The effect of 3D printing orientation on tensile behaviour and fracture mechanisms of Inconel 718

Abstract

The manuscript aims to study the effect of 3D printing orientation on the tensile behaviour and fracture mechanisms of samples made of Inconel 718. Components of metals using additive manufacturing techniques are crucial in applications where safety, reliability, and trouble-free operation are essential. Therefore, it is vital to study and understand the behaviour of 3D-printed components under various loading types and predict potential failures. The EOS Nickel Alloy IN718 material sheet provides tensile properties of heat-treated samples (per AMS 5664 procedure) built exclusively in the Z direction. Consequently, the authors extended the investigation to include the tensile behaviour of 3D-printed samples in seven basic orientations within the 3D printing machine's workspace. For this purpose, the mechanical properties of Inconel 718 alloy samples manufactured using Direct Metal Laser Sintering (DMLS) technology were subjected to uniaxial tensile stress. The samples underwent heat treatment according to the AMS 5664 procedure, with solution annealing and aging temperatures determined using a pseudo-binary phase diagram calculated with Thermo-Calc® software. Post-tensile tests and fracture surface observations were conducted to identify the main failure modes. Microstructural and morphological analyses of 3D-printed INCONEL 718 samples were carried out using light optical microscopy (LOM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) textural analysis. Phase diagrams indicate expected phases such as γ-phase (FCC_A1), δ-phase (NbNi3_D0A), γ’’-phase (Ni3Ti_D024), Laves phase (C14_Laves), and γ’-phase (FCC_L12). Solution annealing was performed above 940 °C while aging treatment was done at temperatures below 800 °C to allow precipitation of γ’ and γ’’ phases. The δ phase also forms during aging. Fractographic examination of the tensile fractures indicated a predominantly quasi-ductile failure mechanism, with fine-sized dimples observed. In the XZ-oriented samples, the measured yield strength was 11 % higher compared to the Z-oriented samples and the yield strength was more than 12 % higher. The difference in mechanical properties between the Z orientation (Rp0.2 = 1284 MPa and Rm = 1429 MPa) and the XZ orientation (Rp0.2 = 1436 MPa and Rm = 1613 MPa) can be mainly attributed to the < 101 > texture in the XZ sample and its more equiaxed grain structure compared to the Z sample.