脉动燃烧控制技术在隧道式淬火炉上的应用

为解决隧道式淬火炉炉温分布不均匀的问题，采用了高速调温烧嘴脉动燃烧控制技术。实践证明：脉动燃烧控制对象是带延迟的一阶惯性环节，因此对控制对象采用常规的PID控制策略完全可行。还阐述了高速调温烧嘴脉动燃烧控制技术运用于隧道式淬火炉的优越性和取得的显著效果。     

高流速含沙浑水体流变特性试验研究

加速行进中的洪水具有高含沙、高流速和粗粒径的特点,而针对洪水的流变特性研究关注点多为高含沙量,忽略了高流速即高剪切速率的特点。以黄河下游泥沙为研究对象,系统地研究了高流速剪切条件下含沙量、剪切模式、温度和盐度对流变特性的影响。结果表明,在高流速剪切条件下（剪切速率≥ 1200 s-1,对应线性流速为3.6 m/s）,含沙量在106.64 ~ 957.83 kg/m3范围内的浑水体符合牛顿流体的应力本构关系,不存在屈服应力,表观黏度与含沙量呈指数关系。温度降低并未改变浑水体的流变特性,但会使其表观黏度增加,且温度越低黏度增幅越大,浑水体黏度增大梯度约为等温度清水的数倍至十几倍。盐度变化对该测试浑水体的表观黏度和流变特性影响甚微,可忽略不计。本研究结果可为高流速水流挟沙和远距离输沙研究提供理论参考。     

Comparative characteristic and erosion behavior of NiCr coatings deposited by various high-velocity oxyfuel spray processes

The purpose of this study is to analyze and compare the mechanical properties and microstructure details at the interface of high-velocity oxyfuel (HVOF)-sprayed NiCr-coated boiler tube steels, namely ASTM-SA-210 grade A1, ASTM-SA213-T-11, and ASTM-SA213-T-22. Coatings were developed by two different techniques, and in these techniques liquefied petroleum gas was used as the fuel gas. First, the coatings were characterized by metallographic, scanning electron microscopy/energy-dispersive x-ray analysis, x-ray diffraction, surface roughness, and microhardness, and then were subjected to erosion testing. An attempt has been made to describe the transformations taking place during thermal spraying. It is concluded that the HVOF wire spraying process offers a technically viable and cost-effective alternative to HVOF powder spraying process for applications in an energy generation power plant with a point view of life enhancement and to minimize the tube failures because it gives a coating having better resistance to erosion.     

Prediction of powder particle behavior during high-velocity oxyfuel spraying

A mathematical model is developed to predict particle velocity and temperature during high-velocity oxyfuel (HVOF) spraying. This model accounts for internal heat conduction in powder particles; particle heating, fusion, cooling, and solidification; the influence of particle morphology on thermal behavior; and the composite structure of the particles. Analytical results are obtained that describe particle velocity and temperature variations. The dependence of fluid velocity on particle density and volume fraction is shown. The results agree with empirically established HVOF spraying practice. Physical Metal-lurgy—Materials Science     

High-velocity oxyfuel reactive spraying of mechanically alloyed Ni-Ti-C powders

Recently, there has been considerable interest in producing cermet coatings with nanoscale carbide grains in the size range 50 to 500 nm. In this article, the production of nanoscale TiC grains in a Ni-based alloy matrix by reactive high-velocity oxyfuel (HVOF) spraying of metastable Ni-Ti-C powder is reported. Mechanical alloying of a Ni(Cr) prealloyed powder and Ti and C elemental powders was performed in a planar-type ball mill, and materials were characterized in detail using x-ray diffraction (XRD) and scanning electron micros-copy (SEM). Phase changes were correlated with milling time and other processing conditions. Results show that, by the selection of appropriate conditions, a metastable Ni-Ti-C powder could be obtained with the nominal composition 50wt.%Ni-40wt.%Ti-10wt.%C. Following sieving and classification, powder was produced with a particle size range of −38 to 8 μm, which is suitable for HVOF spraying. Coatings, approximately 250 μm thick, were deposited by HVOF spraying onto mild steel substrates, and the microstructures formed were investigated. XRD showed that a self-propagating high-temperature synthesis (SHS) reaction had occurred in the powder particles during spraying and that the principal phases present in the coating were TiC and a Ni-rich solid solution; small quantities of NiTi, TiO₂, and NiTiO₃ were also present. SEM revealed that the coatings had a characteristic, splatlike morphology and that TiC formed as a nanoscale dispersion, with a size range of ∼50 to 200 nm, within solidified splats. The microstructures of these reactively sprayed Ni-TiC coatings are briefly compared with those observed in HVOF-sprayed coatings deposited using prereacted SHS powder. The original version of this paper was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.     

超音速火焰喷涂NiTi合金涂层的形状记忆效应

采用超音速火焰喷涂制备超致密NiTi合金涂层,通过后续热处理获得优化相变结构,并通过压痕法分析涂层的形状记忆效应。光学显微镜及扫描电镜对NiTi合金涂层微观结构表征显示,喷涂制备态涂层由内部岛状-链状界面叠片组成,涂层致密孔隙率约为0.82%。X射线衍射分析显示,NiTi涂层制备态为全奥氏体,经时效处理析出Ni₄Ti₃相。压痕法分析表明,在制备态及时效态涂层中均获得了一定的单程及双程形状记忆效应。X射线物相分析及差示扫描量热仪对比分析揭示,时效析出的第二相粒子显著增加形状记忆效应。     

超音速火焰喷涂镍基涂层颗粒沉积特性的数值模拟

目的 考虑后续不同粒径颗粒随机冲击的影响,探索热喷涂涂层颗粒的沉积特性。方法 利用ABAQUS建立颗粒与基底冲击模型,通过颗粒冲击的凹坑深度和应力分布进行网格收敛性研究。通过实验验证模型的可行性。随后,应用验证模型研究颗粒以不同入射角和速度冲击基底时的沉积特性,以及4个颗粒重叠冲击基底及多颗粒随机冲击基底表面时的沉积特性。结果 在颗粒入射角从15°增至60°时,颗粒更好地附着于基底表面;当颗粒速度从350 m/s增至500 m/s时发生了溅射现象,可能造成绝热剪切失稳现象,形成有效结合;在4个颗粒冲击基底时,第2个颗粒对第1个颗粒及基底的影响都最明显;当多颗粒随机冲击基底时,在后续颗粒的冲击和沉积作用下,填充颗粒的形状不规则,同时第1层颗粒可能与基底形成机械咬合。结论 在超音速火焰喷涂时应当倾斜一定角度,同时提升颗粒速度,这对制备涂层更有利;在颗粒重叠冲击时,后续颗粒增大了第1个颗粒的压缩效果,且更深入地嵌入不锈钢基底,这有利于颗粒与颗粒之间的后续黏结;当多颗粒随机冲击基底时,在第1层沉积颗粒与基底之间,以及涂层内相邻颗粒之间均观察到高塑性应变,表明涂层出现黏结,同时后期沉积的颗粒未完整压缩变形。     

全氧燃烧玻璃窑炉的寿命浅析

通过对国内外部分全氧燃烧玻璃窑炉的寿命统计,非正常停炉和常见故障等问题分析,找出影响窑炉寿命的因素,提出要以规范化、科学化、系统化的思维,通过新材料、新技术、新工艺的运用有效延长全氧燃烧玻璃窑炉的寿命,对目前全氧燃烧窑炉的建设、推广应用有积极的参考价值。     

含沙高速水流的磨蚀机理和掺气抗磨作用

含沙高速水流易引起过流面材料的磨蚀破坏。本文探讨了泥沙磨蚀机理,提出了影响磨蚀的因素;基于紊流猝发理论,建立了混凝土材料壁面磨蚀率的计算公式;根据试验数据导出了掺气水流中混凝土材料壁面磨损率的经验公式。研究表明,含沙水流对固壁材料的磨蚀率随掺气浓度、材料强度的增大而减小,随水流流速、含沙量的提高而增大。利用掺气可有效地降低过流表面的泥沙磨蚀率。