Post-processing of laser-directed energy deposited IN718 superalloys through combined heat treatment and shot peening: Microstructural evolution and wear resistance enhancement

Abstract

While the laser-directed energy deposition (LDED) technique is extensively employed for repairing and fabricating complex components, LDED-fabricated IN718 superalloys parts frequently exhibit inadequate wear resistance. This study systematically investigates the combination effects of heat treatment strategies (i.e., direct double aging (DA) and solution + double aging (SDA) treatments) and shot peening (SP) on the microstructural evolution and 600 °C wear performance of LDED-fabricated IN718 alloys. The aging regime promotes the complete precipitation of γ″/γ′ phases, while the prior solution treatment in the SDA process achieves concurrent dissolution of most Laves phases and partial recrystallization. SP converts surface tensile stress into compressive stress, reaching –1030.67 MPa in SDA + SP. Additionally, SP induces a work-hardened layer with a depth of ∼ 250 μm and a ∼ 500 nm thick nanograin layer at the topmost surface. The grain nanocrystallization is attributed to the simultaneous action of dislocations, twins, stacking faults, and Lomer-Cottrell (L-C) locks. The synergistic effects of grain refinement, work hardening, and γ″/γ′ precipitation collectively endow the SDA + SP sample with optimal sliding wear performance at 600 °C, exhibiting a 14.8 % reduction in average coefficient of friction and a remarkable 78.9 % decrease in wear rate compared to the as-received sample. This performance enhancement correlates with a transition in wear mechanisms to predominantly abrasive and oxidation-dominated regimes under elevated temperature conditions.