Spatter removal characteristics and spatter prevention during laser percussion drilling of aerospace alloys

The aerospace industry has been employing laser drilling to produce high quantity closely spaced holes in turbine engine components for effusion cooling. However, laser drilled holes are inherently associated with the deposition of spatter as the ejected material resolidifies and adheres around the periphery of the holes. This article presents an investigation on the effectiveness of an antispatter composite coating (ASCC) for the drilling of closely spaced array (2 mm hole pitch) holes in three aerospace materials (IN 100, Nimonic PK 33, and 263 alloys) with an optical fiber delivered 400 W Nd:YAG laser. The ASCC, comprised of a mixture of ceramic filler particles embedded in a silicone elastomer matrix, was applied on the surfaces of the alloy substrates before laser percussion drilling. The work shows that the ASCC effectively prevents the spatter deposition such that laser drilled through holes are produced while maintaining the as-received surface characteristic when using either $O2$ or Ar assist gas. The spatter prevention mechanism and the characteristic of the ASCC have been investigated. Contact angle analysis revealed that the contact angles for the ASCC and one of alloys (Nimonic 263) were 118° and 46°, respectively. Such a difference was identified to be primarily due to the low surface tension of the silicone elastomer matrix. The thermal resistance of the ASCC was increased due to the embedding of the ceramic particles, which absorb a significant proportion of the heat generated by the ejected molten material and prevented the coating from being burned away.