Laser damage resistance of plasma-sprayed alumina and honeycomb skeleton/alumina composite ceramic coatings

Al₂O₃ and honeycomb skeleton-Al₂O₃ composite coatings on Titanium alloy (Ti–6Al–4V) were prepared by atmospheric plasma spraying. A laser ablation experiment on as-sprayed coatings was performed. In this paper, the laser damage resistance, microstructure, phase composition of Al₂O₃ coatings were examined. 3D Dimensional Confocal Microscopy, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Energy Dispersive Spectrometry (EDS) characterized the laser damage morphology, microstructure, phase composition, and element analysis, respectively. The influence of the honeycomb skeleton on the laser ablation damage on as-sprayed coatings was investigated by a comparative analysis of the laser damage morphology with different laser ablation times and gas flow. The results show that the honeycomb skeleton raises thermal conductivity and thermal diffusivity. Moreover, a “tower”-like dendrite was generated during the laser irradiation of the composite coating. The honeycomb skeleton refined the structure, suppressed crack propagation, and reduced the influence of gas flow on cracks. Under the same experimental laser ablation parameters, the laser damage area of the honeycomb skeleton-Al₂O₃ composite coating was smaller than that of the Al₂O₃ coating. It was demonstrated that the laser damage resistance of the honeycomb skeleton-Al₂O₃ composite coating was superior to that of the Al₂O₃ coating.     

Enhanced tribological behaviors of sintered polycrystalline diamond by annealing treatment under humid condition

The tribological behaviors of the 700 °C annealed sintered polycrystalline diamond (PCD) at various relative humidity (RH) levels were systematically investigated. The comparison of tribological behaviors between the 700 °C annealed PCD and the pristine PCD was made to further understand the tribological mechanisms. The results reveal that the friction inducing carbonaceous transfer film and oxidation and hydrolysis induced tribochemistry reaction dominant the tribological behaviors of the annealed PCD at various RH levels. The low coefficient of friction (COF) obtained in dry environments is attributed to carbonaceous transfer film on the worn Si₃N₄ surface, which was formed by the layers shearing action of massive tiny diamond grains exfoliated from the annealed PCD surface. The graphitization, oxidation and stress relaxation of the PCD induced by the 700 °C annealing treatment make the tiny diamond grains more easily to exfoliate and be grinded on the Si₃N₄ interface. It facilitates the formation of friction reducing carbonaceous transfer film, and finally results in the 30% lower COFs than those of pristine PCD at low RH levels (5%–50% RH). Meanwhile, an enhanced wear resistance of PCD can be achieved after 700 °C annealing treatment. The tribochemistry reaction induced by the oxidation and hydrolysis of Si₃N₄ governs the tribological behaviors of the annealed PCD at high RH levels (60%–99.9% RH). It reveals higher COFs accompanied with serious wear of Si₃N₄ ball and nearly no wear loss of annealed PCD. The produced SiO₂ and silicic acid embeds into massive spalling pits on the annealed PCD surface, resulting in slighter wear of the PCD and Si₃N₄ than that of the pristine PCD/Si₃N₄. These results propose that the tribological behaviors of PCD under humid environment can be significantly improved by the 700 °C annealing treatment.     

球形分流对等通道转角挤压工业纯铝组织性能的影响

基于传统等通道转角挤压(Equal Channel Angular Extrusion, ECAE)的变形原理,开发设计出一种具有球形空腔结构的新型复合大塑性变形工艺——等通道球形转角挤压(Equal Channel Angular Extrusion with Spherical Cavity, ECAE-SC)。以ECAE工艺为对比参照,开展了室温条件下工业纯铝单道次ECAE-SC挤压实验研究,进行了金相显微分析、显微硬度测试和球-面接触往复式摩擦磨损试验,获得了变形材料的显微组织、显微硬度、摩擦系数、磨损率和三维磨损形貌等特征参数.研究表明:ECAE-SC球形转角的圆滑过渡可大幅提高模具外角处金属的流动性,有效避免产生传统ECAE单道次变形“死区”,挤出试样头部翘曲现象得到显著改善;室温单道次ECAE-SC变形后,工业纯铝晶粒细化明显,显微硬度值由初始36.6HV增加至58.7HV,比同条件下ECAE变形试样(52.8HV)提高了11.2%;ECAE-SC变形材料耐磨性能最好,并表现出良好的摩擦磨损稳定性,磨损机制从磨粒磨损和氧化剥层磨损为主导的混合磨损机制转变为以磨粒磨损为主导的磨损机制。     

Strength and ductility of powder consolidated ultrafine-grain tantalum

Bulk ultra-fine grain tantalum was successfully fabricated from pure tantalum powder particles with an average particle size of 50 μm by equal channel angular extrusion at 900° C and 1200° C using three different processing routes. The effects of extrusion route and temperature on the consolidation performance are evaluated through microstructural analysis and room temperature mechanical testing. The consolidated tantalum has a “wood grain” like structure with strong interparticle bonds and a grain size <100 nm. The lamellar structure is helpful in resisting crack formation and fracture. The bulk tantalum consolidates are much stronger than annealed wrought tantalum and have significant ductility. Tensile tests for consolidated tantalum at room temperature show a yield strength of 340–376 MPa, an ultimate strength of up to 618 MPa, and strains to failure of ~19–25%. These properties are comparable to wrought Ta. The present study demonstrates that equal channel angular extrusion is a feasible method for fabricating bulk nanostructured refractory alloys from precursor powder, with a combination of high strength and good ductility.     

Mechanical properties and oxidation resistance of chemically vapor deposited TiSiN nanocomposite coating with thermodynamically designed compositions

TiSiN coating with nanocrystallite surrounded by amorphous phase has attracted a broad interest because of its high hardness and excellent oxidation resistance desired for cutting tools. In the present work, TiSiN coatings were designed and prepared from a gaseous mixture of TiCl₄, SiCl₄, NH₃ and H₂ by low pressure chemical vapor deposition (CVD) process under the guidance of calculated CVD phase diagrams. The calculated compositions and phases in the deposited coatings agree well with the experimental ones. The deposited TiSiN coatings consist of nano-crystalline TiN and amorphous Si₃N₄ (a-Si₃N₄). A maximum hardness of about 2800 HV_0.02 was obtained, corresponding to a minimum crystallite size of 17.7 nm and a-Si₃N₄ volume fraction of 13.3% for TiSiN coating deposited at 1123 K under 3.0 kPa. After oxidation at 973 K for 1 h, TiSiN coating kept intact while TiN was completely oxidized. TiSiN nanocomposite coating formed by Si incorporation to TiN displayed superior hardness and oxidation resistance in comparison with those of TiN. The correlation of TiSiN coating hardness with volume fraction of a-Si₃N₄ and TiN grain size was discussed. The present work demonstrates a novel strategy of thermodynamic calculations and key experiments to deposit CVD TiSiN coatings highly efficiently, which is equally valid for the design of other CVD hard coatings.     

Simulation and Experimental Study on Influence of Multi-port Integrated Hydraulic Transformer Port Number on Transformer Ratio Characteristics

端口数对集成式液压变压器变压比特性影响仿真与实验研究

刘成强¹,罗念宁² ,刘畅¹,周连佺³,张磊¹

（1. 徐州工程学院 机电工程学院,徐州 221018;

2. 哈尔滨工业大学（威海）海洋工程学院, 威海 264209;

3. 江苏师范大学 机电工程学院,徐州 221116）

摘要：集成式液压变压器结构紧凑,压力调节过程没有节流损失,在压力共轨静液传动系统中有着广泛的应用。集成式液压变压器是通过在配流盘上设计3个以上的配流端口实现的,不同端口数的集成式液压变压器的变压特性不同。本文对端口数对集成式液压变压器变压比的影响进行了研究,得到3端口、4端口、5端口集成式液压变压器的变压比特性,并搭建3端口、4端口集成式液压变压器的实验台并进行了实验研究,仿真结果与实验结果相吻合,为集成式液压变压器的设计研究提供了理论依据和实验基础。

关键词：集成式液压变压器,配流盘端口数,变压比,仿真与实验研究

     

A novel water-cooling magnetorheological transmission device

Journal of Mechanical Science and Technology - Magnetorheological (MR) fluid in power transmission devices, especially in high-power transmission devices, sometimes works at high temperatures owing...     

Contour recognition of roadheader cutting head based on shape matching

Pattern Analysis and Applications - In this paper, a shape matching algorithm is presented to perform the cutting head recognition for roadheaders based on a binocular vision system installed on...     

液压挖掘机工作装置的动力学建模与分析

以液压挖掘机工作装置为研究对象,建立其运动学和动力学理论模型。采用多体机械系统仿真软件对工作装置进行运动学和动力学仿真分析,得到各杆件之间铰接点的位移与速度曲线,以及各杆件上各铰接点的受力变化曲线。通过分析铰接点的受力变化曲线,得出各铰接点的受力变化规律,为液压挖掘机工作装置的设计和研究提供理论依据,对提升挖掘机的工作效能和可靠性具有实际意义。     

电解抛光法制备铝合金EBSD试样方法研究

目的 为在导电单相金属中获得高质量EBSD试样表面,研究电解抛光法制备铝合金试样的方法,并提供理论支持。方法 基于Jacquet黏膜模型和金属阳极原理,提出利用阳极极化曲线、电流-时间曲线和扫描电镜二次电子图像获得电解抛光工艺参数,批量制备铝合金EBSD试样的理论方法。采用恒电位法中的静态法记录稳定的电压-电流走势,以获得电流稳定的实验时间,在90 s内进行各电压下的电解抛光实验,获得电压与稳定电流的对应关系,并绘制阳极极化曲线。电流由持续稳定转至持续上升后的斜率与电压横坐标相交处为理论最低分解电压值。结合扫描电镜二次电子图像在最低分解电压以上观察抛光表面。结果 获得最优抛光电压值为31 V。利用电流随时间的变化曲线,结合黏膜模型分析,并通过扫描电镜二次电子图像验证,最优电压下的最佳抛光时间为12 s,该值是电流-时间曲线中的电流最低点。此工艺使制备的铝合金EBSD样品标定率为97%,是理想的电解抛光工艺。结论 采用阳极极化曲线获得的最优电压和最优电压下的最小电流规律由Jacquet黏膜模型支持,其所获得的电解抛光工艺能够制备出优质的样品表面,也能够为其他金属块体导电材料和其他需要电解抛光的实验类型提供获得最佳电解抛光工艺值的理论方法。