飞秒激光加工K24高温合金的仿真与试验分析

Numerical simulation and experimental analysis on femtosecond ablation of K24 superalloy

为探究飞秒激光与K24镍基高温合金的作用机理,应用普朗克方程与菲涅尔公式,推导出K24反射率与吸收率随激光脉宽的变化曲线.利用固体力学的线性假设方程,推导出K24高温合金的晶格热容和电子比热.结合简化的一维双温模型,采用有限差分法解析单脉冲飞秒激光与K24高温合金作用过程中电子和晶格的温度变化,基于K24高温合金的蒸发温度推导得出单脉冲飞秒激光作用下合金的理论蚀除深度.用较低频率的激光进行了验证试验.用正交实验分析激光平均功率、焦点进给距离、扫描次数、扫描速度等工艺参数对加工微孔形貌的影响规律.结果表明:扫描速度对加工微孔形貌的影响最大,进给距离次之,而激光能量和扫描次数对微孔形貌的影响较小.研究结果为飞秒激光对高温合金的高质量微孔加工提供了理论和实验基础.

To explore the interaction mechanism between femtosecond laser and K24 Nickel-based superalloy, Planck equation and Fresnel ＇ s formula are employed to derivate variation curve of pulse width dependent reflectivity and absorption coefficient of K24 superalloy. Linear hypothesis taken from solid mechanics is utilized to derivate lattice heat capacity and electronic specific heat coefficient of K24 superalloy. Temperature variation of electron and lattice during single pulse femtosecond laser ablation process is theoretically described by a simplified one dimensional two temperature model and finite difference method. Theoretical single pulse femtosecond laser ablation depth is calculated referring to vaporization temperature of K24 superalloy. Corresponding experiments are carried out to verify the accuracy of simulation results using low pulse frequency. Orthogonal experiments are carried out to investigate the influence rules of several technological parameters on the morphology features of micro holes. Results show that the scanning velocity is of the most significant effect, followed by feed distance, while scanning time and average power have relatively small effects on morphology of micro holes. This work provides theoretical and experimental foundation for the application of femtosecond laser drilling of superalloy.