Influence of high detonation pressure on the structural, microstructural and mechanical behaviour of IN718 superalloy: numeric simulation vis-à-vis experimental explosive shock processing

Micro-sized IN718 superalloy powder with an average particle size of 70 μm has been explosively shock-processed with high pressure of the order of 41.3 GPa. A hydrocode, AUTODYNE-2D, with Eulerian mesh is used to simulate and to compute the detonation pressure, particle velocity and shock pressure on the superalloy in the reactive zone. The grazing shock pressure at different regions in the compaction system has been calculated and compared with the experimental work. Axisymmetric cylindrical compaction geometry has been used for the shock-loading of IN718 superalloy. The shock pressure at different points was calculated experimentally by pin-oscillography with the help of electrical as well as fibre optical probes. Wide-angle X-ray diffraction study indicates the intact crystalline FCC structure within the shock-processed specimen having dominating (gamma )[Ni-Cr-Fe] and strengthening (gamma^prime)[Ni3(Ti,Al)] phases. Laser diffraction particle size measurement points towards the reduced particle size of the shock-loaded specimen. The Line-broadening Williamson-Hall method shows a very small amount of locked-in microstrain of the order of 0.23%. Energy-dispersive analysis using X-ray examination shows no evidence of any chemical segregation within the compacts. Field-emission scanning electron microscopy shows satisfactory sub-structural strengthening and desired morphology at different regions in the fractographs of the compacted specimen without melting of the core of the specimen. Micro-indentation testing at variable loads of 0.98, 1.96 and 4.9 N shows a good hardness of the order of 642 Hv. The monolith cut-along the consolidation axes show tensile and compressive strengths of the order of 1.126 and 1.04 kN mm–2, respectively. Uniform crack/void-free compacts have been obtained with a density close to 99.2% of the theoretical value with negligible porosity. Graphical abstract