超细晶粒钢HAZ晶粒长大的规律

研究了低碳钢、普通市售Ｘ６５钢和高洁净度Ｘ６５钢三种超细晶粒钢焊接ＨＡＺ的晶粒长大倾向。试验结果表明,这些超细晶粒钢都具有严重的晶粒长大倾向;低碳超细晶粒钢比Ｘ６５超细晶粒钢有更为严重的晶粒长大,这是因为前者不含有能阻碍晶粒长大的稳定碳、氮化物形成元素Ｎｂ和Ｔｉ,而后者中含有这些元素;高洁净度Ｘ６５超细晶粒钢的ＨＡＺ晶粒长大倾向小于普通市售Ｘ６５超细晶粒钢。这是因为钢中杂质元素含量越多,α→γ转变温度越低,即Ａｃ３点越低,在同样的焊接热循环条件下,普通市售Ｘ６５超细晶粒钢中的γ晶粒在高温停留时间就越长,晶粒长大的程度也就越大。     

Calculation of Selective Oxidation in Grain and Grain Boundary

The aim of this paper is to identify selective oxidation of high strength steels under different conditions. FISHER model is introduced to simulate diffusion and precipitation of chemical elements in metallic matrices and grain boundary, a scheme of its analytical solution is given. Effects of grain size, dew point and annealing temperature related to concentration of oxygen during annealing treatment are presented. The results are consistent well with literatures. The calculation shows that the selective oxidation of CMnSi TRIP steel at ferritic annealing in a low dew point N₂-10%H₂ atmosphere of ?30 °C result in the formation of internal MnO in the matrix and SiO₂ particles in the subsurface. The calculations agree well with the experimental results.     

Al-Ti-C晶粒细化剂对工业纯铝的晶粒细化

采用自制的Al-Ti-C晶粒细化剂，检验了Al-Ti-C晶粒细化剂对工业纯铝的晶粒细化能力，研究了Al-Ti-C的含碳量、添加量、保温时间、浇注温度等对工业纯铝晶粒细化效果的影响。结果表明，对于工业纯铝添加质量分数为0.2％的Al-5.14Ti-0.3C晶粒细化剂，在725℃的铸造温度下保温2.5min，所得的铸锭晶粒细化效果最好。     

精密铸造等轴晶涡轮叶片晶粒度控制方法

从精密铸造的型壳温度、浇注温度、细化剂粒度和含量、凝固方法、组合方式、型壳材料和厚度,以及型壳造型等方面,分析了各因素对涡轮叶片等轴晶粒度的影响,并结合实际生产提出了主要的控制方法和工艺参数,为进一步优化工艺、提高产品质量提供了一定的理论指导和参考。     

氮化硅陶瓷的玻璃相及其晶粒异常长大

利用透射电镜(TEM)研究无压烧结Si3N4-MgO-CeO2系陶瓷的显微结构。发现并用微观衍射分析证实了晶界处有玻璃相出现。透射电镜能谱分析得出,当没有MgO时CeO2的主要功能便是形成玻璃相。硅酸铈玻璃相的出现有利于Si3N4液相的产生。MgO-CeO2是Si3N4陶瓷优秀的烧结助剂。当在1850℃以上温度烧结是会出现Si3N4陶瓷晶粒的异常长大,这将导致裂纹和位错并最终影响其机械性能。     

超细晶粒钢焊接HAZ晶粒长大规律分析

根据传统金属学和焊接冶金学理论，对800MPa和400MPa两个强度级别新一代钢铁材料进行焊接热模拟试验，分析了焊接HAZ晶粒长大规律。结果表明，随着峰值温度和‰的逐渐增大，新一代钢铁材料焊接HAZ的奥氏体晶粒都存在严重的长大倾向，且400MPa级比800MPa级的HAZ奥氏体晶粒长大更为严重。     

Grain growth of silicon

In this paper we report on 2-D phase-field simulations in order to study the influence of the growth kinetics and the surface energy on the growth behaviour of grains during solidification of silicon. We investigated in detail the growth of two grains.     

Grain Refinement of Steels

The possible advantages and mechanisms of obtaining grain refinement in carbon, low-, and high-alloy steels are reviewed. The role of vibration and the addition of materials to provide heterogeneous nuclei formation and grain growth inhibition are discussed. The effect of composition on the solidification of steels is described. The pertinent work reported in the literature on the application and results of the various procedures for grain refining cast steels are reviewed.     

普通低碳钢形变诱导铁素体晶内和晶界的析出行为

利用TEM，萃取和X－ray衍射方法分析了利用形变诱导铁素体和铁素体再结晶机制获得超晶铁素体的晶内和晶界析出碳化物的成分和析出行为，证明晶内以M3C形成弥散析出，晶界面以层片状形式析出和碳为短程扩散行为。     

双晶硬质合金WC晶粒分布特征的研究

本文选用4种不同粒度的WC粉,采用典型硬质合金制备方法制备出4批普通合金样品,在4种WC粉中选两种不同粒度的WC粉按照一定的质量配比制备出4批双晶硬质合金样品,用LAMOS Master金相分析软件计算样品金相照片上的WC晶粒截面面积并进行升序排序并得出面积差曲线。结果表明,普通合金样品的面积差曲线无特征峰,双晶粒度样品有特征峰。特征峰的中间位置为粗细WC的分界点,用截线法测出的粗WC与细WC的平均晶粒度与样品所用WC粉对应普通合金样品的WC平均晶粒度一致。将双晶硬质合金样品的显微组织、粗细WC平均晶粒度、粗细WC颗粒数量比及WC粉质量比等数据建立双晶硬质合金的WC组织特征参数。     

不同参数下超级钢焊接热影响区晶粒尺寸

采用数值模拟方法得到超级钢焊接温度场，在热影响区温度场基础上，结合晶粒长大动力学原理计算热影响区晶粒尺寸，并实验加以验证，绘制不同参数下超级钢热影响区晶粒尺寸图．以作为优化其焊接工艺的依据。     

异常晶粒长大法制单晶铜或大晶粒多晶铜

采用了一种方便快捷、无杂质污染的异常晶粒长大方法,以多晶铜为原材料,获取小尺寸单晶铜/大晶粒多晶铜.利用光学显微镜观察了室温压缩之后的多晶Cu块体材料的异常晶粒长大现象,分析了异常长大的晶粒尺寸与冷变形量和退火温度的关系,以及异常晶粒长大现象与晶界形貌的关系.在能够发生异常晶粒长大的范围内,随着冷变形量的减小以及退火温度的降低,异常长大的晶粒尺寸增加.异常晶粒长大现象与小平面晶界晶粒的二维晶核长大机制以及各向异性有关.目前实验得到的最大晶粒尺寸约为5.5mm,可制得边长为2～3mm的小块单晶铜.     

5A90铝锂合金Nd:YAG激光焊缝组织的晶粒形态与晶粒取向

采用Gleeble-1500D热模拟试验机进行热压缩实验,研究了TC4-DT钛合金在温度850～980℃、应变速率为0.001～10 s-1、变形量为50％条件下的热变形行为.根据应力-应变曲线分析了该合金的流变应力变化特点,建立了该合金的Arrhenius型本构方程及加工图.结果表明:流变应力随变形温度降低及应变速率增大而升高;变形温度与应变速率对TC4-DT合金应力影响显著;本实验测得的平均激活能为587.2 kJ/mol;该合金合适的加工条件为ε＜0.6 s-1,温度大于850℃.     

Solidification of Mg-Zn-Zr Alloys: Grain Growth Restriction,Dendrite Coherency and Grain Size

The solidification characterization of Mg-xZn-0.5Zr (x = 0, 1, 3, 4, 5 wt%) alloys has been extensively investigated through thermal analysis, microstructure characterization and thermodynamic calculations. The impact of Zn content on the grain growth restriction, dendrite coherency and thus the final grain size has been investigated and discussed. Increasing Zn content, the grain size of Mg-xZn-0.5Zr alloy was firstly refined and then coarsened with the finest grain size of ~ 50 μm for the Mg-3Zn-0.5Zr (ZK31) alloy. Significant effects of the grain size on the mechanical properties were observed in the investigated alloys. The combination of growth restriction factor theory and dendrite coherency point provides a reasonable explanation of the grain size results. It helps to further understand the mechanisms of grain refinement and grain coarsening related to solute content, providing reference for alloy design and grain size prediction.     

热爆法合成Al-Ti和Al-TiC晶粒细化剂及其晶粒细化效果

采用铝熔体热爆法直接合成了Al-Ti和Al-TiC两种晶粒细化剂,研究了这两种细化剂的相组成及对工业纯铝的晶粒细化效果.结果表明,合成的Al-Ti细化剂只含有第二相TiAl3相,Al-TiC细化剂只含有第二相TiC相,无其它杂相生成.TiC和TiAl3单独作为α-Al的形核相时,二者形核能力均较差,但TiC的形核、抗细化衰退能力优于TiAl3.当TiC和TiAl3共同作为α-Al的形核相时,其表现出较强的形核能力和抗晶粒细化衰退能力.这表明Al-Ti-C晶粒细化剂良好的细化效果离不开TiC和TiAl3的共同作用,适当的TiC和TiAl3组合是晶粒细化剂优良细化能力的保证.