Monel合金高速塑性剪切变形与动态再结晶

采用Ｈｏｐｋｉｎｓｏｎ杆加载技术和帽状试样，研究Ｍｏｎｅｌ合金在εｓ≈４．３×１０５ｓ－１的高应变速率条件下的应力－应变关系及塑性变形行为．实验及计算结果表明，塑性区（简称剪切带）内温度随剪切应变增加呈线性升高．透射电镜证实剪切带组织发生了动态再结晶，再结晶晶粒约为１７０ｎｍ．分析了剪切带中组织结构的演变过程，讨论了动态再结晶的机制     

Al-5．8Mg—Mn-Sc—Zr合金的再结晶行为

采用活性熔剂保护熔炼,水冷铜模激冷铸造技术制备了Al-5.8Mg-0.4Mn-0.25Sc-0.1Zr（质量分数,%）合金板材。通过显微硬度测试、光学显微镜和透射电镜观察等分析手段研究了该合金的再结晶温度和再结晶形核机制。结果表明：通过添加微量的Sc和Zr元素使Al-Mg-Mn合金的抗再结晶能力得到显著提高,即添加了Sc和Zr的Al-Mg-Mn合金再结晶温度（450℃）比没有添加的合金（150℃）的高。Al-Mg-Mn-Sc-Zr合金的再结晶温度较高的主要原因是细小、弥散的Al 3（Sc,Zr）粒子对位错和亚晶界的钉扎作用。合金的再结晶形核机制为亚晶合并和亚晶长大的双重机制。     

动态冲击条件下Ti-15Mo时效钛合金的变形机制

通过固溶时效处理Ti-15Mo合金获得片层组织,采用分离式霍普金森压杆（SHPB）研究应变速率对变形机制产生的影响,结合绝热温升、显微组织和硬度分析表明：由于位错与第二相的相互作用,导致流变应力曲线发生波动。提高应变速率,一方面造成应变速率强化;另一方面促进绝热升温软化。合金温度达到379K时,热软化效应超过应变硬化效应,变形方式由均匀塑性变形变为绝热剪切变形。绝热剪切带的宽度随切应变的增加而增大,通过亚晶旋转再结晶机制产生等轴晶粒。再结晶的界面强化导致组织硬度由高到低为：混合组织>条状组织>基体组织。时效处理抑制应力诱发孪生（TWIP）效应,造成合金较低的应变硬化能力,劣化材料的动态力学性能。     

钛合金TC16中绝热剪切带的微观结构演化

利用分离式Hopkinson压杆（SHPB）技术对钛合金TC16的帽形试样进行动态加载,采用光学显微镜和透射电镜技术观测TC16中绝热剪切带内的微观结构和相变情况。结果表明,剪切带的边缘由具有高位错密度的沿着剪切方向排列的宽度为0.2-0.5μm的伸长组织构成,其与基体组织的形貌显著不同;剪切带中部由大量低位错密度的直径约为0.2μm的再结晶等轴晶组成。衍射花样的标定表明α-Ti和α″相共存于剪切带中部,剪切带内发生了相变。绝热剪切变形过程中剪切带内的温度约为796℃。讨论了TC16中绝热剪切带内的相变规律和微观结构演化过程。     

连续铸挤成形Al-Mg-Sc合金的再结晶

采用显微硬度计、金相和透射电镜等测试分析手段,研究了连续铸挤成形Al-Mg-Sc合金的冷拔线材的再结晶温度和再结晶的形核机制。结果表明,该合金线材的再结晶起始温度为375℃,再结晶终了温度为520℃;再结晶温度高的原因是细小弥散的Al3Sc粒子对位错和亚晶界的钉扎作用;该合金线材的再结晶形核机制为亚晶合并和亚晶长大的双重作用。     

在工业中采用钛合金的微弧氧化

采用硬度测试，金相显微观察和透射电镜分析等方法，研究了微量稀土Er对高纯铝再结晶行为的影响，结果表明，弥散分布的细小Al3Er质点对位错和亚晶界具有钉扎作用，可以有效抑制再结晶，将高纯铝的再结晶温度提高50左右，同时还能显著细化再结晶晶粒，再结晶形核机制是亚晶聚合和亚昌长大双重机制。     

Al—Mg—Sc合金的再结晶

采用硬度、金相和透射电镜等分析测试手段研究了一种ＡｌＭｇＳｃ合金的再结晶温度和再结晶形核机制。结果表明：合金的再结晶起始温度为３７５℃,终了温度为５２０℃;合金再结晶温度高的原因是细小弥散的Ａｌ３Ｓｃ质点对位错和亚晶界的钉扎作用;合金的再结晶形核机制为亚晶合并和亚晶长大的双重作用。     

微量Sc和Zr对2618铝合金再结晶行为的影响

配制了２６１８ 及２６１８ ＋ Ｓｃ＋ Ｚｒ 两种不同成分的合金, 采用硬度测试初步研究了微量Ｓｃ 和Ｚｒ对２６１８ 合金冷轧板材退火后再结晶行为的影响, 并采用金相显微镜和透射电镜观察了合金不同状态下的显微组织结构。结果表明： 加入Ｓｃ 和Ｚｒ 后生成的Ａｌ３（Ｓｃ ,Ｚｒ） 质点细小弥散, 与基体共格, 可钉扎位错, 稳定亚结构, 阻碍亚晶长大及晶界的迁移, 从而抑制合金的再结晶, 使含Ｓｃ 和Ｚｒ 的合金再结晶温度比参比的２６１８ 合金的再结晶温度提高约２００ ℃; 亚晶聚合机制对合金的再结晶发挥了作用。     

ECAP强变形过程中θ'相的碎化及溶解行为分析

试验研究了铝-铜二元合金中的θ′相在ECAP强变形中的碎化及溶解行为。X射线衍射分析结果表明,ECAP变形至8道次时θ′相的衍射峰消失。透射电镜观察表明,在切应力作用下θ′相发生弯曲变形,内部形成位错墙、亚晶、剪切带及扭转带结构。θ′相首先在亚晶界面、剪切带及扭转带与基体的界面结合处发生溶解,继而断裂碎化及球化,并逐渐发生分解溶入基体。分析表明,θ′相在强变形中主要通过其亚晶界面、扭转带及剪切带界面等缺陷处的溶解效应而发生碎化,而其溶解过程并非由表面能主导引起的。     

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。     

Microstructural evolution in adiabatic shear bands in Ta and Ta–W alloys

Microstructural evolution of adiabatic shear bands originated due to high strain, high strain rate deformation in Ta and Ta–W alloys has been examined. Tests were performed using a specially designed stepped specimen in a Hopkinson bar. Upon completion of the deformation, the region is cooled to below one half of the temperature achieved during adiabatic heating in less than one millisecond. Microstructural characterization of the shear bands was performed using optical microscopy as well as scanning and transmission electron microscopy. No evidence of recrystallization within the shear bands could be found. This is in contradiction with several recent reports, which claim that recrystallization may take place at these stringent time and temperature conditions. These studies, however, do not take into account the kinetics of boundary refinement processes, which are a distinctive characteristic of a recrystallized microstructure. It will be shown that the absence of recrystallization in Ta and Ta–W adiabatic shear bands can be predicted by a progressive subgrain misorientation (PriSM) recrystallization model, applied successfully in previous studies to predict the microstructure evolution in copper adiabatic shear bands.     

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.     

TA15钛合金β热变形中的动态再结晶形核

利用Thermecmaster-Z型热模拟试验机在β相区对TA15钛合金进行了热压缩试验,采用金相显微镜及EBSD取向差分析技术,研究了TA15钛合金β热变形中动态再结晶形核.结果表明,随内、外界条件的不同,TA15钛合金存在两类典型的动态再结晶形核地点,即晶界周围及变形带.相应地,随应变速率增大,存在两种动态再结晶形核机制,在较低应变速率下,晶界弓弯形核是动态再结晶的主要形核机制,晶界、三岔界是主要形核地点;在高应变速率下,动态再结晶不仅可以在晶界、三岔界附近形核,还可以借助变形带形核.此时的动态再结晶形核为晶界弓弯与亚晶旋转机制共同作用.     

多向锻造纯钨形变储存能及动态再结晶行为分析

对纯钨烧结体进行多向锻造试验,运用OM和DSC分析了纯钨多向锻造组织演化规律及形变储存能的变化,结合XRD、EBSD对纯钨形变储存能的来源及动态再结晶行为进行了研究。结果表明:多向锻造后纯钨内部孔隙明显减少,热变形过程中的动态再结晶导致晶粒显著细化,变形后保留在晶粒及亚晶内部的高密度位错结构导致形变储存能的增加,再结晶晶粒主要沿能量较高的晶界及晶界交汇处分布,其动态再结晶机制为形变诱导晶界迁移机制与亚晶粗化及晶粒机械破碎的混合机制,多向锻造后纯钨再结晶温度基本不变,材料热稳定性有所提高。     

TC18钛合金绝热剪切带晶粒细化机制

采用分离式霍普金森压杆,对TC18钛合金试样进行室温高应变率(103s-1)剪切试验,通过光学显微镜、扫描电镜及透射电镜观察绝热剪切带微结构,研究高应变率变形条件下TC18钛合金中所形成绝热剪切带的晶粒细化机制。TEM观察表明:绝热剪切带中晶粒细化是由3种机制共同作用的结果。第1种机制是由于变形晶粒中位错快速增殖、快速运动、塞积,塞积处产生巨大应力集中,导致形成裂纹并最终断裂形成细小晶粒;第2种机制为本研究提出的细小晶粒由拉长晶粒的"内颈缩"方式形成;第3种机制——细小晶粒由动态再结晶形成。     

Ti40阻燃合金粗晶超塑性变形行为及机理

借助OM、TEM研究了高温条件下Ti40阻燃合金的粗晶超塑性变形行为及机理。结果表明:在920℃下,应变速率为5×10-5～1×10-2s-1的Ti40合金表现出良好的超塑性行为,拉伸延伸率均超过250%,应变速率敏感指数m大于0.3。超塑变形后,粗大的等轴组织细化。TEM分析表明,在变形过程中,位错运动形成亚晶界,亚晶界通过吸收滑移位错形成小角度晶界甚至大角度晶界。Ti40合金的粗晶超塑性是由动态回复和再结晶共同作用的结果。     

Ti-5553合金高温变形时动态再结晶行为

采用热压缩试验方法,对Ti-5553钛合金的动态再结晶行为进行研究。结果表明,在温度800～860℃、应变速率0.01～10s-1的范围内,Ti-5553合金在高温、低应变速率变形时,晶界弓出形核是其主要的动态再结晶形核机制;在低温、高应变速率、大变形量变形时,位错塞积形核是主要的动态再结晶形核机制。在非均匀变形的条件下材料产生绝热剪切现象,其形核主要以亚晶吞并长大形核机制进行。     

Mechanism of dynamic continuous recrystallization during superplastic deformation in a microduplex stainless steel

Microstructural evolution during the cyclic cold-rolling and annealing process in an (α + γ) microduplex stainless steel, which consists of α subgrains and fine γ particles, has been studied in detail with the aim of clarifying the mechanism of dynamic continuous recrystallization. A continuous increase in α subgrain boundary misorientation is obtained by the present processing where grain boundary sliding does not occur and the effect of increasing boundary misorientation with cumulative strain is comparable to those observed in dynamic continuous recrystallization of superplastic aluminium alloys. The increase in boundary misorientation is accounted for by the absorption of dislocations into subgrain boundaries during annealing, dislocations which had operated to accommodate the plastic strain incompatibility of the neighboring phases undergoing slip deformation. The present results show that grain boundary sliding is not indispensable but the difference in accommodation deformation between adjacent subgrains is of great importance for the dynamic continuous recrystallization during superplastic deformation.     

同时添加钪、锆对Al-10Mg合金再结晶机制的影响

利用电子背散射衍射(EBSD)和透射电子显微镜(TEM)研究了Al-10Mg及Al-10Mg-0.1Sc-0.1Zr合金在热压缩过程中的组织演变及动态再结晶机制。结果表明：同时添加Sc、Zr能够明显细化Al-10Mg合金的铸态晶粒,热处理后,Sc、Zr能够形成与α-Al基体共格的Al₃(Sc,Zr) 相,这些沉淀相能够提高合金的热变形抗力;在变形过程中,Al₃(Sc,Zr)相能够钉扎位错运动、降低晶界及变形带处的位错密度,使位错在沉淀相周围聚集,因而改变了Al-10Mg合金内部位错增殖与湮灭的过程、进而使Al-10Mg合金动态再结晶方式由不连续动态再结晶(DDRX)转变为连续动态再结晶(CDRX)。     

On abnormal subgrain growth and the origin of recrystallization nuclei

Abnormal subgrain growth has been proposed as the nucleation mechanism for recrystallization. To test this hypothesis, Monte Carlo Potts model simulations of subgrain growth were performed on single-phase, strain-free subgrain structures with experimentally validated microstructure, texture, boundary character, and boundary properties. Results indicate that abnormal growth events emerge spontaneously during evolution in such systems, and abnormal subgrains behave as predicted by mean field theory. An analysis predicts the frequency of abnormal growth events as a function of local neighborhood and the boundary misorientation distribution. A recrystallization model is derived based on the abnormal subgrain growth analysis. Using data for aluminum subgrain structures, the model predicts reasonable recrystallized grain sizes as a function of von Mises strain. The extension of these results to abnormal grain growth is discussed.