：经1道次变形后,产生大量10～40 nm宽的形变孪晶,同时出现的微观剪切带对孪晶进行了切割。随着道次的增加,孪生系统增多,形变孪晶相互交割,孪晶板条出现弯曲和断裂;同时剪切带的数量和宽度都增加,产生相互交错并切割孪晶板条,使基体的细化面积增大。4道次变形后,组织变成由碎化带和割裂开的孪晶相互交织的变形结构。碎化部分超细晶晶粒尺寸为40～120 nm,而未碎化孪晶板条宽度降至5～20 nm。     

Twinning-Induced Plasticity Aided High Ductile Duplex Stainless Steel

Extended ductility over 70 pct was realized in duplex stainless steel by implementing twinning-induced plasticity (TWIP). The steel also exhibited the tensile strength over 800 MPa. The steel chemistry was designed so that the stacking fault energy of austenite was high enough to induce TWIP during deformation. After the initial decrease, the strain hardening rate increased at high tensile strains above ~30 pct. The microstructures of austenite at such high strains were manifested by well-developed primary twins and nanotwins between them, which effectively block dislocation motion. This observation ensures that extended ductility and high strength of a newly designed duplex stainless steel are originated from TWIP in austenite.     

Effects of High Strain Rate on Properties and Microstructure Evolution of TWIP Steel Subjected to Impact Loading

 The mechanical properties of the TWIP steel subjected to impact loading at various strain rates were analyzed by the Split Pressure Hopkinson Bar. Meanwhile the microstructure of the TWIP steel fore-and-after the dynamic deformation were characterized and analyzed by optical microscopy (OM), X-ray diffraction (XRD), and transmission electron microscope (TEM). The result shows that when the TWIP steel was deformed under dynamic station, the stress, microshardness and work hardening rate increase with the increment of strain and strain rate; there exist stress fluctuation and decline of work hardening rate for adiabatic temperature rising softening. There exist many pin-like deformation twins in the microstructure of the TWIP steel subjected to impact loading, the grain size after deformation is bigger than that before; the interaction of twins with dislocation and twins with twins, especial emergence of high order deformation twins are the main strengthening mechanisms of the TWIP steel. The nucleation mechanism of deformation twins will be “rebound mechanism”; the incomplete deformation twins can be observed when the strain rate is low; when strain rate raises, deformation twins unite together; furthermore, deformation twins become denser because the nucleation rating enhancing with strain rate increasing.     

Microstructure and Mechanical Properties of Hot-Rolled Fe-Mn-C-Si TWIP Steel

 Mechanical properties and microstructural evolution of the hot-rolled Fe-Mn-C-Si TWIP steel were investigated and the deformation mechanism was analyzed. The results showed that the tensile strength and elongation were about 1050 MPa and 60%, respectively. The hot-rolled steel had high specific energy absorption and impact toughness between -120 ℃ and 20 ℃. Some inhomogeneous dislocation zones were observed in the undeformed steel. Lots of deformation twins and twin-dislocation interactions were observed in the deformed steel. TWIP effect was the major deformation mechanism for the excellent mechanical properties.     

Structure and fatigue properties of 08Kh18N10T steel after equal-channel angular pressing and heating

The structure of corrosion-resistant austenitic 08Kh18N10T steel is studied after equal-channel angular pressing (ECAP), heating, and subsequent cyclic tests. After ECAP, an oriented mainly subgrain structure with a structural element size of 100–250 nm and a high fraction of deformation twins forms in the austenite of the steel, and 42 vol % of lath martensite appears. Dynamic twinning, martensitic transformation, dynamic recovery, and even recrystallization take place in the 08Kh18N10T steel during cyclic deformation in the course of fatigue tests according to the scheme of repeated tension. The fatigue strength increases after ECAP due to the refinement and twinning of an austenite structure and the appearance of martensite. The fatigue limit is maximal after ECAP and heating at 550°C for 20 h due to a high annealing twin density in a predominantly austenitic recrystallized matrix, intense dynamic twinning, and martensitic transformation during cyclic deformation.     

固溶温度对节约型双相不锈钢TRIP/TWIP行为的影响

 通过微拉伸、电子背散射（EBSD）、透射电子显微镜（TEM）等手段,研究了具有亚稳奥氏体相的节约型双相不锈钢在1 000～1 200 ℃范围内不同固溶温度下的组织与性能的演变规律;探讨了固溶温度对形变诱导塑性（TRIP/TWIP）的作用机制。结果表明,随着固溶温度的升高,抗拉强度与伸长率均先升高后降低,而亚稳奥氏体相比例由74%（1 000 ℃）降低到37%（1 200 ℃）;1 050 ℃固溶时,试验钢表现出最佳综合性能,抗拉强度达到960 MPa,伸长率达到62%,强塑积达到60 GPa·%。在经拉伸变形的微观结构中形变诱导马氏体与形变孪晶共存,表明试验钢中亚稳奥氏体相的变形机制主要受TRIP及TWIP共同控制,从而导致其塑性变形过程呈现多阶段应变硬化特征,而钢中铁素体相的变形机制主要变形为位错的滑移。     

异步轧制TWIP钢的力学性能和微观组织

 利用金相显微镜、X射线衍射仪和透射电子显微镜对异步轧制及热处理TWIP钢的力学性能与微观组织进行了研究。结果表明,TWIP钢经500℃异步轧制后强度显著提高,而塑性降低,这是位错与孪晶共同作用的结果。轧制后的热处理降低了位错密度以及变形孪晶数量,导致强度降低,伸长率升高。经600℃和700℃退火后,TWIP钢表现出良好的强度和塑性综合性能。因此,异步轧制后热处理是获得具有优良综合力学性能TWIP钢的可行途径。     

Effect of the Deformation Twin Density on the Corrosion Behavior in TWIP Steel

Based on its excellent tensile strength-ductility property combination,twinning-induced plasticity (TWIP) steel shows great potential in applications for structural components in automobile industry.The aim of this research is to investigate the corrosion resistance properties and corrosion mechanism under room temperature in TWIP steel.The influence of the deformation twin density on corrosion property was primarily considered by salt spray test.The specimens used in the investigation are as-annealed and as-deformed respectively.The microstructure and corrosion resistance property were characterized by scanning electron microscope (SEM),optical microscope (OM) and so on.There are some annealing twins distributed randomly in austenitic grains in the as-annealed specimen.After the specimen was subjected to tensile experiment,the density of the deformation twins increased sharply,which are different from the annealing twins in size and morphology.It was found that the corrosion potential of the as-annealed is lower than that of the as-deformed and the corrosion current density behaves contrarily.After immersed in 5% NaCl solution salt spray for 48h,the as-deformed showed a bit better than the as-annealed in corrosion resistance.With the time prolonged,the gap between the two specimens in corrosion resistance increased rapidly.The corrosion morphologies varied in color and shape.Further investigation,carried out by SEM and EDS,indicated that as-annealed and the as-deformed followed pitting corrosion and uniform corrosion mechanism respectively.The reason for the difference in corrosion mechanism is possibly the presence of the deformation twins.The deformation twins formed during the tensile test refine grains by way of segmentation.The twin boundaries largely belong to the coincidence site lattice (CSL),which is on lower energy state.It suggests that the twins not only play a role in strengthening,but also improve effectively the corrosion resistance in TWIP steel.