基于蒙特卡罗随机模型,模拟铝钢焊接接头界面金属间化合物Fe2Al5的生长过程。针对Fe2Al5的特殊晶体结构,通过随机选定Fe2Al5的 c 轴方向与形核界面的夹角来确定晶粒生长取向,以实际焊接过程的热循环作为模型的温度参考,采用局部抽象的...基于蒙特卡罗随机模型,模拟铝钢焊接接头界面金属间化合物Fe2Al5的生长过程。针对Fe2Al5的特殊晶体结构,通过随机选定Fe2Al5的 c 轴方向与形核界面的夹角来确定晶粒生长取向,以实际焊接过程的热循环作为模型的温度参考,采用局部抽象的网格之间的结合能的变化作为生长驱动力来建立模型。模拟结果表明,不同形核取向下的晶粒生长存在明显的竞争生长现象,而夹角为90°的晶粒生长竞争优势明显,使界面上生长的Fe2Al5呈现“板条状”分布,导致这一现象的根本影响因素为Fe,Al原子在Fe2Al5晶粒中的扩散机制不同,这与实际的试验结果非常符合。展开更多
The crystallographic and magnetic structures of Er2Fe15Al2 and Er2Fe12Al5 have been refined in Gaussian peak-shape by Rietveld analysis of Neutron diffrac- tion data. The refined results indicated that Er2Fe15Al2 comp...The crystallographic and magnetic structures of Er2Fe15Al2 and Er2Fe12Al5 have been refined in Gaussian peak-shape by Rietveld analysis of Neutron diffrac- tion data. The refined results indicated that Er2Fe15Al2 compound has Th2Ni17-type hexagonal structure （space group: P63/mmc） and Er2Fe12Al5 has Th2Zn17-type rhom- bohedral structure （space group:R 3m）. The Al atoms prefer 12j and 12k sites with occupancies 0.21 and 0.13, respectively, in Er2Fe15Al2 and prefer 18f, 18h and 6c sites with occupancies 0.35, 0.36 and 0.37, respectively, in Er2Fe12Al5. The magnetic mo- ments of all Fe atoms display ferromagnetically arrangement and the moments of Er atoms couple ferrimagnetically to the moments of the Fe atoms. The moments lie in the plane perpendicular to the six-fold axis and exhibit planar magnetic anisotropy in both samples. The values of To were given and the neutron refined results coincide with that of the magnetic measurements. The relation between magnetic properties and structures was discussed.展开更多
As a type of titanate,the pseudobrookite(MTi_(2)O_(5)/M_(2)TiO_(5))exhibits a low thermal expansion coefficient and thermal conductivity,as well as excellent dielectric and solar spectrum absorption properties.However...As a type of titanate,the pseudobrookite(MTi_(2)O_(5)/M_(2)TiO_(5))exhibits a low thermal expansion coefficient and thermal conductivity,as well as excellent dielectric and solar spectrum absorption properties.However,the pseudobrookite is unstable and prone to decomposing below 1200℃,which limits the practical application of the pseudobrookite.In this paper,the high-entropy pseudobrookite ceramic is synthesized for the first time.The pure high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5) with the pseudobrookite structure and the biphasic high-entropy ceramic composed of the highentropy pseudobrookite(Cr,Mn,Fe,Al,Ga)_(2)TiO_(5) and the high-entropy spinel(Cr,Mn,Fe,Al,Ga,Ti)_(3)O_(4) are successfully prepared by the in-situ solid-phase reaction method.The comparison between the theoretical crystal structure of the pseudobrookite and the aberration-corrected scanning transmission electron microscopy(AC-STEM)images of high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5) shows that the metal ions(M and Ti ions)are disorderly distributed at the A site and the B site in high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5),leading to an unprecedentedly high configurational entropy of high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5).The bulk high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5) ceramics exhibit a low thermal expansion coefficient of 6.35×10^(−6) K^(−1) in the temperature range of 25-1400℃ and thermal conductivity of 1.840 W·m^(−1)·K^(−1) at room temperature,as well as the excellent thermal stability at 200,600,and 1400℃.Owing to these outstanding properties,high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5) is expected to be the promising candidate for high-temperature thermal insulation.This work has further extended the family of different crystal structures of high-entropy ceramics reported to date.展开更多
文摘基于蒙特卡罗随机模型,模拟铝钢焊接接头界面金属间化合物Fe2Al5的生长过程。针对Fe2Al5的特殊晶体结构,通过随机选定Fe2Al5的 c 轴方向与形核界面的夹角来确定晶粒生长取向,以实际焊接过程的热循环作为模型的温度参考,采用局部抽象的网格之间的结合能的变化作为生长驱动力来建立模型。模拟结果表明,不同形核取向下的晶粒生长存在明显的竞争生长现象,而夹角为90°的晶粒生长竞争优势明显,使界面上生长的Fe2Al5呈现“板条状”分布,导致这一现象的根本影响因素为Fe,Al原子在Fe2Al5晶粒中的扩散机制不同,这与实际的试验结果非常符合。
基金Nuclear Industry Science Foundation !(H7196B0109) National Nature Science Foun dation of China (19835050)
文摘The crystallographic and magnetic structures of Er2Fe15Al2 and Er2Fe12Al5 have been refined in Gaussian peak-shape by Rietveld analysis of Neutron diffrac- tion data. The refined results indicated that Er2Fe15Al2 compound has Th2Ni17-type hexagonal structure （space group: P63/mmc） and Er2Fe12Al5 has Th2Zn17-type rhom- bohedral structure （space group:R 3m）. The Al atoms prefer 12j and 12k sites with occupancies 0.21 and 0.13, respectively, in Er2Fe15Al2 and prefer 18f, 18h and 6c sites with occupancies 0.35, 0.36 and 0.37, respectively, in Er2Fe12Al5. The magnetic mo- ments of all Fe atoms display ferromagnetically arrangement and the moments of Er atoms couple ferrimagnetically to the moments of the Fe atoms. The moments lie in the plane perpendicular to the six-fold axis and exhibit planar magnetic anisotropy in both samples. The values of To were given and the neutron refined results coincide with that of the magnetic measurements. The relation between magnetic properties and structures was discussed.
基金the National Natural Science Foundation of China(No.52172072).
文摘As a type of titanate,the pseudobrookite(MTi_(2)O_(5)/M_(2)TiO_(5))exhibits a low thermal expansion coefficient and thermal conductivity,as well as excellent dielectric and solar spectrum absorption properties.However,the pseudobrookite is unstable and prone to decomposing below 1200℃,which limits the practical application of the pseudobrookite.In this paper,the high-entropy pseudobrookite ceramic is synthesized for the first time.The pure high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5) with the pseudobrookite structure and the biphasic high-entropy ceramic composed of the highentropy pseudobrookite(Cr,Mn,Fe,Al,Ga)_(2)TiO_(5) and the high-entropy spinel(Cr,Mn,Fe,Al,Ga,Ti)_(3)O_(4) are successfully prepared by the in-situ solid-phase reaction method.The comparison between the theoretical crystal structure of the pseudobrookite and the aberration-corrected scanning transmission electron microscopy(AC-STEM)images of high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5) shows that the metal ions(M and Ti ions)are disorderly distributed at the A site and the B site in high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5),leading to an unprecedentedly high configurational entropy of high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5).The bulk high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5) ceramics exhibit a low thermal expansion coefficient of 6.35×10^(−6) K^(−1) in the temperature range of 25-1400℃ and thermal conductivity of 1.840 W·m^(−1)·K^(−1) at room temperature,as well as the excellent thermal stability at 200,600,and 1400℃.Owing to these outstanding properties,high-entropy(Mg,Co,Ni,Zn)Ti_(2)O_(5) is expected to be the promising candidate for high-temperature thermal insulation.This work has further extended the family of different crystal structures of high-entropy ceramics reported to date.
