Effect of rolling force on tensile properties of additively manufactured Inconel 718 at ambient and elevated temperatures

Inferior mechanical properties and severe anisotropy behavior of wire + arc additive manufactured (WAAM) Inconel 718 due to the large epitaxial grown columnar dendrites restrict the industrial application of WAAM deposition. Cold rolling was integrated into the WAAM deposition process and the effect of rolling force on microstructure, precipitatation distribution and tensile properties at ambient and elevated temperatures were investigated. The results show that the hardness of cold-rolled samples is much larger than that of the as-deposited and it increases with the increase in the rolling force. The columnar dendrites of the as-deposited sample changed to finer equiaxed grains of 26.5 and 14.7 μm after cold rolling with the force of 50 kN and 75 kN, respectively. Meanwhile, more uniformly distributed grains and less δ phase appear for 75 kN rolled sample. The stress-strain curves are smooth for the tensile tests at ambient temperature, while there are serrations at elevated temperature due to the dynamic strain aging behavior. The as-deposited sample shows inferior tensile properties to the wrought material at ambient and elevated temperatures. The cold-rolled samples both exceed the wrought material at ambient temperature; however, they show higher strength but lower elongation compared to the wrought material. The 75 kN cold rolled sample shows much higher strength and similar elongation to the wrought material for the test at elevated temperature. The grain morphology and recrystallization, as well as the strengthening mechanism of hybrid deposition and cold rolling process were discussed.