The effect of laser scanning strategies on the microstructure, texture and crystallography of grains exhibiting hot cracks in additively manufactured Hastelloy X

Abstract

In the present study, grain size and grains exhibiting hot cracks of laser powder bed fusion (LPBF) processed Hastelloy X as-built parts under two scanning strategies i.e., 90° and 45° rotation vectors have been characterized using electron back scattered diffraction (EBSD) technique. EBSD orientation maps revealed relatively finer grain size in 45° scanning strategy as compared to 90° scanning strategy. Laser scanning speed was found to be the governing parameter for variation in grain size as compared to laser power and energy density. Maximum crack density was observed at the highest value of energy density and it appears that energy density has more dominant effect on hot cracking tendency as compared to laser power. At the maximum value of the energy density under 45° scanning strategy, the preferred texture type changes from <001> to <111> orientation. EBSD orientation maps revealed that a specific combination of grains, one of which is stiffer as compared to other, is more susceptible for hot cracks. They are either Goss ({110}<001>), Brass ({110}<112>) or Copper ({112}<111>) oriented grains. It is proposed that these stiffer grains, with high elastic modulus and low capacity of tolerating higher magnitude of thermal strains, paves the way for relieving locked-in thermal stresses during LPBF process.