Strong crystal size effect on deformation twinning

Abstract

Deformation twinning in crystals is a highly coherent inelastic shearing process that controls the mechanical behaviour of many materials, but its origin and spatio-temporal features are shrouded in mystery. Using micro-compression and in situ nano-compression experiments, here we find that the stress required for deformation twinning increases drastically with decreasing sample size of a titanium alloy single crystal, until the sample size is reduced to one micrometre, below which the deformation twinning is entirely replaced by less correlated, ordinary dislocation plasticity. Accompanying the transition in deformation mechanism, the maximum flow stress of the submicrometre-sized pillars was observed to saturate at a value close to titanium's ideal strength. We develop a 'stimulated slip' model to explain the strong size dependence of deformation twinning. The sample size in transition is relatively large and easily accessible in experiments, making our understanding of size dependence relevant for applications.

Atomistic Simulations of Compression Tests on Ni3Al Nanocubes

“…However, in the experiments, the fast, highly correlated, 'laser-like, [7]' dislocation motion during pseudo-twinning would significantly reduce the possibility for their interaction with each other or with stacking faults compared with the more chaotic ODP. Thus, pseudo-twinning seems a natural alternative to the 'avalanche-like' ODP-processes proposed in [14] to explain the lack of strain hardening and the instability causing the strain burst in the closed-loop displacementcontrolled experiments of γ nanocube compression.…”

“…Only recently more work on body centered cubic (bcc), hexagonally closed packed (hcp) and more complex alloys is being performed. [7,10,11] * Corresponding author. Email: erik.bitzek@fau.de Last year, two research groups used a wet-chemical process to extract 200-600 nm sized cubic precipitates from the γ /γ -microstructure of a Ni-based superalloy (CMSX-4) to perform nanocompression tests.…”

“…[3,4] Furthermore, the nature of dislocation-based elementary mechanisms itself may become size-dependent at the nanoscale, where plasticity based on partial dislocations and deformation twinning (DT) can replace bulk-like ordinary dislocation plasticity (ODP). [3,[5][6][7][8][9] Most of the studies on small-scale plasticity were performed on face centered cubic (fcc) metals. Only recently more work on body centered cubic (bcc), hexagonally closed packed (hcp) and more complex alloys is being performed.…”

Strengthening at nanoscaled coherent twin boundary in f.c.c. metals

“…The three flow stresses above, τ m , τ t and τ f , follow the generalized Hall-Petch relationship [39], τ = k 1 + k 2 /d α . In agreement with previous observation, the slope of the deformation twin formation stress is larger than that of the flow stress for partials' glide without twinning in nanograins [17], but is smaller than the slope of Hall-Petch relationship for deformation twins in micrograins [35].…”

Ambient-stable tetragonal phase in silver nanostructures

“…M etal nanoparticles with tailored crystalline phases and internal microstructures (for example, twins and stacking faults) represent a class of promising building blocks in achieving ultrahigh-strength materials [1][2][3][4][5][6][7][8] and efficient catalysts 9 . Controlled synthesis of metal nanoparticles with well-defined compositions, sizes and morphologies has been extensively studied in the last decade [10][11][12][13][14] .…”