Influence of Isothermal Holding on the Microstructure and Mechanical Properties of Electron Beam Welded Dissimilar Inconel 718/ATI 718Plus (R) Joint

摘要

Microstructural changes of the Inconel 718 and ATI 718Plus(R) base materials and the fusion zone caused by the isothermal hold at 760 degrees C for up to 500 h were investigated. The evaluation was performed using a scanning electron microscope with backscattered electrons detector and scanning transmission electron microscopy supported by energy-dispersive x-ray spectroscopy. Furthermore, to evaluate the effect of microstructural changes on mechanical properties Vickers microhardness measurements were performed. Exposure of welded joint at high temperature led to coarsening and/or dissolution of main strengthening phases' particles and nucleation and growth of plate-like precipitates. In the interdendritic region of the fusion zone, the transformation of the Laves phase to a complex cluster of precipitates contained sigma phase had taken place. Analysis of microstructure and microhardness measurements showed that ATI 718Plus has better mechanical properties and microstructural stability at elevated temperature than Inconel 718.