THE EFFECT OF HEAT TREATMENT ON THE STRUCTURE OF THE SLM OF THE INCONEL 718 ALLOY

Abstract

The current study investigates the effects of the selective laser melting (SLM) and homogenization (as a part of following solution heat treatment) on the structure and hardness of austenitic iron-nickel base Inconel 718 superalloy. The microstructure of the selective laser melted alloy 718 in an as- manufactured condition consists of "knitted pattern" layers typical for SLM. Moreover, there are long vertical dendrites, stretched towards build direction through multiple layers. The forming of that long dendrites is probably caused by the small build size, and combination of layers cooling rate and laser second moving speed in the current point. That leads to the crystallization of the layer below into the vertical dendrites. The homogenization of SLM Inconel 718 has leaded to some loss of microhardness caused by dissolving of hardening phases. After the homogenization the structure still include both "knitted pattern" layers and the vertical dendrites. To measure the fraction of the dendrites is difficult, according to low accuracy of their boundaries in the structure after the homogenization. Following investigations will include influence of the sample size on the structure and properties of the Inconel 718 superalloy.