低温取向硅钢初次再结晶织构及晶界特征分析

应用EBSD技术对低温取向硅钢初次再结晶样品表层、次表层及中心层微观组织进行了研究并基于HE与CSL晶界理论对各层的晶界特征分布进行了分析。结果表明:各层初次再结晶织构以γ织构及{114}〈418〉织构为主,Goss晶粒主要分布在表层与次表层,平均晶粒尺寸由表层至中心层逐渐减小。基体与Goss晶粒取向差分布主要集中在能构成高能晶界关系的20°~45°间,并且次表层所占比例最高。基体中CSL晶界类型以∑3为主,在Goss晶粒周围分布着极少量的∑5、∑7、∑9晶界。     

高温渗氮Hi-B钢二次再结晶中组织及织构演变

模拟CSP工艺试制Hi-B钢在二次再结晶过程中不同退火温度下的组织和织构。使用Zeiss Axioplan金相显微镜(OM)观察试样组织,借助于NOVA400Nano SEM型场发射扫描电子显微镜进行微观织构EBSD检测分析。结果表明:Goss晶粒在1 040℃发生异常长大,异常长大之前晶粒细小均匀,有利的{111}〈112〉和{411}〈148〉织构为主要织构,异常长大后部分晶粒发生快速长大,组织则以Goss织构为主。Goss织构及{111}〈112〉和{411}〈148〉织构的取向差分布主要集中在20°~45°之间,高能晶界理论(HE)能够解释Goss晶粒的异常长大。基体的CSL晶界比例较低,且移动性差的∑3晶界比例较高,移动性好的∑5、∑7、∑9晶界比例较低,CSL晶界理论对于Goss晶粒的异常长大则不具有说服力。     

Nimonic 80A合金螺栓的组织织构及高温应力松弛行为

利用SEM与EBSD技术研究Nimonic 80A高温合金螺栓的组织织构特点,并对不同温度下的高温应力松弛行为及组织织构演变进行分析。结果表明,合金中γ相组织未形成显著织构,晶粒取向择尤情况与晶粒尺寸无对应性。合金中第二相主要为γ′相与Cr的碳化物,γ′相在基体中弥散分布,而Cr的碳化物分别在晶界析出和沿螺栓轴向“链状”分布,其分布特征与γ晶粒组织及取向无显著关联性。应力松弛前后,晶粒组织、碳化物分布及织构均无明显变化,但γ′相发生了一定的粗化。载荷一定时,温度对应力松弛行为存在显著影响,即较高温度下样品的应力松弛率较高。较高温度下位错滑移更易开动,与样品中更多晶粒表现出较高晶粒取向散布(GOS)值相对应,但各晶粒GOS值的高低未表现出晶粒取向与晶粒尺寸依赖性。     

Nimonic 80A合金螺栓的组织织构及高温应力松弛行为

利用SEM与EBSD技术研究Nimonic 80A高温合金螺栓的组织织构特点,并对不同温度下的高温应力松弛行为及组织织构演变进行分析。结果表明,合金中γ相组织未形成显著织构,晶粒取向择尤情况与晶粒尺寸无对应性。合金中第二相主要为γ′相与Cr的碳化物,γ′相在基体中弥散分布,而Cr的碳化物分别在晶界析出和沿螺栓轴向“链状”分布,其分布特征与γ晶粒组织及取向无显著关联性。应力松弛前后,晶粒组织、碳化物分布及织构均无明显变化,但γ′相发生了一定的粗化。载荷一定时,温度对应力松弛行为存在显著影响,即较高温度下样品的应力松弛率较高。较高温度下位错滑移更易开动,与样品中更多晶粒表现出较高晶粒取向散布(GOS)值相对应,但各晶粒GOS值的高低未表现出晶粒取向与晶粒尺寸依赖性。     

薄板坯连铸连轧工艺下Hi-B钢的组织及织构

采用金相显微镜和扫描电镜研究实验室模拟薄板坯连铸连轧（TSCR）工艺试制的高磁感取向硅钢（Hi-B钢）组织、织构的演变特征.研究发现实验室模拟薄板坯连铸连轧工艺试制的Hi-B钢热轧板显微组织及织构在厚度方向上存在不均匀性.常化板表面脱碳层铁素体晶粒明显粗化,常化板织构基本继承了热轧板相应的织构类型,仅织构强度不同.一次大压下率冷轧后,晶粒及其晶界沿轧向被拉长形成鲜明的纤维组织,织构主要为α纤维织构和γ纤维织构,脱碳退火后试样发生回复和再结晶现象并形成初次晶粒组织,脱碳退火后织构分布较为集中.温度升高至1000℃时二次再结晶开始,1010℃时钢中晶粒发生异常长大,高斯织构强度达到61.779.成品磁感为1.915 T,铁损为1.067 W·kg-1.      

Fe-6.5%Si合金温轧后退火过程中再结晶行为

用电子背散射技术观察了700℃温轧板在退火过程中的组织及织构演变以了解其再结晶行为.结果表明,温轧织构由强的（111）〈112〉、较弱的〈110〉∥RD及Goss组成,再结晶织构与之相似.〈110〉∥RD及（111）〈112〉新晶粒首先形成于与之构成小角度晶界的形变晶粒的晶界附近,而在角隅及组织不均匀区等位置孕育出与周围晶粒构成大角度晶界的晶核,择优取向不明显.退火过程中（111）〈112〉在形变组织中累积,最终转化为（111）〈112〉再结晶晶粒.分析认为,温轧后退火是不均匀组织在低储存能驱动下的再结晶过程.（112）〈110〉及（111）〈112〉形变拉长晶粒多发生连续再结晶从而退火织构与形变态相似.在角隅区形成核心进而发生不连续再结晶,核心取向的统计性及不连续晶核的长大弱化再结晶织构,其中Goss晶粒多以此方式形成于（111）〈112〉晶粒内部.      

热轧Al- Mg- Si合金厚度方向显微组织及织构梯度演化

通过拉伸试验、扫描电镜(SEM)、透射电镜(TEM)、 X射线衍射(XRD)等研究Al-Mg-Si热轧板材沿厚度方向显微结构及织构的变化,结果表明织构类型沿表层至中心层出现明显的变化,表层主要为剪切织构r-cube{001}110;中心层表现出明显的平面应变织构特征,主要为沿着β取向线的C{112}111, S{123}634和B{011}211织构;过渡层由于粒子诱导形核(PSN)效应,再结晶晶粒倾向于沿着大尺度第二相粒子形核长大,使晶粒择优取向性减弱,造成织构取向密度的强散射和random织构P的生成。Cube织构在平面应变条件下更容易发生,中心层cube织构的形成是由于再结晶晶核与S变形织构存在着40°111的特殊位向关系,择优生长模型认为晶界具有很高的迁移速度,发生择优生长,吞并相邻的S织构。     

9Cr-2W耐热合金高温变形机制研究

对9Cr-2W耐热合金进行了热变形温度900～1300℃和应变速率0.005～5.000 s-1条件下热压缩模拟实验,分析该合金热变形应力应变曲线、热变形组织演变,并测试1150和1300℃下的热变形织构。结果表明,9Cr-2W耐热合金热变形软化方式主要与温度有关,在应变速率0.500 s-1时,900～1050℃出现明显加工硬化,为动态回复型;1100～1200℃动态再结晶新晶粒沿原晶界分布,为不连续动态再结晶型;1250～1300℃沿原晶界出现锯齿形,为几何动态再结晶型。同时,应变速率对热变形软化方式也有一定的影响,随着应变速率的提高,发生不连续动态再结晶温度范围变宽,细化晶粒效果明显。结合9Cr-2W耐热合金变形织构特征,1150℃热变形组织以动态回复为主,织构相对集中,晶粒择优取向强一些;而1300℃热变形组织基本为等轴晶粒,发生了完全动态再结晶,相对应织构漫散,择优取向相对弱一些。     

一种高Nb-IF冷轧薄板钢的组织性能及织构

 采用拉伸试验、金相、ODF织构分析及电子背散射衍射(EBSD)技术研究了一种冷轧高Nb-IF钢和传统Nb+Ti-IF钢在不同退火温度下的组织性能、织构及晶界特征。结果表明：与传统Nb+Ti-IF钢相比,该新型高Nb-IF钢由于添加了质量分数为60×10-6的碳和010%的铌,其再结晶温度和再结晶完成温度均大幅度提高;新型高Nb-IF钢具有晶粒细小、组织均匀性良好的组织和γ取向织构发展充分且强点密度高的织构,能够获得强度高、伸长率高和r值高的优异的综合性能。EBSD分析结果表明,该新型高Nb-IF钢中小角度晶界和低指数重位点阵(ΣCSL)晶界含量较多,这也是试验钢获得优良成形性能的原因之一。     

EBSD技术在不锈钢研究中的应用

电子背散射衍射(EBSD)是一种用来分析多晶材料显微结构和组织的扫描电子显微镜技术,近年来已经被广泛应用于不锈钢材料的分析,对其晶界类型、织构、位向差和相结构等进行观察。结合不锈钢研发和生产过程中遇到的实际问题,介绍了EBSD技术中的一些功能在解决应力分布、相结构关系的表征、相鉴定、晶界类型及其分布、织构分布、真实晶粒度测定等方面的应用。     

Simulation of Semi-Solid Material Mechanical Behavior Using a Combined Discrete/Finite Element Method

As a necessary step toward the quantitative prediction of hot tearing defects, a three-dimensional stress–strain simulation based on a combined finite element (FE)/discrete element method (DEM) has been developed that is capable of predicting the mechanical behavior of semisolid metallic alloys during solidification. The solidification model used for generating the initial solid–liquid structure is based on a Voronoi tessellation of randomly distributed nucleation centers and a solute diffusion model for each element of this tessellation. At a given fraction of solid, the deformation is then simulated with the solid grains being modeled using an elastoviscoplastic constitutive law, whereas the remaining liquid layers at grain boundaries are approximated by flexible connectors, each consisting of a spring element and a damper element acting in parallel. The model predictions have been validated against Al-Cu alloy experimental data from the literature. The results show that a combined FE/DEM approach is able to express the overall mechanical behavior of semisolid alloys at the macroscale based on the morphology of the grain structure. For the first time, the localization of strain in the intergranular regions is taken into account. Thus, this approach constitutes an indispensible step towards the development of a comprehensive model of hot tearing.     

Microstructural changes during wear by plastic deformation of cemented carbide and cermet cutting inserts

The microstructure of one WC-Co and two Ti(C,N)-WC-Co cutting inserts has been studied before and after plastic deformation, caused by high-speed turning. It was found that after deformation, the binder phase had infiltrated some of the grain boundaries and formed lamellae between the hard phase grains. The infiltration of grain boundaries was assumed to occur by a stress-induced dissolution along the grain boundaries of the hard phase grains as a wide front of binder phase, rather than gradually by Co grain boundary diffusion. Some localized dissolution of the hard phase could also be seen as faceting of grains in WC-Co and at triple points in cermets. It was concluded that the plastic deformation occurs by grain boundary infiltration with simultaneous grain boundary sliding. The rate of deformation is controlled by grain boundary infiltration through dissolution of the hard phase grains.     

连续柱状晶BFe10-1-1合金管材无模拉拔过程中组织演变

在拉拔速度O.6-0.9mm·s-1、变形温度750-900℃条件下,对具有连续柱状晶组织的BFe10-1-1合金管材进行了无模拉拔成形,研究了变形后的微观组织,探讨了其组织演变规律及机理.在本文工艺参数范围内,晶界平直的连续柱状晶组织BFe10-1-1合金管材在无模拉拔成形后微观组织演变为锯齿形晶界的连续柱状晶组织.随拉拔速度和变形温度的增加,锯齿的齿深不断加大.位错易在接近晶界的区域塞积并跃出晶界,导致在晶界处出现滑移台阶,形成锯齿形晶界;在滑移变形的同时,粗大的连续柱状晶开始转动,加剧了锯齿化的程度.高的热激活能和变形储存能未能及时释放是BFe10-1-1合金保持连续柱状晶组织的根本原因.      

Phenomenology of Abnormal Grain Growth in Systems with Nonuniform Grain Boundary Mobility

We have investigated the potential for nonuniform grain boundary mobility to act as a persistence mechanism for abnormal grain growth (AGG) using Monte Carlo Potts model simulations. The model system consists of a single initially large candidate grain embedded in a matrix of equiaxed grains, corresponding to the abnormal growth regime before impingement occurs. We assign a mobility advantage to grain boundaries between the candidate grain and a randomly selected subset of the matrix grains. We observe AGG in systems with physically reasonable fractions of fast boundaries; the probability of abnormal growth increases as the density of fast boundaries increases. This abnormal growth occurs by a series of fast, localized growth events that counteract the tendency of abnormally large grains to grow more slowly than the surrounding matrix grains. Resulting abnormal grains are morphologically similar to experimentally observed abnormal grains.     

Influence of Solution Treatment on Microstructure of AEREX350 Alloy

The microstructure of hot rolled AEREX350 alloy under various solution treatments was investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). It was found that with increasing solution temperature,η phase precipitated firstly at grain boundaries in parallel at 800℃ and then within grains at about 980℃. The η phase precipitated at grain boundaries played a role in preventing the migration of grain boundaries,and the η phase precipitated within grains would form Widmannsttten structure with further increasing solution temperature. η phase precipitated at grain boundaries was dissolved at temperature ranging from 1080℃ to 1095℃,resulting in grain growth promptly owing to release of the pinning effect on grain boundaries. γ' phase precipitated during the process of air cooling after hot rolling and dissolved at temperature ranging between 1010℃ and 1020℃.     

Effects of Pore Nucleation,Growth and Solidification Mode on Pore Structure and Distribution of Lotus Type Porous Copper

Effects of pore nucleation, growth and solidification mode of matrix on pore structure and distribution of lotus-type porous Cu fabricated by Gasar process were investigated. The results showed that it was difficult to obtain an ordered pore structure when the matrix contained equiaxed grain. An ordered pore structure, with increased pore length and circularity, could be obtained when the matrix consisted of columnar grains. The pore distribution moved from the grain boundaries to the interior of grain with increasing gas pressure. It was further noticed that the average pore diameter decreased and the pore density increased due to decreased activation energy and increased rate of nucleus formation. Due to slight depressions at grain boundaries of the solid/liquid interface, the pore nucleation was favored at grain boundaries and thus the average pore diameter in grain boundaries was larger than that in grains.     

On the Relation between Carbide Density and Grain Boundary Character in Tempered Martensite Ferritic Steels

In the present study we investigate the microstructure of tempered martensite ferritic steels. It is well known that inside former austenite grains and inside packets of former martensite laths ultrafine micro grains (average size near: 1 μm) govern the strength of this material class. Micro grain boundaries are decorated by carbides (average size after creep near: 0.05 μm). However, in transmission electron micrographs it is commonly found that there are micro grain boundaries with a high carbide density while there are others where no carbides can be detected. In the present study we make an attempt to decide whether the crystallographic character of micro grain boundaries can be related to the number density of carbides at the boundaries. Kikuchi line diffraction patterns were used to determine the misorientation angle between two adjacent micro grains; we select only micro grain boundaries which represent <110> ‐ and <100> ‐ twist boundaries. A quantitative microstructural analysis was performed to determine the density of carbides on boundaries. Our results are discussed on the basis of general tendencies which were reported for grain boundaries in the literature.     

Finite Element Study of Intragrain Plastic Heterogeneity near a Triple Junction

In plastically deforming polycrystals, grains interact with their surroundings resulting in heterogeneous deformation fields both at inter- and intragrain level. When the crystal plasticity finite element method (CPFEM) is employed to predict such heterogeneity, splitting of grains is occasionally observed. In the present study, detailed local strain analysis is performed in such subdivided grain and its neighbors. The role of local interactions at the grain boundaries and of the initial orientation of the grain is investigated. It is shown that a hard grain surrounded by relatively softer grains is prone to subdivide when subjected to opposing shears.     

An analysis of grain boundaries and grain growth in cemented tungsten carbide using orientation imaging microscopy

Tungsten carbide grains are usually prism-shaped triangular platelets in cemented tungsten carbide materials, owing to the highly anisotropic nature of tungsten carbide grains. The misorientation distribution function (MODF) shows a preferred misorientation relationship between WC/WC crystals. The misorientation relationship is characterized as 90 deg misorientation about the [1010] axis. The carbide-carbide boundaries with 90 deg rotation about the [1010] axis are low-energy boundaries and play an important role in grain growth and densification during sintering. In this study, the evolution of carbide-carbide boundaries with 90 deg rotation about the [1010] axis during the sintering process is determined quantitatively using orientation imaging microscopy (OIM). The evolution of boundaries is correlated with grain growth. The rapid grain growth at early stages of sintering is attributed to coalescence of grains along the 90 deg low-energy boundaries. The origin of these boundaries and their role in grain growth during sintering are also discussed.