Dense and fine grained IN718 superalloy additively manufactured by cold spraying with N₂ gas at 10 MPa

As compared with high-energy beam based additive manufacturing technologies, cold spraying is capable to deposit metals of fine grain and without compositional segregation. However, expensive He gas is usually needed for the metals with relatively high hardness such as IN718 superalloy. Moreover, although various heat treatment was done to tailor the mechanical properties, especially to increase the ductility of cold sprayed IN718, the elongation still cannot meet the requirement for industry applications. In this work, low-cost N₂ is employed to deposit IN718 at gas pressure and temperatures of 10 MPa and 1000 °C, respectively. Effect of the post-spray heat treatment parameters on the microstructure and tensile properties was also examined. Results show the IN718 deposits with a relative density as high as 99.95 %, which is even higher than those by He cold spraying and laser-based additive manufacturing technologies. Due to the particle impact induced localized dynamic recrystallization, the deposit reveals a dual sized grain distribution with an average size of only 0.78 μm. Due to the greatly refined microstructure, the IN718 deposit has a high room temperature ultimate tensile strength (UTS) of 792 ± 44 MPa, but poor elongation of only 0.37 ± 0.01 %. After solution treatment at 1100 °C for 2 h and double aging (720 °C × 2 h + 620 °C × 2 h), the average grain size increases to 2.9 μm, which is still much smaller than that of PM counterparts. Both strength and plasticity are notably improved after the heat treatment. A yield strength of 1085 ± 22 MPa, UTS of 1352 ± 32 MPa, and the elongation up to 15.2 ± 0.22 % are achieved. The present work proves that the high-quality IN718 of fine grain can be additively manufactured by cold spraying with N₂ as the spraying gas.