高、低喷涂功率下内送粉等离子喷涂YSZ粒子熔化状态研究

等离子喷枪采用内送粉方式后,喷涂功率对YSZ热障涂层微观结构和性能有着独特的作用,高功率下制备的涂层结合强度反而较低。本文研究了内送粉等离子喷枪在高功率(42.5 kW)和低功率(33.6 kW)时距喷嘴出口90 mm处的粒子熔化状态(粒子温度、粒子飞行速度、粒度分布及扁平粒子形貌)。研究结果表明,采用高喷涂功率时,由于等离子射流较高的热焓值使粒子迅速熔化并细化成粒径较小的熔滴,熔滴在撞击基体前发生再凝固降低了扁平粒子间的粘结。涂层出现横向裂纹,结合强度平均值仅为22.58 MPa。采用小喷涂功率时,既能保证粒子熔化良好又不会导致粒子发生明显细化。涂层结合强度平均值为37.25 MPa,随试片弯曲180(°)后仅出现一处剥落,1100℃炉中保温10 min取出后迅速置于水中淬冷130次后,试片中部涂层完好,显示出良好的抗热震性能。

Study on the Melting State of YSZ Particles Sprayed by Plasma Spray Torch in Internal Feedstock Mode at High and Low Arc Power

When plasma spray torch used the internal feedstock mode, spray power had a novel effect on microstructure and properties of YSZ thermal barrier coatings. For this reason, different melting state of particles, sprayed at spray power of 42.5 and 33.6 kW respectively, were particularly analyzed in this work. The temperature and velocity of yttria-stabilized zirconia particles were measured by Spray Watch 2i online monitoring system. Sprayed droplets were collected in water which can cool the molten particles instantly without changing their size distribution. Splats were collected by plugging a stainless steel plate in the plasma flame rapidly. The results show that when sprayed at arc power of 42.5 kW, particles can be completely melted instantly and broke down into some smaller sized particles. Subsequently re-solidification of these refined particles reduced the adhesion between each splat. Therefore, lateral cracks were took place in the coatings, which average adhesion strength was just 22.58 MPa. However, it is feasible to sufficiently melt the particles without refining them at a arc power of 33.6 kW. In this condition, coatings average adhesion strength was as high as 37.25 MPa. Only one place of the coating broke off after bend of 180° . After 130 times water quenching, central section of the coating was undamaged, indicating a high thermal shock resistance performance.