List of Abstracts 2024: SESSION B - PROCESSING AND CHARACTERIZATION OF METALLIC MATERIALS
Date: September 10, 2024
This presentation explores the modeling of transformation kinetics in steels, focusing on augmenting standard data, such as those from the Stahldat Database, with advanced mathematical models. We specifically address the kinetics of bainite formation using a modified Kirkaldy approach, providing a more accurate representation of the transformation process. Additionally, the presentation will demonstrate how strength can be modeled as a function of transformation temperature, offering predictive insights into material performance.
The generated data can be seamlessly integrated into engineering and production processes using the Matplus EDA platform. Matplus EDA serves as a comprehensive materials knowledge management and integration tool, offering interfaces to CAE/CAD systems. This integration enables efficient utilization of the data, driving improvements in both design and manufacturing.
Shrinking resources of primary raw materials, as well as environmental and economic considerations, are prompting casting manufacturers to use a higher proportion of process secondary aluminum. This also applies to aluminum alloys, from which the resulting castings should be made with at least 60-80% secondary material content. Unfortunately, this process results in an increased proportion of various impurities (metallic and gaseous), with iron being one of the most important. Depending on the crystallization conditions, chemical composition and technology for obtaining aluminum alloys, it can be a component of eutectics and exist in the form of many intermetallic phases with different stoichiometric compositions, with Al5FeSi as one of the worst. This phase, in the poured state, crystallizes in a lamellar form (on the surface of acicular microstructure), with sharp edges and “pointed” corners, causing stress concentration and propagation of micro-cracks. This causes brittleness of castings, makes machining more difficult and reduces their mechanical properties, which are often a marketability criterion.
The article includes a study of the effect of process scrap/secondary aluminum, and therefore increasing iron content, on hardness and mechanical properties (Rm; R0,2; A) of AlSi7Mg alloy from which car rims are low-pressure die cast. The testing was performed at Superior Industries Poland sp. z o.o.
Miniaturized tensile testing (MTT) has several advantages across the industrial spectrum. There are many possible applications for MTT specimens as monitoring the progress of mechanical properties of components during their use, development of new materials, testing of welding joints and much more. Therefore, miniaturized samples are used in applications where it is required to reduce the volume of test specimens. For standard sizes specimens are conventional measuring methods like calipers and micrometers precise enough to measure all dimensions before and after fracture, even for 3D printed samples. The surface of additively manufactured specimens shows lower quality than those made by conventional technologies. This effect is amplified by miniaturized dimensions of samples. From this point of view the conventional measuring methods do not have to be sufficient and could distort the outcome in the form of yield strength and ultimate tensile strength. Those facts open the possibility for 3D scanning and digital evaluation of specimen’s dimensions. The approach that was applied in this work uses fringe projection technology to digitize the whole geometry of MTT specimens. The data outcome of this technology is in form of triangulated 3D model, which is ready for further measurements via sections and possible 2D optical measurements. It is possible to get precise data regardless of the surface quality by calculating the cross-section area and avoid distortion of the mechanical properties of the specimen.
Aluminium high pressure die casting (HPDC) parts are widely used as structural components and housings in the mobility sector. The components possess a favourable density to strength ratio and an excellent castability in HPDC process. The ongoing change towards electric drive systems transformed casting parts and sets other standards for the properties of these parts. The functional integration of cast parts becomes more important for the new applications in the electromobility sector. Most of the new housing components include electrical components that emit heat and need cooling. Thus, heat transfer and conductivity of cast parts become a focal point in these applications. However, there is little information about how the conductivity in HPDC parts is influenced by the casting process. Furthermore, the resulting microstructure influence on the conductivity within a component is unclear. The aim of this work is to study the influence of the HPDC mould filling process onto the developing microstructure and eventually the influence on the conductivity. The analysis is based on the comparison of mould filling simulations with electrical conductivity measurements and microstructural investigations of HPDC components. The results indicate that the electrical conductivity is a function of the local microstructure within the cast part based on the mould filling.
By incorporating the concept of high-entropy alloys into traditional Ni-Ti shape memory alloys (SMAs) through the addition of Cu, Hf, and Zr, it is possible to obtain high-entropy shape memory alloys (HESMAs) with higher operating temperatures and broader application ranges. The macroscopic behavior obtained through differential scanning calorimetry (DSC) can be compared with the microscopic behavior observed through in-situ X-ray diffraction (XRD), X-ray nano-diffraction (XND), and X-ray fluorescence (XRF). The influence of the core-shell structure formed by an uneven distribution of alloying elements on the phase transformation behavior of CuNiTiHfZr enables to explain the mismatch between the macroscopic and microscopic behaviors, providing a better understanding of the combined effects of high-entropy and shape memory.
Company TMVSS cooperates with universities, research centers and academies of sciences in the field of active thermography for many years and thanks to this has already got a lot of experience. We also colaborate with active thermography packages suppliers and offer special measurements, including analysis, laboratory and automated systems as well.
Active thermography is non-contact and non-desctructive testing (NDT) method in general, nearly regardless of the object material. This technique in combination with high-resolution and high-sensitive infrared cameras is an elegant testing method to analyse measuring objects of both smallest as well as large-area objects made from a wide variety of materials and for most different types of failures. As it is an optical measurement method, it enables fast defect detection and high efficient quality assurance. The object to be inspected is either externaly or internaly excited by different type of source, which generates a heat flow within the object. This leads to a pattern of different temperatures on the object surface and analysis of these patterns enables conclusions to be drawn about the material properties and the condition of the test object. The test object still remains intact and can be used for further tests or improvement, if necessary, which is a big advantage.
Designing complex concentrated alloys (CCA), also known as high entropy alloys (HEA), requires reliable and accessible thermodynamic predictions due to vast space of possible compositions. Numerous semiempirical parameters have been developed for phase predictions over the years. However, none of these parameters seems to be a robust indicator of phase content in various refractory CCA. CALPHAD proved to be a more powerful tool for phase predictions. AlTiNbMoV, AlTiNbTaZr and AlTiNbMoCr alloys were prepared using blended elemental powder metallurgy. Their phase and chemical composition were investigated by the means of scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. AlTiNbMoV and AlTiNbMoCr exhibited single-phase solid solution microstructure at the homogenization temperature of 1400 °C, while Al3Zr5 based intermetallics were present in the AlTiNbTaZr alloy. None of the simple semiempirical parameter was able to predict phase content correctly in all three alloys. Predictions by CALPHAD (TCHEA4 database) were able to predict the phases with limited accuracy only. Critical limitation of the TCHEA4 database is that only binary and ternary phase diagrams are assessed, and more complex phases cannot be predicted. Furthermore, the inevitable presence of interstitial contaminants such as O or N is not accounted for.
The refinement of prior austenite grains (PAGs) and subunits of PAGs during the quenching and subsequent tempering, leads to multi-level refinement of hierarchical martensitic microstructure. Such processing can provide significant changes in mechanical properties, in particular, the high strengthening and fatigue properties with a satisfactory level of ductility. The proposed study has revealed the relevant processing modes for medium carbon spring steel 54SiCr6. The microstructure and phase composition examination was performed using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Mechanical properties were determined using tensile tests performed with cylindrical specimens under experimental conditions according to the ČSN EN ISO 6892-1 standard. The contribution of each microstructural feature (chemical composition, dislocation density, grains boundaries, size, number density carbides, and intertwining space) to the yield strength has been established. For the first time, it was found that the effective grain size (EGS) according to the Petch-Hall relationship for 54SiCr6 steel can be considered the intertwining space, rather than the size of the PAG, block, packet, or lath, as is commonly used as the EGS for steels with lower carbon content than steel 54SiCr6.
The failure behaviour is investigated for the 2024-T351 aluminium alloy subjected to monotonic and cyclic loading conditions using the void growth model. Notched cylindrical specimens are employed to analyse the behaviour under monotonic loading, while smooth cylindrical specimens are used for cyclic loading. The analysis encompasses a broad spectrum, ranging from the ultra-low cycle fatigue regime to the low-cycle fatigue. This comprehensive approach aims to provide a thorough understanding of fracture behaviour across a wide range of loading severities.
Complex concentrated alloy with nominal composition (CoCrFeNi)94Al3Ti3 (in at. %) was prepared by vacuum induction melting in a ceramic crucible and tilt casting into a cylindrical ceramic mould. As-cast ingots were subjected to the solution annealing and multi-step hot forging followed by heat treatment at 1225 °C with the aim to achieve evenly distributed equiaxed grains. DSC analyses indicated solid state phase transformations between 700 and 900 °C. Formation of L12 precipitates in this temperature range was revealed by TEM. The evolution of precipitation hardening of FCC(A1) matrix by particles rich in Al, Ni and Ti was studied at the temperatures from 700 to 900 °C for 2 up to 500 hrs. Microhardness measurements indicate the highest level of precipitation hardening during annealing at the temperature of 750 °C. The effect of annealing time at 750 °C on tensile properties is discussed. Relation between discontinuous precipitation and fracture mode is elucidated.