细长轴类锻件的缺陷方向通常与轴线平行，因此一般超声检测采用纵波直探头在锻件圆周面上进行扫查。由于细长轴类锻件的直径较小，其圆柱曲界面与探头很难实现完全接触而使得耦合层厚度不均，进而导致超声波透射系数减小以及检测灵敏度下降。为实现对细长轴类锻件缺陷的有效检测，从理论上分析了圆柱曲晶片及曲晶片相控阵的检测原理，提出了曲晶片超声相控阵聚焦技术。通过仿真软件CIVA对常规探头、曲晶片探头以及曲晶片相控阵探头形成的声场聚焦分布规律进行研究，设计加工了曲面对比试块和带人工缺陷的细长轴类小型锻件，开展了平面晶片和曲面晶片的相控阵探头超声检测试验，验证了提出的曲晶片超声相控阵聚焦方法的可行性与合理性，结果表明该方法的检测灵敏度和定位定量精度均优于常规直探头和平晶片相控阵探头的。

Slender-shaft forgings usually have their defects in a direction parallel to the axis. These defects are normally detected by an ultrasonic longitudinal wave straight probe along the forging curved surfaces. As a result of the small diameter of the slender-shaft forging, a tight contact between the curved surface and the probe is difficult to realize, which could lead to different thicknesses of the coupling layer. Thus, a lower ultrasonic transmission coefficient is produced and the ultrasonic detection sensitivity is reduced. In order to realize the effective detection of the defects in slender-shaft forgings, the detection principles of the curved element and phased arrays were analyzed theoretically, and the relevant focusing technique was proposed. The ultrasound field and focusing distribution of the conventional probe, curved element and curved-element phased array probe were investigated by CIVA ultrasonic simulation. Additionally, curved specimens with artificial defects for comparison tests were manufactured and relevant inspection experiments were conducted. It was validated that the proposed technique was suitable for slender-shaft forging detection. The proposed technique had better detection sensitivity, positioning accuracy and quantitative accuracy on slender-shaft forgings compared with traditional straight probe and planar phased array probe.