Microcracking in additively manufactured tungsten: Experiment and a nano-micro-macro multiscale model

Abstract

Microcracking is a prevalent and critical issue in additively manufactured tungsten, significantly restricting its safety-critical engineering applications. Till now, most of our current knowledge about microcracking is based on the observation after additive manufacturing (AM) processing, the real-time evolution of microcracking is still largely unexplored, which is challenged by the complex multi-physics and multiscale nature of AM. To gain deeper insights, a multiscale model is developed in the current work, which integrates a multiphysics thermal-fluid model to consider the solidification process and the evolution of temperature, a crystal plasticity model to explore the evolution of dislocations and stress, as well as an atomistic simulation informed cohesive zone model to consider the microcracking at grain boundary (GB). The simulation results show great agreement with in-situ and ex-situ AM experiments of tungsten. The real-time microcracking evolution at GB in the grain-size scale is captured. It is found that the transverse microcracks that traverse the entire GB typically form after multiple scan tracks. A phase diagram is obtained to correlate microcrack density with scanning speed and power. The effect of non-Schmid effect, GB strength and substrate preheating are also systematically analyzed. This work advances the understanding of microcracking mechanisms in AM, offering valuable guidance for improving the fabrication process to mitigate microcrack formation.