Microstructural analysis of a HP 40Nb alloy aged

In this paper, the change in the microstructure of the centrifugally cast heat-resistant alloys of HP40 Nb after exposure to 0.5h and 2h of ageing times at 1123K and 1323K were investigated. The microstructures of the as-received alloy and aged conditions were examined using light microscopy (LM) and scanning electron microscopy (SEM) equipped with an energy dispersive spectroscopy (EDS). The chemical composition of various phases and precipitates observed in the aged sample microstructure was characterized by the means of scanning electron microscopy SEM via backscattered electron (BSE). The present results indicate that ageing enhanced the occurrence of different phenomena such as the transformation of primary M7C3 to M23C6 carbides and precipitation of secondary M23C6 carbides. It can be summarized that the present phases and the morphology of secondary carbides in the microstructure of aging results in higher values of hardness.Publishe

Vickers hardness indentation size effect in selective laser melted MS1 maraging steel

© IMechE 2019. In this paper, selective laser melting fabricated specimens in non-heat-treated and heat-treated conditions were subjected to Vickers microhardness testing, by using a full range of loadings: 10, 25, 50, 100, 200, 300, 500, and 1000 g. Microhardness of longitudinal sections and cross-sections were correlated and the obtained values were plotted against loadings and indentation size effect was studied, in order to find the optimal loading range, that gives the material true microhardness, or load-independent hardness. The load dependence of the measured Vickers hardness values was described quantitatively through the application of the Meyer’s law, proportional specimen resistance, and the modified proportional specimen resistance model. It was found that the microhardness rises as the loading is higher, causing a reversed indentation size effect, clearly indicating the range of true hardnesses of the tested material. Also, proportional specimen resistance and modified proportional specimen resistance models were found to have the highest correlation factors indicating their higher adequacy compared to Meyer’s prediction model.The authors wish to acknowledge the support of European Commission through the project “Advanced design rules for optimal dynamic properties of additive manufacturing products – A_MADAM”, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 734455

Modified 2D arc-star-shaped structure with negative Poisson’s ratio

The metamaterials with negative Poisson's ratio have played an important role in engineering practice in the last decade. Their use in space, aviation, the automotive industry, and biomedicine increasing constantly. The basic idea of making these metamaterials is to use additive manufacturing to create a structure that has a negative Poisson’s ratio, unlike conventional materials that are most often used in industry (steel, wood, rubber, etc.). The design process of these metamaterials takes place by first considering the properties of the elementary structure, and then by multiplying that structure, a metamaterial with the same Poisson's ratio as the basic structure will be obtained. The paper discusses a modified 2D arc-star-shaped structure in relation to the already existing variant in the literature. The influence of the parameters of the newly proposed structure on Poisson's ratio by using the finite element method was analyzed.Publishe

Tensile properties of ADI material in water and gaseous environments

Austempered ductile iron (ADI) is an advanced type of heat treated ductile iron, having comparable mechanical properties as forged steels. However, it was found that in contact with water the mechanical properties of austempered ductile irons decrease, especially their ductility. Despite considerable scientific attention, the cause of this phenomenon remains unclear. Some authors suggested that hydrogen or small atom chemisorption causes the weakening of the surface atomic bonds. To get additional reliable data of that phenomenon, in this paper, two different types of austempered ductile irons were tensile tested in various environments, such as: argon, helium, hydrogen gas and water. It was found that only the hydrogen gas and water gave a statistically significant decrease in mechanical properties, i.e. cause embrittlement. Furthermore, the fracture surface analysis revealed that the morphology of the embrittled zone near the specimen surface shares similarities to the fatigue micro-containing striation-like lines, which indicates that the morphology of the brittle zone may be caused by cyclic local-chemisorption, micro-embrittlement and local-fracture. (C) 2015 Elsevier Inc. All rights reserved

The effect of water concentration in ethyl alcohol on the environmentally assisted embrittlement of austempered ductile irons

© 2021 by the authors. Licensee MDPI, Basel, Switzerland. Austempered ductile iron (ADI) is an advanced cast iron material that has a broad field of application and, among others, it is used in contact and for conveyance of fluids. However, it is noticed that in contact with some fluids, especially water, ADI material becomes brittle. The most significant decrease is established for the elongation. However, the influence of water and the cause of this phenomenon is still not fully understood. For that reason, in this paper, the influence of different water concentrations in ethyl alcohol on the mechanical properties of ADI materials was studied. The test was performed on two different types of ADI materials in 0.2, 4, 10, and 100 vol.% water concentration environments, and in dry condition. It was found that even the smallest concentration of water (0.2 vol.%) causes formation of the embrittled zone at fracture surface. However, not all mechanical properties were affected equally and not all water concentrations have been critical. The highest deterioration was established in the elongation, followed by the ultimate tensile strength, while the proof strength was affected least

Austempering kinetics of Cu-Ni alloyed austempered Ductile Iron

The aim of the paper was to investigate the effect of austempering parameters (time and temperature) on the microstructure and mechanical properties of ADI alloyed with 1.5% Cu and 1.6% Ni (in wt.%) in order to establish the optimal processing window. It was shown that the strength, elongation and impact energy strongly depend on the amounts of ausferritic ferrite and retained austenite. A processing window was established according to the results of the kinetics of the isothermal transformation. The results show that the processing window for ADI alloyed with Cu and Ni at 350 degrees C was relatively wide, while the processing window for the isothermal transformation at 400 degrees C becomes narrower and shifted to the left. The processing window of ADI austempered at 300 degrees C is also narrower, but shifted to the right towards the longer times compared to the processing window of ADI austempered at 350 degrees C