某电厂锅炉引风机叶片在服役中发生断裂。采用宏观观查、化学成分分析、拉伸性能试验、金相检验和硬度测试等方法对叶片断裂的原因进行了分析。结果表明：引风机叶片厚边存在脆硬的堆焊层，在堆焊层表面进行的热喷涂工艺控制不当，导致涂层内部及涂层和基体的界面产生孔洞，降低了涂层的强度、韧性以及涂层和基体界面的结合强度，在风压、飞灰和烟尘的冲刷以及振动应力的作用下，叶片涂层表面或涂层与基体界面发生开裂，裂纹向叶片内部扩展，造成叶片厚边缺口应力集中，裂纹不断向叶片薄边扩展，最终导致叶片发生断裂。

The blade of induced draft fan of a power plant boiler broke in service. The causes of blade fracture were analyzed by means of macroscopic observation, chemical composition analysis, tensile property test, metallographic examination and hardness test. The results show that the thick edge of the induced draft fan blade had a brittle and hard surfacing weld layer. The improper thermal spraying process on the surface of surfacing weld layer resulted in holes in the coating and the interface between the coating and the substrate, which reduced the strength and toughness of the coating and the bonding strength between the coating and the substrate. Under the action of wind pressure, scouring of fly ash and dust, vibration stress, the surface of blade coating or the interface between coating and substrate cracked, and cracks expanded to the inside of blade, resulting in the stress concentration on the thick edge notch of the blade, and the crack expanded to the thin edge of the blade, finally leading to the blade fracture.