Atomic-scale insights into liquid phase sintering of intermittent hot isostatic pressing (HIP) experiments

Abstract

In this work, liquid phase sintering (LPS) process in hot isostatic pressing (HIP) is systematically investigated at atomic scale with the help of advanced spherical aberration correction transmission electron microscope and nanoindentation. Five intermittent HIP experiments of a self-designed 90W-4.2Ni-1.8Fe-4Cu (wt. %) alloy are interrupted and characterized. Together with DSC curve, the pressure-assisted LPS could be divided into two stages, the incipient and fully LPS stages. The results show that the relative density is saturated immediately at the incipient LPS stages and particle rearrangement takes place, leading to the formation of large matrix pools. However, the matrix elements are separated into nano-precipitates during the cooling of liquid phase in the matrix pool. On the other hand, the elements are mixed into a solid solution phase during fully LPS stage, even though the dispersed particles (in our case W) grow bigger and bigger. The mechanical tests show that the solid solution strengthening of matrix phase and redistributed microstructure driven by external hydrostatic pressure and capillary force after fully LPS result in the improved mechanical properties at higher pressure.