Timely and atomic-resolved high-temperature mechanical investigation of ductile fracture and atomistic mechanisms of tungsten

Abstract

Revealing the atomistic mechanisms for the high-temperature mechanical behavior of materials is important for optimizing their properties for service at high-temperatures and their thermomechanical processing. However, due to materials microstructure’s dynamic recovery and the absence of available in situ techniques, the high-temperature deformation behavior and atomistic mechanisms of materials are difficult to evaluate. Here, we report the development of a microelectromechanical systems-based thermomechanical testing apparatus that enables mechanical testing at temperatures reaching 1556 K inside a transmission electron microscope for in situ investigation with atomic-resolution. With this unique technique, we first uncovered that tungsten fractures at 973 K in a ductile manner via a strain-induced multi-step body-centered cubic (BCC)-to-face-centered cubic (FCC) transformation and dislocation activities within the strain-induced FCC phase. Both events reduce the stress concentration at the crack tip and retard crack propagation. Our research provides an approach for timely and atomic-resolved high-temperature mechanical investigation of materials at high-temperatures.

In Situ Observation of the Atomic-scale High-temperature Phase Transition Enhancement Mechanism at the ODS-W Interface

“…Compared with the phase transition behavior of other BCC structural metals at room temperature, W exhibits a strong temperature dependence. The phase transition process near the crack tip under high-temperature tensile conditions is captured and reported by in situ TEM 26 , and the corresponding molecular dynamics (MD) simulations also confirmed that a phase transition occurs in W at high temperature 27 . Therefore, we predicted that the ODS-W alloy has a phase transition under high-temperature tensile stress, and this phase transition effect increases the tensile strength of the alloy.…”

“…Fig. 1(e)shows the schematic of a highresolution transmission electron microscope for high-temperature in situ analysis 26 . diffraction (SAED) pattern of selected area of the sample.…”

Ductile fracture modeling of metallic materials: a short review

“…Thanks to the high-resolution and real-time imaging of this technique it was possible to observe several micro-scale and atomic-scale phenomena leading to the material failure (e.g., dislocation-dominated, twinning-dominated, mechanical annealing, phase transformation). Zhang et al [39] proposed a methodology that adopts a microelectromechanical systems-based thermomechanical testing apparatus that enabled to observe the atomic-scale ductile mechanism in single crystal tungsten at high temperatures. This type of material is characterized by a brittle type of fracture at room temperature, but the failure mechanism shifts to ductile fracture with the increase of the temperature.…”

Effect of twin boundaries on the strength of body-centered cubic tungsten nanowires

“…Tungsten (W) is a refractory BCC metal, which exhibits excellent mechanical properties and outstanding thermal stability, and is mainly used in high temperature structural applications in aerospace, rocket propulsion and nuclear engineering 15,16 . TBs are uncommon in W because of its high stacking fault energy but it has been recently reported by in situ transmission electron microscopy (TEM) observations that twins can develop during deformation in W nanowires [17][18][19] .…”