Abstract：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.
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