Na2O的含量对MoSi2/Oxide系发热元件材料力学性能的影响

对比了脱Na处理工艺前后Na2O含量变化对MoSi2/Oxide系发热元件材料力学性能的影响。研究结果表明，虽然Na2O含量的高低对发热体材料常温力学性能影响不大，但是对发热元件材料高温力学性能有重要影响。主要表现在：经1573K热处理100h后脱Na材料仍拥有很高的强度和韦伯分布；而且经过真空脱Na后材料的高温蠕变特性也有了明显改善，在1243和1303K的条件下脱Na材料的蠕变速率分别是未脱Na材料的2／5和1／3以下，另外，Na2O含量对材料延性脆性转变温度（BDTT）也有重要影响，脱Na材料的BDTT较未脱Na材料升高约100K。     

Na2O的含量对MoSi2/Oxide系发热元件材料力学性能的影响

对比了脱Na处理工艺前后Na₂O含量变化对MoSi₂/Oxide系发热元件材料力学性能的影响.研究结果表明,虽然Na₂O含量的高低对发热体材料常温力学性能影响不大,但是对发热元件材料高温力学性能有重要影响.主要表现在:经1573K热处理100h后脱Na材料仍拥有很高的强度和韦伯分布;而且经过真空脱Na后材料的高温蠕变特性也有了明显改善,在1243和1303K的条件下脱Na材料的蠕变速率分别是未脱Na材料的2/5和1/3以下.另外,Na₂O含量对材料延性脆性转变温度(BDTT)也有重要影响,脱Na材料的BDTT较未脱Na材料升高约100K.     

MoSi2发热元件的微观结构对使用性能的影响

通过对ＭｏＳｉ２发热元件的微观结构分析，探影响使用性能的微观因素。研究发现ＭｏＳｉ２结晶相细小，尤以Ａｌ、Ｓｉ等为主的氧化物组成的玻璃相细等、分布均匀，孔洞少是提高使用性能的必要条件。     

SiC对MoSi2烧结行为的影响

通过排水法测定了ＭｏＳｉ２和ＳｉＣ／ＭｏＳｉ２烧结块的密度,讨论了烧结温度的影响。结果表明,ＳｉＣ的加入提高了ＭｏＳｉ２材料的烧结开始温度约２００℃。     

MoSi2及MoSi2基复合材料制备技术的新进展

MoSi2是极具应用前景的新型高温结构材料.综述了利用放电等离子烧结、微波烧结、先驱体转化法、自蔓延高温合成和反应熔渗法制备MoSi2及其复合材料的最新研究进展,并提出合金化和纳米颗粒复合化是今后MoSi2基复合材料的研究发展方向.     

MOSi2材料摩擦磨损特性的研究与发展

金属间化合物二硅化钼（MoSi2）兼具金属和陶瓷材料的双重特性，成为开发和研究的重点。从耐磨性角度出发，重点评述了MoSi2基复合材料以及MoSi2增强陶瓷材料的摩擦磨损特性的研究现状，并展望了MoSi2材料仍为耐磨材料的前景。     

二硅化钼发热元件的热弯研究

研究了烧结温度对MoSi2发热元件性能的影响,使用SEM观察了各种烧结温度试样的微观组织、氧化层厚度及高温弯曲试样的表面形貌,测定了各种温度烧结试样的氧化动力学曲线、电阻率及抗弯强度.结果表明,高温烧结的MoSi2可进行热态弯曲成形,表面没有发现裂纹,试样中的气孔已明显球化,氧化层厚度明显小于低温烧结试样的.高温烧结试样的电阻率较低,抗弯强度较高,烧损温度达到1 750℃.     

MoSi2发热元件冷热端扩散接合工艺的研究

为了研究扩散接合工艺参数对二硅化钼发热元件冷热端的接合强度的影响,对接合端面状态、接合温度、保温时间、接合压力和接合气氛等工艺条件进行了对比分析,并根据接合部位的断裂强度和微观结构的研究结果,建立了在本实验条件下最佳发热元件冷热端扩散接合工艺条件:接合端面粗糙度为1.5 μm,接合温度1570～1600℃,保温时间30～60s,接合载荷15kg,接合气氛为氩气.     

SiC对MoSi2低温氧化行为的影响

利用热重量分析、Ｘ射线衍射和扫描电镜观察分析了ＳｉＣ在ＭｏＳｉ２低温化中的作用。结果表明ＳｉＣ的加入促进了ＭｏＳｉ２的氧化,但未发现“ＰＥＳＴ”现象。     

TiC颗粒增韧MoSi2基复合材料的力学性能

通过湿法混合和热压法制备了不同体积百分比的TiCp-MoSi2复合材料,研究了TiC颗粒对MoSi2基体材料显微结构和力学性能的影响。实验结果表明,在MoSi2基体中加入TiC颗粒,细化了基体的晶粒,改善了其力学性能。与纯MoSi2相比,含40vol% TiC颗粒的复合材料的室温抗弯强度提高了65％,含20vol%TiCp的复合材料的室温断裂韧性提高了53％,而且TiC颗粒的加入大大提高了MoSi2的高温承载能力,随TiC颗粒含量的增加,复合材料的高温抗弯强度大为增加。     

Oxidation of MoSi2 and MoSi2-based materials

Oxidation experiments, at 500°C, of MoSi₂ and MoSi₂-based compounds such as Mo(Al,Si)₂ and MoSi₂+1 wt% C compacts have been carried out. These compacts were prepared byin situ synthesis and a compaction method, starting from the elemental powders. For comparison, commercial MoSi₂ and Mo(Al,Si)₂ infiltrated into SiC preform were also studied under similar conditions. It was found that the synthesized high density MoSi₂ and Mo(Al,Si)₂ infiltrated into SiC preform did not show any oxidation even after 100 h of heating in air. The colour of the polished surfaces of commercial MoSi₂, Mo(Al,Si)₂ and MoSi₂+1 wt% C had changed. The SEM of Mo(Al,Si)₂ showed open blisters with rods of MoO₃ in them whereas MoSi₂+1 wt% C surface had MoO₃ rods but no blisters and the oxidation was superficial with no penetration into the compact. It is suggested that in compounds, the presence of small amounts of impurities is not as detrimental to pesting as presence of defects like open pores or cracks. Hence, high density of the compact is essential for the prevention of complete disintegration of the compact.     

自蔓延高温燃烧合成MoSi2

以Mo粉和Si粉为原料,通过自蔓延高温燃烧合成(SHS)的方法成功地制备了MoSi2材料.研究了反应物原料粒度、反应物料坯相对密度、反应物预热温度、稀释剂加入量以及反应气氛对MoSi2燃烧合成的影响.并通过XRD和SEM对燃烧合成产物的物相组成和形貌进行了分析.     

Effect of the W addition content on valence electron structure and properties of MoSi2-based solid solution alloys

Based on the empirical electron theory (EET) of solids and molecules, the valence electron structures (VES) of MoSi₂-based solid solution alloys have been analyzed using the average atom model. The results showed that with the increase of the W addition content, the hybridization steps of Mo and Si atom of the alloys occurred in C3 and 1, respectively. The hybridization step of W was always C5. The bond energy of the main bond branch, the covalence electron number on the strongest bond and the percentage of the total covalent electron numbers accounting for the total valence electron number of (Mo_1−x, W_x)Si₂ solid solutions increased with the increase of W addition content. These suggested that the addition of W would increase the melting point, hardness and strength and decrease the fracture toughness of (Mo_1−x, W_x)Si₂ solid solutions. Based on those results, MoSi₂-based solid solution alloys were manufactured, and the results of the experiments were in accordance with those of the theory.     

Al对热压MoSi2材料显微结构的影响

本文研究了添加Al对热压MoSi₂材料显微结构的影响,提出了过渡气相烧结的概念．结果表明,Al可消除纯MOSi₂材料中的SiO₂相,生成Al₂O₃颗粒．Al原子的扩散引起MOSi₂晶格膨胀．由于Al蒸汽排除了孤立气孔内影响烧结的残留气体,从而降低了烧结体的气孔率,同时,MOSi₂晶格畸变也促进了烧结．Al粉添加量为3.5Wt％时气孔率最低．     

Chemical-mechanical failure of oxide scales on 9% Cr steels in air with H2O

Abstract

The oxidation behaviour of 9% Cr steels P91 and Nf616 has been investigated at 650°C in dry air and in air with water vapour, where particular attention was given to breakaway failure. Additional emphasis was given to the quantitative characterisation of the kinetics of chromium depletion in the metal subsurface zone resulting from scale growth, CrO₂H₄ evaporation, and scale cracking and healing, with scale cracking being monitored by acoustic emission measurements. While in dry air the steels show protective oxidation behaviour up to 10000 h, breakaway oxidation may occur already after 100 h in humid environments, which was correlated with the stronger Cr-depletion and the development of intrinsic oxide scale growth stresses exceeding a critical value, in the case of water vapour containing air. In the paper the different parameters that are responsible for breakaway oxidation were identified and discussed with regard to the role of water vapour in the environment. As a conclusion it turns out that breakaway is not a consequence of Intrinsic Chemical Failure (InCF) but of a Mechanically Induced Chemical Failure (MICF).     

Deposition and characterisation of MoSi2 films

Deposition of MoSi₂ films on silicon and tantalum substrates applying pulsed laser deposition technique has been performed. Crystalline, hexagonal symmetry, MoSi₂ films were prepared directly from stoichiometric MoSi₂ tetragonal target on room temperature and heated substrates (500 °C). Textured MoSi₂ films having privileged (110) and (115) orientations and average crystallite size of about 105 nm were grown on Si(111) substrates with a good degree of axial texture (rocking curve full width half maximum of 1.5°). MoSi₂ films grown on Ta(211) substrates, instead, turned out to be polycrystalline, with an average crystallite size of about 100 nm and 50 nm on substrates kept at room temperature and at 500 °C, respectively. Vickers hardness for 1.2 μm thick MoSi₂ films on Si(111) substrates resulted to be 15 GPa both at room temperature and 500 °C, while for 0.4 μm thick MoSi₂ films on Ta(211) substrates — 26 GPa at room temperature and 30 GPa at 500 °C.     

Effect of MoSi2 and Nb reinforcements on mechanical properties of Al2O3 matrix composites

The room temperature mechanical properties of Al₂O₃ composites reinforced with 25 vol% of either MoSi₂ or Nb particulates were investigated. It was found that addition of Nb particles resulted in a reduction in the elastic modulus, but caused a significant increase in both flexural strength and fracture toughness. On the other hand, the addition of MoSi₂ particles resulted in only a marginal decrease in elastic modulus and marginal increase in both flexural strength and fracture toughness. The elastic modulus results were explained on the basis of Tsai - Halpin model. For both the composites, the increase in flexural strength was attributed to the grain refinement of the Al₂O₃ matrix as well as the load transfer to the reinforcement particles. The marginal increase in fracture toughness in Al₂O₃ / MoSi₂ composites was attributed to crack deflection, whereas the threefold increase in fracture toughness in Al₂O₃ / Nb composites was attributed to crack blunting and bridging.     

Effect of B2O3 on the microstructure and strength of SiC/MoSi2 composite

The effect of boron oxide (B₂O₃) on the microstructure and strength of 20% (by volume) silicon carbide (SiC) reinforced molybdenum disilicide (MoSi₂) composites was examined. Microstructural analysis using optical and electron microscopes was performed. A standard four-point bending test and Weibull statistics were applied to evaluate the flexural strength of the composites. The addition of boron oxide to composite was found to reduce the processing temperature and the grain sizes, result in formation of glassy boundary phase, and to increase the flexural strength of the composite.