The plastic deformation micro-mechanisms of extruded pure Zn deformed in tension along the extrusion direction were investigated by means of in situ scanning electron microscopy (SEM) integrated with electron back-scatter diffraction (EBSD). Plastic deformation began with the activation of < a > basal slip in grains with the highest Schmid factor while, the incompatibility of deformation between neighbour grains was accommodated by grain boundary sliding. The geometrically necessary dislocation density increased sharply from 1.53 x 10(13) m(-)(2) to 9.03 x 10(13) m(-)(2) when applied strain reached 6.7%, and this increase coincides with the strong initial strain hardening region. The incompatibility of deformation between neighbour grains was accommodated by grain boundary sliding at strains above 3.3%, which somehow limited the strain hardening rate. Evidence of < c + a > pyramidal II slip was also found through slip trace analysis from the early stages of deformation, i.e. 1.6% strain, but it was always limited to a small fraction of suitably oriented grains. Moreover, transmission electron microscopy (TEM) observations showed that many < c + a > pyramidal dislocations were dissociated into the basal plane and became sessile. {[Math Processing Error]}<[Math Processing Error]> compression twins were nucleated at 3.3% strain and the fraction of grains undergoing twinning as well as the area fraction of twins increased proportionally to the applied strain. Twinning was favoured by the fiber texture and the twin variant with the highest Schmid factor was primarily activated in each grain. The contribution of twinning to the total strain was limited (around 11% when the applied strain was 16.7%). The strain hardening rate decreased sharply beyond 6.7% and the hardening contribution of basal slip was balanced by grain boundary sliding and compression twinning. Finally, a high fraction of sub-grain boundaries that trigger recrystallization at larger strains was found at 16.7%. These observations reveal the sequence and interaction of plastic deformation mechanisms in Zn, which may help design novel Zn alloys with improved mechanical properties.
A deterministic finite automaton (DFA) is composite if its language can be decomposed into an intersection of languages of smaller DFAs. Otherwise, A is prime. This notion of primality was introduced by Kupferman and Mosheiff in 2013, and while they proved that we can decide whether a DFA is composite, the precise complexity of this problem is still open, with a doubly-exponential gap between the upper and lower bounds. In this work, we focus on permutation DFAs, i.e., those for which the transition monoid is a group. We provide an NP algorithm to decide whether a permutation DFA is composite, and show that the difficulty of this problem comes from the number of non-accepting states of the instance: we give a fixed-parameter tractable algorithm with the number of rejecting states as the parameter. Moreover, we investigate the class of commutative permutation DFAs. Their structural properties allow us to decide compositionality in NLOGSPACE, and even in LOGSPACE if the alphabet size is fixed. Despite this low complexity, we show that complex behaviors still arise in this class: we provide a family of composite DFAs each requiring polynomially many factors with respect to its size. We also consider the variant of the problem that asks whether a DFA is k-factor composite, that is, decomposable into k smaller DFAs, for some given integer k. We show that, for commutative permutation DFAs, restricting the number of factors makes the decision computationally harder, and yields a problem with tight bounds: it is NP-complete. Finally, we show that in general, this problem is in PSPACE, and it is in LOGSPACE for DFAs with a singleton alphabet.
Magnesium alloys stand as promising candidates for orthopedic implants due to their biodegradability, which eliminates the need for secondary removal surgery and potentially reduces hospital care costs. However, the biodegradation of magnesium alloys AZ31 and ZK60A in vivo may occur before bone implants stabilize. Therefore, the objective of this study was to enhance the corrosion resistance and cytocompatibility of two magnesium alloys through coating treatments. Specifically, both alloys, AZ31 and ZK60A, were exposed to surface modification by plasma electrolytic oxidation (PEO) in a sodium metasilicate and potassium hydroxide-based electrolyte. Subsequently, polylactic acid (PLA) was applied using a dip-coating method. Comprehensive physical and chemical characterizations of the materials were conducted. The coatings exhibited a thickness of approximately 3.7 mu m with pore sizes ranging from 0.8 to 1.4 mu m. The PEO-PLA coatings significatively reduced the degradation rate. In particular, PEO-AZ31and ZK60-PEO exhibited a 93 % and 95 % reduction, respectively, in hydrogen evolution compared to bare metals. In addition, the AZ31 coating demonstrated superior corrosion resistance in a simulated biological fluid (SBF). Moreover, the coated ZK60 and AZ31 alloys displayed enhanced cell viability when compared to the uncoated alloys. The AZ31-PEO-PLA and ZK60-PEO-PLA samples exhibited mitochondrial activity greater than 80 % at dilutions greater than 1:2. As a result, PEO-PLA films were proposed as a physical barrier to corrosion.
Intumescent flame-retardant (IFR) systems are attractive alternatives to conventional halogenated flame retardants due to their halogen-free composition, efficiently reduced heat release, and low toxicity generation. Herein, a nitrogen-boron (N-B) dual-element flame retardant, melamine borate (MB), was synthesized and subsequently incorporated into a UV-curable resin based on bis(2-methacryloxyethyl) phosphate to construct a ternary synergistic N/P/B IFR coating system. The structure, thermal stability, and flame-retardant properties of the resulting coatings were systematically investigated by various techniques and combustion tests. Increasing MB content raised the glass transition temperature (Tg), indicating enhanced network compactness and stability. The coating containing only 4 wt% MB achieved a UL-94 V-0 rating and exhibited a 56.35 % reduction in total smoke production (TSP), along with significantly improved thermal stability in terms of decomposition temperature and char residue. The synergistic contributions of phosphorus, nitrogen, and boron promote catalytic charring, gas release, and glass-phase reinforcement, leading to the formation of a dense, stable char barrier. This eco-friendly ternary IFR system overcomes the high loading requirements and toxicity concerns of conventional flame retardants, providing a promising strategy for the efficient and sustainable flame-retardant modification of polymeric coatings.
Lattice materials are widely used in many fields requiring lightweight structures with tunable properties. Designing an optimal architecture remains a challenging task due to a vast parameter space and resources required to numerically evaluate the performance of candidate structures. This study presents a workflow the optimization of 3D lattices constructed by a combination of different cell topologies. It combines genetic algorithm, mechanical simulations, and a 3D convolutional neural network. The workflow was tested two objectives: optimization for the maximum average specific elastic modulus between X, Y, and Z directions and optimization for the maximum in only one direction. The optimized lattices demonstrated up to 91.5% increase in specific elastic modulus compared to the pure single-type composition. The two tested objectives converged to distinct patterns: the single-direction case led to the formation of column-like features, while average between three directions favored more diverse designs. The proposed approach can be adapted the optimization of other physical properties or material types.
