Valence electron structure of cementite phase and its interface and the tempering phenomenon

Tempering is an important phenomenon in ferrous alloys. Most steels, especially alloying steels, are used after quenching and tempering. To design the composition of quenching and tempering steels, control the tempering process more effectively, improve the properties after tempering and realize the potentials of steels, the essence of tempering process and the properties of tempering products have to be understood. In this paper, the phase structure factors and interface conjunction factors of common alloying elements in cementite and its interface are calculated out. The relationships between these valence electron structure parameters and (i) the phenomena of martensite decomposition, (ii) transformation, gathering and growth of the carbides and (iii) the mechanical properties of tempering products are built up. The nature of the effect of alloying elements on tempering process and properties of tempering products is uncovered on the level of valence electron structure. One new theoretical foundation     

Modeling the Trans-Varestraint test with finite element method

The Trans-Varestraint test is modeled as three dimensional contact problem with finite element method (FEM). The local strains at the trailing of weld molten pool of samples with the Trans-Varestraint test are calculated under different bending strains. The calculated local strains are in good agreement with the experimental measurements. Meanwhile, the simulated results show that the maximum local strain on the top surface of the plate exceeds 5% in the brittle temperature range, obviously higher than the applied 1.5% average strain of the Trans-Varestraint test which is usually used as threshold of material resistance to the solidification cracks. As a result, it is suggested that the simulated local strains replace the average strains to represent the material resistance. At the same time, the comparison between the calculated driving force and the simulated material resistance predict the weld metal solidification cracking. It is therefore practicable that the local strains of the Trans-Varestraint test obtained with FEM replace the average strains to predict weld metal solidification cracking.     

Effects of WO3 addition on the structure and electrical properties of Pb3O4 modified PZT–PFW–PMN piezoelectric ceramics

The ceramics were prepared successfully by Pb₃O₄ and WO₃ additions to 0.90Pb(Zr,Ti)O₃–0.03Pb(Fe_2/3W_1/3)O₃–0.07Pb(Mn_1/3Nb_2/3)O₃ (0.90PZT–0.03PFW–0.07PMN). Effects of the additions on the structure, bulk density and electrical properties of ceramics were investigated. The results revealed that the proper additions of WO₃ with 2.0 wt.% Pb₃O₄ excess could form liquid phase that promoted the densification of the ceramics. The fracture mode changed from transgranular to intergranular as increasing WO₃ with 2.0 wt.% Pb₃O₄ excess. The piezoelectric and dielectric properties were also promoted by excess of Pb₃O₄ and WO₃ additions. The optimized electrical properties were obtained at excess of 2.0 wt.% Pb₃O₄ and 0.15 wt.% WO₃. The parameters were as follows: d₃₃ = 351 pC/N, K_p = 0.64, Q_m = 1882, ɛ_r = 1798, tan δ = 0.0052, P_r = 19.94 μC/cm² and E_c = 11.98 kV/cm, which shows high K_p, Q_m, d₃₃ and low tan δ can be obtained simultaneously by adding WO₃ addition to Pb₃O₄ modified PZT–PFW–PMN system.     

Carbon-supported platinum catalysts for on-site hydrogen generation from NaBH4 solution

A flexible hydrogen generation (HG) method based on catalytic hydrolysis of NaBH₄ solution is developed. Carbon-supported platinum (Pt/C) samples served as the catalysts, and the catalytic strategies for hydrolysis of NaBH₄ solution are analyzed via the studies on apparent morphology, catalytic activity, BET surface, and sustaining H₂ supply test. Pt/C catalysts are proved to be excellent accelerators, and Pt-loading plays an important role in the hydrogen generation reactions. For a reactor loaded with 100 mg 13.1% Pt/C catalyst, when 10% NaBH₄–5% NaOH solution is pumped into the reactor with a speed of 10 ml/min, it can achieve a maximum HG rate of 29.6 (l/min/g catalyst), and give sustaining H₂ supply for a proton exchange membrane fuel cell (PEMFC) with an average HG rate of 23.0 (l/min/g catalyst).     

P-type tin–indium oxide films prepared by thermal oxidation of metallic InSn alloy films

P-type transparent conducting tin–indium oxide (TIO) films were successfully fabricated on quartz substrates by thermal oxidation of InSn alloy (In / Sn = 0.2) films that were deposited by magnetron sputtering at room temperature (R.T.). Structural and electrical properties of TIO films were investigated. X-ray diffraction studies showed that all TIO films were polycrystalline with an orthorhombic structure. The surface morphology of TIO films viewed by field emission scanning electron microscope (SEM) revealed that the films are composed of uniformly distributed submicron grains. Hall effect measurement results indicated that hole concentration as high as 9.61 × 10¹⁸ cm^− 3 was achieved. It's found that 600 °C was the optimum thermal oxidation temperature to get p-type TIO films with highest hole concentration.     

Integral transform solution for natural convection in three-dimensional porous cavities: Aspect ratio effects

Three-dimensional natural convection in box-like cavities filled with a porous material is revisited, by considering a transient formulation for the energy balance and a quasi-steady formulation for the flow problem. The Generalized Integral Transform Technique (GITT) is employed in the hybrid numerical-analytical solution of the Darcy law based model for vertical cavities (insulated vertical walls with differentially prescribed horizontal wall temperatures), employing the vorticity-vector potential formulation. Comparisons with previously reported numerical solutions are performed and the transition between conductive and convective states is illustrated, centering on the aspect ratio influence on the flow and heat transfer phenomena. A set of reference results for the steady-state behavior under different aspect ratio is provided for covalidation purposes.     

A numerical study of flow and thermal fields in tilted Rayleigh–Bénard convection

Convection in enclosures heated from below can affect crystals grown from melts. Experiments designed to study such convection can be influenced by small tilts of the experimental system with respect to gravity. Because of the additional body force, tilting can mask flow transition points, making comparisons with stability studies difficult. In this study, the classic Rayleigh–Bénard problem is re-examined numerically with the addition of various tilt angles in cubical enclosures of liquid tin (Pr = 0.008). The results presented are applied to experiments which measure both molecular diffusivities as well as convection in the melt.     

基于DM642的视频处理系统设计

本文介绍了一种基于TMS320DM642和Philips视频编解码芯片的视频处理系统,给出了系统的硬件设计、视频接口连接图、以及软件配置。通过实际应用证明该方案具有高速视频输入输出能力,为视频编解码算法开发、视频处理产品设计搭建了高性能的平台。     

稀土对等离子束表面冶金涂层抗裂性的影响

 采用直流放电压缩电弧等离子束表面冶金技术，在Q235钢表面制备了添加La2O3和CeO2的铁基冶金涂层。研究了冶金涂层开裂的主要形式、稀土氧化物对冶金涂层组织及抗裂性的影响，初步探讨了稀土氧化物改善界面显微结构、抑制冶金涂层开裂的机制。结果表明：稀土除可与氧、硫、硼等反应外，还可固溶于晶内、晶界或晶界附近；添加适量的稀土氧化物可有效改善冶金涂层的组织和性能，抑制等离子束表面冶金涂层中的裂纹和孔洞。