Interest in the correlation between microstructure and properties of compositionally complex alloys (CCAs) has risen owing to their excellent mechanical properties. Additive manufacturing routes have further opened the pathway to obtain both near-net shapes and novel microstructures in these alloys. In this work, single-phase equiatomic CoCrFeNi was reinforced with nanoparticles of TiN and TiO2. The nanoparticles of varying particle sizes (80 nm and 800 nm) and volume fractions (0.5 vol. % and 5 vol. %) were used to enhance the strength and hardness both at cryogenic and room temperature.

Scanning electron microscopy imaging and electron backscatter diffraction revealed columnar grain growth along the building direction with a strong (001) cube texture. Scanning transmission electron microscopy (STEM) equipped with electron energy loss spectroscopy (EELS) was used to investigate the size, distribution, elemental mapping, and oxidation state of the particles. TiN particles are seen to have a strong tendency to form TiOxNy. Furthermore, in-situ straining was performed in the TEM to reveal the deformation mechanisms and to observe the pinning of dislocations due to reinforcing particles.

Additionally, an electrolytic hydrogen charging setup was utilized to evaluate the hydrogen permeability and thermal desorption analysis identified quantitatively the number and kinds of hydrogen trap sites present. Subsequently, in-situ hydrogen charging was performed during the nanoindentation to investigate the hydrogen embrittlement susceptibility in p-CCAs.