Effects of solution treatments on the microstructure and mechanical properties of Inconel 625 fabricated by electron beam freeform fabrication

Abstract

The present study investigated the effects of solution treatments on the microstructure and mechanical properties of Inconel 625 fabricated by electron beam freeform fabrication. The results indicated that the microstructure of the as-deposited specimen exhibited typical dendritic characteristics. Meanwhile, the Laves ((Ni,Fe,Cr)2(Nb,Mo,Ti)) phases and needle-shaped δ phases precipitated. The deposition process led to the development of a preferred orientation feature along the building direction, and the typical {001}<100> plate texture was observed. Solution treatments at 900 °C and 1000 °C resulted in the precipitation of more δ phases, and the volume fraction was approximately 5.29 % and 7.96 %, respectively. The precipitated phases fully dissolved at solution temperatures of 1100 °C and 1200 °C, and equiaxed grains with a twin substructure were formed. The recrystallization weakened the preferred orientation, leading to a decrease in grain size and the formation of {111}<1–10> texture. The as-deposited specimen exhibited an ultimate tensile strength (UTS) of 682 MPa, a yield strength (YS) of 410 MPa, and an elongation of 56.4 %. Solution treatment had minimal impact on the UTS, and the YS was mainly contributed by the solid solution strengthening. However, the elongation was greatly improved at elevated solution temperatures, and the elongation was increased to 72.1 % at most. The primary mode of fracture was toughness fracture, which was attributed to the coalescence of microvoids. The solution treatment at 900 °C led to a fracture pattern that exhibited a combination of toughness and brittleness, and decreased the elongation to 48.5 %.