Effects of pressure and vibration on the thermal decomposition of cubic Ti1-x Al x N, Ti1-x Zr x N, and Zr1-x Al x N coatings: a first-principles study

Thermodynamic properties as well as the miscibility gap (binodal) and spinodal decompositions of the cubic Ti_1-x Al _x N, Ti_1-x Zr _x N, and Zr_1-x Al _x N coating alloys have been computed using first-principles calculations. Herein, the cluster expansion method and especially the special quasirandom structure are employed to describe the disordered alloys. The effects of pressure and lattice vibration on the miscibility gaps and spinodal decompositions of the above alloys have been investigated by means of Helmholtz free energy with the vibrational contribution depicted with the Debye-Grüneisen model. It is found that the application of hydrostatic pressure promotes the isostructural decomposition of Ti_1-x Al _x N, Ti_1-x Zr _x N, and Zr_1-x Al _x N alloys, whereas the vibrational contribution decreases the consolute temperature of the phase separation. Our results indicate that the improved age-hardening behavior of cubic Ti_1-x Al _x N coatings with the addition of Zr arises from the enlarged composition range of binodal and spinodal curves at specified temperatures. Our results are in good agreement with the available experimental data and provide a useful insight into the investigation of age-hardening and characterization of Ti–Al–Zr–N-based coatings for high-temperature applications.     

Effect of sodium silicate pretreatment on phosphate layer: Morphology and corrosion resistance behavior

Phosphating is a widely adopted treatment in industry for many purposes. In this paper, carbon steel was pretreated with sodium silicate before phosphating. X‐ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements were used to evaluate the pretreatment effect by sodium silicate on the phosphating layer. The results demonstrate that the phosphate layer pretreated by sodium silicate has a better corrosion resistance as compared with the un‐pretreated ones. More compact and uniform coatings composed of finer crystals were obtained with the pretreatment of sodium silicate.     

Effect of porosity on the crack pattern and residual strength of ceramics after quenching

The effect of porosity on the crack characteristics of ceramics after water-quenching is studied by measuring the cracks in ceramic sheets. The result reveals that the pore volume fraction has a slight effect on the enhancement of thermal shock resistance of ceramics when the porosity ranges from 0 to 20 %, because the length and density of the long crack in porous alumina are always slightly less than that in dense alumina. This result is in agreement with the prediction based on the minimum potential energy principle using experimentally measured data. Moreover, the proportion of the strength reduction in the third regime decreases significantly with increasing porosity, because the strength of unquenched specimens decreases more rapidly than that of quenched specimens with increasing porosity. The results of this study may help to further understand the thermal shock behavior of ceramics.     

可维修备用系统的可靠度分析

对于只能通过定期检查发现故障的可维修备用系统,由于可维修时间的不连续性,无法使用一般方法进行可靠性预计的情况,给出了一种可靠性预计方法,并通过实例说明了此方法的合理性。     

Mathematical model and algorithm of toolpath optimisation on aircraft structural parts

An intelligent toolpath (processing sequence) planning for fabricating aircraft structural parts is developed to obtain a minimum-length toolpath while maintaining the required machining time. The problem is first solved in the following ways. Firstly, an abstraction of the machining process is proposed to pick up the feed/retract points of each feature to be machined as the toolpath calculation basis. Secondly, the chaotic simulated annealing method is improved through storing the optimal solution, adding the control condition and selecting each parameter reasonably during the iteration of the algorithm so as to enhance its performance. What’s more, three solution-generating methods are used chaotically to obtain a better result. Lastly, the verification is conducted on four different aircraft structural parts, and the results prove that the proposed algorithm performs very well in terms of toolpath quality and computation time.     

Ionomer content effects on the electrocatalyst layer with in-situ grown Pt nanowires in PEMFCs

The effects of ionomer contents were investigated in composite electrodes with in-situ grown single crystal Pt nanowires (Pt-NWs) for PEMFCs, including the amount in the carbon matrix and impregnated on the surface of the electrocatalyst layer. The electrocatalyst layer was prepared by growing Pt-NWs directly on the carbon matrix with a simple one-step wet chemical approach at room temperature. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), polarization curve tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were employed to evaluate the ionomer effects. The experimental results showed that the ionomer in the carbon matrix had an influence on the ionic conductivity and aggregation and distribution of the Pt-NWs, and the ionomer impregnated on the surface of the electrocatalyst layer affected the mass transport and ionic conductivity. The performance of the MEA was improved by optimizing the ionomer contents.     

Directional hydraulic fracturing to control hard-roof rockburst in coal mines

Hard roof is the main factor that induces rock-burst.In view of the present obvious weakness of control measures for hard roof rockburst in domestic collieries,the mechanism and field application of di...     

G3i光缆在地震勘探中的使用及维护

G3i仪器的光缆是地震数据传输主干网络的关键设备,光缆的状况及在野外使用中的维护将直接影响到勘探生产的效率。本文依据G3i仪器光缆在勘探施工中发现的问题,就G3i光缆的使用及维护给出了一些建议。     

Impact of prefabrication technology on the cradle-to-site CO2 emissions of residential buildings

Clean Technologies and Environmental Policy - In recent years, the industrialization of construction has been promoted to achieve sustainable development within the construction industry;...     

可重组制造环境下系统重构的方法研究

为了满足可重组制造环境下动态多变的市场需求,通过分析零件的相似度,以及系统重构的重构度,提出了系统重构与重构方案评价的方法。根据零件的加工特征对新零件进行相似性评估,量化零件的相似度。基于零件加工的可行性,在系统重组平台上面向系统层和设备层调整系统配置,获得系统重构方案,并给出了基于系统重构度的重构方案评价指标计算方法。实例验证结果表明了该方法的有效性和优越性。