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51.
An analysis of a low temperature high velocity air fuel (LTHVAF) thermal spray process is presented using computational fluid
dynamics (CFD). The originality of the process lies in the injection of liquid (water) upstream of the powder injection to
control to gas temperature and, therefore, the heat transfer to the injected particles. First, computation fluid dynamic techniques
are implemented to solve the mass, momentum, and energy conservation equations in the gas phase. A turbulence model based
on the renormalized group theory (RNG) is used for the turbulent flow field. The gas dynamic data are, then, used to model
the behavior of the liquid droplets and particles in the gas flow field. The calculated results show that the liquid flow
rate should range between 20 and 30 kg/h to achieve the optimal gas characteristics for particle treatment. They also show
that particle velocity and temperature are strongly affected by particle size. At the gun exit, the particle velocity and
temperature range between 700 and 300 m/s and between 900 and 400 K, respectively, for Cu and Ni particles with size distributions
of 1 to 50 μm. As expected, the smaller particles have higher velocity and temperature. The metal coatings (Nickel and copper)
produced by the LTHVAF spray process are characterized by low oxide content, low residual stresses, high deposition rates,
and good bonding to the substrate. 相似文献
52.
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. 相似文献
53.
针对TiNi基合金在空间使役环境可靠性评价的迫切需求,开展高速撞击TiNi基合金马氏体相变、微观组织结构及力学性能研究。采用火药炮对Ti_(44)Ni_(47)Nb_9进行高速撞击,撞击速度为1020m/s,并对高速撞击后Ti_(44)Ni_(47)Nb_9合金3个不同方向的结构与性能进行测试。结果表明,沿撞击方向没有发生相变,与撞击方向呈45°和垂直于撞击方向的相变峰均向低温区偏移。弹坑底部以及侧壁出现大量裂纹,在TiNi基体中发现马氏体板条,同时在β-Nb粒子和TiNi基体中观察到大量位错。弹坑附近的硬度最高,随着与弹坑距离的增加,硬度降低,这可能是由于加工硬化及撞击能量分布不均匀而引起的。 相似文献
54.
O. C. Brandt 《Journal of Thermal Spray Technology》1995,4(2):147-152
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. 相似文献
55.
Vorob'ev Yu. S. Chernobryvko M. V. Kolodyazhnyi A. V. Kruszka L. 《Strength of Materials》2002,34(4):407-411
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. 相似文献
56.
57.
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。 相似文献
58.
针对高速撞击结构的局部化毁伤特性,利用LS-DYNA动力学程序,基于Lagrange法对弹丸高速撞击自由圆柱壳进行了数值模拟。分析自由放置圆筒在高速撞击下的穿孔效应和能量消耗、再分配关系。结果表明:随着撞击速度的增加,弹丸穿孔直径也呈线性增加;撞击速度在2.0~3.0 km/s范围内,其扩孔比为1.45~1.65,模拟结果与试验吻合较好。穿孔能量消耗随撞击速度提高而呈线性增加,其所占总能量的比例为16%~17%。自由圆柱壳变形内能随撞击速度增加而降低,更多的能量用于形成碎片云和增加碎片云的动能。 相似文献
59.
60.
富氧燃烧是能够大规模商业化捕集CO2的主流技术之一,为进一步探讨富氧燃烧压缩过程捕集CO2性能、并同时一体化脱硫脱硝技术的能力,在搭建的50 kg/h规模的试验平台上,通过调整不同的参数,采用液体CO2洗涤混合气体技术,表明压缩过程可同时脱除NOx和SOx等污染物,通过试验进一步研究液气比对NOx和SOx脱除的影响。结果表明,整体脱硫率、脱硝率可达98%以上,尾气中SO2体积分数低于50×10-6,NOx体积分数小于30×10-6,富氧燃烧系统中压缩纯化过程具备实现一体化脱硫脱硝的潜力。 相似文献