TiAl合金涡轮压缩损伤与拉伸断裂行为

Compression Damage and Tensile Fracture Behavior of TiAl Alloy Turbine

摘要:

为研究TiAl合金涡轮经压力作用后的组织损伤机制及性能弱化规律,设计了对TiAl合金涡轮先压缩再拉伸的实验方法。利用扫描电镜(SEM)对压缩后的涡轮轴颈表面及内部的滑移和微裂纹进行了分析,并观察了拉伸断口形貌。实验结果表明：随着前期涡轮所受的压力的增大,压缩后的TiAl涡轮剩余抗拉强度逐渐降低,当压力为610 MPa时,剩余抗拉强度仅为86 MPa,强度损失率高达70%。TiAl合金压缩过程中形成了以沿层裂纹为主、穿层裂纹为辅的变形损伤特征。与压缩轴成45°的最大剪应力方向上的沿层裂纹是TiAl合金压缩损伤的主要形式。压缩损伤后的TiAl合金涡轮拉伸断裂均发生在靠近涡轮浇铸冒口侧的细轴颈部位。受压变形后的片层组织中的微小裂纹在随后拉应力作用下继续扩展直至韧带桥被贯穿,小裂纹合并成大裂纹,在断口上表现出沿层和穿层的混合断裂形貌。

Abstract:

To study the mechanism of structure damage and the law of performance weakening of TiAl alloy turbine under pressure, an experimental method is designed that compresses and then stretches the TiAl alloy turbine. The slips and microcracks on the surface and inside of the compressed turbine journal are analyzed by scanning electron microscope (SEM), and the tensile fracture morphology is observed. The experimental results show that the residual tensile strengths of the compressed TiAl turbines gradually decrease as the pressure on the turbine. When the pressure reaches 610 MPa, the residual tensile strength is only 86 MPa, and the strength loss rate is as high as 70%. During the compression process of TiAl alloy, the deformation damage characteristics, which are mainly inter-lamellar cracks and supplemented by trans- lamellar cracks, are formed. Lamellar cracks in the direction of maximum shear stress at 45 ° to the compression axis are the main form of compression damage found in the TiAl alloy. The tensile fracture of TiAl alloy turbine after compression damage occurred at the thin journal near the casting riser side of turbine. The microcracks in the lamellar structure after compression deformation continue to expand under the subsequent tensile stress until the ligament bridge is penetrated, and the small cracks merge into large cracks, resulting in a mixed fracture morphology along the layer and through the layer on the fracture surface.