小规格钛合金棒材的超声波探伤中，成分偏析类缺陷的判定是一难点。在 9.0 mmTC4钛合金磨光棒材的探伤中，发现一次底波与等边三角波之间存在游动回波，解剖分析属于合金成分偏析缺陷。TC4钛合金中合金元素贫化偏析区域与基体的声阻抗值相差很小，属透射类缺陷；同时这种缺陷使声波衰减，具有在一次底波信号之后出现游动回波的特点。并指出成分偏析缺陷可以大致分为两类：一种是与基体组织声阻抗相差较大的反射类缺陷；一种是与基体组织声阻抗相差很小的透射类缺陷。建议在小规格钛及钛合金棒材的超声波探伤中，关注一次底波与等边三角波之间的波形情况，避免漏检可能存在的透射类成分偏析缺陷。

To decide the defect of composition segregation is difficult in the ultrasonic inspection of small diameters titanium alloy bars. Wandering echo is observed between the bottom wave and equilateral triangle wave on inspecting the TC4 diameter 9mm titanium alloy bars. Through dissecting the bars, there is composition segregation with alloying agent-depleted zone in the titanium alloy. The character of the defect is its acoustic impedance similar to that of parent mateial, which belongs to penetrant defect. The sound beam is attenuated while passing through the defect, resulting in that the echo wave appears between the primary bottom wave and equilateral triangle wave. There are two types of defects of composition segregation: one is penetrant defect whose acoustic impedance is similar to that of parent mateial,the other is reflected defect whose acoustic impedance is different to ones.It is important to observe the echo wave appearing between the primary bottom wave and equilateral triangle wave in oder to avoid failing to detect the penetrant defect of composition segregation.