Nanoscale-twinning-induced strengthening in austenitic stainless steel thin films

Abstract

Magnetron-sputter-deposited austenitic 330 stainless steel (330 SS) films, several microns thick, were found to have a hardness ∼6.5 GPa, about an order of magnitude higher than bulk 330 SS. High-resolution transmission electron microscopy revealed that sputtered 330 SS coatings are heavily twinned on {111} with nanometer scale twin spacing. Molecular dynamics simulations show that, in the nanometer regime where plasticity is controlled by the motion of single rather than pile-ups of dislocations, twin boundaries are very strong obstacles to slip. These observations provide a new perspective to producing ultrahigh strength monolithic metals by utilizing growth twins with nanometer-scale spacing.

Deformation and spallation of shocked Cu bicrystals withΣ3 coherent and symmetric incoherent twin boundaries

“…In epitaxial nanotwinned Cu, growth twin lamellae have long CTBs normal to the growth direction, and truncated by short SITBs [31,32,34]. The nanotwinned Cu has been shown to exhibit a superior combination of ultrahigh strength, low electrical resistance, good ductility, high thermal stability, and fatigue resistance [31][32][33][34][35][36][37][38][39][40]. The unusual mechanical properties of nanotwinned Cu originate from CTBs, which act as strong barriers to slip transfer of single dislocations (thus, enhancing strength), and simultaneously create more local sites for nucleating and accommodating dislocations (thus, elevating ductility and improving work hardening) [31].…”

“…Recently, Σ3{111} coherent twin boundaries (CTBs) and Σ3{112} symmetric incoherent twin boundaries (SITBs) have attracted considerable attention, since they often form during fabrication of as growth twins and play a crucial role in the mechanical performance of nanotwinned metals [30][31][32][33][34][35][36][37][38][39][40][41][42]. In epitaxial nanotwinned Cu, growth twin lamellae have long CTBs normal to the growth direction, and truncated by short SITBs [31,32,34].…”

Interface structures and twinning mechanisms of twins in hexagonal metals

“…Growth twins form by the nucleation of faulted layers in growth by solidification or during vapor deposition [1][2][3][4][5]. Annealing twins form similarly during recrystallization and grain growth [6,7].…”

Formation of incoherent deformation twin boundaries in a coarse-grained Al-7Mg alloy

“…At the same time, the CTBs enable absorption and transmission of dislocations and hence contribute significantly to macroscopic ductility. 5 Up to now, several methods have been developed for fabrication of nano-twinned materials, such as pulsed electrodeposition, [6][7][8] magnetron sputtering, 9,10 and dynamic plastic deformation (DPD). 11,12 Note that the above mentioned methods are mainly for metals with low stacking fault energy (SFE) or a low ratio of unstable twinning (ut) to unstable stacking energy (us).…”