Unusual two-step dealloying mechanism of nanoporous TiVNbMoTa high-entropy alloy during liquid metal dealloying

In this study, 3D interconnected nanoporous (3DNP) TiVNbMoTa HEAs were synthesized from the (TiVNbMoTa)(25)Ni-75 as-cast precursor alloy using the liquid metal dealloying (LMD). The as-cast precursor demonstrated the initial dendritic microstructure consisting of fcc and hcp phases. At 600 degrees C after 1 h, tiny ligaments about 10 nm thickness were homogeneously synthesized. At 900 degrees C, the bulk transformation intensively took place at the original precursor alloy. Specifically, the dendritic morphology of the original phases disappeared, and the fraction of fcc phase decreased from 63% to 20%. This pre-transformation behavior significantly influences the dealloying mechanism. Kurdjumov eSachs orientation relationship (OR) governed the ligament formation at the prior fcc phase while Pitsch-Schrader (PeS) OR controlled the ligament evolution at the prior hcp phase. An unusual mechanism of two-step dealloying was observed at the fcc phase region when the dealloying rate was decreased at the reaction front. The dissolution of Ni occurs by stepwise transformations of fcc->hcp->bcc. The prior fcc grain was transformed to the abnormally large hcp ligaments and tiny bcc ligaments. Then, the abnormal hcp ligaments were further dealloyed to smaller bcc ligaments following the PeS OR. This study pave the way for the design of compositionally complex porous materials with a customized morphology and advanced physical properties by dealloying. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

In this study, 3D interconnected nanoporous TiVNbMoTa HEAs were synthesized using liquid metal dealloying. Pre-transformation behavior significantly influences the dealloying mechanism, and two different orientation relationships were observed to affect ligament formation. This research paves the way for designing complex porous materials with customized morphology and advanced physical properties.