The Influence of the Process Parameters on the Densification and Microstructure Development of Laser Powder Bed Fused Inconel 939

Abstract

This work aims to investigate the effect of the process parameters on the densification and microstructure of Inconel 939 (IN939) alloy processed by laser powder bed fusion (LPBF). IN939 is a Ni-based superalloy with high creep and corrosion resistance that can be used up to around 850 °C under load, resulting in higher operative temperatures than the ones commonly allowed for Inconel 718 and Inconel 625 alloys (around 650 °C). However, this alloy can suffer from poor weldability involving possible crack formation. In order to minimize the residual porosity and the cracking density, specific process parameters were investigated. The parameters to generate IN939 samples almost pores-free (porosity ≤0.22%) with a cracking density ≤1.36 mm/mm2 as well as samples almost crack-free (≤0.10 mm/mm2) with limited residual porosity (≤0.89%) were determined. The microstructure revealed fine dendritic/cellular structures with the formation of sub-micrometric phases. A high concentration of these phases was also found along the intergranular cracks, suggesting that their presence, coupled to the high thermal stresses, can be the primary reason for crack formation during the LPBF process.

Keywords

• Ni-based superalloys
• Inconel 939
• additive manufacturing
• laser powder bed fusion
• cracking mechanisms