Effect of different heat treatments on the microstructure and mechanical properties in selective laser melted INCONEL 718 alloy

The microstructure and tensile properties of selective laser melted (SLM) Inconel 718 alloy were studied in the as-printed and different heat treat conditions. The SLM as-print microstructures exhibited columnar grain structures with very fine dendritic structure with segregation of elements. Apart from the standard heat treatment, three other heat treat cycle variants were carried out in an attempt to remove the extensive segregation of elements and modify the textured grain structure of the SLM as-print microstructure. Increasing the homogenization temperature reduced the segregation and coarsened the grain structure. However, the grains still remained columnar, and the material became softer with reduction in strength. After the ageing treatment, the tensile strength improved significantly for all the heat treated samples, which is typical for precipitation hardening of IN718 alloy. The microstructures of the heat treated samples exhibited the needle shaped delta, carbides, and finely dispersed gamma', gamma' phases.