Tuning heterogeneous microstructures to enhance mechanical properties of nano-TiN particle reinforced Haynes 230 composites by laser powder bed fusion

Laser powder bed fusion (LPBF) is considered to be one of the most promising additive manufacturing technologies for producing components with geometries and high geometrical precision that are unattainable by traditional technologies. The superalloy exhibits exceptional mechanical and high-temperature performances, rendering it a prime candidate for advanced aero-engine applications. Despite the high demand for LPBF-manufactured superalloys, the superalloy is one of the materials manufactured difficultly by LPBF due to their large laser absorptivity fluctuation, poor molten pool stability and sharp temperature gradient. Hence, superalloys are characterized by severe pores, undesirable coarse columnar grains and poor mechanical properties. In this work, the effect of nano-TiN particles on defects, molten pool characteristics and microstructure and performance of the composites were investigated. The 4.5 wt% TiN/Haynes 230 samples exhibited exceptional nanohardness and elastic modulus with maximum values reaching 5.53 GPa and 240.03 GPa, respectively. These superior mechanical properties were attributed to the combined effects of spatter and gas pore inhibition, grain refinement and duplex nano-phases strengthening. Moreover, the stability of molten pool was enhanced, and spatter was effectively suppressed by adding nano-TiN particles, while grain refinement and columnar to equiaxed transitions were promoted. Furthermore, the matrix exhibited a high dislocation density due to a significant hindrance of dislocation movement caused by massive nano-phases (e.g., TiN and M23C6), resulting in the formation of extensive dislocation tangles and rings. This work offers novel insights into the role of nanoparticles reinforced superalloy composites by LPBF.