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

The influence of polymer addition on flexural strength, fracture mode and porosity of traditional ceramics

The usage of air-swept milling of raw materials is the most efficient method for preventing the negative lime-blowing process of ceramic roofing tiles. How-ever, after air-swept milling the clay minerals lose water which has to be re-turned back before the shaping procedure. Addition of surface active materials could increase hydrophilicity of the raw material and reduce needed time for re-wetting trough the control of meso-, micro- and nanoporosity of the clay ma¬terial. In view of that, the object of this research was to study the influence of polyethylene glycol (PEG600) on porosity, mechanical properties and fracture surface characteristics of traditional ceramic materials. It was founded that with the addition of polyethylene glycol (PEG600) to traditional clay materials it is possible to achieve desired porosity, from meso, through micro and up to na¬no, without degrading the mechanical properties of the final products

Knoop hardness optimal loading in measuring microhardness of maraging steel obtained by selective laser melting

© IMechE 2019. Knoop microhardness method possesses several advantages over Vickers testing: lower penetration depth, higher accuracy in indentation measurement, and a better suitability to measuring thin and elongated morphological features. This study explores the optimal loading and load independent hardness of selective laser melted specimens in non-heat-treated and heat-treated conditions, by using different Knoop test loads. The obtained results were used to plot load to indentation size charts, which, in turn, were used to obtain prediction curves in accordance to Meyer, proportional specimen resistance, and modified proportional specimen resistance models. The fitting of fitting curves to the measured values was used to calculate appropriate correlation factors. The results indicate that indentation size effect occurs in all measured specimens. This suggests that there is material true microhardness. Also, the most adequate model was modified proportional specimen resistance, with correlation factors just under one.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

Tensile and fatigue properties, machinability and machined surface roughness of Al-Si-Cu alloys

In this paper, the aim was to determine if ASC91 (9 % Al, 1 % Cu) could be replaced with ASC73 (7 % Al,3 % Cu) aluminium alloy, with presumably improved machinability due to lower silicon content (9 to 7 %)and retained mechanical properties due to a higher copper content (1 to 3 %). The test samples were excisedfrom cylinder heads produced by the lost-foam casting technique in industrial conditions. The tensile properties(proof strength, ultimate tensile strength, elongation and modulus of elasticity), fatigue performance,microstructure and machinability of two as-cast aluminium alloys were examined. The results of the fatiguetests were statistically analyzed using the stair-case method described in the UNI 3964 standard. Tensileproperties of the ASC91 were higher, while fatigue properties were higher in the ASC73 alloy. The resultantforce was lower for the ASC73, while roughness was lower for the ASC73 alloy, if the feed per tooth is higherthan 0.21 mm/t. Two main factors that influence such behaviour are the amount of eutectic silicon and theα-solid solution adhesion to the cutting tool.Keywords: aluminium cast alloys; tensile properties; fatigue; machinability; roughness

Solutions of critical raw materials issues regarding iron-based alloys

The Critical Raw Materials (CRMs) list has been defined based on economic importance and supply risk by the European Commission. This review paper describes two issues regarding critical raw materials: the possibilities of their substitution in iron-based alloys and the use of iron-based alloys instead of other materials in order to save CRMs. This review covers strategies for saving chromium in stainless steel, substitution or lowering the amounts of carbide-forming elements (especially tungsten and vanadium) in tool steel and alternative iron-based CRM-free and low-CRM materials: austempered ductile cast iron, high-temperature alloys based on intermetallics of iron and sintered diamond tools with an iron-containing low-cobalt binder

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

Determination of the Grain Size in Single-Phase Materials by Edge Detection and Concatenation

This paper presents a novel approach for edge detection and concatenation. It applies the proposed method on a set of optical microscopy images of aluminium alloy Al 99.5% (ENAW1050A) samples with different grain size values. The performance of the proposed approach is evaluated based on the intercept method and compared with the manual grain size determination method. Edge detection filters have proven inefficient in grain boundaries’ detection of the presented microscopy images. To some extent only the Canny edge-detection filter was able to compute grain boundaries of lower-resolution images adequately, while the presented method proved to be superior, especially in high-resolution images. The proposed method has proven its applicability, and it implies higher automatisation and lower processing times compared to manual optical microscopy image processing

Metallographic Determination of Strain Distribution in Cold Extruded Aluminum Gear-Like Element

In this study, an experimental, metallographic method for determining strain distribution in a cold extruded aluminum gear-like element, based on the dependence of recrystallized grain size on prior deformation, was devised in order to overcome design problems in manufacturing of complex parts where critical values of strain and stress could cause a fracture. The method was applied on a 99.5% aluminum bar subjected to cold, radial extrusion, in order to produce complex gear-like element. To reveal the strain and stress distribution in specimens, the calibration and flow curves were first obtained by uniaxial compression (Rastegaev test). Afterwards, the grain size in different parts of the gear section was examined, the strain and stress distributions were calculated, and the results were confirmed by microhardness measurements. It was found that grain size, strain, stress, and microhardness considerably differed throughout the cross-section of the gear. The coarsest grain, and thus the lowest strain zone, was obtained in the central part of the tooth and in the zone between teeth. Conversely, the finest grains appeared in the highest strain zone at the specimen surface, particularly in the root of the teeth. Furthermore, results were supported by microhardness measurements, i.e., microhardness corresponded to grain size and strain hardening. Finally, the real view of material flow in the complex extruded part was successfully obtained by the metallographic method