TiN/Cr/Al2O3 and TiN/Al2O3 hybrid coatings structure features and properties resulting from combined treatment

New experimental results are presented on the structure and the elemental and phase composition of hybrid coatings, which were deposited on a substrate of AISI 321 stainless steel using a combination of plasma-detonation, vacuum-arc and subsequent High-Current Electron Beam (HCEB) treatment. We found that an increase in energy density intensified mass transfer processes and resulted in changes in aluminum oxide phase composition (γ → α and β → α). Also we observed the formation of a nanocrystalline structure in Al₂O₃ coatings. Electron beam treatment of a hybrid coating surface induced higher adhesion, decreased the intensity of surface wear and increased corrosion resistance in a sulphuric acid solution. The corrosion resistance of the coatings was studied in several electrolytic solutions (0.5 M H₂SO₄, 1 M HCl, 0.75 M NaCl) using electrochemical techniques. In most cases the corrosion resistance was improved, except those in NaCl solutions. The nano-hardness of the protecting coating was 13 GPa before electron beam melting and 9 GPa after it (as a result of TiN and Al₂O₃ sub-layers mixing).     

The characteristics of a low-power-consumption plasma jet and ceramic coatings

The effects of the composition of plasma gases (Ar-N₂, Ar-H₂), arc current, and voltage on the temperature and velocity of a low-power (5 kW) plasma torch in the arc field free region has been investigated using an enthalpy probe. Coatings of Al₂O₃-13TiO₂ were deposited under different conditions. The results show that in the Ar-N₂ plasma, the enthalpy, temperature, and velocity change little with arc current and voltage when regulating the nitrogen proportion in the plasma gas. The hardness of the resulting coatings is 800 to 900 kg/mm² HV.300. For Ar-H₂ plasma, however, increases in the H₂ content in the mixture of the gases remarkably enhanced the velocity and heat transfer ability of the plasma jet, with the result that the coatings showed high hardness up to 1200 HV.     

Hydraulic erosion of concrete by a submerged jet

The hydraulic erosion of concrete is often found in civil and marine engineering construction. The present study explores the effects of several erosion parameters on the material loss of a concrete specimen subject to the hydraulic flow produced by a submerged jet. Such an investigation has rarely been reported in the literature. The concrete specimen has a typical compressive strength of 35 MPa, and the experimental parameters include the exposure time, incidence angle, standoff distance, and the hydraulic jet pressure. The impinging velocity is estimated based on the distance considered in the round jet model. The regression analysis shows the relationship between each parameter and the material loss. One finds that the material loss is proportional to the exposure time and the hydraulic pressure. The maximum erosion lies at an incidence angle of around 30° to 45° and is affected by the fourth-order polynomial of impinging velocity. The result of the present study provides a reference to engineering practice where concrete erosion is a concern.     

Surface nitridation of titanium metal by means of a gas tunnel type plasma jet

The surface nitridation of titanium was carried out at a low pressure in nitrogen atmosphere using a gas tunnel type plasma jet. The titanium nitride (TiN) film, 10 μm thick and 2000 HV, could be formed in 10 s. The structure of the TiN film was investigated by XRD. The Vickers hardness on the surface of the film was measured. The effects of deposition conditions on the properties of TiN films (TiN thickness,Vickers hardness, etc.) were investigated, and the advantage of this deposition method was identified from those results.     

高速电喷镀制备纳米PTFE镍基复合镀层

研究了以Q235和65Mn钢为基底,经高速电喷镀形成的纳米PTFE镍基复合镀层,考察了喷射速度对镀层沉积速率、表面显微硬度、结晶组织形貌以及镀层结合力的影响,探讨了喷射速度影响镀层性能组织的原因机理。结果表明,喷射速度在4.2～6.3m/s时获得的镀层有较高的沉积速率和表面硬度,晶粒细小、组织致密,镀层结合力较高。     

Ski jump trajectory with consideration of air resistance

In the case of the ski-jump type energy dissipation,the jet trajectory will be greatly affected by the air entrainment and the air resistance.It is necessary to consider those factors when estimating the trajectory of the jet flow.In this work,the effect of the air resistance on the jet trajectory is theoretically and experimentally investigated.A comprehensive resistance coefficient is proposed.To determine this coefficient,experiments of five models are conducted with the circular-shaped flip bucket placed at the point of the takeoff of ski jumps.It is shown that,this coefficient of the lower jet trajectory is only related to the approach flow Froude number,while that of the upper jet trajectory is dominated by both this Froude number and the deflection angle.Furthermore,the present methodology is validated by experimental data in this work and the maximum errors are not larger than 3.2%and 8.6%for the lower and upper jet trajectories,respectively.     

NUMERICAL STUDY OF HYDRODYNAMICS OF MULTIPLE TANDEM JETS IN CROSS FLOW

The hydrodynamics of a single jet and four tandem jets in a cross flow are simulated by using the Computational Fluid Dynamics (CFD) software Fluent. The realizable model is used to close the Reynolds-Averaged equations. The flow characteristics of the jets, including the jet trajectory, the velocity field and the turbulent kinetic energy are obtained with various jet-to-cross flow velocity ratios in the range of 2.38-17.88. It is shown that a single jet penetrates slightly deeper than the first jet in a jet group at the same , although the difference decreases with the decrease of . It is also found that the way in which the velo-city decays along the centerline of the jet is similar for both a single jet and the first jet in a group, and the speed of the decay increases with the decrease of . The downstream jets in a group are found to behave differently due to the sheltering effect of the first jet in the group. Compared with the first jet, the downstream jets penetrate deeper into the cross flow, and the velocity decays more slowly. The circulation zone between the two upstream jets in the front is stronger than those formed between the downstream jets. The Turbulent Kinetic Energy (TKE) sees a distinct double-peak across the cross-sections close to each nozzle, with low values in the jet core and high values in the shear layers. The double-peak gradually vanishes, as the shear layers of the jet merge further away from the nozzle, where the TKE assumes peaks at the jet centerline.     

DRILLING CHARACTERISTICS OF COMBINATIONS OF DIFFERENT HIGH PRESSURE JET NOZZLES

The high speed fluid jet for directly or indirectly breaking rock is one of the most effective ways to improve the deep penetration rate.In order to maximize the efficiency of energy use,the flow characteristics of different combinations of high pressure jet nozzles are analyzed through numerical simulations.According to the velocity vectors at the bottom and the bottom hole pressure diagram,the effects of the high pressure nozzle combinations on the flow structure and the penetration rate are analyzed.It is shown that the combination of three vertical edge nozzles is very efficient,but inefficient in cleaning the bottom hole and eroding the wall.The jet velocity is 400 m/s and the radius is 5 mm,with a center nozzle added,the problem can be solved,but the high-pressure fluid displacement would increase.The center nozzle’s jet velocity is 200 m/s and the radius is 8 mm,the combination of two vertical edge nozzles and a center tilt nozzle or that of a vertical edge nozzle and a center tilt nozzle would provide a flow structure favorable for drilling.The angle of inclination is 10o.To take advantage of high pressure jet energy to improve the efficiency of drilling,it is important to select a suitable nozzle combination according real conditions.     

新立城水库坝基防渗高压摆喷灌浆参数试验

新立城水库土坝坝基属于双层地基,即表层为粘性土层,下面为沙砾石层。坝基下砾质粗砂和细砾为强透水层,连续分布。因需要防渗的透水层不厚(仅2～5m),采用高压喷射灌浆封堵透水层。施工前选定与坝段同样地质条件的试验场,用实际施工的喷灌设备分不同方案进行原型试验,开挖后观察成墙效果,最后确定施工技术参数。     

金刚石自支撑膜的高温红外透过性能

由于金刚石具有低吸收和优异的力学与导热性能使其成为长波(8~12μm)红外光学窗口材料的重要选择。对于许多极端条件的应用,化学气相沉积(CVD)金刚石自支撑膜的高温光学性质至关重要。应用直流电弧等离子喷射法制备光学级金刚石自支撑膜进行变化温度的红外光学透过性能研究,采用光学显微镜、X射线衍射、激光拉曼和傅里叶变换红外-拉曼光谱仪检测CVD金刚石膜的表面形貌、结构特征和红外光学性能。结果表明:在27℃时金刚石膜长波红外8~12μm之间的平均透过率达到65.95%,在500℃时8~12μm处的平均透过率为52.5%。透过率下降可分为3个阶段。对应于透过率随温度的下降,金刚石膜的吸收系数随温度的升高而增加。金刚石自支撑膜表面状态的变化,对金刚石膜光学性能的影响显著大于内部结构的影响。