A novel method enhanced mechanical properties of a selective laser melted Mar-M247 superalloy by progressive remelting

A novel method has been proposed to avoid the cracks in the Mar-M247 alloy manufactured via selective laser melting (SLM) related to high cooling rate interacted with carbides and eutectics, i.e., progressive remelting used to design the temperature field reducing the thermal stresses in SLM process. The microstructure evolves from a partly fused state to a completely solid block during progressive remelting, and those cracks inhibit effectively. The temperature gradient is gradually reduced in the process of progressive remelting, and eventually 29% lower than that in original SLM process. Quantitative temperature-field analysis signifies a substantial decrease in the cooling rate during manufacturing via progressive remelting, which explains crack inhibition. Compared to the original SLM-built Mar-M247, progressive remelting leads to a 35.1% increase in ultimate tensile strength (UTS) at RT. The UTS and elongation of progressive remelted Mar-M247 exhibit 747.2 MPa and 6.1% at 900 °C, respectively, superior to that of materials fabricated by casting and heat-treatment. This work helps further comprehend the relationship of volumetric energy density - thermal gradient - cooling rate - microstructure - mechanical properties, especially utilizing accumulative input energy to control temperature field, and offers a new opportunity to non-weldable superalloys fabricated in commercially available SLM systems.