熔模精密铸造技术广泛应用于高温合金叶片生产。 高温合金单晶叶片铸件尺寸精度高, 内部和表面不得有缺陷, 但在浇铸时易受浇铸温度场、 熔体流场及与模壳发生界面反应的影响而导致表面结瘤、 凹陷、 缩孔等缺陷。 激光诱导击穿光谱(LIBS) 是一种非常有效的表面及界面分析技术, 对于诊断分析铸件表面/界面质量具有明显的优势, 对样品损伤小, 可对不平整表面进行分析。 研究优化了LIBS深度分析的条件, 采用2 mm孔径光阑分光, 500 mJ, 1 064 nm脉冲高斯激光在焦外激发单晶高温合金获得了良好的空间分辨力, 降低了能量密度较低的二级以上衍射环能量辐射造成表层烧蚀引起的深度分析信号失真。 体积烧蚀速率与激光输出能量线性正相关, 与光阑直径正相关, 与激发频率无关。 采用LIBS技术对DD407高温合金单晶叶片表面和近表面进行了深度分析。 发现SiO2-Al2O3莫来石结构的型壳在铸造过程中会引起DD407单晶叶片表面和近表面的Al, Ti, Ni, Cr, Co贫化, 其中Al和Ti贫化显著且深度达50 μm。 铸件尖锐部位较厚大部位的合金元素贫化明显。 叶片经过脱芯脱壳后表面沉积钙镁盐类、 钠盐物质。 通过沸水清洗和超声清洗后, 钠盐完全去除, 钙镁物质均大幅减少, 仍有3~5 μm厚。 LIBS可方便的进行合金铸件表面和界面的成分分布分析, 给出表面/界面质量的清晰判据, 展现了较好的应用前景。

The investment precision casting technology is widely adopted in manufacturing superalloy castings. Single crystal superalloy casting blades have high precision in dimension, without inner defects and surface defects. Knobs, pits and shrinkage cavity on surface of castings are caused by unsuitable temperature field, melted alloy flow field, and interface reaction of melted alloy with ceramic shell. The laser induced breakdown spectroscopy (LIBS) is an efficient surface and interface analysis technique, with obvious advantage in diagnosis of casting surface/interface, with micro destruction, independent on surface planeness of sample. The parameters were optimized in depth analysis of single crystal superalloy by LIBS. A good spatial resolution has been obtained at 2 mm aperture, 500 mJ of output energy and off focus radiation with 1 064 nm pulse Gaussian laser beam; meanwhile spectrum signal distortion brought from ablation and excitation of surface by exceeding secondary diffraction ring with low laser energy density was reduced. Ablated volume per pulse was linear to output of laser energy with good correlation, positively correlated to the aperture diameter, independent on shot frequency. Depth analysis of surface and interface of single crystal superalloy blade was performed by LIBS. Alloy depletion of Al, Ti, Ni, Cr and Co in DD407 single crystal blade was observed with significant depletion of Al and Ti up to 50 μm depth, using SiO2-Al2O3 ceramic shell with mullite phase in cast process. The alloy depletion of edge of the blade was more outstanding than thick part. Precipitation of calcium salt, magnesium salt, sodium salt and carbon matters on blade surface occurs after dissolution to remove ceramic shell and ceramic core. Sodium salt has been removed completely after washed with boiling water and ultrasonic washing; most of calcium matters, magnesium matters and carbon matters have been removed and small amount remained in 3~5 μm depth. LIBS is efficient in terms of composition-depth distribution analysis of alloy casting surface and interface, providing surface/interface quality criteria and presenting bright application prospect.