Optimum process parameters of IN718 alloy fabricated by plasma arc additive manufacturing using Taguchi-based grey relational analysis

The process parameters of IN718 alloy fabricated by plasma arc additive manufacturing (PAAM) were evaluated by Taguchi-based grey relational analysis, and the microstructure and mechanical properties of the PAAM alloy were analyzed to verify the optimized process parameters. The results show that the influence of each process parameter on the dilution ratio and forming coefficient is consistent. Based on the results of Taguchi-based grey relational analysis, the optimized process parameters for PAAM IN718 alloy are plasma arc current 115 A, scanning rate 1000 mm/min, powder feeding rate 16 g/min, and shielding gas flow 800 L/h. The plasma arc current and powder feeding rate play primary roles in the dilution rate and forming coefficient of PAAM IN718 alloy. With the optimized process parameters, the forming and internal crack of the PAAM IN718 alloy is controlled. The microstructure of PAAM IN718 alloy is dominated by temperature gradient and constitutional supercooling, which is sequentially transformed from cellular crystal in the bottom region to coarse columnar dendrite and equiaxed crystal in the top region. Laves phase exhibits a concentration gradient that gradually increases from top to bottom on the cross-section from the range 11.3-18.6 vol%. Due to the solid solution strengthening of Nb/Mo elements and dispersion strengthening by gamma '' phase, the microhardness and tensile strength of PAAM alloy after full heat treatment reach about 500 HV and 1284 MPa, respectively. These are satisfactory mechanical properties compared to other additive manufactured IN718 alloys, and PAAM is suitable to prepare IN718 alloy to obtain favorable microstructure and mechanical properties.