Study on location-related thermal cycles and microstructure variation of additively manufactured inconel 718

The complicated thermal history of wire + arc additive manufacturing (WAAM) will affect the microstructure variation and mechanical properties of the as-deposited material. Numerial models of Inconel 718 in WAAM deposition were established and the location-related thermal history and temperature distribution were analyzed. A hybrid method of WAAM and cold rolling was investigated and its effect on the microstructure distribution and texture was investigated compared to that in as-deposited condition. The results show that WAAM deposition features repeated thermal cycles, high heating rate and low cooling rate. The trough values of the thermal cycles first increases and then decreases, while the peak temperature always decreases with the proceeding of the deposition process. The as-deposited samples show columnar dendrites and its average dendrite arm spacing increases with the increased build height due to the location-related heat accumulation. The strongly textured columnar dendrites with preferred <001> orientation transform to equiaxed grains with random orientation in heat-affected zone after cold rolling process, and its average size decreases with the increased rolling force. The as-deposited samples show the strongest intensity of 7.609 for the {100} family of grains oriented along the transverse direction; while it decreases to 3.629 and 2.057 for the cold rolled conditions with the force of 50 kN and 75 kN, respectively. The relationship between thermal history and the microstructure distribution was discussed. The mechanism of hybrid WAAM and cold rolling method consisted of spatially and temporally heterogeneous work hardening and recrystallization.