E2EM’s prediction of LaB_(6) as nucleation substrate for primary Mn-rich phase in Al-Si-Cu-Mn heat-resistant alloy and its refining effect

Edge-to-edge matching(E2EM)model was used to predict the potency of LaB_(6) as the heterogeneous nucleation substrate for primary Al_(13)Mn_(4)Si_(8) phase formed during the solidification of Al−Si−Cu−Mn heat-resistant alloy.There are five pairs of orientation relationships(ORs)between LaB_(6) and Al_(13)Mn_(4)Si_(8) phases which meet the criteria of E2EM model.One pair of plane ORs((110)LaB_(6)//(110)Al_(13)Mn_(4)Si_(8))are demonstrated by TEM observation.This strongly indicates that the LaB_(6) phase can act as the heterogeneous nucleation substrate for the primary Al_(13)Mn_(4)Si_(8) phase.1.0 wt.%of Al−2La−1B master alloy was also added into Al−12Si−4Cu−2Mn alloy to evaluate the refining effect by microstructure observation and tensile test.Experimental results show that addition of Al−2La−1B master alloy can significantly refine the primary Al_(13)Mn_(4)Si_(8) phase,supporting the prediction accuracy of E2EM model.However,such refinement of primary Al_(13)Mn_(4)Si_(8) phase does not lead to an improvement in strength.This is due to the larger difference in elastic modulus between the finally formed Al_(13)Mn_(4)Si_(8) phase and aluminum matrix than that of Al_(15)Mn_(3)Si_(2) phase.

Mg-Al合金晶粒细化研究进展

对Mg-Al合金晶粒细化的研究进展进行了综述。在理论研究方面,边-边匹配模型(E2EM)成功用于预测镁合金的异质形核颗粒,相互依存理论清晰的表述了镁合金晶粒的形核与长大过程,合金平均晶粒尺寸由无形核区大小和异质形核颗粒平均间距共同决定;在实验研究方面,高纯Mg-Al合金的天然形核机制来源于Al-C相的异质形核作用,而Mg-Al合金中含有Fe和Mn元素时,Al-C相的异质形核作用被破坏,Al-Fe-Mn三元相取代Al-C相起到异质形核作用。对比了Mg-Al合金不同细化方式的优缺点,指出过热处理和C细化方法是目前Mg-Al合金最有效的细化方法,并对今后Mg-Al合金晶粒细化研究的方向进行了展望。

Crystallographic study of Al_3Zr and Al_3Nb as grain refiners for Al alloys

The potency of Al3Zr and Al3Nb as grain refiners for Al alloys was investigated from a crystallographic point of view using the edge-to-edge matching （E2EM） model. The results show that both Al3Zr and Al3Nb have small values of interatomic spacing misfit and interplanar spacing mismatch with respect to Al. Furthermore, energetically favourable orientation relationships predicted by the model exist between Al and each of these two intermetallic phases. In the light of the edge-to-edge matching model predictions, it is suggested that both Al3Zr and Al3Nb are potent heterogeneous nucleation refiners for Al grains from the crystallographic point of view. The present crystallographic analysis provides a more reasonable explanation for the significant grain refinement obtained in the peritectic Al-Zr and Al-Nb alloys and also provides fresh insight into the understanding of the grain refinement mechanism of Al alloys.

La含量对高钛钢缓冷凝固组织及TiN析出行为的影响

本工作采用高温熔炼实验以及光学显微镜(OM)、扫描电镜(SEM)等方法,研究了四种La含量对高钛钢缓冷凝固组织及其钢中TiN析出行为的影响。结果表明,凝固冷速为0.17℃/s时,各实验钢凝固组织均为等轴晶。在低La含量(0.0013wt%)下,La体现出明显脱O,S,Al能力,因此其钢中主要生成LaAlO_(3),La_(2)O_(2)S;在高La含量(0.0052wt%,0.0223wt%)下,La刚开始体现出明显脱O,S,Al能力,随着O原子的大量消耗,La的脱O,S能力快速增强。因此,其钢中主要生成La_(2)O_(2)S且部分La_(2)O_(2)S会依附于先析出的LaAlO_(3),表面形核、长大。本实验钢中TiN主要析出于Liquid+δ两相区,LaAlO_(3),La_(2)O_(2)S优先于TiN析出且与TiN的错配度小是其易成为TiN异质形核核心的主要原因。当钢中La含量为0wt%,0.0013wt%,0.0052wt%,0.0223wt%时,各实验钢中等轴晶粒平均尺寸分别为354,223,154,126μm,TiN面密度为42.2,82.9,86.3,90.7个/mm^(2),TiN平均尺寸为7.8,4.6,4.5,4.4 μm。

LaS/CeS与γ-Fe异相界面性质的第一性原理计算

为了探讨LaS/CeS与γ-Fe两相之间的异相界面性质,采用边-边匹配(E2EM)模型计算了LaS/CeS与γ-Fe两相之间晶体学上的原子匹配情况,基于晶体学计算结果,采用基于密度泛函理论的第一性原理,从原子尺度计算了LaS/CeS与γ-Fe之间的界面结合性质与界面能。晶体学计算表明,LaS/CeS与γ-Fe之间沿匹配列的原子间距错配度最小值为10.63%/10.52%,密排面间距错配度最小值为2.04%/3.32%;LaS与γ-Fe之间粗略的位向关系为:[110]LaS//[100]γ-Fe&(222)Las//(002)γ-Fe和[100]Las//[101]γ-Fe&(022)LaS//(111)γ-Fe;CeS与γ-Fe之间粗略的位向关系为:[110]LaS//[100]γ-Fe&(222)Las//(002)γ-Fe和[100]Las//[101]γ-Fe&(022)LaS//(111)γ-Fe。基于预测的晶体学位向关系,采用相干界面近似构建了6种不同终端界面模型,第一性原理计算表明,LaS/CeS与γ-Fe之间原子匹配错配度最低界面的粘附功为4.78 J·m^(-2)/3.65 J·m^(-2),界面结合强度较高,界面键合以金属键为主。异相界面能计算表明,LaS/CeS与γ-Fe两相之间的原子匹配错配度越小,界面能越低,原子匹配错配度最小时,界面能分别为-0.58 J·m^(-2)/-3.43 J·m^(-2),计算结果能够为LaS/CeS与γ-Fe之间的晶体学匹配提供能量学依据。