Cracking in laser additively manufactured W: Initiation mechanism and a suppression approach by alloying

Highlights: • Nanopores segregation at grain boundaries was responsible for crack initiation in laser additively manufactured W. • The nanopores originated from the tungsten oxides vaporization during solidification process. • Cracks were reduced by 80% in the built W-6Ta alloy. • Submicron intragranular cellular structure was identified in the W-Ta alloy. • The cellular structure contributed to crack reduction by not only trapping the nanopores but also toughening the grains. -- Abstract: Cracking represents the main challenge for exploiting tungsten in additive manufacturing. In this study, laser powder-bed-fusion technique was applied to additively manufacture tungsten. In the built bulks, the grain boundaries were found to be rich in nanoscale gas pores. On the basis of that, a nanopore segregation induced cracking initiation mechanism was proposed. In order to control cracks, W-6wt.%Ta alloy was produced and the cracking suppression mechanism was investigated. The W-6Ta alloy is characterized by a submicron intragranular cellular structure, which composed large amount of interlocked dislocations as revealed by transmission electron microscopy. Owing to the cellular structure, the nanopores were trapped inside grains, which can reduce the cracking possibility. Moreover, the W-Ta alloy possesses higher strength (by 17%) and higher energy dissipation rate (by 52%) than pure tungsten, which both are beneficial for crack reduction.