Structural characteristics and high-temperature oxidation behaviour of nano-HfO2-doped thermal barrier coatings

The uneven growth of thermally grown oxides (TGOs) in thermal barrier coating systems is an important cause of cracking failure at the coating interface in high-temperature environments. The doping of rare earth elements in the bonding layer can effectively inhibit the formation of spinel oxides in the TGO and improve the high-temperature oxidation resistance of the coating. However, a single rare earth element has a limited effect on inhibiting TGO failure. In this study, a NiCoCrAlYHf coating was prepared using a supersonic flame spraying (HVOF) technique. The effects of HfO₂ doping on the high-temperature oxidation behaviour of the coatings and diffusion behaviour of metallic elements in the coatings were investigated at 1100 °C. The results showed that the nano-sized HfO₂ filled the pores between the powder particles and improved the hardness of the coating. During the high-temperature oxidation process, the oxides formed by Hf and Y had a large size and low solubility, which effectively blocked the diffusion of Al. This slowed the generation of spinel oxides, effectively inhibited the growth of the TGO, it inhibits the initiation and propagation of cracks within the coating, reduces damage to the coating from tensile and compressive stresses at the interface, and improved the high-temperature oxidation resistance of the coating.     

High temperature tribology of heavily boron doped diamond films against steel

Despite the fact that Fe, Co, and Ni catalyze the phase transition of diamond into graphite, the question of the applicability of diamond as a functional coating of a metal-cutting tool is still open. For this reason, our work contains investigation of wear and friction of heavily boron doped diamond films against steel at elevated temperature, as well as influence of boron concentration on diamond film oxidation resistance. The obtained data indicated that minimum CoF value is achieved in the temperature range within 570–670 °C and strongly depends on boron concentration in coating (CoF decreases with increasing of boron concentration). Wear rate has the same dependence as the CoF, whereas oxidation resistance decreases with increasing of boron concentration. Besides, the presented results are first obtained for boron doped diamond films synthesized under high B/C ratio conditions (of up to 333 ppb).     

核壳结构复合吸波材料研究进展

在综述电磁波材料吸波工作原理的基础上, 讨论了核壳结构材料在吸波领域的优势.重点介绍了近年来不同类型核壳结构复合吸波材料的研究进展, 主要包括铁氧体型、磁性金属微粉及其氧化物型、陶瓷型、导电聚合物型、碳系材料型等核壳结构复合吸波材料.同时对不同类型的核壳结构吸波材料的制备方法、组织结构和微波吸收性能进行了详细的归纳评述.最后对核壳结构复合吸波材料的发展趋势进行了展望, 主要包括多层核壳结构, yolk-shell结构以及与其他材料结构相复合的特殊结构, 为进一步研究核壳结构复合吸波材料提供参考.      

Microstructure and mechanical properties of Mo coating deposited by supersonic plasma spraying

The inherent technological limitations of traditional thermal spraying technologies have the relatively high oxidation degree and porosity of prepared Molybdenum (Mo) coating. Hence, in this study, a Mo coating was fabricated using supersonic plasma spraying technology. Scanning electron microscopy (SEM), X-ray diffraction (XRD), tensile testing machine, high-precision macro/micro-indentation tester and ball-on-disc tribometer were used to investigate the microstructure, phase composition, mechanical and tribological properties of the coating. The results showed that the Mo coating had dense structure and highly diminished oxidation degree. The phase composition was pure Mo. The tensile strength failure occurred within the coating layer. In the meanwhile, the Mo coating exhibited a superior hardness, a high elastic work/total work (W_e/W_t), and excellent tribological properties. The wear mechanisms were fatigue wear and adhesive wear.     

爆炸喷涂工艺参数对AlCuFeSc准晶涂层力学性能的影响

目的 研究爆炸喷涂工艺参数对AlCuFeSc准晶涂层力学性能的影响规律,进一步提升铝合金表面AlCuFeSc准晶涂层的性能。方法 采用爆炸喷涂工艺制备准晶涂层,以正交试验方法对爆炸喷涂氧燃充枪比、喷涂距离、喷涂频率3个影响涂层性能的关键参数进行优化。借助显微硬度计、拉力试验机研究涂层的力学性能。采用SEM、XRD、EDS等手段表征粉末及涂层的微观物相结构。结果 在试验参数范围内,以涂层的表面硬度和结合强度性能为主要判定指标,各因素对涂层性能的影响从大到小依次为氧燃充枪比、喷涂距离、喷涂频率。综合考量涂层表面硬度和结合强度2个指标,得到了AlCuFeSc涂层的最佳制备工艺,氧燃充枪比为56%,喷涂距离为210 mm,喷涂频率为1次/s。在该最佳工艺参数下制备的准晶涂层致密且与铝合金基体结合良好,涂层表面硬度为583.4HV0.3,结合强度为63.24 MPa,孔隙率为0.648%,准晶相的含量为69%。结论 采用最佳工艺参数制备的AlCuFeSc准晶涂层相较于非最佳工艺参数喷涂涂层,其性能得到较大提高,可为未来准晶涂层的应用提供参考。     

铝合金搅拌摩擦焊接头缺陷及焊件结构问题控制策略的研究进展

搅拌摩擦焊(Friction Stir Welding,FSW)是近些年发展起来的一种固态连接工艺,尤其适用于铝合金材料的焊接。概述了搅拌摩擦焊的局限性,主要包括接头处存在钥匙孔、焊缝减薄等缺陷及复杂结构铝合金难以焊接等问题。研究表明,通过工艺方法、流程及参量的优化能够对焊接接头缺陷和焊件结构问题进行有效控制。由此,归纳了铝合金搅拌摩擦焊接头存在的关键问题及解决策略,分析了每种工艺方法的适用对象及条件,包括摩擦塞焊(Friction Plug Welding,FPW)、填充式搅拌摩擦焊(Filled Friction Stir Welding,FFSW)、回抽式FSW、静止轴肩搅拌摩擦焊(Stationary Shoulder Friction Stir Welded,SSFSW)、沉积式FSW、双轴肩搅拌摩擦焊(Bobbin Tool Friction Stir Welding,BT-FSW)和无倾角FSW。详细探讨了每种工艺的原理和机制,阐述了每种工艺的优缺点,重点介绍了工艺的参数优化调控、辅助设备的添加及工序的改进对修复接头组织与力学性能的影响。对铝合金搅拌摩擦焊的回顾总结,将为获得高质量搅拌摩擦焊接头,实现复杂结构件焊接提供参考依据。在此基础上,对铝合金搅拌摩擦焊现存问题及挑战的解决进行了展望。     

三维光子晶体红外隐身材料特性

随着红外探测技术的飞速发展,红外隐身材料的研制与应用在世界各国受到强烈关注。光子晶体凭借其带隙的可调控性脱颖而出。利用带隙处于红外波段的光子晶体作为表面涂层材料能够有效改变目标的红外辐射特性,实现红外隐身。利用理论和实验验证相结合的方法,对基于胶体基元自组装技术制备蛋白石型光子晶体红外隐身材料进行研究,为新型红外隐身材料的发展提供理论指导和技术支持。根据布拉格衍射定律分别确定带隙处于红外探测仪和红外夜视仪的检测波段（3～5 μm和8～14 μm）的光子晶体胶体基元直径范围,并通过分散聚合法合成1～2.21 μm单分散性良好的聚苯乙烯胶体基元。对垂直自组装法、重力沉降法和层层自组装法3种常用的胶体基元自组装方法进行研究,提出一种恒温水浴烘培法。研究结果表明,采用该方法得到的光子晶体结构规整,带隙范围内红外透射率从80%可降至25%,红外热成像仪测试显示对60 ℃的背景材料红外隐身效果好;该方法具有实验设备和工艺简便、耗时较短（仅3 h）、适用微球种类多、阵列规整有序等优点。     

再制造喷涂层界面结合性能脉冲红外热像评估技术

针对再制造工程中常见的喷涂层界面结合性能评价问题,采用脉冲红外热像技术对3Cr13合金涂层的界面脱粘缺陷进行检测评估。以信噪比(SNR)为评价标准,对比了两种不同热图序列处理方法在预处理和后处理阶段的效果。结果表明:在预处理阶段,基于表面热信号的多项式拟合算法(PF)将原始热图的信噪比由5.34提升到9.61,其效果优于基于单张图像中值滤波算法(MF);而在后处理阶段,基于单张图像的主成分分析法(PCA)对缺陷特征的表征比基于表面热信号的脉冲相位法(PPT)更加准确,第三主成分重建热图的信噪比达到17.99。综合而言,基于单张图像的热图序列处理方法在再制造喷涂层界面结合性能评价中具有更好的效果。     

热障涂层TGO界面应力分布及裂纹扩展行为的研究进展

热障涂层以其优异的抗氧化? 隔热? 耐腐蚀性而广泛应用于热端部件表面.在超过1000℃高温的服役环境下,外界的氧元素通过陶瓷层扩散到粘接层界面,与其中的金属元素发生氧化反应生成一层热生长高温氧化物(TGO)? 随着服役时间的增加,TGO不断生长,TGO界面产生较大的热应力,导致裂纹的萌生与扩展,使得涂层大面积剥落,因此TGO氧化失效的研究既是难点也是热点问题.总结了研究TGO界面建立的主要几种模型,例如同心圆界面模型? 曲线弦界面模型和真实界面模型,其中曲线几何结构通常只需要振幅和波长即可很好地描述界面,因此大多数模型建立采用了曲线模型.在此基础上,重点综述了界面形貌、界面粗糙度和TGO厚度对应力分布的影响,以及从应变能释放率和裂纹路径两个角度探讨了界面损伤行为.上述研究很好地阐明了TGO生长过程,但是仅考虑了形态特征对应力分布的影响,接下来的研究应考虑真实TGO界面并完善模拟的准确性,同时发展有限元技术实现在实际条件下裂纹扩展路径和使用寿命的预测.     

Effect of loading system inertia on tribological behaviour of ceramic–ceramic,ceramic–metal and metal–metal dry sliding contacts

Machine dynamics can contribute to a difference between results in coefficient of friction, vibration level and wear rate of the same tribo-couple concerning the compliance of the support provided to a sliding counterbody. The aim of the present work is revealing the effect of loading system inertia on laboratory tests results. A developed pendulum-type tribo-tester was used for testing ceramic–ceramic, ceramic–metal and metal–metal sliding contact combinations. Diamond-like, AlTiN, TiCN and AlCrN/Si₃N₄ PVD coatings and bare EN X30WCrV9-3 steel disks were tested against yttria-stabilized zirconia and EN 100Cr6 steel balls. Discussion on the mechanisms of materials degradation is based on SEM and EDS observations. It was found that inertia of loading system influences compaction of wear debris.