Population Diversity in Ant-inspired Optimization Algorithms

Finding a balance between exploration and exploitation is very important in the case of metaheuristics optimization, especially in the systems leveraging population of individuals expressing (as in Evolutionary Algorithms, etc.) or constructing (as in Ant Colony Optimization) solutions. Premature convergence is a real problem and finding means of its automatic detection and counteracting are of great importance. Measuring diversity in Evolutionary Algorithms working in real-value search space is often computationally complex, but feasible while measuring diversity in combinatorial domain is practically impossible (cf. Closest String Problem). Nevertheless, we propose several practical and feasible diversity measurement techniques dedicated to Ant Colony Optimization algorithms, leveraging the fact that even though analysis of the search space is at least an NP problem, we can focus on the pheromone table, where the direct outcomes of the search are expressed and can be analyzed. Besides proposing the measurement techniques, we apply them to assess the diversity of several variants of ACO, and closely analyze their features for the classic ACO. The discussion of the results is the first step towards applying the proposed measurement techniques in auto-adaptation of the parameters affecting directly the exploitation and exploration features in ACO in the future

Anodic oxidation of the Ti-13Nb-13Zr alloy

This work presents the results of the investigations on the electropolishing and anodic oxidation of the Ti–13Nb–13Zr titanium alloy. Electropolishing was conducted in the solution containing ammonium fluoride and sulfuric acid, whereas the solution of phosphoric acid was used for anodic oxidation of the alloy. The influence of electropolishing and anodization process parameters on the texture (scanning electron microscopy (SEM)) and chemical composition (X-ray photoelectron spectroscopy (XPS)) of the surface layer was established. Electrochemical impedance spectroscopy in 5 % NaCl solution was used for the determination of the corrosion resistance of the alloy

The Turnover Cycle of Capital in Small and Medium-Sized Enterprises from the Construction Sector Listed on Newconnect

The dynamics of small and medium-sized enterprises play a key role in the development of the Polish economy. These entities are essential for the sustainable functioning of the economy, allowing one to benefit from the effects of the dynamic development of future generations. In the first part of the article the diagnostics on the liquidity of a company is presented. Then liabilities turnover, receivables turnover cycle and inventory turnover cycle are briefly characterized. In the second part of the article issues concerning cash management are discussed. Proper capital management is a major media to a company and added value because it improves efficiency and contributes to the proper planning in terms of financial requirements and the rational obligations incurred. The third part of the paper verifies the effectiveness of usability indicators to determine the time length of the cycle. Using the indicators discussed a company obtains information about the levels of cash to enable it to minimize maintenance costs

Microstructure Evolution and Mechanical Stability of Retained Austenite in Thermomechanically Processed Medium-Mn Steel

A microstructure evolution of the thermomechanically processed 3Mn-1.5Al type steel and mechanical stability of retained austenite were investigated during interrupted tensile tests. The microstructural details were revealed using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) techniques. It was found that the strain-induced martensitic transformation began in central regions of the largest blocky-type grains of retained austenite and propagated to outer areas of the grains as the deformation level increased. At rupture, the mechanical stability showed only boundaries of fine blocky grains of γ phase and austenitic layers located between bainitic ferrite laths. The effects of various carbon enrichment, grain size, and location in the microstructure were considered. The martensitic transformation progress was the highest at the initial stage of deformation and gradually decreased as the deformation level increased

Microstructure Evolution and Mechanical Stability of Retained Austenite in Medium-Mn Steel Deformed at Different Temperatures

The temperature-dependent microstructure evolution and corresponding mechanical stability of retained austenite in medium-Mn transformation induced plasticity (TRIP) 0.17C-3.1Mn-1.6Al type steel obtained by thermomechanical processing was investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) techniques. Specimens were deformed up to rupture in static tensile tests in the temperature range 20–200 °C. It was found that an increase in deformation temperature resulted in the reduced intensity of TRIP effect due to the higher stability of retained austenite. The kinetics of strain-induced martensitic transformation was affected by the carbon content of retained austenite (RA), its morphology, and localization in the microstructure

Metallurgical Characterization of Welded Joint of Nanostructured Bainite: Regeneration Technique versus Post Welding Heat Treatment

One of the main limitations in application of nanostructured carbide-free bainite as a construction material is the difficulty of joining. This research presents a structural characterization of welded joints of medium carbon 55Si7 grade steel after the welding process with a regeneration technique as well as post welding heat treatment (PWHT). The hardness distribution of the welded joint with regeneration exhibit an overall decrease in hardness when compared to the base material and a significant decrease in hardness was observed in the heat-affected zone (HAZ). Unfavorable hardness distribution was caused by the presence of diffusion-type transformations products (pearlite) in the HAZ and bainite degradation processes. On the other hand, welding with the PWHT promotes the achievement of a comparable level of hardness and structure as in the base material. However, a slight decrease in hardness was observed in the weld zone due to the micro-segregation of the chemical composition caused by the indissoluble solidification structure. Based on the structural analysis, it was found that steel with relatively low hardenability (55Si7) should be welded using PWHT rather than a regeneration technique

Two design strategies for enhancing the thermal stability of bainitic structures

In response to the growing interest of the industry in advanced high-strength steels subjected to extreme operating conditions, two novel grades BainTS and BainNiAlCu bainitic steels have been developed. Since the in-use properties of bainitic steel are directly related to the thermal stability of the bainitic structure, two different alloy design concepts to improve tempering resistance considering various strengthening mechanisms were proposed. BainTS steel follows the standard assumptions of nanocrystalline bainitic steel design, where the retained austenite is stabilized with silicon. A potential secondary hardening was also considered using Cr, Mo, and V alloying additives. On the other hand, BainNiAlCu steel was designed taking into account the precipitation strengthening with intermetallic compounds (nickel aluminide and copper particles). It was revealed that both steels after heat treatment consist of bainitic ferrite laths and a significant content of retained austenite (above 25%) with film and blocky morphologies. After the tempering process (350 °C–650 °C), there was significant structural evolution following the gradual decomposition of the metastable bainitic structure. It was proved that BainTS steel is characterized by the higher thermal stability of both bainitic ferrite and retained austenite compared to BainNiAlCu. Despite this, the hardening effect after tempering BainNiAlCu steel was higher (by about 140 HV compared to heat treatment, approx. 30% increase). The presented results suggest that bainitic steels strengthened with intermetallic phases are extremely promising in the context of future industrialization in applications where operating conditions are exposed to elevated temperatures.The authors would like to acknowledge Dr. Andrzej Żak (Wrocław University of Science and Technology) for his support in conducting part of the investigations and for valuable proofreading. This work was supported by the National Science Centre (Preludium Project, No. 2020/37/N/ST8/03324, title: “The concept of high-strength, thermal stable nanostructured bainitic steel with increased weldability”). Part of the investigations was carried out with the support of The Polish National Agency for Academic Exchange, The Bekker Programme, title: “Modeling of the multi-phase structure of nanostructured bainitic steels focused on improving their technological properties"

Two design strategies for enhancing the thermal stability of bainitic structures

In response to the growing interest of the industry in advanced high-strength steels subjected to extreme operating conditions, two novel grades BainTS and BainNiAlCu bainitic steels have been developed. Since the in-use properties of bainitic steel are directly related to the thermal stability of the bainitic structure, two different alloy design concepts to improve tempering resistance considering various strengthening mechanisms were proposed. BainTS steel follows the standard assumptions of nanocrystalline bainitic steel design, where the retained austenite is stabilized with silicon. A potential secondary hardening was also considered using Cr, Mo, and V alloying additives. On the other hand, BainNiAlCu steel was designed taking into account the precipitation strengthening with intermetallic compounds (nickel aluminide and copper particles). It was revealed that both steels after heat treatment consist of bainitic ferrite laths and a significant content of retained austenite (above 25%) with film and blocky morphologies. After the tempering process (350 °C–650 °C), there was significant structural evolution following the gradual decomposition of the metastable bainitic structure. It was proved that BainTS steel is characterized by the higher thermal stability of both bainitic ferrite and retained austenite compared to BainNiAlCu. Despite this, the hardening effect after tempering BainNiAlCu steel was higher (by about 140 HV compared to heat treatment, approx. 30% increase). The presented results suggest that bainitic steels strengthened with intermetallic phases are extremely promising in the context of future industrialization in applications where operating conditions are exposed to elevated temperatures

Microstructure and Mechanical Properties of Spark Plasma Sintered and Severely Deformed AA7075 Alloy

In this paper, the microstructure and mechanical properties of AA7075 with a coarse-fine-grained laminated microstructure produced by spark plasma sintering (SPS) and the cyclic extrusion severe deformation (KOBO) technique were investigated. It was found that an inhomogeneous grain microstructure was formed from coarse and fine grains by the SPS process and then was transformed into a coarse-fine-grained laminated microstructure by means of KOBO extrusion at room temperature. The grain refinement during KOBO extrusion resulted in a fine grained laminated microstructure created due to the formation of low-angle grain boundaries (LAGBs), followed by dynamic recrystallization, leading to high-angle grain boundaries (HAGBs). The EBSD analysis results reveal the formation of a deformed and partially recrystallized ultrafine grain microstructure owing to the generation and development of shear bands during KOBO extrusion. The ultimate tensile strength (UTS) of the AA7075 alloy rose after SPS-KOBO severe deformation up to 422 MPa, with high strains of about 33%. The obtained results clearly show that the SPS-KOBO extrusion technique allows a bimodal laminated fine gradient grain microstructure to be obtained due to deformation and dynamic recrystallization, which result in both high strength and good ductility. The new heterogeneous AA7075 alloys obtained by the SPS-KOBO combined techniques demonstrate that microstructural heterogeneities can assist in overcoming the strength–ductility trade-off