Study of additively manufactured Inconel 718 with lanthanum zirconate coating

This study examines the thermal and mechanical stability of lanthanum zirconate thermal barrier coating with additively manufactured and wrought Inconel 718 substrates under thermal exposures (800 degrees C, 1130 degrees C, 1600 degrees C). The coatings exhibited strong interfacial adhesion, with strengths of 7 MPa for AM Inconel 718 and 9 MPa for wrought Inconel 718. Interfacial adhesion strength is attributed to the micro-cracks and pores that exist in the coating and at the interface of topcoat and bond coat. During thermal exposure at 800 degrees C and 1130 degrees C, LZ coatings reduced substrate core temperatures by 50-60 %, maintaining them below 650 degrees C for over 94 and 60 cycles, respectively. Under plasma plume exposure at 1600 degrees C, the coated substrates withstood 29 cycles while maintaining temperatures around 980 degrees C, preserving mechanical integrity. The AM coated specimen sustained almost eight cycles more than the counter-wrought specimen. LZ-coated AM Inconel 718 demonstrated superior tensile strength (1253 MPa) and ductility (28.2 %) compared to uncoated samples (1115 MPa, 18.5 %) after exposure to 1130 degrees C. Microhardness increased by 7 % (483 HV0.5), and the coatings helped in recrystallizing the microstructure and retaining gamma ' and gamma '' strengthening phases while limiting delta-phase and carbide formation. LZ-coated AM Inconel 718 withstood similar to 113 thermal cycles at 800 degrees C and 87 at 1130 degrees C, outperforming wrought Inconel 718 (76 cycles). LZ coating with the additively manufactured Inconel718 minimized thermally grown oxide thickness (20 mu m) due to the formation of a diffusion barrier layer (Al2O3) at the interface and substrate having a coarser grain compared to the wrought counterpart. Enhancing adhesion during thermal cycling. These results highlight LZ coatings' potential to enhance thermal stability and mechanical reliability in AM Inconel 718, making them suitable for aerospace and power generation applications.