Characteristics and mechanisms of multiple pulsed laser drilling of blind-holes in Inconel 718 alloy

This study investigates the fabrication of blind holes in Inconel 718 alloy using a quasi-continuous wave (QCW) laser under varying pulse numbers. The geometric features, spatter formation, inner wall morphology, and microstructures of the drilled holes were systematically analyzed. Experimental results demonstrate that increasing the number of laser pulses from 1 to 13 significantly improves the hole depth, ranging from 565.09 to 3952.54 μm, achieving a maximum depth-to-diameter ratio of 9.5. Shallow holes exhibited optimal morphology with clean edges and smooth inner walls, whereas deeper holes displayed a composite structure consisting of inverted cone (upper), cylindrical (middle), and spindle-shaped (lower) sections. The thickness of the recast layer increased along the depth as the pulse numbers rose. Microstructural analysis revealed that the recast layer contained refined grains, with kernel average misorientation analysis indicating high residual stress within this layer. The hardness of the recast layer, measured at 2.13 GPa, was notably lower than that of the base material (4.49 GPa), primarily due to the depletion of the strengthening phase and the formation of the Laves phase. This work provides an in-depth understanding of the characteristics and mechanisms of QCW laser drilling in Inconel 718 alloy, offering valuable insights to optimize the laser processing parameters for industrial applications.