Comparative analysis of cold and warm rolling on tensile properties and microstructure of additive manufactured Inconel 718

Abstract

Despite the high efficiency and low cost of wire + arc additive manufacture (WAAM), the epitaxial grown columnar dendrites of WAAM deposited Inconel 718 cause inferior properties and severe anisotropy compared to the wrought components. Fundamental studies on the influence of one-pass cold and warm rolling on hardness and microstructure were investigated. Then the interpass cold and warm rolling on tensile properties were also analyzed. The results show that the one-pass rolling increases the hardness and displays a heterogeneous hardness distribution compared to the as-deposited material, and the warm rolling exhibits a larger and deeper strain compared to cold rolling. The columnar dendrites gradually change to cell dendrites under the rolling process and then change to equiaxed grains with the subsequent new layer deposition.The average grain size is 16.8 μm and 23.5 μm for the warm and cold rolling, respectively. The strongly textured columnar dendrites with preferred <001> orientation transform to equiaxed grains with random orientation after rolling process. The grain refinement contributes to the dispersive distributed strengthening phases and the increase in its fraction with heat treatment. The as-deposited samples show superior tensile properties compared to the cast material but inferior compared to the wrought components, while the warm-rolled samples show superior tensile properties to wrought material. Isotropic tensile properties are obtained in warm rolling compared to cold rolling. The rolling process and heat treatment both decrease the elongation and lead to a transgranular ductile fracture mode. Finally, the rolling induced strengthening mechanism was discussed.

Directed energy deposition + mechanical interlayer deformation additive manufacturing: a state-of-the-art literature review

“…Figure 35 depicts the main interlayer deformation systems, which can be classified by the deformation temperature (cold and hot) and the deformation type (rolling and peening/hammering/forging). It is worth noting that rolling is a unique deformation process executed under a wide range of temperatures, as indicated by Martina et al [169] (cold, 25-150 °C), Zhang et al [92,158,185] (warm, ~ 450 °C), and Zhang et al [32] (hot, > 900 °C). Peening and hammering were adopted in the vast majority of cases in cold deformation conditions, while forging is commonly used in a hot deformation condition [111].…”

“…In addition, the tensile properties of Inconel 718 at elevated temperatures (649 °C) must also be considered for high-temperature applications, such as jet turbine blades and the nuclear industry [157]. In this scenario, only the warm rolling material [92,158,185] met the AMS 5662 requirements despite all DED + deformation conditions also improving the material properties concerning DED. Zhao et al [79] (Ni60 alloy) and Li et al…”