Key Engineering Materials Vol. 1014

Abstract: High entropy alloys (HEAs) are a novel type of material with distinct features caused by their atypical compositions. However, their microstructure and mechanical qualities are greatly dependent on processing parameters. Laser cladding is a versatile method for producing HEA coatings, but optimizing the process to achieve the required microstructure and hardness remains a difficulty. Therefore, this work analyses the impact of laser processing parameters, especially laser power and scan speed, on the microstructure and hardness of AlCrFeNiMn HEAs manufactured via laser cladding. The AlCrFeNiMn HEA was successfully created utilizing the laser metal deposition process and several analyses were conducted. Columnar grains were discovered on alloy samples produced with 1500W laser power. As the laser power rose to 2200W coarse columnar dendritic microstructures were discovered. Samples processed with 2400W laser power showed the fewest visible fractures with an increase in scanning speed. As the laser power increased, the hardness of samples decreased from 427 Hv to 382 Hv.

Abstract: This study investigates the performance of Electrical Discharge Machining (EDM) on magnesium alloy grade AZ91 using a graphite electrode, with a focus on optimizing the material removal rate (MRR) and electrode wear ratio (EWR). The machining parameters such as current, on-time, and duty factor were systematically varied and assessed using the Taguchi method with an L9 orthogonal array design. The results identified current and on-time as significant factors influencing both MRR and EWR. Higher current values led to increased MRR, enhancing material removal efficiency, but also resulted in greater electrode degradation. Similarly, increased on-time durations significantly impacted MRR and EWR, indicating that prolonged exposure to discharge conditions can improve material removal while contributing to higher electrode wear. Conversely, the duty factor did not show a statistically significant impact on either MRR or EWR within the experimental conditions of this study.

Abstract: The demand for lightweight and high-strength materials in automotive applications has been a driving force for research and development of ductile iron. This study investigates the influence of casting parameters on the nodule count of ultrafine spheroidal graphite iron, as nodule count is the major factor for enhancing mechanical properties. Several heats of ductile iron were produced using an induction furnace, varying silicon content, carbon equivalent, mold preheating temperature, and inoculation levels. Optical Emission Spectrometry (OES) and image analysis were used to determine chemical composition and nodule count, respectively. Results showed that silicon content significantly affects graphite fineness (e.g. nodule count) and carbide formation, with a minimum of 3.7% silicon required to prevent carbide formation. Higher mold preheating temperatures and increased inoculation levels promote higher nodule counts by slowing down the cooling rates and promoting the heterogeneous nucleation of graphite. Microstructural analysis revealed that increasing silicon increased ferrite fraction and decreased pearlite. The results suggest optimal casting parameters to maximize nodule count and enhance the strength and ductility of ultrafine spheroidal graphite iron.

Abstract: Wire Arc Additive Manufacturing (WAAM) is an emerging technology for producing large scale metal components, offering significant advantages in material efficiency and reduced production time compared to conventional methods. This study investigates the microstructure and mechanical properties of carbon steel produced using two different WAAM systems: the Fronius TransPuls Syn ergic 2700 CMT and the Kemppi X5 500 Pulse+ systems. Both systems utilized similar operating parameters, yet exhibited subtle differences in microstructure, including grain size and phase distri bution. Due to slight microstructural variations, the mechanical properties, such as tensile strength, hardness, and fatigue performance, were nearly identical for both materials. The findings demonstrate the potential of WAAM to produce high-quality carbon steel components with consistent mechanical properties, highlighting its suitability for applications requiring large, custom metal parts.

Abstract: Heat pumps are rapidly emerging as a crucial solution in the pursuit of decarbonization, offering significant advantages over traditional boilers due to their superior energy efficiency. The outdoor unit of a heat pump consists of around twenty key components, including a complex network of copper pipes and sheets welded to valves, connectors, and other fittings. With over thirty welded joints, there is substantial potential to reduce manufacturing time through process optimization. Copper, known for its excellent thermal and electrical conductivity, is essential in many applications. However, these same properties make welding copper particularly challenging, especially when automating industrial processes. This study explores the ultrasonic welding of copper, aiming to determine the optimal parameters for maximizing the mechanical strength of overlapping sheet joints. The optimal parameters identified for the welding process are as follows: a welding time of 3 seconds, a pressure of 6 bar, a retention time of 0.62 seconds, an initial pressure of 2 bar, a retention pressure of 2 bar, and a rising pressure for the sonotrode of 3 bar.

Abstract: The purpose of this study is to develop a general bending fatigue strength design method that can be applied to various geometries. Considering the conditions for fatigue crack initiation and crack arrest, the bending fatigue strength was evaluated using the actual stress at the critical point where the maximum stress occurs, and the relationship between the bending fatigue strength and the geometry close to the critical point was investigated. The results indicate that the bending fatigue strength evaluated using the actual stress depends on the shape close to the critical point. A higher stress concentration leads to a higher fatigue strength, which is defined as the apparent bending fatigue strength. The apparent bending fatigue strength decreased with a decreasing stress gradient. The lowest value of the apparent bending fatigue strength was observed at a zero stress gradient, which corresponded to the tensile fatigue strength of a smooth test piece. Therefore, the tensile fatigue strength of a smooth material can be used as a criterion for estimating the apparent bending fatigue strength. Moreover, the stresses at the critical point were much larger than the yield stresses of the test pieces, indicating the necessity of considering small-region yields in the evaluation of bending fatigue strength.

Abstract: Crack propagation behavior is a critical factor influencing the service life of thermal barrier coatings (TBCs). With the use of hydrogen as a fuel in a carbon-neutrality context, incomplete combustion of hydrogen gas will introduce potential new failure modes for TBCs. Therefore, it is crucial to evaluate the crack propagation behavior of TBCs subjected to a hydrogen environment. In this study, in-situ three-point bending tests were used to investigate the crack propagation behavior within the top coat after heat treatment under air and hydrogen environments. The results reveal that the sintering degree is reduced after heat treatment in hydrogen environments, accompanied by the formation of numerous microcracks before the displacement reaches 0.6mm. Conversely, heat treatment in air environments results in a higher sintering degree and promotes the propagation of main vertical cracks on the surface of the top coat as the displacement gradually increases to 0.8 mm. Additionally, this study discusses the effect of sintering on the fracture toughness of the top coat and further elucidates the effect of hydrogen fuel on the overall durability of TBCs.

Abstract: Leather is a fiber-reinforced material with a more concentrated fiber distribution in three dimensions perpendicular to the tangential plane than in-plane. The asymmetric dispersion of fibers can have a significant effect on the mechanical properties of natural leather. The transverse isotropic constitutive model is unable to accurately describe the anisotropy of natural leather. Accordingly, we have devised a novel anisotropic theoretical framework that incorporates asymmetric fiber dispersion, with the objective of accurately characterizing the mechanical behavior of anisotropy with asymmetric fiber distribution. Our approach entails the incorporation of the Yeoh model into the theoretical framework, as well as the introduction of a specific anisotropy term within the strain energy function, with the objective of describing the nonlinear properties. By fitting the theoretical results of the model to tensile test data of natural leather specimens, the structural and material parameters were determined. We provided specific stress tensors to enable finite element analysis. Our finite element analysis investigates the effect of asymmetric fiber dispersion on the mechanical response under uniaxial and biaxial stretching. By simulating the tensile behavior of natural leather specimens under different tensile angles, we observe a non-homogeneous stress distribution and non-homogeneous deformation due to fiber families under fixed stretching. This theoretical framework based on a continuum model provides a theoretical reference for describing the mechanical properties of leather materials with asymmetric fiber dispersion.

Abstract: Nickel and cobalt recovered from ternary leaching solutions have high market value and stability. In addition to preventing environmental damage, this recovery process is also very useful in the application of power energy storage and electric vehicles. Solvent extraction is an effective and selective method for separating elements in ternary leaching solutions. This research focuses on the separation stage of feed solution impurities, especially Cu, by optimizing the extraction process using multi-stage extraction. This method, which is adapted to a laboratory scale, mixes the feed solution with saponified P204 (prepared with NaOH) and then stirred until phase separation into a loaded organic phase and raffinate occurs. The use of P204 with 3-stage extractions with O/A= 1.5/1 and pH= 4.5 succeeded in separating 99.96% extraction of Cu with a primary yield of Cu value of 99.999%. This solvent extraction also successfully separated 99.23% of Mn, Ca=95.62%, and other impurity metals such as Fe, Zn, Li, and Si reaching a final concentration in the raffinate solution of only 10^-3 g/L. The results of this research are very useful in the subsequent extraction process in the form of separating the valuable elements nickel and cobalt. This method can potentially overcome environmental problems resulting from the disposal of NCM battery waste in the metallurgical field.