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This work presents the results of deposition by magnetron sputtering nanostructured multilayer Cr/(Cr/a-C)ml coatings on AISI 316L and AISI 321 steel substrates. Chemical compositions were confirmed through EDX analysis with scanning electron microscopy. The coating thickness was measured with Calotester (KaloMAX II) and the total thickness of the coatings obtained ranged from 1.684 ± 0.193 μm for AISI 316L to 1.749 ± 0.123 μm for AISI 321. A Daimler-Benz Rockwell indentation test for adhesion quality and a nanoindentation test with a Berkovich indenter were carried out. According to the Raman spectroscopy analysis and in agreement with mechanical tests, it is supposed that it is the formation of a diamond-like carbon phase which enhances the mechanical properties. The hardness values obtained for the nanostructured multilayer Cr/(Cr/a-C)ml coatings were improved compared to those of the base stainless steels.

Comparative analysis of nanostructured multilayer Cr/(Cr/a-C)ml coatings on HS6-5-2 steel was carried out. The coatings were deposited at various chromium target power values using PVD technology, particularly the magnetron sputtering method. The effect of different technological regimes on the properties of the nanostructured multilayer Cr/(Cr/a-C)ml coatings was studied. Identical characterization methods were used for the three types of coatings obtained. Cross-sections of the coated samples were prepared in order to directly determine the thickness of the resulting coatings, their uniformity, and the presence of defects or imperfections, both at the substrate–coating interface and within the coatings themselves. Calotest and Daimler-Benz adhesion test were also performed to evaluate the coated layers’ thickness and evaluate their adhesion strength. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses were carried out to define the chemical composition of the multilayered coatings. To evaluate the hardness and modulus of elasticity of the resulting coatings, nanoindentation measurements were also conducted. The data obtained under the three different deposition regimes were analyzed and compared, which allowed us to assess the influence of the chromium target power during the deposition process on the properties of the obtained coatings.

The article considers issues related to improving the surface characteristics of titanium Gr2 using one of the lightest, cheapest and most ecological methods—electrospark deposition with low pulse energy and with ultradisperse electrodes TiB2-TiAl with nanosized additives of NbC and ZrO2. Using profilometric, metallographic, XRD, SEM and EDS methods, the change in the geometric characteristics, composition, structure, micro and nanohardness of the coatings as a function of the electrical parameters of the ESD regime has been studied. The results show that the use of TiB2-TiAl electrodes and low pulse energy allows the formation of dense, continuous and uniform coatings that demonstrate a significant reduction in roughness, inherent irregularities and structural defects of electrospark coatings. Coatings with minimal defects, with crystalline–amorphous structures, with newly formed intermetallic and wear-resistant double and triple phases of the type AlTi3, TiAl3, TiB, TiN0.3, Al2O3, AlB2, TiC0.3N0.7, Ti3.2B1.6N2.4, Al2.86O3.45N0.55 have been obtained. Possibilities have been found for controlling and obtaining specific values for the roughness and thickness of coatings in the ranges Ra = 1.5–3.2 µm and δ = 8–19.5 µm, respectively. The electrical parameters of the modes ensure the production of coatings with previously known thickness and roughness, with increased microhardness up to 13 GPa, with the maximum possible content of deliberately synthesized high-hard phases and with ultra-fine-grained structures have been defined.

Test specimens fabricated from 42CrMo4 steel were subjected to heat treatment comprising quenching followed by high-temperature tempering. This treatment is commonly referred to as hardening, and the result is a tempered sorbite microstructure that provides a balanced combination of strength and plasticity. In order to improve the hardness and wear resistance of the contact surfaces, two types of physical vapor deposition (PVD) coatings were deposited onto the specimens: the first was a two-component architecture Cr/CrTiAl and the second was a multilayer Cr/(CrTiAl)N/CrTiAl. In both configurations, an intermediate chromium adhesion layer was initially deposited to enhance interfacial bonding with the substrate. The adhesion strength of the deposited coatings to the steel substrates was evaluated using a standardized adhesion test. The adhesion quality was classified as HF1 (the highest adhesion class in the HF1–HF6 scale, defined in EN ISO 26443), indicating excellent interfacial bonding. The hardness and modulus of elasticity of both coatings were determined through nanoindentation. According to the measured hardness values of the two coatings, 27.3 GPa (Cr/CrTiAl) and 37.5 GPa (Cr/(CrTiAl)N/CrTiAl), they can be classified as hard coatings (hardness greater than 20 GPa). Despite the difference in hardness, the two coatings have comparable elastic modulus values: Eit = 353 GPa for the two-component architecture coating and Eit = 349 GPa for the three-component architecture coating. Tribological characterization was performed using the ball-on-disc method under dry sliding conditions over a total sliding distance of 59 m, whereby the friction coefficient (µ) was recorded. Additionally, the wear rate of the applied coatings was calculated from the measured wear volumes or profiles. The two coatings have comparable friction coefficient values (Cr/CrTiAl–μ = 0.362, Cr/(CrTiAl)N/CrTiAl–μ = 0.325), but the three-component architecture coating Cr/(CrTiAl)N/CrTiAl has a lower wear rate (k = 1.64 × 10−4) compared to the two-component architecture coating Cr/CrTiAl, which has a wear rate of k = 7.6 × 10−4. The investigated coatings have hardness, modulus of elasticity and friction coefficient values competitive with those of nitride coatings (two-component architecture and three-component architecture), and their wear rate also corresponds to generally accepted values.

Magnetron-sputtered coatings consisting of multiple alternating layers of chromium and amorphous carbon (Cr/a-C)ml were deposited on HS6-5-2 steel with an intermediate chromium layer by varying deposition rates. Three series of coatings, S1, S2, and S3, with thicknesses of 1.74, 1.15, and 1.14 μm and average chromium contents of 89.3, 66.0, and 59.7 wt.% Cr, respectively, were obtained. Open-circuit potential, cyclic potentiodynamic measurements, and electrochemical impedance spectroscopy were used to characterize their corrosion resistance in 3.5% NaCl. The surfaces were observed with optical and scanning electron microscopy before and after the corrosion tests, and changes in the elemental composition were monitored by energy-dispersive spectroscopy. The protective properties of coatings from series S2 and S3 are similar and significantly better than those of S1. They are characterized by a corrosion current below 1 μA cm–2 and a stable passive state up to over 0.9 VAg/AgCl. The coatings have cathodic behavior towards the substrate, and when the coatings are damaged, galvanic corrosion causes deep pits. Coatings deposited at lower rates and with higher carbon content demonstrate significantly enhanced corrosion resistance in 3.5% NaCl. All three series of Cr/(Cr/a-C)ml@HS6-5-2 exhibit identical corrosion behavior after compromising the coatings’ integrity.

A challenging problem for autonomous systems is to synthesize a reactive controller that conforms to a set of given correctness properties. Linear temporal logic (LTL) provides a formal language to specify the desired behavioral properties of systems. In applications in which the specifications originate from various aspects of the system design, or consist of a large set of formulas, the overall system specification may be unrealizable. Driven by this fact, we develop an optimization variant of synthesis from LTL formulas, where the goal is to design a controller that satisfies a set of hard specifications and minimally violates a set of soft specifications. To that end, we introduce a value function that, by exploiting the LTL semantics, quantifies the level of violation of properties. Inspired by the idea of bounded synthesis, we fix a bound on the implementation size and search for an implementation that is optimal with respect to the said value function. We propose a novel maximum satisfiability encoding of the search for an optimal implementation (within the given bound on the implementation size). We iteratively increase the bound on the implementation size until a termination criterion, such as a threshold over the value function, is met.

With respect to the corrosion-protective and decorative characteristics of the Cu-Ni-Cr systems the advance of the technology resulted in products covering the required technical and economic norms and indicators. However, the knowledge about the mechanical characteristics such as elastic and plastic properties of the individual layers and the whole multilayered system is still sparse. The objective of this study is to obtain by means of nanoindentation experiments the mechanical characteristics of standard triple Cu-Ni-Cr coating system whose morphology, structure, texture, composition, and the copper-, nickel- and chrome-layer thickness are predefined. A series of nanoindentation tests in vertical direction to the layered coating and in the lateral direction (along a vertical cut) is analyzed to assess the changes of the mechanical properties of the investigated system in depth and along the layer as well as at layer-to-layer and layer-to-substrate interfaces.

#SMT, or model counting for logical theories, is a well-known hard problem that generalizes such tasks as counting the number of satisfying assignments to a Boolean formula and computing the volume of a polytope. In the realm of satisfiability modulo theories (SMT) there is a growing need for model counting solvers, coming from several application domains (quantitative information flow, static analysis of probabilistic programs). In this paper, we show a reduction from an approximate version of #SMT  to SMT. We focus on the theories of integer arithmetic and linear real arithmetic. We propose model counting algorithms that provide approximate solutions with formal bounds on the approximation error. They run in polynomial time and make a polynomial number of queries to the SMT solver for the underlying theory, exploiting “for free” the sophisticated heuristics implemented within modern SMT solvers. We have implemented the algorithms and used them to solve the value problem for a model of loop-free probabilistic programs with nondeterminism.

Extensions to finite-state automata on strings, such as multi-head automata or multi-counter automata, have been successfully used to encode many infinite-state non-regular verification problems. In this paper, we consider a generalization of automata-theoretic infinite-state verification from strings to labelled series–parallel graphs . We define a model of non-deterministic, 2-way, concurrent automata working on series–parallel graphs and communicating through shared registers on the nodes of the graph. We consider the following verification problem: given a family of series–parallel graphs described by a context-free graph transformation system (GTS), and a concurrent automaton over series–parallel graphs, is some graph generated by the GTS accepted by the automaton? The general problem is undecidable already for (one-way) multi-head automata over strings. We show that a bounded version, where the automata make a fixed number of reversals along the graph and use a fixed number of shared registers is decidable, even though there is no bound on the sizes of series–parallel graphs generated by the GTS. Our decidability result is based on establishing that the number of context switches can be bounded and on an encoding of the computation of bounded concurrent automata that allows us to reduce the reachability problem to the emptiness problem for pushdown automata.

The article considers issues related to improving the surface characteristics of titanium Gr2 using one of the lightest, cheapest and most ecological methods-electrospark deposition with low pulse energy and with ultradisperse electrodes TiB -TiAl with nanosized additives of NbC and ZrO . Using profilometric, metallographic, XRD, SEM and EDS methods, the change in the geometric characteristics, composition, structure, micro and nanohardness of the coatings as a function of the electrical parameters of the ESD regime has been studied. The results show that the use of TiB -TiAl electrodes and low pulse energy allows the formation of dense, continuous and uniform coatings that demonstrate a significant reduction in roughness, inherent irregularities and structural defects of electrospark coatings. Coatings with minimal defects, with crystalline-amorphous structures, with newly formed intermetallic and wear-resistant double and triple phases of the type AlTi , TiAl , TiB, TiN , Al O , AlB , TiC N , Ti B N , Al O N have been obtained. Possibilities have been found for controlling and obtaining specific values for the roughness and thickness of coatings in the ranges Ra = 1.5-3.2 µm and δ = 8-19.5 µm, respectively. The electrical parameters of the modes ensure the production of coatings with previously known thickness and roughness, with increased microhardness up to 13 GPa, with the maximum possible content of deliberately synthesized high-hard phases and with ultra-fine-grained structures have been defined.