Selective laser melting of Hastelloy X nanocomposite: Effects of TiC reinforcement on crack elimination and strength improvement

The Hastelloy X (HX) nickel-based superalloy is increasingly applied in the aerospace industry because of its exceptional combination of oxidation resistance and high-temperature strength. The addition of nanoscale ceramic reinforcements to the HX alloy is expected to further improve its mechanical and thermophysical performance. The research challenge is to manufacture HX nanocomposites using additive manufacturing (AM) technologies, particularly selective laser melting (SLM), which has been used successfully to produce other nanocomposites. This paper systematically studies the microstructure and tensile performance of HX-3 wt.% TiC nanocomposite fabricated via SLM and explores the effects of TiC nanoparticles on hot-cracking elimination and strength enhancement. The findings reveal that the addition of 3 wt% TiC nanoparticles resulted in (1) an extra 73 J/mm3 laser-energy density needed to manufacture nearly full-density nanocomposite samples and (2) intergranular microcrack elimination due to the significant increase in grain boundaries induced by the grain refinement. The results showed a 17% increase in yield strength, while the elongation to failure was not significantly reduced. The results from the microstructure examination suggest that the strengthening mechanisms of load bearing and enhanced-dislocation density were the most pronounced mechanisms in the SLM-fabricated nanocomposite. These findings offer a promising pathway to strengthen mechanical performance by addressing the hot-cracking issue in the AM of nickel-based superalloys that suffer from cracking susceptibility. The results can also help to accelerate the uptake of AM in high-performance and defect-free superalloys for various applications.