Surface Characteristics of Low Plasticity Burnished Laser Directed Energy Deposition Alloy IN718

The research work focuses on a novel post-processing sequence to improve the surface integrity and residual stress characteristics of as-printed Inconel718 (IN718) samples. The as-printed IN718 samples are subjected to solution treatment at 1050 degrees C, two-step precipitation hardening (@ 720 degrees C for 8 h and @ 620 degrees C for 8 h), and low plasticity burnishing. Two different sequences were attempted. Sequence-1 involves solutionizing -> low plasticity burnishing followed by precipitation hardening, and sequence-2 includes solutionizing -> precipitation hardening followed by low plasticity burnishing. The experimental observations and detailed investigations revealed that the samples processed via sequence 2 exhibited a better surface finish. The microhardness of the samples of sequence 2 is 10% higher than their counterparts in sequence 1. The maximum residual stress of -1375.33 MPa is obtained in sequence 1 as compared to the residual stress of -1100.67 MPa in sequence 2. The influence of the processing sequences on the surface properties has been discussed in detail using the XRD and microstructural characterization supported with EBSD analysis.