Laser Weld-Induced Formation of Amorphous Mn–Si Precipitate in 304 Stainless Steel

We first report the formation of partially amorphous Mn–Si precipitates due to laser welding of face centered cubic (fcc) 304 stainless steel. Transmission electron microscopy and precession electron diffraction studies in the heat affected zone (HAZ) of the weldment indicate the formation of Mn–Si precipitates in grain interiors. Precipitates exhibit Mn–Si stoichiometry and the partially crystalline regions have a lattice constant of 0.45 nm. It is surmised that the rapid cooling rates during the laser weld melt pool solidification process may be sufficient to inhibit the complete crystallization of these precipitates

Directly Probing the Fracture Behavior of Ultrathin Polymeric Films

Understanding fracture mechanics of ultrathin polymeric films is crucial for modern technologies, including semiconductor and coating industries. However, up to now, the fracture behavior of sub-100 nm polymeric thin films is rarely explored due to challenges in handling samples and limited testing methods available. In this work, we report a new testing methodology that can not only visualize the evolution of the local stress distribution through wrinkling patterns and crack propagation during the deformation of ultrathin films but also directly measure their fracture energies. Using ultrathin polystyrene films as a model system, we both experimentally and computationally investigate the effect of the film thickness and molecular weight on their fracture behavior, both of which show a ductile-to-brittle transition. Furthermore, we demonstrate the broad applicability of this testing method in semicrystalline semiconducting polymers. We anticipate our methodology described here could provide new ways of studying the fracture behavior of ultrathin films under confinement