Inherent Strain Modelling and Neutron Diffraction Stress Analyses in Invar-10wt%TiCN Manufactured by Laser Powder Bed Fusion

In this study, the residual stress state of an Invar-10wt%TiCN composite was evaluated through experimental non-destructive neutron diffraction (ND) of the FeNi phase and inherent strain modelling (ISM) simulations. Comparisons were made to the stress state of FeNi in Invar to investigate the degree of change in the alloy due to the addition of the TiCN. The materials were fabricated using laser powder bed fusion (LPBF) according to a full factorial Central Composites Design of Experiments approach to develop the optimal process parameters. High densities of 99.87% for Invar and 99.28% for Invar-10wt%TiCN were achieved, with the TiCN addition leading to a hardness improvement of approximately 71.8%. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were done to study the microstructure. The TiCN resulted in a high distortion of 113% in the ISM cantilever sample due to its higher coefficient of thermal expansion. Close agreement was found between the ISM simulation and the ND experimental residual stress results. The stresses are predominantly compressive in the interior and tensile on the surfaces. This agreement enabled extrapolations of the estimated stresses in the near-surface regions. Magnitudes are dependent on the stress component considered and build position. Grain refinement in the Invar-TiCN composite enhanced the compressive residual stresses.