镍基高温合金中的初生碳化物及其强化作用

对K465和K492合金进行室温拉伸、高周疲劳和差热分析实验,使用扫描电镜和透射电镜观察和分析铸态K465和K492合金中初生碳化物的形态、类型及分布。研究铸态K465和K492合金中初生碳化物对合金强度的影响。结果表明,在K465合金中形成MC型初生碳化物,呈骨架状,对合金室温强度有利;在K492合金中也形成MC型初生碳化物,当碳化物呈尺寸较大的块状时,降低合金的高周疲劳强度;为弥散分布的细小颗粒时,提高合金的高周疲劳强度。     

Crystallization and microstructure formation of glass with Y2Si2O7-mullite eutectic composition

The crystallization and microstructure formation of glass with a Y₂Si₂O₇-mullite eutectic composition were examined. A crystallization of Y₂Si₂O₇ and the mullite phase due to phase separation occurred at 1174 °C, and a well-developed Y₂Si₂O₇ facet crystal was formed. This sample was melted down and solidified via heat treatment at 1250 °C and 1300 °C, temperatures below the melting point of a Y₂Si₂O₇-mullite eutectic. As a result of this solidification, a directional eutectic microstructure was formed.     

锅炉压力管道材质分析

针对主蒸汽管道出现的材质问题,对其球化原因进行了分析和探讨,并提出了改进及预防措施.     

Effect of rare earth on microstructure and carbides in WC-Fe composite coating

WC-Fe composite coatings were prepared on IC45/080A47 steel substrates by argon arc cladding technique. Minute amounts of La were added into the coating, and the microstructure was investigated to find the relation to rare earth. Results show that RE does not change the categories of phases, and the main components remain α-Fe, Fe₃W₃C, WC and W₂C. However, the distribution of carbide particles is optimised. It reduces the agglomeration and bridging in the cladding layer's structure, makes the particles distribute homogeneously and restrains the dissolution of WC and the formation of fishbone shaped dendritic carbides. It promotes the formation of granular carbide and refines grains. It also reserves the WC particles in the composite coating and improves the average hardness and wear resistance.     

低铬白口铁碳化物团球化机理探讨

在研究低铬白口铸铁时曾用不同钾盐与钠盐作变质剂,发现它们均能促使这种铸铁中的碳化物团球化。本文对这种铸铁在凝固与热处理阶段的球化机理作了初步探讨。     

Studies on the preparation of C/SiC composite as a catalyst support by CVI in a fluidized bed reactor

In this research, in order to improve the mechanical strength and oxidation resistance of a catalyst support, we studied the formation of SiC layer on the pore surfaces of activated carbons by permeating and depositing SiC from a reaction between hydrogen and dichlorodimethylsilane (DDS). The porous structure should be kept during deposition. A fluidized bed reactor and activated carbons of size of 20-40 mesh were used. By studying characteristics of deposits under various deposition conditions, we confirmed that the best conditions of manufacturing catalyst support are a lower pressure and a lower concentration. In this work, at the conditions of 5 torr of total pressure and 3% of DDS concentration, during the 10 hr processing time, deposition occurred on the pore walls before plugging pores. The results from the mathematical modeling were compared with the experimental results.     

Localized laser assisted eutectic bonding of quartz and silicon by Nd:YAG pulsed-laser

A localized laser assisted eutectic bonding process to bond 80 μm thick single crystal quartz chips to silicon substrates has been successfully developed and characterized. The two bond partners are bonded via intermediate layers of Cr, Au and Sn, with the composition of Au:Sn set close to 80:20 wt.%. Laser light source from the Nd:YAG Q-switched laser processing system with a wavelength of 355 nm, a spot diameter of 25 μm and variable power up to a maximum of 2 W is used as the energy source to initiate bonding at any user-defined region(s). Effects of important laser process parameters, such as laser power, scanning velocity and repetition rate on bond strength, interface quality and heat affected zones are investigated and documented. The resultant bonds are forcefully pulled apart to measure their bond strength. Optimal mean bond strength of 15.14 MPa is recorded for 355 nm wavelength at parameters combinations with highest laser power within the fluence window and low scanning velocity.     

The Dependence of the Melting Temperature of Cobalt–Carbon Eutectic on the Morphology of its Microstructure

Fixed points provide a reliable way to realize and verify temperature scales. High-temperature fixed points are being developed based upon alloys, since single-phase materials are impractical to use above the copper freezing point. In particular, eutectic alloys have been shown to be sufficiently reproducible to warrant consideration as a way to significantly improve high-temperature metrology. However, eutectic alloys have certain characteristics requiring that they are used differently from the current ITS-90 fixed points. As their freezing temperature depends on the freezing rate, the melting temperature is preferred, though it has been shown that for some alloys, notably iron–carbon and cobalt–carbon, the apparent melting temperature can depend on the rate of the preceding freeze. This behavior will need to be explained and quantified if such fixed points are to be acceptable. The effect of varying the freezing rate on subsequent melting has been investigated for cobalt–carbon eutectic fixed points. The apparent melting temperature varies by up to 50 mK. Measurements were made of two different fixed-point blackbodies with very similar results. Optical microscopy of samples produced at different freeze rates shows a change in scale of the microstructure. Electron back-scatter diffraction (EBSD) shows evidence of high levels of residual strain in rapidly frozen samples. The effect of annealing on the melting behavior and microstructure has also been investigated. It is suggested that disordered phase boundaries and residual strain lead to changes in the melting behavior as nonequilibrium conditions may lead to a significant level of pre-melting. Whether this actually changes the liquidus temperature, or whether the melting temperature variation is due to the way the melting point is defined, is also discussed. The variation requires consideration if the highest accuracy is to be achieved, and will be a contributory factor to any uncertainty budget.     

Structural Investigation of Catalytically Grown Carbon Nanotubes

Carbon nanotubes (CNTs) having diameters in the range of 30–50 nm and few micrometers in length were synthesized in one step through a chemical-reduction route under autogenous pressure of H₂/CO₂. The synthesized materials prepared under different experimental conditions were characterized using different techniques. Results showed that V₂O₅ used as a catalyst for the nucleation of CNTs become carburized to vanadium carbide (V₈C₇) and provides a site for growth of CNTs. At high temperature, carbide particles thus formed become encapsulated at the tip of nanotube followed by the growth of CNTs through the tip-growth mechanism. Thermogravimetric analysis results showed that the CNTs obtained after the longer reaction time are more stable at high temperatures. Raman analysis showed a well-ordered graphite structure.