Toughening of Fe-based laser-clad alloy coating

An investigation is reported on crack-free laser clad Fe-based alloy by use of biaxial powder feeding shielded with argon gas. The microstructure and phase structure of the coating were studied, and mechanical properties were analyzed through hardness, tension strength and wear resistance of the coating. Microstructure analysis showed that there was retained austenite with spherical particles distributed therein in the interdendritic and nearby grain boundary regions. The mechanical test results showed that net-like distributed retained austenite in the interdendritic region had certain toughening effect through blunting crack-tip. Under wear condition of high sliding speed and high loading, the wear resistance of the coating with net-like retained austenite was much higher than that of the coating with some discontinuous carbide network or carbide blocks. The results showed that toughening of laser clad Fe-based alloy with high hardness over 850 HV could be achieved by modifying interdendritic phases from net-like carbide to net-like austenite with spherical particles.     

铁基超导体的微结构和结构相变研究

铁基超导体表现出丰富的结构和物理性质,在多个典型体系中存在着结构相变和多重有序态之间的关联与竞争.例如,母相化合物LaFeAsO在150K附近发生从四方相（P4/nmm）到正交相（Cmma）的结构相变,同时其电输运性质和磁化率也表现出明显的反常行为.微结构分析发现,在CaFe2As2样品中,存在准周期调制结构,而且在低温区,122体系存在丰富的孪晶畴结构,这种孪晶结构是结构相变的直接结果.另外,在超导材料KxFe2-ySe2（0.7≤x≤0.8,0.2≤y≤0.4）中,Fe空位有序态和结构相分离是理解其结构,也是理解其磁性和输运性质的关键问题,特别是沿[130]晶体带轴方向的5倍超结构与系统的超导电性存在密切关系.     

双掺杂铁基1111型超导体Nd1-xBaxFeAsO1-2xF2x的磁传输性能研究

采用两步固相反应法,在母相FeAs=1111结构的NdFeAsO中掺入BaF2,实现电子与空穴的双掺杂．该体系超导转变温度（Tc）在33-50K范围,取决于名义BaF2掺杂量x．在实验范围内,掺杂量越大,转变温度越高,当x=0．2时,Tc达到50K．磁电阻测量表明：高掺杂量样品（例如x=0．2）具有较高的上临界场（Hc...     

Nb含量对FeSiBCuNb系铁基纳米晶合金结构和磁学性能的影响

为模拟Nb含量对FeSiBCuNb系铁基纳米晶合金结构和磁学性能的影响,采用Amorphous模块构建了Fe_88-xSi₉B₂CuNb_x(x=1,3,5,7)的硬球密剁模型,通过分子动力学方法进行弛豫,淬火以及退火处理,得到了Fe_88-xSi₉B₂CuNb_x(x=1,3,5,7)铁基纳米晶合金结构.基于第一性原理的计算方法,分析了不同Nb含量的铁基纳米晶合金的晶体结构和磁学性能.结果表明:随着Nb含量的增加,体系的晶格常数和体积都有所增大,导电性减小,磁矩不断减小,并且Fe的3d轨道是体系磁矩的主要贡献者,Nb元素对体系非晶化的形成有一定的作用.     

De-vitrification of nanoscale phase-separated amorphous thin films in the immiscible copper–niobium system

Copper and niobium are mutually immiscible in the solid state and exhibit a large positive enthalpy of mixing in the liquid state. Using vapour quenching via magnetron co-sputter deposition, far-from equilibrium amorphous Cu–Nb films have been deposited which exhibit a nanoscale phase separation. Annealing these amorphous films at low temperatures (~200?°C) initiates crystallization via the nucleation and growth of primary nanocrystals of a face-centred cubic Cu-rich phase separated by the amorphous matrix. Interestingly, subsequent annealing at a higher temperature (>300?°C) leads to the polymorphic nucleation and growth of large spherulitic grains of a body-centred cubic Nb-rich phase within the retained amorphous matrix of the partially crystallized film. This sequential two-stage crystallization process has been investigated in detail by combining transmission electron microscopy [TEM] (including high-resolution TEM) and atom probe tomography studies. These results provide new insights into the crystallization behaviour of such unusual far-from equilibrium phase-separated metallic glasses in immiscible systems.     

温度对陶瓷/铁基金属结合剂性能与结构的影响

采用粉末冶金法制备低温陶瓷/铁基金属结合剂.结合材料电子万能试验机、SEM、XRD等检测手段,研究了烧结温度对低温陶瓷/铁基金属结合剂性能与结构的影响.结果表明:当热压烧结温度为740 ℃时,低温陶瓷/铁基金属结合剂具有最佳的力学性能(抗折强度206 MPa,冲击强度6.4 kJ/m2);温度升高促进了低温陶瓷与铁基结合剂界面之间元素的相互渗透,铁基金属结合剂与低温陶瓷达到最佳的机械嵌合,提高结合剂强度.     

协同高效的铁催化剂构建及其在CO_2加氢制高碳烃中的应用

采用物理掺杂法制备了生物质灰分作为助剂的融铁催化剂,通过X射线衍射、透射电镜、穆斯堡尔谱等方法对催化剂进行了表征,并在固定床反应器中对其CO_2加氢制高碳烃的催化性能进行了评价。结果表明,与不含生物质灰分助剂的催化剂相比,添加助剂的融铁催化剂粒径较小且尺寸分布较窄,Fe_3O_4、Fe_5C_2、Fe_3C和α-Fe四相协同共存,进而促使逆水气变换反应与C-C偶联的串联反应高效进行,在有效抑制甲烷生成的同时,可明显提升高碳烃选择性。高碳烃产物以C_(4-18)的烃类为主,在300℃、1. 0 MPa、4800 h~(-1)、H~2/CO_2=3. 0、助剂添加量为5%(质量分数)的条件下,其在烃类产物中选择性最高可达73. 9%。     

铁基超导1111体系CaFeAsF的单晶生长和物性研究

自2008年发现铁基高温超导以来,人们对该体系的材料探索和物理性质开展了广泛而深入的研究.然而,作为最早被发现并且体材料中临界转变温度最高的一大类材料, 1111体系长期以来一直缺乏大尺寸高质量的单晶样品,这严重制约了对这一材料体系相关物理问题的深入研究.最近几年,氟基的1111体系材料CaFeAsF的单晶生长取得了较大进展:以CaAs作为助熔剂,在常压下成功地生长出了毫米尺寸高质量的CaFeAsF母体以及Co掺杂的超导体单晶;在此基础上,多个研究组利用不同实验手段对该体系的物理性质进行了研究,并得到了一些比较重要的结果.本综述对该方向的进展进行初步总结,内容涵盖晶体生长、各向异性、强场下的磁阻、磁力矩、红外光谱、高压调控、量子振荡等内容.     

Effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites

This paper investigates the effect of warm compaction on the magnetic and electrical properties of Fe-based soft magnetic composites at operating frequencies between 0.1 and 10 kHz. The magnetic and electrical properties of samples were measured by an LCR meter and morphology of the samples was characterized by scanning electron microscopy. It was shown that the compacted sample prepared at 800 MPa and 550 °C had the lowest magnetic loss and electrical resistivity, and highest magnetic induction and effective permeability in comparison with other samples compacted at 800 MPa and room temperature, 150, 250, 350 and 450 °C.     

铁基大块非晶合金的摩擦磨损性能研究

采用电弧熔炼、铜模吸铸法制备Fe基大块非晶合金,利用球-盘式摩擦磨损试验机进行干摩擦磨损试验,研究了铸态Fe基大块非晶合金的摩擦磨损行为及热处理对其耐磨性的影响,利用扫描电子显微镜观察合金磨损表面形貌,分析了Fe基大块非晶合金以及相同成分晶态合金的磨损机理.结果表明:在本试验条件下,铸态Fe基大块非晶合金的耐磨性高于相同成分的晶态合金,热处理可以有效提高铸态Fe基大块非晶合金的耐磨性,在保持完全非晶状态的前提下,退火态非晶合金的磨损率较铸态非晶合金减小约40%;材料的结构和性能对合金的摩擦系数影响不大,当进入稳定阶段后Fe基大块非晶合金的摩擦系数稳定在0.58左右;不同处理状态的Fe基大块非晶合金和相同成分晶态合金的磨损机制不同,非晶合金的磨损机制以疲劳磨损为主兼有磨粒磨损,相同成分晶态合金的磨损机制为粘着磨损和磨粒磨损共同作用的结果.