Laser additive manufacturing of ultrafine TiC particle reinforced Inconel 625 based composite parts: Tailored microstructures and enhanced performance

Laser metal deposition (LMD) additive manufacturing process was applied to produce ultrafine TiC particle reinforced Inconel 625 composite parts. The effects of laser energy input per unit length (LEIPUL) on microstructure development, densification response, and mechanical performance including wear performance and tensile properties were comprehensively studied. A relationship of processing conditions, microstructural characteristics, mechanical performance, and underlying strengthening mechanisms was proposed for a successful LMD of high-performance Inconel based composite parts. It revealed that using an insufficient LEIPUL of 33 kJ/m lowered the densification behavior of LMD-processed parts, due to the appearance of residual large-sized pores in inter-layer areas of the parts. An increase in LEIPUL above 100 kJ/m yielded the near fully dense composite parts after LMD. On increasing LEIPUL, the TiC reinforcing particles became significantly refined and smoothened via the elevated melting of particle surfaces and the dispersion state of ultra-fine reinforcing particles was homogenized due to the efficient action of Marangoni flow within the molten pool. The dendrites of Ni-Cr γ matrix underwent a successive change from an insufficiently developed, disordered microstructure to a refined, ordered microstructure with the increase of LEIPUL. However, the columnar dendrites of the matrix were coarsened apparently at an excessive LEIPUL of 160 kJ/m because of the elevated thermalization of the input laser energy. The formation of the refined columnar dendrites of Ni-Cr γ matrix combined with the homogeneously distributed ultra-fine reinforcing particles contributed to the enhancement of wear performance of LMD-processed composites with a considerably low coefficient of friction (COF) of 0.30 and reduced wear rate of 1.3×10−4 mm3/N m. The optimally prepared TiC/Inconel 625 composite parts demonstrated a ductile fracture mode with a sufficiently high tensile strength of 1077.3 MPa, yield strength of 659.3 MPa, and elongation of 20.7%. The superior tensile properties of LMD-processed parts were attributed to the significant grain refinement effect of the matrix during laser processing and the efficient prohibition of ultrafine reinforcing particles on the mobility of dislocations.