Hot compression behavior and microstructure of selectively laser-melted IN718 alloy

Abstract

The integration of additive manufacturing into traditional manufacturing processes presents the future of engineered components with similar or superior performance levels to wrought or cast materials. In this work, the hot-deformation behavior and the microstructural changes of heat-treated SLM-printed IN718 specimens are investigated. Samples having the same shape and size were 3D-printed, homogenized (1100 °C, 1 h, and furnace-cooled), and hot-compressed, using a Gleeble® 3800 physical simulator at 1000 and 1050 °C and 0.1 and 0.01 s−1 strain rates. A 3D diagram showing the effect of temperature and strain rate on the flow stress behavior of IN718 during hot deformation is plotted. The dynamic recrystallization (DRX) mechanism was dominant in all specimens tested at 0.1 s−1, while dynamic recovery (DRV) dominated in 0.01 s−1 tests. Changing the strain rate from 0.01 to 0.1 s−1 at 1000 °C increased the peak stress from 150 to 290 MPa (93%), while with a temperature decrease from 1050 to 1000 °C at 0.1 s−1, the peak stress increased by 45%. Thus, the mechanical behavior was found to be more dependent on the strain rate than on the temperature. The DRX structure showed new grains developing at the boundaries of the original grains, whereas with the DRV structure, new grains grew within the original grains. A phenomenological model based on the Zener-Hollomon parameter was proposed in order to predict the size of recrystallized grains during hot deformation of the SLM-printed IN718 superalloy. The thermal softening due to recrystallization was compensated by precipitation hardening, as was revealed by phase analysis.