Ti6Al4V钛合金脉冲激光抛光微裂纹产生机理与尺寸特征研究
Mechanism and Size Characteristics of Micro Crack on Polished Ti6Al4V

为研究脉冲激光抛光过程中微裂纹产生机理及抛光主要参数对微裂纹尺寸特征的影响规律,建立了脉冲激光抛光温度场与应力场的有限元计算模型。在有限元模型建立过程中,采用温度场与应力场的顺序耦合方式,考虑了相变潜热和随温度显著变化的材料参数,得到了温度场与应力场在时间上和空间上的变化规律。通过温度场、应力场以及Ti6Al4V钛合金的凝固过程分析,揭示了Ti6Al4V钛合金激光抛光过程中微裂纹产生机理与尺寸特征规律。通过脉冲激光抛光实验验证有限元计算模型的有效性,结果表明:Ti6Al4V钛合金激光抛光微裂纹产生于Ti6Al4V钛合金的凝固时刻,微裂纹的宽度决定于Ti6Al4V钛合金凝固时刻热应力引起的塑性变形,微裂纹的深度决定于Ti6Al4V钛合金激光抛光熔池深度;激光功率是微裂纹尺寸特征的主要影响因素,激光功率增大时微裂纹宽度及深度均显著增大;在脉冲激光抛光中可通过外加预热的方式减缓熔融态金属的冷却速度,以减小抛光后的表面裂纹,有效减小微裂纹尺寸特征。
The mechanism and size characteristics of micro crack on polished surface of Ti6Al4V are discussed by numerical simulation and experimental investigation. The latent heat of material phase change and material parameters varying with temperature are considered in this model. The change rules of temperature and stress fields in time domain and space domain are acquired and the finite element model is verified by experiments. The micro cracks generation mechanism and size characteristics of pulse polished Ti6Al4V are revealed via analysis of temperature field, stress field and solidification processes of the Ti6Al4V. The micro cracks of laser polishing are formed at solidification initiation moment, and the width of micro cracks is determined by plastic deformation and the micro crack depth depends on depth of molten pool. The laser power exerts the most significant influence on the size characteristics of micro cracks. The width and depth of the micro cracks all obviously increase with the increasing laser power. The cooling rate of the molten metal can be slowed down by preheating in the pulse laser polishing process to effectively decrease the size of micro cracks