Simulation of precipitates evolution driven by non-isothermal cyclic thermal history during wire and arc additive manufacturing of IN718 superalloy

Abstract

For wire and arc additive manufacturing (WAAM) of IN718 superalloy, predicting the evolution of precipitates driven by non-isothermal cyclic thermal history has been guiding significance for tailoring the manufacturing process to obtain satisfactory microstructure and properties. Based on the thermodynamic calculation for IN718 superalloy and the thermal simulation for multi-layers & multi-passes WAAM process, the simultaneous transformation kinetics (STK) model derived from the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory was used to simulate the evolution of precipitates in the WAAM process. The evolution and final spatial distribution characteristics of different precipitates in the WAAM sample were investigated. When the time subdivision increment of thermal history is between 0.1∼0.4 s, the phase fraction calculated by the STK model tends to be stable. The macro distribution of constituent phases on the middle section of the 8-layers & 10-passes WAAM sample is inhomogeneous. In particular, the strengthening phases γ’/γ” precipitate more in the middle and upper region than that in other regions of the WAAM sample, and this result is indirectly evaluated by the distribution of micro-hardness. Moreover, in the last one or two passes of the WAAM sample, the NbC is depleted and the brittle Laves phase is enriched, which means that the regions where WAAM processing ended are likely to become the performance weak region of the whole part.