基于CSP工艺下稀土元素对低碳钢冷轧板再结晶的影响

在实验室进行了冷轧板再结晶退火实验,结合再结晶实验结果及再结晶形核和长大动力学模型,研究了稀土元素对低碳钢冷轧薄板再结晶及晶粒长大的影响。结果表明,低碳钢冷轧薄板中加入稀土元素提高了再结晶温度,阻碍了再结晶形核及再结晶晶粒长大。低碳钢冷轧薄板中加入稀土元素增加了晶粒长大激活能。稀土元素提高了低碳钢冷轧薄板的再结晶形核激活能约3.87 kJ/mol,提高再结晶晶粒长大激活能约11.7%。     

Cu-0.3Cr-0.15Zr-0.05Mg合金形变时效强化与再结晶

对Cu-0．3Cr-0．15Zr-0．05Mg合金形变时效强化和再结晶过程进行了考察和研究。析出相对位错的钉扎作用强烈阻碍合金再结晶的形核和长大，使合金产生明显的时效硬化。60％冷变形450℃～500℃时效1h～2h，硬度和导电率分别可达162HV和73％IACS左右。大变形量降低了合金再结晶激活能(Qr)，加速再结晶过程，以致于在较高温度下时效，出现了再结晶形核和长大的现象，再结晶产生的软化导致析出硬化程度下降。     

FGH96高温合金的再结晶组织特征

FGH96高温合金的再结晶主要包括孕育期、形核期和晶核长大期。再结晶形核与长大对温度非常敏感:当变形量较小时,在1050℃充分形核,在1080℃再结晶晶核等轴化过程稳定,能够得到均匀细小的等轴晶,而当温度高于1110℃时,再结晶等轴晶粒显著长大;随着变形量的增大,获得细晶粒的温度由1110℃降低到1080℃左右。促进形核、抑制晶粒长大均有利于晶粒细化。另外,再结晶优先在原始颗粒边界发生,当变形不充分时,内部残留未再结晶区,得到不完全再结晶组织,即"项链"组织。同时,这种组织也是粉末冶金材料晶粒细化过程中必然存在的中间态特征组织,随着变形方向的增加、累积变形量的增大,原始颗粒中心区域能够发生再结晶,"项链"组织也逐渐转化成等轴细晶组织。     

热变形低碳钢中奥氏体静态再结晶介观尺度模拟

采用晶体塑性有限元（CPFEM）和元胞自动机（CA）耦合的方法模拟了热变形低碳钢的静态再结晶．CPFEM的计算结果定量描述了介观尺度上奥氏体变形储能的不均匀分布,为模拟再结晶的形核和长大提供了依据,从而在再结晶CA模型中考虑了不均匀变形的影响．模拟结果显示：变形储能分布不均匀使得再结晶在不同位置的形核密度不同,形核集中在晶界以及晶内储存能较大的区域;随着临界形核储能的降低,形核数量增加,再结晶晶核的位置分布趋于均匀．对不同形核判据下的再结晶动力学也作了讨论．     

高牌号无取向硅钢常化过程织构演变行为

采用EBSD技术研究了某钢厂厚板坯流程试制的50W270高牌号无取向硅钢980℃常化过程中显微组织及织构的演变。结果表明:常化过程是热轧板再结晶及晶粒长大的过程,常化使组织均匀化,但厚度方向上始终存在织构梯度。常化过程中再结晶初期形核主要发生在s=0.5层中的{116}110变形晶粒上,新晶粒主要织构为{116}110~{001}110,再结晶后期形核主要发生在旋转立方织构变形晶粒上,与热轧板织构的区别是s=0.5层出现较强的高斯织构。再结晶形核阶段符合亚晶聚合机理,织构的演变可以解释为再结晶阶段的特殊取向的择优形核和晶粒长大阶段的特殊取向晶粒择优长大。     

相场方法研究变形镁合金的晶粒分布

结合多态相场(MSPF)模型与晶体畸变模型,获得变形镁合金初始变形晶粒组织以及合金内部的非均匀储存能分布,计算模拟不同退火温度条件下的再结晶形核和晶粒长大的微观演化过程,分析退火温度对再结晶晶粒长大和晶粒尺寸的影响,对比不同时刻的再结晶晶粒分布特征。结果表明:在相同的变形条件下,位错密度高的区域,如晶界附近,储存能较高,再结晶形核最先在高储存能区域出现,并通过合并与吞噬机制长大;而在变形晶粒内部,储存能较低且分布相对均匀,再结晶过程中形核长大较慢。不同退火温度下晶粒尺寸权重概率的分布表明:低温下会出现双峰结构和异常晶粒长大现象;高温下晶粒长大较快,晶粒尺寸分布向大尺寸方向变化且趋于均匀。     

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。     

Al-Zn对称成分合金不连续析出组织的再结晶

采用光学显微镜、扫描电镜和透射电镜研究了Al 4 0 %Zn(摩尔分数 )二元合金的不连续析出细片层组织在冷轧后重新加热时所发生的再结晶。根据加热过程中的显微组织变化 ,确定了该合金再结晶的形核及长大机制。结果发现 ,再结晶的 2种机制为非典型形核长大机制的连续粗化和典型形核长大机制的不连续粗化 ,后者又分为在团域界面、滑移带等处发生的以变形储能为主要驱动力的粗化和在变形量很小区域发生的以界面能为主要驱动力的粗化。     

冷加工态Ti6Al4V合金的回复和再结晶行为研究

对冷拉拔变形量为60%的钛合金进行700～880℃,1～240min再结晶退火,利用金相显微镜、X射线衍射仪和透射电镜等手段分析不同状态下的组织演变、织构组成和位错组态。结果表明:冷变形后的Ti6Al4V合金经完全再结晶后α晶粒呈等轴状,β相在α相周围以条状沿α晶界析出或以小晶粒形式存在。计算表明,经60%冷变形量的钛合金再结晶激活能为107kJ/mol,较相同变形量的纯钛再结晶激活能高约50%。钛合金的再结晶分为回复、形核和晶核长大阶段,包括位错胞向亚晶转变、回复亚晶通过合并或长大形核、形核诱导高角度晶界形成而长大成新晶粒。经过冷拉拔后的丝材,存在着较强的100织构,而在再结晶过程中,沿100方向上产生的回复亚晶优先形核并长大形成新的晶粒。这导致在初始再结晶阶段,再结晶织构与冷变形织构取向一致,而在晶粒长大阶段,原先取向不利的晶粒吞并周围小晶粒长大,形成新的织构组元使原来的织构被弱化。     

冷轧TA5钛合金退火过程的再结晶行为及织构演变

采用电子背散射衍射技术(EBSD)对冷轧及退火态TA5钛合金板材的晶粒尺寸、再结晶及织构进行了表征,并讨论了变形不均匀对再结晶行为及织构演变的影响。结果表明:<0002>//TD取向晶粒比<0002>//ND取向晶粒更容易发生变形,结合hcp结构滑移系统的有限性,共同决定了TA5合金板材冷轧变形具有不均匀性的特点。退火早期再结晶在局部应变大的区域快速形核,且变形量越大,形核数量也越多,再结晶后样品的晶粒尺寸也越小。局部应变大的区域在退火早期以“定向形核”机制快速发生再结晶形核并长大,包括少量剩余的严重变形<0002>//TD取向晶粒;同时,其余应变较低的组织在再结晶形核全过程以“应变诱发晶界迁动形核”机制缓慢形核,这两种机制共同作用导致退火后板材的织构弱化,但仍以冷轧态的基面织构为主。硬度变化曲线可以很好的反映再结晶程度;但受织构影响,不同测试面的硬度值存在显著差异,加载轴与晶体c轴之间的夹角越大,硬度值越小。     

A comparison of the mesomechanism of dynamic deformation between copper and aluminum

In this paper, a comparison of the mesomechanism of dynamic deformation between Cu alloy and Al alloy is made. It is shown that, during dynamic deformation, two effects occur, one being a hardening effect by the increasing of dislocations, the other being a softening effect by the nucleation, growth and coalescence of microvoids. Fracture is due to the coalescence of a large amount of voids. It is shown also that the nucleation of microvoids is due to fault energy and second-phase particles. The nucleations of Al alloy rely on the second-phase particles and the nucleations of Cu alloy rely on the second slipping of dislocation by lower fault energy.     

bcc-Fe等温压缩下相变的微观模拟与分析

使用嵌入原子势分子动力学方法,对bcc-Fe在等温压缩(沿[001]晶向)下的相变(bcc至hcp)的微观过程进行了数值模拟.结果表明,当应力超过相变阈值,hcp相开始形核并沿(011)面长大成片状体系,同时系统进入超应力松弛状态;平均应力及hcp相质量分数在初始形核时发生突变,之后与体系的体积变化近似呈线性关系;纵向偏应力与相变质量分数在整个相变过程保持线性关系;混合相中,hcp相的平均势能高于bcc相.     

20MnMoNi55钢的后动态再结晶模型

后动态再结晶是亚动态再结晶与动态再结晶晶粒长大两种机制的综合 ,本文采用热模拟与定量金相分析法研究了 2 0 Mn Mo Ni5 5钢的后动态再结晶 ,发现 :动态再结晶百分比对亚动态再结晶过程没有明显的影响。采用多元非线性回归法得到了后动态再结晶模型 ,并用高温锻造实验验证了该模型     

Phase-field simulation of formation of cellular dendrites and fine cellular structures at high growth velocities during directional solidification of Ti56Al44 alloy

A phase-field model whose free energy of the solidification system derived from the Calphad thermodynamic modeling of phase diagram was used to simulate formation of cellular dendrites and fine cellular structures of Ti56Al44 alloy during directional solidification at high growth velocities. The liquid-solid phase transition of L→β was chosen. The dynamics of breakdown of initially planar interfaces into cellular dendrites and fine cellular structures were shown firstly at two growth velocities. Then the unidirectional free growths of two initial nucleations evolving to fine cellular dendrites were investigated. The tip splitting phenomenon is observed and the negative temperature gradient in the liquid represents its supercooling directional solidification. The simulation results show the realistic evolution of interfaces and microstructures and they agree with experimental one.     

TA15钛合金动态再结晶晶粒生长模型

从理论上分析TA15钛合金动态再结晶晶粒生长驱动力,提出动态再结晶晶粒生长等效反驱动力的概念。基于动态再结晶晶粒生长驱动力,建立（描述动态再结晶晶粒尺寸演变）的晶粒生长速率模型及晶粒尺寸模型。以TA15钛合金动态再结晶晶粒尺寸实验测定数据为例,采用遗传算法(GA)优化尺寸模型参数。结果表明,模型计算结果与实验数据能够达到较好的吻合,平均误差为7.4%。     

A508c1.3钢动态再结晶晶粒长大模型的研究

本文采用热模拟与定量金相分析法研究了核电 A5 0 8c1.3钢的动态再结晶晶粒长大过程 ,结果表明 ,在变形后的高温停顿初始阶段 ,温度越高 ,动态再结晶晶粒长大速度越快。采用多元非线性回归分析得到了动态再结晶晶粒的长大模型 ,并通过高温锻造实验进行了验证     

Development of the cube texture at low annealing temperatures in highly rolled pure nickel

The development of texture and microstructure during recrystallization of pure nickel rolled to very high strains has been investigated. Low-temperature annealing was chosen in order to separate the effects of recrystallization and grain growth. Particular attention was focused on the nucleation and growth of the cube orientation texture component, and on the effect of twinning in producing texture components of other orientations. The growth rates for recrystallizing grains of cube and non-cube orientations were analyzed from the EBSP data using an extended Cahn–Hagel method. Within the estimated experimental errors the growth rates of both orientation classes remain constant during recrystallization, with the cube orientation grains having a higher growth rate by a factor of ∼3. Some minor recrystallization texture components result from twinning, with the role of twinning being most important in the early stages of recrystallization.     

Recrystallization kinetics of individual bulk grains in 90% cold-rolled aluminium

The recrystallization kinetics of a 90% cold-rolled commercial aluminium alloy AA1050 annealed at 270 °C has been investigated by use of 3-dimensional X-ray diffraction (3DXRD) microscopy. For the first time growth curves of a large number of individual bulk grains have been measured in situ during recrystallization providing unique information on the nucleation and growth behaviour of the individual grains. From observations of 244 individual growth curves, it is found that each grain has its own growth kinetics. The orientation dependencies of the recrystallization kinetics are investigated by grouping the measured growth curves into cube, rolling and other orientation classes. Based on analysis of the growth curves, distributions of nucleation time, grain size and growth rate has been derived, and are used for a discussion of the recrystallization kinetics of aluminium AA1050.     

Effect of Sn Micro-alloying on Recrystallization Nucleation and Growth Processes of Ferritic Stainless Steels

We investigated the effect of Sn micro-alloying on recrystallization nucleation and growth processes of ferritic stainless steels. The as-received hot rolled sheets were cold rolled up to 80% reduction and then annealed at 740–880 °C for 5 min. The cold rolling and recrystallization microstructures and micro-textures of Sn-containing and Sn-free ferritic stainless steels were all determined by electron backscatter diffraction. Our Results show that Sn micro-alloying has important effects on recrystallization nucleation and growth processes of ferritic stainless steels. Sn micro-alloying conduces to grain fragmentation in the deformation band, more fragmented grains are existed in Sn-containing cold rolled sheets, which provides more sites for recrystallization nucleation. Sn micro-alloying also promotes recrystallization process and inhibits the growth of recrystallized grains. The recrystallization nucleation and growth mechanism of Sn-containing and Sn-free ferritic stainless steels are both characterized by orientation nucleation and selective growth, but Sn micro-alloying promotes the formation of γ-oriented grains. Furthermore, Sn micro-alloying contributes to the formation of Σ13b CSL boundaries and homogeneous γ-fiber texture. Combining the results of microstructure and micro-texture, the formability of Sn-containing ferritic stainless steels will be improved to some extent.     

Recrystallization and grain growth in Ni3Al with and without boron

The recrystallization and grain growth of boron-free and boron-doped (500 ppm by weight) Ni₃Al polycrystals were investigated in the temperature range 700–1000°C. The levels of deformation were 17% reduction in length in compression for both alloys and 40% rolling reduction applied only to the boron-doped alloy. For alloys with or without boron, the Kolmogorov-Johnson-Mehl-Avrami relationship holds, with the Avrami exponent near unity, and the recrystallization rate is very slow. The activation energies for recrystallization are respectively 480 and 492 kJ/mol for boron-free and boron-doped to 40%. The grain growth kinetics obey a power law with the time exponent ranging from 0·2 to 0·4. The boron effect at 500 ppm was found to be small on both recrystallization and grain growth in Ni₃Al.