AlH_3的最新研究进展

AlH3是一种性能优异的功能材料,在复合固体推进剂、电池或燃料电池、有机和高分子合成化学、原子层沉积技术等方面均有广泛应用。综述了国外在AlH3的性能、合成方法和应用方面的研究进展。     

原位合成Mo-Si-B三元系多相合金的热力学评估

对Mo-Si-B三元系中各化合物不同温度下的标准生成自由焓和不同开始温度下合成Mo-Si-B三元系多相合金反应的绝热温度以及生成物的熔化比进行了计算和分析评估。结果表明,在元素配比合适的情况下,原位合成热力学稳定的α-Mo+Mo3Si+Mo5SiB2(T2)和Mo3Si+Mo5Si3(T1)+T2多相合金是完全可行的,合成反应的绝热温度以及生成物的熔化比与开始温度有关,原位合成这些多相合金不宜采用燃烧合成的SHS(自蔓延高温合成)模式,适合采用燃烧合成的热爆模式。     

银基电接触材料的研究现状及发展趋势

从电接触材料的电学、力学和加工性能等要求出发,介绍了银基电接触材料的种类、特点、性能及研究进展。分析比较了常用银基合金(Ag-Ni系、Ag-W系和Ag-RE系)和银基氧化物(Ag-ZnO、Ag-CuO和Ag-SnO2)电接触材料的制备方法及优缺点。发展无公害环保型并能广泛适用的新型节银电接触材料,已成为目前银基电接触材料研究、应用的重点。     

高温Mo-12Si-8.5B合金制备工艺和性能

采用粉末冶金技术制备Mo-12Si-8.5B(at%)合金,对制备材料的微观组织形貌进行观察。结果表明:合金的微观组织为Mo-Mo3Si-Mo5SiB2,与Mo-Si-B相图预测一致;Mo-Si-B合金中新相(如Mo3Si,Mo5SiB2等增强相)的出现取决于Mo-Si-B合金中Mo、Si、B组分的相对含量以及制备工艺条件,符合相图的变化规律。断裂韧性和抗氧化性测试表明:制备材料的抗氧化性明显优于文献值;断裂韧性稍好于MoSi2。其机制可能为Mo-12Si-8.5B合金材料是富Mo(体心立方结构)的Mo-Si-B合金,并且Mo能够与Mo3Si、Mo5SiB2形成低共熔的微结构,合金设计的假设是体心立方Mo固溶体的存在将改善多相合金的性能。     

触媒合成金刚石的效果研究

叙述了触媒材料合成金刚石的效果，讨论了触媒材料性能对金刚石的合成及其性能的影响。在对多种触媒材料性能进行测试与分析的基础上，综合了使用触媒材料的经验、看法和金刚石形成的生长机理及对金刚石合成的触媒材料的有效选择方法。     

金属氮氢化合物的贮氢性能及反应机制评述

介绍了金属氮氢化合物贮氢材料吸放氢性能和反应机制的研究进展,阐述了该系列贮氢材料的热力学和动力学性能及其影响因素.分析结果表明:Li-Mg-N-H系贮氢材料具有合适的热力学性能,其动力学问题成为制约该系列贮氢材料应用的瓶颈.根据两种反应机制理论讨论了Li-Mg-N-H系贮氢材料动力学问题中的关键控制步骤,并进一步分析了两种贮氢材料放氢反应机制的合理性和存在的问题.     

Fe-Mn-Al-C系高Mn-Al轻质钢研究进展

Fe-Mn-Al-C系轻质钢以其低密度和高强韧性在车辆、交通运输、航空航天和发电厂等零部件的结构材料应用领域中受到广泛关注。基于当前Fe-Mn-Al-C系轻质钢的研究成果及其表现出的优异性能，综述了Fe-Mn-Al-C系高Mn-Al轻质钢在成分设计、显微组织特征和力学性能以及应用性能等方面的研究进展，重点阐述了轻质钢强韧化机制、力学性能和应用性能特点，并结合目前国内外学者对Fe-Mn-Al-C系高Mn-Al轻质钢的最新研究成果进行了展望。该系轻质钢的强韧化机制与析出相(MC型碳化物、κ-碳化物、B2和DO₃粒子等)的析出机理及其对轻质钢强韧化机制的影响机理和析出相对该系钢的氧化性、腐蚀性和耐磨性等各项应用性能的作用机制是今后该系轻质钢的重要研究方向。开展析出相可控析出研究有助于突破新一代钢铁材料增强增韧技术瓶颈，加快其实际应用。     

不同B含量Mo-Si-B合金的高温抗氧化性能

测试了不同B含量(5%～17%,原子分数)的Mo-Si-B合金在1000～1300℃的抗氧化性能,并对其微观组织及抗氧化机制进行了分析。结果表明,Mo-Si-B合金的氧化行为受B含量和氧化温度共同影响,B元素主要通过改善表面玻璃相流动性和调节合金内a-Mo、Mo_3Si和Mo_5SiB_2三相的体积分数和微观组织来影响氧化膜的形成和生长过程。B含量的增加虽然有助于提升玻璃相在低温下的流动性而促使表面氧化膜快速成形和均匀覆盖,但在高温下氧化膜充足的流动性却不利于合金抗氧化性能的提升。在低温时Mo-Si-B合金的抗氧化性能受控于B含量,而在高温时抗氧化性能取决于a-Mo相含量。对于B含量较高的细晶Mo-12Si-17B合金,由于含有较多的Mo_5SiB_2相和较少的a-Mo相,在1000～1300℃整个氧化温度区间内,表面均能形成一层完整、致密的氧化膜。金属间化合物弥散分布的细晶结构可以确保Mo-Si-B合金表现出优异的抗氧化性能。     

SiO_2-BN-Si_3N_4系复相陶瓷制备及性能

以Y_2O_3和Al_2O_3陶瓷粉体作为烧结助剂,对不同含量BN原料配比无压烧结制备SiO_2-BN-Si_3N_4系复相陶瓷,生坯采用注凝成型制备,然后在1780 ℃保温2 h烧结,烧结体主要由板条状的Si_2N_2O及长柱状的β-Si_3N_4晶粒构成,BN晶粒弥散在各晶粒之间.Si_2N_2O相通过反应SiO_2+Si_3N_4=2Si_2N_2O原位生成.Si_2N_2O具有优异的抗氧化性,Si_3N_4具有高的强度,而BN的加入大大提高了材料的可加工性能,材料结合了各相的优异性能.实验结果表明:材料热冲击性能优异,热冲击温差在800 ℃时,材料的弯曲强度还略有提高,1200 ℃时,材料的残余弯曲强度保持不变.     

层状LiNixCoyMn1-x-yO2正极材料的制备及改性研究进展

综述了近年来有关于层状LiNixCoyMn1-x-yO2正极材料的研究进展,重点介绍了LiNi1/3Co1/3Mn1/3O2的结构及4种主要合成方法--高温固相法、共沉淀法、溶胶-凝胶法和喷雾干燥法,比较了不同合成方法及组成对材料性能的影响.层状LiNixCoyMn1-x-yO2正极材料具有价格低廉,热稳定性好,容量高等优点,但由于其制备比较困难,振实密度低,高倍率放电性能不好,影响了其商业化的进程.因此,探索新的制备方法,对材料进行掺杂和包覆改性,进一步提高正极材料的振实密度和电化学性能仍是今后的研究热点.     

Mo—Si—B合金的制备及性能研究现状

综述了Mo—Si—B合金的研究现状,分别从制备工艺、抗氧化性、断裂韧性、微观结构等方面进行了综述。Mo—Si—B合金可以作为新一代的航空发动机用结构材料和高温抗氧化涂层材料。研究表明,Mo—Si—B合金具有更加优异的高温力学性能和高温抗氧化性能。最后讨论了Mo—Si—B合金未来的发展方向。     

Effects of Zr Additions on the Microstructure and the Mechanical Behavior of PM Mo-Si-B Alloys

In this article, our current understanding on the effects of Zr additions on the properties of three-phase Mo-Si-B alloys is reported. This novel group of materials having high melting points around 2000°C have been identified as potential alloy systems for structural applications at temperatures beyond 1200°C, e.g., for substituting or supplementing state-of-the-art nickel-base superalloys in the power generation industry. In earlier work, we developed various Mo-Si-B materials with very good high-temperature deformation behavior and, in addition, that satisfy oxidation performance. Minimum brittle-to-ductile transition temperatures of around 950°C, however, do not meet the requirements for high-grade stressed structural materials. Therefore, in a second trial, we investigate the influence of the alloying element Zr (which was already proven to increase the strength as well as the ductility of a single-phase Mo-Si alloy) on three-phase Mo-Si-B alloys.     

Mechanical properties of Mo-Si-B alloys fabricated by using core-shell powder with dispersion of yttria nanoparticles

In recent years, refractory materials with excellent high-temperature properties have been in the spotlight as a next generation’s high-temperature materials. Among these, Mo-Si-B alloys composed of two intermetallic compound phases (Mo₅SiB₂ and Mo₃Si) and a ductile α-Mo phase have shown an outstanding thermal properties. However, due to the brittleness of the intermetallic compound phases, Mo-Si-B alloys were restricted to apply for the structural materials. So, to enhance the mechanical properties of Mo-Si-B alloys, many efforts to add rare-earth oxide particles in the Mo-Si-B alloy were performed to induce the improvement of strength and fracture toughness. In this study, to investigate the effect of adding nano-sized Y₂O₃ particles in Mo-Si-B alloy, a core-shell powder consisting of intermetallic compound phases as the core and nano-sized α-Mo and Y₂O₃ particles surrounding the core was fabricated. Then pressureless sintering was carried out at 1400 °C for 3 h, and the mechanical properties of sintered bodies with different amounts of Y₂O₃ particles were evaluated by Vickers hardness and 3-point bending test. Vickers hardness was improved by dispersed Y₂O₃ particles in the Mo-Si-B alloy. Especially, Mo-3Si-1B-1.5Y₂O₃ alloy had the highest value, 589 Hv. The fracture toughness was measured using Mo-3Si-1B-1.5Y₂O₃ alloy and the value indicated as 13.5 MPa·√m.     

Printability of gas atomized Mo-Si-B powders by laser metal deposition

Mo-Si-B alloys, as a more and more frequently considered high-temperature material, face the challenge of machining complex shapes. In the present work, the feasibility of printing pre-alloyed Mo-Si-B powder materials via laser metal deposition (LMD) process was firstly demonstrated. Mo-Si-B powder was manufactured via gas atomization (GA) process out of solid raw materials meeting the requirements for additive manufacturing (AM) regarding flowability and particle size. Investigations of the powder particles after GA and detailed analyses of the printability and microstructural evolution of the multi-phase Mo_ss-Mo₃Si-Mo₅SiB₂ built are presented. As a result, distinct zones resulting from the layer-wise LMD process were observed next to a microstructure of primarily solidified Mo_ss phases embedded in fine dispersed eutectic regions. The hardness of the LMD processed material is shown to be comparable with Mo-Si-B alloys produced by ingot metallurgy (IM).     

Application of phase diagram calculations to development of new ultra-high temperature structural materials

ln-situ refractory metal intermetallic composites（RMICs） based either on （Nb, Si） or （Mo, Si, B） are candidate materials for ultra-high temperature applications （〉1 400℃）. To provide a balance of mechanical and environmental properties, Nb-Si composites are typically alloyed with Ti and Cr, and Mo-Si-B composites are alloyed with Ti. Phase diagrams of Nb-Cr-Ti-Si and Mo-Si-B-Ti, as prerequisite knowledge for advanced materials design and processing development, are critically needed. The phase diagrams in the metal-rich regions of multicomponent Nb-Cr-Ti-Si and Mo-Si-B-Ti were rapidly established using the Calphad （Calculation of phase diagram） approach coupled with key experiments. The calculated isotherms, isopleths, and solidification paths were ：validated by experimental work. The important heterogeneous multiphase equilibria in both quaternary systems identified will offer engineers the opportunity to develop materials with a balance of properties for high-temperature applications.     

Mechanical properties of Mo-Nb-Si-B quaternary alloy fabricated by powder metallurgical method

Mo-Si-B alloys composed of two intermetallic compound phases (Mo₅SiB₂ and Mo₃Si) and a molybdenum solid solution matrix phase have been investigated for use as high-temperature structural materials due to their high melting point and good creep resistance. However, despite these advantages, Mo-Si-B alloys are difficult to use in practical applications because they have insufficient fracture toughness at room temperature. So, in many researches, microstructure control and the addition of other elements in the α-Mo matrix phase are conducted as an effective way to improve the fracture toughness.In this study, niobium (Nb) was added to a Mo-Si-B alloy by a powder metallurgical method to improve the mechanical properties. First, the Mo and Nb powders were pulverized by high-energy ball milling. Then, the synthesized intermetallic compound powders, which were fabricated by continuous heat treatment under a H₂ atmosphere, were mixed with ball-milled Mo and Nb powder. Pressureless sintering was conducted at 1400 °C for 3 h under a H₂ atmosphere. The Vickers hardness and fracture toughness were measured to investigate the mechanical properties of the sintered Mo-Si-B and Mo-Nb-Si-B alloy. The Vickers hardness was about 425 Hv for a Mo-Nb-Si-B alloy, which was lower value of 165 Hv compared to Mo-Si-B alloy (590 Hv). On the other hand, the fracture toughness of the Mo-Nb-Si-B alloy (14.5 MPa·√m) greatly increased compared to that of the Mo-Si-B alloy (12.6 MPa·√m).     

Effect of titanium addition on mechanical properties of Mo-Si-B alloys

In this study, we investigated the effect of titanium addition on microstructure and mechanical properties in Mo-Si-B alloys. The Mo-Ti-Si-B alloy (Mo-3.9Ti-3Si-1B, wt%), which has α-Mo, Mo₃Si, Mo₅SiB₂ and TiO₂ phases_, was fabricated by a powder metallurgy (PM) method. The starting materials were pulverized by using a high-energy ball milling and the resultant powder was subjected to a reduction process followed by cold isostatic pressing (CIP) compaction and pressureless sintering. In the microstructure, intermetallic compound phases were uniformly distributed in the α-Mo matrix. Some titanium atoms solved into the α-Mo matrix and the others formed a TiO₂ phase caused by reaction with oxygen at the grain boundary. Fracture toughness of the Mo-Ti-Si-B sintered body was recorded as 10.42 MPa·m^1/2, which is lower than that of the Mo-Si-B sintered body without addition of titanium. In the Mo-Ti-Si-B sintered body, the fracture mode is similar to the Mo-Si-B sintered body where intergranular fracture through the Mo grain boundary and transgranular fracture cross the intermetallic compound phase. The decrease of fracture toughness is due to the relatively large TiO₂ at the grain boundary, promoting intergranular fracture.     

Fabrication of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> Dispersion-Strengthened Mo-Si-B Alloy by Powder Metallurgical Method

In this study, we investigate the effect of oxide dispersion strengthening on mechanical properties by dispersion of nano-sized Ta₂O₅ particles in Mo-Si-B alloy. A Mo-Si-B core-shell powder consisting of two intermetallic compounds of Mo₅SiB₂ and Mo₃Si as the core and nano-sized Mo solid solution surrounding intermetallic compounds was fabricated by chemical vapor transport. And Mo-Si-B core-shell powder with uniformly dispersed nano-sized Ta₂O₅ particles on the surface of a Mo solid solution shell was produced by a wet blending process with TaCl₅ solution and heat treatment. Then, pressureless sintering was performed at 1400°C for 3 h under a H₂ atmosphere. The hardness and fracture toughness of the Ta₂O₅-dispersed Mo-Si-B alloy were measured using Vickers hardness and 3-point bending tests, respectively. The Vickers hardness and fracture toughness of the fabricated Mo-Si-B-Ta₂O₅ alloy were more improved than that of the Mo-Si-B alloy fabricated using core-shell powder with no addition of Ta₂O₅ particles (Mo-Si-B alloy: 353 Hv, 13.5 MPa·√m, Mo-Si-B-Ta₂O₅ alloy: 509 Hv, 15.1 MPa·√m).     

Volume and size effects of intermetallic compounds on the high-temperature oxidation behavior of Mo-Si-B alloys

In this study, we investigated the high-temperature oxidation behavior of Mo-Si-B alloys with different volume fractions or sizes of intermetallic compound phases. Mo-Si-B alloys with uniformly dispersed intermetallic compound phases (Mo₅SIB₂ and Mo₃Si) in Mo solid solution matrix phase were fabricated using a novel powder metallurgical route, as introduced in our previous study. An isothermal oxidation test was conducted at 1300 °C for up to 10 h. The high-temperature oxidation resistance of Mo-Si-B alloys improved by increasing the volume fraction of intermetallic compound phases; this was a result of the increased amount of protective oxidized layers, which protect the Mo_ss phase from oxidation by covering the surface. In addition, Mo-Si-B alloy with smaller intermetallic compound phases pulverized by high-energy ball milling had better high-temperature oxidation resistance compared to Mo-Si-B alloy with as-synthesized intermetallic compound phases.     

Ab Initio Calculated Thermodynamic Properties of Mo5SiB2 Phase and Nb5SiB2 Phase

Due to their attractive high-temperature properties, multiphase Mo-Si-B alloys in the Mo-rich Mo-Si-B ternary system have been identified for high-temperature applications. The ternary intermetallic T₂ (Mo₅SiB₂) phase is a central feature of the phase equilibria within this ternary system. Experimental stability analyses of the T₂ phase shows its broad homogeneous composition ranges that can yield a constitutional defect structure such as vacancies for Mo-rich compositions and antisite defects for Mo-lean compositions. Previous thermodynamic model did not conform to the defect structures as reported in experiments, and thus subsequently a new sublattice thermodynamic model for the T₂ phase is initiated in this study. To support the new sublattice thermodynamic model, ab initio calculations were implemented to compute formation energy data. The calculated formation energy data explain a source for broad compositional homogeneity range of T₂ structure.