某钻井用钛合金挠性轴在钻进一段时间完钻起钻后，其变径靠近插接端处出现光亮带，通过受力分析、宏观与微观形貌观察、化学成分分析、力学性能测试、有限元模拟等方法对光亮带出现的原因进行了分析，提出了延长钛合金挠性轴寿命的方法。结果表明：挠性轴变径处发生微动磨损，剪切应力以及挠性轴主体部分与插接部件间的相对位移是导致微动磨损的主要原因；微动磨损导致裂纹在挠性轴变径处萌生，在交变载荷及扭矩的作用下，裂纹扩展并造成了微动疲劳；裂纹起源为周边均匀起源，扩展方式为穿晶扩展。采用超音速火焰喷涂技术制备涂覆层后，钛合金的表面硬度和耐磨性能提高，这对于由微动磨损引起的周边起源性裂纹具有抑制作用，从而延长了挠性轴的寿命。

A titanium alloy flexible shaft for drilling had a bright band at the reducer near the plug end after a period of drilling and start-up. The cause of the bright band was analyzed by force analysis, macroscopic and microscopic morphology observation, chemical composition analysis, mechanical property test, and finite element simulation. The method of prolonging the life of titanium alloy flexible shafts was put forward. The results show that fretting wear occurred at the reducer of the flexible shaft, and the fretting wear was mainly caused by the shear stress and the relative displacement between body part of flexible shaft and plug parts. The fretting wear resulted in the initiation of cracks at the reducer of the flexible shaft. Under the alternating load and torque, the cracks propagated, resulting in the fretting fatigue. The cracks originated uniformly from the periphery and propagated with transgranular forrn. The surface hardness and wear resistance of the titanium alloy increased after the coating layer was prepared by supersonic flame spraying technique, which could restrain the peripheral origin cracks caused by fretting wear, thus prolonging the life of the flexible shaft.