【作者】 孙玉伟；

【导师】 王引真；

【作者基本信息】 中国石油大学 ， 材料科学与工程， 2011， 硕士

【摘要】 本文采用计算与试验相结合的方法,对超音速火焰喷涂的燃烧特性及粒子行为对涂层性能影响进行了研究。以计算流体力学（CFD）为理论基础,采用商用软件Fluent,对不同助燃条件下超音速火焰喷涂（HVOF及HVAF）的燃烧特性、粒子行为进行计算,计算结果表明,焰流的温度主要由燃气与助燃气的当量比决定,当量比越接近理论计算值,焰流的温度越高。焰流速度主要由燃气及助燃气流量决定,流量越大,燃烧室的压力越大,焰流的最高速度越大。空气助燃时焰流的温度低、速度大,适宜喷涂低熔点、易氧化的粉末材料。氧-空气联合助燃时,随着助燃气中氧气比例的增大,焰流的温度越高,氧气比例高于75%（体积分数）以后,焰流温度和纯氧助燃时无差别。对粒子行为的计算结果表明,超音速火焰喷涂中粒子行为受焰流特性和自身特性两方面的影响;喷涂粒子温度、速度随焰流温度、速度的增大而增大;粒子直径越小受焰流的影响越明显,粒子直径越大受到焰流的加热、加速效果越小。适宜喷涂的粒子直径范围为20 m -40 m。采用CH-2000超音速火焰喷涂系统制备了纯氧助燃时不同粒子行为下的NiCr-25%Cr₃C₂涂层,并对涂层性能进行了测试。粒子行为与涂层性能的研究结果表明,粒子行为对涂层的性能有着显著影响。对温度一定的粒子（未完全熔融）形成的涂层,碰撞时速度越大涂层孔隙率越小,并且粒子速度高于一定值以后,由于涂层间沉积机制改变,粒子速度越高涂层的耐冲蚀性能越好。对于速度一定的粒子,粒子温度越高,形成涂层致密性越好,孔隙率越小,并且碰撞时粒子的温度会严重影响涂层的耐冲蚀性能。更多还原

【Abstract】 Combining with the experiment and calculating method, the effect which is caused by combustion characteristic and particle behavior of coating’s properties are studied in this letter. Based on computational fluid dynamics, a computational framework is developed to calculate the combustion characteristic and particle behavior of HVOF Spraying using the commercial software Fluent. The result shows that the temperature of flame is decided by equivalence ratio of fuel and oxidant gas. When the equivalence ratio is closer to theoretical value, the maximum temperature of flame is higher. The velocity of flame is decided by the pressure of combustion chamber which is affected by the flow rate. It also shows that the particle behavior of HVOF is affected by Combustion Characteristic and self-Characteristic. Both particle velocity and temperature are affected by Combustion Characteristic. Moreover, both particle velocity and temperature at impact are strongly dependent on particle size. The larger the particle size is, the smaller effect the flame has. Even particle size is large enough to lead to undeposition. Result shows that the particle size between 20 m to 40 m is available.The coatings are prepared with CH-2000 HVOF system under the condition of different particle behaviors when oxygen is the oxidant gas and the performance of these coatings are tested. The relationship between particle behavior and coating performance is studied. The result shows obviously that coating performance is depended on particle behavior. When particle temperature fixed, the higher the particle velocity is, the smaller the coating porosity is. In addition, the deposition mechanism is changed when particle velocity is higher than a critical value which is different for different particle temperature. And also, when particle velocity is higher than the critical value, the higher the particle velocity is, the better the coating erosion resistance is. When particle velocity is fixed, the compactness and porosity of coating is depended on particle temperature. And also, the erosion resistance of coating is much affected by particle temperature.更多还原