碳化钨涂布刮刀的研制

刮刀是涂布机的关键部件,传统的(无涂层)蓝钢刀片戓工具钢带制造的涂布刮刀由于其磨损快、寿命短,己经不能满足高速涂布机的生产要求,需要开发具有金属/陶瓷碳化钨(WC/Co) 涂层的高耐磨型涂布刮刀。业界曾采用等离子喷涂等方法在钢带上制备各种陶瓷材质的耐磨涂层以提高涂布刮刀的使用寿命。但现行的工艺方法获得的涂层存在着涂层不致密、孔隙率高、结合强度低等不足之处,本研究采用国产的HVAF超音速火焰喷涂系统成功研制具有WC10Co4Cr碳化钨耐磨涂层的涂布刮刀,各项质量指标均超过等离子喷涂等方法制备的陶瓷涂布刮刀,其平均使用寿命为陶瓷刮刀的2倍以上,涂层质量可以与国际同类产品相媲美。     

Flame front structure of turbulent premixed flames of syngas oxyfuel mixtures

In order to investigate oxyfuel combustion characteristics of typical composition of coal gasification syngas connected to CCS systems. Instantaneous flame front structure of turbulent premixed flames of CO/H₂/O₂/CO₂ mixtures which represent syngas oxyfuel combustion was quantitatively studied comparing with CH₄/air and syngas/air flames by using a nozzle-type Bunsen burner. Hot-wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous flame front structure, respectively. Image processing and statistical analyzing were performed using the Matlab Software. Flame surface density, mean progress variable, local curvature radius, mean flame volume, and flame thickness, were obtained. Results show that turbulent premixed flames of syngas possess wrinkled flame front structure which is a general feature of turbulent premixed flames. Flame surface density for the CO/H₂/O₂/CO₂ flame is much larger than that of CO/H₂/O₂/air and CH₄/air flames. This is mainly caused by the smaller flame intrinsic instability scale, which would lead to smaller scales and less flame passivity response to turbulence presented by Markstain length, which reduce the local flame stretch against turbulence vortex. Peak value of Possibility Density Function (PDF) distribution of local curvature radius, R, for CO/H₂/O₂/CO₂ flames is larger than those of CO/H₂/O₂/air and CH₄/air flames at both positive and negative side and the corresponding R of absolute peak PDF is the smallest. This demonstrates that the most frequent scale is the smallest for CO/H₂/O₂/CO₂ flames. Mean flame volume of CO/H₂/O₂/CO₂ flame is smaller than that of CH₄/air flame even smaller than that of CO/H₂/O₂/air flame. This would be due to the lower flame height and smaller flame wrinkles.     

超音速火焰喷涂过程中粒子运动特性的数值模拟

热喷涂涂层质量很大程度上是由颗粒沉积时的状态决定,颗粒不仅受到粒径尺寸的影响,还与飞行过程中焰流特性密切相关.本文以JP8000型超音速火焰喷涂系统(HVOF)喷涂过程为研究对象,采用计算流体动力学方法探究不同氧油质量比下焰流行为和计算域内的燃烧特性;分析不同粒径的颗粒在焰流场内的轨迹特性和速度、温度演变规律,依据数值模拟结果优化工艺参数.计算结果表明:氧油比为3时,HVOF系统内焰流温度最高、速度最快,表明氧油充分燃烧;颗粒注入后可能与枪管壁发生碰撞,且其粒径越大,碰撞发生的临界入射速度越小,碰撞后的粒子会二次穿越焰流中心;颗粒粒径越大,受焰流作用时加热、加速越缓慢,在喷枪内到达的最高温度和最大速度越小.     

高速冲击形成微带组织的研究进展

总结了高速冲击微带的微观形貌及晶体学取向共性;比较分析了冲击微带的几种具体形成机制,认为交滑移机制与二次滑移机制较符合高速冲击变形的特征;总结得出靶材的层错能和晶体结构是影响微带出现几率的主要因素;简略概括了微带与晶界的相互作用及形成微带对材料后续抗冲击性能的影响;最后展望了冲击微带的进一步研究.     

动态爆炸战斗部对舰船舱壁的破片载荷特性研究

为研究舰船内部舱壁结构在半穿甲反舰导弹战斗部动态爆炸情形下承受的破片载荷特性,基于合理假设,根据弹目相对初始运动状态建立了空间坐标系,运用爆炸力学经验公式,推导了一种较为实用的数学计算模型。对该数学计算模型进行MATLAB语言编程,考虑装药引爆时战斗部不同的初始位置、姿态、平面运动以及因撞击舷侧外板而获得的转动等初始运动特性参数,采用破片着靶范围、着靶位置、舱壁各区域破片着靶总质量、破片着靶均速等评估参量,进一步研究战斗部初始运动特性对舱壁结构承受的破片载荷特性影响。结果表明：舰船舱壁破片载荷特性因战斗部不同初始运动特性而呈现不同分布规律,因战斗部装药爆炸驱动而获得的破片飞散特性是决定其分布特性的根本因素;对舱壁破片载荷特性有重要影响的首要参数是战斗部初始位置和姿态,其次是战斗部平面运动,而战斗部转动仅引起舱壁破片载荷分布的小幅改变。     

Dependence of the Depth of Penetration on the Parameters of an Elongated Striker

On the basis of numerical simulation of the process of penetration of impact-destructible elongated metallic strikers into impact-destructible thick plates, we study the influence of the geometric shape and material of the striker on the depth of penetration and the possibility of through penetration. The depth of penetration is analyzed for the case where the impact velocity approaches the hydrodynamic limit.     

High weibull modulus HVOF titania coatings

The mechanical behavior of high-velocity oxyfuel (HVOF) sprayed titania (TiO₂) coatings was evaluated using Vickers hardness measurements on the cross section and top surface. The distribution of hardness values for the cross-section and top surface under 25, 50, 100, 300, 500, and 1000 g loads was analyzed via Weibull statistics. The coating microstructure was evaluated using scanning electron microscopy (SEM). It was observed that the microstructural features were similar in the top surface and cross-section, different from the lamellar structure commonly found in thermal spray coatings. X-ray diffraction (XRD) analysis identified rutile as the major coating phase. The in-flight sprayed particle parameters such as temperature and velocity were determined using a commercial diagnostic system based on pyrometry and time-of-flight measurements. The uniformity of the microstructure resulted in a near isotropic behavior of the mechanical properties, such as hardness, in the coating cross-section and top surface. High Weibull modulus values were observed when compared with results of other thermal spray coatings available in the literature. These initial results should contribute to a more general understanding of the conditions necessary to achieve coatings with high uniformity and assist in the engineering of coating microstructures for specific applications.     

Mechanical properties of HVOF coatings

High-velocity oxygen fuel (HVOF) thermal-sprayed carbide coatings are distinguished by high hardness, low porosity, and good wear resistance compared to other thermal spray technologies. However, for many engineering applications the ductility and fatigue resistance are the most important material properties. In the use of HVOF systems, these properties are influenced by many boundary conditions. This paper presents the effects of different spraying parameters on the fatigue resistance of samples coated by the HVOF process.     

Analysis of the Process of Explosion Braze-Welding of Heat Exchanger Tube Plates

The process of kinematic braze-welding of thin-walled tube plates and tubular elements in making heat exchangers is considered. The process is simulated by the high-velocity contact interaction of coaxial cylinders with a thin layer of high-strength amorphous solder between them. The inner cylinder expands by the action of explosive pulse load. When solving the thermoelastoplasticity problem, the dynamic properties of the material are taken into account. This process has been experimentally investigated using test specimens.     

高速透气阀压力流量特性实验和入级型式试验

研究阐述了透气阀结构及工作原理,并以DN200型高速透气阀为例,设计了透气阀实验使用系统及实验方法、步骤,揭示了透气阀的压力-流量特性。研究结果表明:正压阀开启压力为14.1 kPa,正压阀关闭压力为10.0 kPa;真空阀开启压力为-3.5 kPa,真空阀关闭压力为-2.6 kPa。正压阀瞬间的排气速度高达42 m/s,符合各船级社规范、SOLAS公约和IMO规则对应的章程条款要求。同时发现:透气阀设定压力通常设定正压阀为14.1~21.4 kPa、真空阀为-3.5~-7.01 kPa范围内,在规定值内即阀瓣起跳。