SiC纤维增强TB8复合材料工艺对组织影响规律

通过箔-纤维-箔法制备了SiC纤维增强TB8复合材料，采用光学电子显微镜（OM）、扫描电镜（SEM）和电子探针（EPMA）对复合材料的微观组织进行表征与分析，研究了真空热压复合时压力、温度和时间等工艺参数对SiC纤维增强TB8复合材料微观组织的影响规律。结果表明：压力显著地影响着复合材料基体与基体以及纤维与基体的结合，而温度对纤维基体界面反应情况影响较大。通过热压工艺的优化，可以有效控制界面反应层厚度，获得组织优良的SiCf/ TB8复合材料。     

In-situ synthesis of Al2O3-reinforced high Nb–TiAl laminated composite with an enhanced strength-toughness performance

In this work, the Al₂O₃-reinforced high Nb–TiAl laminated composite is successfully fabricated by an innovative way of direct-current magnetron sputtering combined with the foil-foil metallurgy, with assistance of vacuum hot-pressed sintering. Here, the Nb-coated aluminum foil and titanium foil, microstructure evolution, the lamellar plane distribution and the mechanical performances are carefully studied. Specifically, the composite is composed of the α₂-Ti₃Al, γ-TiAl and α-Al₂O₃ phase, in which the high Nb–TiAl matrix has a fully lamellar microstructure and a high content (～6.5%) of Nb. Taken the textured titanium foil as raw material, the multi-stage annealing process is proved to be an effective way to control the lamellar plane distribution in the high Nb–TiAl matrix, showing that 82.3% of the lamellar planes forms an angle less than 30° from the RD-ND plane of the composite. Moreover, the bending strength and fracture toughness of the composite reach 817 MPa and 12.41 MPa m^1/2, respectively. Further, the toughening and strengthening mechanisms are also detailly discussed. We believe that the major findings in this work can provide a new idea to design the high strength-toughness intermetallic-ceramic composites.     

Vision-based spatial damage localization method for autonomous robotic laser cladding repair processes

Repair technologies have been considered as sustainable approaches due to their capability to restore value in a damaged component and bring it to like-new condition. However, in contrast to a manufacturing process benefiting from an automated environment, the automation level for repair and remanufacturing processes remains low. With the aim of moving the repair industry towards autonomy, this study proposes a novel repair framework. The developed methodology presents a vision-based Robotic Laser Cladding Repair Cell (RLCRC) that has two features: (a) an intelligent inspection system that uses a deep learning model to automatically detect the damaged region in an image; (b) employing computer vision-based calibration and 3D scanning techniques to precisely identify the geometries of damaged area. The repair of fixed bends is selected as the case study. The results obtained validate the efficacy of the proposed framework, enabling automatic damage detection and damaged volume extraction for worn fixed bends. Following the suggested framework, a time reduction of more than 63% is reported.     

Effect of ammonium polyphosphate on flame retardancy,thermal stability and mechanical properties of alkali treated kenaf fiber filled PLA biocomposites

In present research polylactic acid (PLA) biocomposites were prepared from PLA and kenaf fiber using dry blending, twin screw extrusion and compression molding techniques. PLA was blended with kenaf core fiber, polyethylene glycol (PEG) and ammonium polyphosphate (APP). Kenaf fiber was treated with 3%, 6% and 9% NaOH solution separately. Both raw and treated kenaf along with 10, 15 and 20 phr APP was utilized during composite preparation. The effects of APP content and alkali treatment on flammability, thermal and mechanical properties of kenaf fiber filled PLA biocomposites were investigated. APP is shown to be very effective in improving flame retardancy properties according to limiting oxygen index measurement due to increased char residue at high temperatures. However addition of APP decreased the compatibility between PLA and kenaf fiber, resulting in significant reduction of the mechanical properties of PLA biocomposites. Thermogravimetric analysis (TGA) showed that NaOH treatment improved the thermal stability of PLA biocomposites and decreased carbonaceous char formation.     

Electrical properties of cold-pressing welded NbTi persistent joints

The cold-pressing welding method is employed to fabricate persistent joints between NbTi multifilamentary conductors, and a series of persistent joints are thus made at different mechanical pressures. The electrical properties of these persistent joints are tested by a joint resistance measurement device based on the current decay measurement method. Test results show that the cold-pressing welding method is reliable and applicable to NMR and MRI applications. Experiment results also shows that the joint resistances and current-carrying capacities of the joints seem to have no apparent relevance to the mechanical pressure in a wide range of 4–20 MPa, but the current decay ratio due to flux creep has obvious relevance to the mechanical pressure. Further research is needed to advance this joint manufacturing technology. Besides, measured current increase under 1 T background magnetic field is observed and explained, which has a reference meaning for testing persistent joint resistances.     

基于S7-300 PLC在湿法混合制粒机控制系统中的应用

系统采用S7-300PLC作为控制器,重点介绍了其结构化编程在制粒机设备中的应用;主要介绍HLSG600型湿法混合制粒机控制系统的构成、硬件配置和软件设计。目前该设备已投入运行,控制系统运行稳定、可靠,设备运行情况良好,用户反映良好。     

电磁耦合处理对Ti2AlNb合金电子束焊缝疲劳寿命的影响研究

在航空发动机机匣的焊接过程中,焊缝作为薄弱部位,将直接影响整个机匣的疲劳性能及服役寿命。通常采用焊后热处理消除焊接热应力,均匀焊缝组织,提高焊缝性能,但对于疲劳寿命的改善效果不明显。本研究创新性地提出电磁耦合处理技术,对热处理后的Ti₂AlNb合金电子束焊缝进行调控,提升焊接接头的疲劳寿命,同时研究了在电磁耦合作用下焊缝区材料组织演变规律。结果表明,焊缝疲劳极限由134.2MPa增至159.4MPa,提升18.8%。经电磁耦合处理后,焊缝区域的残余压应力最高提升128.7%。同时,在不改变材料组织和相成分的情况下,在材料内部生成位错墙与位错纠缠,疲劳裂纹源由表层移至次表层,疲劳裂纹扩展速度降低,使得疲劳性能提升。焦耳热效应、电子风力效应与磁致塑性效应的耦合作用促进了位错运动,同时增强了疲劳裂纹扩展障碍。本研究为提升焊缝疲劳寿命提供了一种新方法,并为电磁耦合处理提升焊缝疲劳性能提供了可行性依据。     

激光冲击强化TC17钛合金室温和高温拉伸性能研究

目的分析激光冲击强化对钛合金室温和高温拉伸性能的影响。方法用YAG纳秒脉冲激光器对TC17钛合金板状拉伸试样表面进行双面激光冲击强化,脉冲能量为25 J,脉冲宽度为15 ns,光斑尺寸为4.2 mm×4.2 mm,搭接率为10%,强化1次。通过室温及400℃下拉伸试验,获得强化前后试样的抗拉强度、屈服强度和断裂伸长率,利用X射线衍射法测试拉伸前后试样表面的残余应力,并在扫描电镜下观察拉伸试样断口微观形貌。结果室温拉伸试验时,激光冲击强化对TC17钛合金的室温抗拉强度和伸长率几乎无影响,但强化后的室温屈服强度下降约6.1%,有/无强化试样均没有明显的屈服点,距离强化试样断裂位置10 mm的表面残余压应力较拉伸前下降约12%。400℃拉伸试验时,激光冲击对TC17钛合金的高温抗拉强度和屈服强度均影响较小,有/无强化试样均出现明显的屈服点,距离强化试样断裂位置10 mm的表面残余压应力较拉伸前下降约44%。结论激光冲击强化在TC17钛合金表面引入显著的残余压应力分布,对屈服强度具有一定程度的影响。强化后试样的屈服强度与拉伸过程中残余压应力松弛速率有关,室温拉伸过程的残余应力松弛较高温拉伸过程慢,试样内部的平衡拉应力区更容易先发生屈服。这是造成室温拉伸屈服强度小幅降低的主要原因。     

超高温Nb-Si基复合材料研究现状

主要论述了Nb-Si系原位复合材料的研究近况,主要总结通过合金化和制备工艺的改善,以期使室温断裂韧性、高温强度及抗氧化性能获得良好匹配,对进一步提出优化的制备和研究方案奠定了基础。