Deformation Mechanisms in Nanotwinned Tungsten Nanopillars: Effects of Coherent Twin Boundary Spacing

Abstract

Nano-scale coherent twin boundaries (CTBs) significantly alter the mechanical and electrical properties of metallic materials. Despite a number of studies of the nanotwinned nanopillars in face-centered cubic metals, investigations of them in body-centered cubic (BCC) systems are rare. In this Letter, we explore the uniaxial deformation mechanisms of BCC tungsten nanopillars containing nano-scale {112} CTBs using molecular dynamics (MD) simulations. Our work reveals a novel tension-compression asymmetric stress-strain response and deformation behavior, in conjunction with the effects of CTB spacing. With a relatively large CTB spacing, the plastic deformation in nanotwinned nanopillars is mainly controlled by dislocation nucleation from surface/CTB intersections, gliding on distant and adjacent slip planes under tensile and compressive loading, respectively; as a result, the tensile yield stress is almost invariant with respect to the CTB spacing, while the compressive yield stress increases with a decreasing CTB spacing. As the CTB spacing reduces to 1 nm, detwinning, exhibited by annihilation of {112} twin layers as a result of partial dislocations gliding on CTBs, is observed in both tension and compression; at higher strains, however, {111} incoherent twin boundaries, whose resistance to cracking contributes to strain hardening, are formed under tensile loading but not under compressive loading.

Tensile and Compressive Mechanical Properties of Polycrystalline Tungsten–Molybdenum Alloy

“…The EAM potentials proved effective in investigating the mechanical performance of W and Mo. [34][35][36] The simulation models are initially optimized using the conjugate gradient (CG) method and fully relaxed 100 ps at the target temperature under the NPT (where N ¼ number of atoms, P ¼ pressure, and T ¼ temperature) ensemble (0 GPa). Figure 1b reveals the variations of temperature and total energy for the W 50 Mo 50 sample under tension at 300 K. It is evident that the temperature and total energy are stable at the end of relaxation, indicating that the equilibrium of the simulation system is contented.…”

Atomistic simulations of mechanical characteristics dependency on relative density, grain size, and temperature of nanoporous tungsten

“…The mechanical properties of NPW are tested by uniaxial tensile simulation with LAMMPS [46]. The embedded atom method (EAM) potential functions proposed by Zhou et al [47] are adopted to describe the interactions of W-W atoms, which have proven effective by [48,49]. For the energy minimization of NPW samples, the conjugate gradient method is applied.…”

Modeling Plastic Deformation of Nano/Submicron-Sized Tungsten Pillars Under Compression: A Coarse-Grained Atomistic Approach

“…Although {111} planes are the primary slip planes in FCC crystals, dislocations in BCC systems can glide on {110}, {112}, and {123} planes (Weinberger et al, 2013a). However, specifically for W, only dislocation slip on {110} planes was observed in uniaxially deformed 112 -oriented nanopillars/tubes in MD simulations (Xu and Chavoshi, 2018;Xu et al, 2017aXu et al, , 2018a using the same EAM potential (Marinica et al, 2013), plausibly due to the lowest stacking fault energy on {110} planes among all three sets of likely slip planes. The kink pair theory proposed by Butt (2007) also predicts that the primary slip planes at relatively low temperatures (< 220 K) are {110} planes.…”