Vacuum heat treatment induced excellent low-temperature tensile performance of EAM fabricated 96 W alloys

Abstract

To address the low-temperature performance degradation of tungsten heavy alloys fabricated by extrusion-based additive manufacturing (EAM) process with hydrogen sintering, the vacuum heat treatment was utilized to improve the low-temperature tensile properties of 96 W alloy in this study. The DSC, XRD, SEM, TEM, EBSD were adopted to analyze the thermophysical properties, phase composition, microstructure morphology and lattice mismatch of 96 W-2.8Ni-1.2Fe alloys under different sintering and vacuum heat treatment parameters. Based on the optimized sintering parameters induced high-tensile-performance 96 W alloys, this study investigated their low-temperature performance degradation and low-temperature performance strengthening via vacuum heat treatment under different holding time and temperature. Surprisingly, the hydrogen content change after vacuum heat treatment was found to be inconspicuous, and the results showed that vacuum heat treatment benefited γ phase infiltration at WW interfaces, relieved residual stress from thermal expansion difference, altered W/γ interface structure (lattice mismatch and interface layer thickness) and precipitate size, and promoted nano-twin nucleation. Under optimal vacuum heat treatment parameter 1200 °C-60 min, the low-temperature (−30 °C) tensile strength and elongation of 96 W alloy were 1027 ± 15 MPa and 11.9 ± 1.0 %, which is even superior to the 92 W ∼ 93 W alloys with more ductile phases. These findings distinguish this study from similar researches about tungsten heavy alloys, and make it instructive for the application of EAM and powder metallurgy fabricated tungsten heavy alloys under low-temperature environments.