合金钢热障涂层等离子喷涂及高温力学特性研究

目的研究等离子喷涂热障涂层微观组织与高温力学性能,为热障涂层在合金钢的应用及其失效机制提供理论支撑。方法采用等离子喷涂技术在30Cr Mn Si A钢基体上制备Ni Co Cr Al Y/YSZ热障涂层,利用扫描电镜显微观察、物相分析、热震试验、拉伸试验等技术方法,考察涂层在高温条件下的失效行为。结果合金钢等离子喷涂热障涂层为典型双层层片状结构,YSZ涂层仅含有稳定四方相。800℃时,涂层试样拉伸试验后的断裂载荷与无涂层试样相比高10%。热障涂层的抗热震性良好,经900℃热震循环试验10次后,涂层完好;经1000℃热震循环6次后,涂层剥落失效,剥落面位于粘结层与基体之间。热震循环过程中,钢基体被氧化甚至腐蚀。涂层试样边缘产生应力集中,随着热震次数的增加,裂纹逐渐扩展,最终导致涂层成块剥落。温度由700℃升至900℃,Ni Co Cr Al Y涂层硬度下降幅度大于YSZ涂层和30Cr Mn Si基体。结论粘结层与钢合金基体的热膨胀不匹配是导致热震试验涂层剥落的主要原因。热障涂层的隔热作用使涂层试样的基体温度较低,导致其断裂载荷与无涂层试样相比较高。

Preparation and Mechanical Behavior at High Temperature of Plasma Sprayed Thermal Barrier Coatings on Alloyed Steel

The work aims to investigate microstructure and mechanical behavior at high temperature of thermal barrier coatings (TBCs) by air plasma spraying (APS), and provide theoretical evidences for application and failure mechanism of TBCs on alloy steel. The TBCs of NiCoCrAlY/YSZ were prepared on 30CrMnSiA steel substrate by APS. Failure behavior ofTBCs at high temperature was studied by means of such techniques as scanning electron microscope observation, phase analy-sis, thermal shock test and tensile test. The TBCs prepared by APS on alloyed steel were typical double-layer lamellar structures and YSZ coating had a stable tetragonal phase. Breaking load of the coating samples at 800 was slightly 10% higher than that℃of uncoated samples. TBCs exhibited good thermal shock resistance. TBCs remained intact after 10 times of thermal shock test at 900 ; TBCs peeled off and failed after 6 times o℃ f thermal shock test at 1000 . The peeled℃ -off coating was located between the bonding layer and substrate. The steel substrate was oxidized and corroded during thermal shock cycle. Stress concentration shall occur along edges of the coating samples and then cracks extended from edges to the center, and eventually caused the coating to peel off in bulk. The temperature increased from 700 to 900 , decrease amplitude of NiCoCrAlY coating har℃ ℃ d-ness was bigger than that of YSZ coatings or 30CrMnSi substrate. Thermal expansion mismatch between bonding layer and al-loy steel is the primary cause of coating peeling-off after thermal shock test. Heat insulation effect of the TBCs lowers tempera-ture of the substrate, hence its breaking load is higher than that of uncoated samples.