Papers by Keyword: Thermal Cycling

Abstract: Due to material and structural issues, fire-assaying crucibles used for analyzing precious metals in ores have encountered challenges related to poor thermal cycling in Ghana’s sub-Saharan region. This study aimed to enhance the crucibles by analyzing aluminosilicate minerals' multiphase development using X-ray diffraction and understanding the effects of composition determined by X-ray fluorescence on thermal behavior and water absorption observed through optical microscopy. The improved crucible design exhibited enhanced thermal cycling stability and lower permeability to the assay charge. Analysis showed that Fosu Clay (FC) demonstrated promise with a favorable Al₂O₃:SiO₂ ratio and low impurities; mullite was identified as the primary phase formed at high temperatures, with quartz and cristobalite also present. Introducing 6% CSM dopant to FC increased the mullite content while supporting the transformation from quartz to cristobalite. The optimal crucible sample included coarse and fine-doped grog with an FC-clay binder, demonstrating excellent thermal stability, adequate porosity, and water absorption. Adjusting the percentage of doped grog further increased mullite content while reducing silica content; this suggests that locally produced improved crucibles are feasible through sintering commercial clay with mullite doping and precise composition adjustments.

Abstract: Fused Deposition Modelling (FDM) is a three-dimensional (3D) printing technology known for its low-cost rapid manufacturing of parts. Nowadays, various industries such as automotive, aerospace, and maritime are using this technology to manufacture 3D-printed parts that have undergone high temperatures. The material used in this study is the Thermoplastic Polyurethane (TPU), which is the most commonly-used type of Thermoplastic Elastomer (TPE) in 3D printing. This material is a combination of substances from the qualities and characteristics of both thermoplastic and vulcanized thermoset rubber. TPU has excellent abrasion resistance, hardness, chemical, and thermal resistance properties. In addition, TPU is a great fit for making hoses, gaskets, and seals due to its oil and grease resistance properties. Due to the growing application of 3D-printed materials at elevated temperatures, this study aims to characterize the tensile strength of TPU 3D-printed materials when thermal cycled. The test results concluded that the tensile properties of TPU 3D-printed specimens were significantly influenced by the number of thermal cycles it was subjected to. The samples that underwent four thermal cycles exhibited the highest modulus of elasticity and stress at 200% strain. While samples which underwent 2, 8, and 16 thermal cycles resulted to a higher modulus of elasticity and tensile stress at 200% strain than the untreated specimen.

Abstract: Metallic thermal barrier coatings (TBCs) consisting of a bond coating and a top coating have been extensively utilized for protecting the walls of rocket combustion chambers. However, standard coating systems often encounter failures due to the significant differences in coating composition and thermal expansion coefficient compared to the substrate under high heat flux conditions. To protect liquid rocket combustion chamber walls, a novel metallic multilayer TBC system applied with atmospheric plasma spraying is developed in the present work. It attempted to deposit dense Ni-based alloy and Cu-based bonding coatings with low oxide contents achieved by introducing boron as a deoxidizer element through atmospheric plasma spraying. The structural stability of the TBC was assessed through high temperature thermal exposure experiments, while the thermal cycle life is evaluated using laser thermal shock. Results show that the NiCrCu2B and CuNi2B bonding coatings prepared through in situ deoxygenation effect of boron exhibit dense structures, low oxide content, and excellent bonding quality. The high temperature thermal exposure experiment reveals that the multilayer structural TBC can withstand 850 °C for 10 hours without the formation of Kirkendal effect pores. Moreover, the thermal cycling life results indicate that the multilayer structural TBC designed in this study, employing a composition gradient transition and the in situ deoxygenation effect of boron, possesses a significantly improved thermal cycle lifetime compared to traditional structural TBCs.

Abstract: Investment casting of an orthopedic implant plate based on stainless steel 316L was considered an economical process. Nevertheless, the mechanical properties of the investment casting product were found to be inferior as compared to the implant plate fabricated with other methods such as forging due to their differences in the microstructure. Investment casting mostly produced coarser grain as compared to those with forging or rolled process. In order to improve their mechanical properties, cold-rolling followed by a repetitive thermal cycling process is proposed. The goal is to generate finer grain size through recrystallization process leading to nucleation of new grain during the thermal cycling process thus increasing their strength. Stainless steel 316L was cold-rolled to 52% reduction in thickness and this process generate stored strain energy in the form of dislocation density in the material. The thermal cycling treatment performed within several cycles after cold rolling enabling gradual disperse of stored strain energy that facilitates the recrystallization process that initiates new grain formation. The short holding time within several cycles limits the grain growth that normally occurs during annealing. It was found that thermal cycling treatment at a temperature of 950 °C for 35 seconds within four cycles led to the formation of finer grain size of 22 µm on average as compared to the initial investment casting average grain size of 290 µm. The hardness also increases to 253 HV_0.3 in this condition as compared to 155 HV_0.3 of investment casting products. Lower thermal cycling temperature than 950 °C during the test did not result in grain refinement thus indicating that strain energy relieves were not enough to aid the recrystallization process.

Abstract: Surface properties are essential for many engineering material ́s design issues, such as fatigue and corrosion performances. Austenitic stainless steels used in high-temperature applications, as for instance components in biomass-fired power plants, need sufficient corrosion resistance. At temperatures above 600 °C and in water vapor environment, Cr-vaporization will create Cr-depletion, causing a local change in chemical composition. This local change in chemical composition leads to phase transformation in some austenitic stainless steels. This paper reports the surface properties regarding the local phase transformation during thermal cycling in water vapor environment. Three commercial austenitic stainless steels are investigated, AISI 304, AISI 316L and Sandvik SanicroTM 28. The thermal cycling was performed up to 650 °C in a 15 mol.% water vapor environment. AISI 304 shows local surface phase transformation related to martensitic transformation due to locally changed chemical composition and increase in the martensitic transformation temperature (M_s). However, the other two austenitic stainless steels don’t show this martensitic transformation. The phase transformation and oxidation is discussed using microstructural investigations methods such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS).

Abstract: Directional growth behavior of intermetallic compound (IMC) layer of Sn3.0Ag0.5Cu (SAC305) on immersion tin (ImSn) surface finished Cu substrate was investigated. The samples of SAC305 on ImSn/Cu substrate were subjected to thermal cycling at temperatures between 0 °C and 100 °C for 0 cycle up to 500 cycles. The cross-sectioned microstructures of soldered samples, SAC305 on ImSn/Cu were observed using optical microscope. The shape and orientation of IMC growth on the SAC305 on ImSn/Cu indicates that the orientation of IMC growth were observed to be non-uniform and dispersed throughout the solder joint with longer thermal cycling test.

Abstract: Based on the understanding of Friction Stir Welding (FSW) and the effect of ultrasound, the purpose of the paper is trying to find the effective access to reduce the welding resistance and improve the quality of weld during FSW. The best vibration point was first determined through the vibration test system. Then, the thermal cycling, three-force and torque were tested by using paperless recorder and mechanical sensor in heat-power test bench for 4mm thick AZ31 magnesium alloy. The results showed that the periodic vibration took place at the weld under the excitation of ultrasonic vibration, and the frequency of this vibration was as same as the frequency of ultrasonic vibration. The best tracking distance of ultrasonic vibration was 40 mm, and its optimal incident angle was 45°. By applying ultrasonic vibration to FSW, the forward resistance, the axial force and the torque of the tool can be significantly reduced. In addition, the distribution of temperature field was basically consistent with the two conditions, presenting “asymmetrical, non-linear” distribution characteristic. The heating effect of ultrasonic vibration was not obvious, but it was able to make the temperature field of the welding seam become more uniform.

Abstract: Cracking behavior of positive electrode-electrolyte-negative electrode (PEN) assembly in a planar solid oxide fuel cells (pSOFC) during thermal cycling are investigated by using a commercial finite element analysis (FEA). The stress intensity factor for various combinations of surface crack size of 1 μm, 10 μm, and 100 μm and shape of semi-circular and semi-elliptical at highly stressed regions in the PEN are repeatedly calculated at room temperature and steady stage for twenty cycles. Simulation results indicate the stress intensity factor is significantly decreased at room temperature and is slightly increased at steady stage with increasing number of cycle. However, all the calculated stress intensity factors during thermal cycling in the present investigation are less than the corresponding fracture toughness given in the literature.

Abstract: In this study, effect of thermal cycling after water absorption on flexural property of CFRP(Carbon Fiber Reinforced Plastics) was examined. Water absorption tests were conducted for 24 hours, 100 hours and 500 hours at 90^°C. Thermal cycling test was conducted by using water absorbed specimen. The temperature range of thermal cycling test was from room temperature to-196^°C. The static three-point flexural test of CFRP with freezing after water absorption was conducted based on JIS(Japanese Industrial standard) K 7074. Following conclusions are obtained. In case of immersion for 24 hours, flexural strength and modulus of CFRP with freezing after water absorption decreased with an increase of the number of cycles. In case of immersion for 100 hours and 500 hours, flexural strength and modulus of CFRP with freezing after water absorption did not change. The water absorption of CFRP was the phenomenon that the water penetrated into fiber/resin interface. So, in the case of immersion for 24 hours that the absorption time is not so long, damage progresses gradually in thermal cycling test. On the other hand, in the case of immersion for 500 hours is long, the damage progresses at the early stage of the thermal cycling test, and after that the damage does not almost progress.

Abstract: The research on a new low-Ag lead-free solder has become a hot spot in the field of electronic packaging. In this work, the effects of Bi addition on microstructure, melting temperature, wettability of low-Ag solder, shear strength of solder joint and the growth of interfacial intermetallic compound (IMC) before and after thermal cycling were investigated. A moderate amount of Bi element resulted in the microstructural refinement and melting temperature reduction of Sn-0.2Ag-0.7Cu solder. Wetting test results showed that a small amount of Bi produced the significant effect on improving the wettability. In addition, it is shown that the thickness of interfacial IMC during thermal cycling decreased first and then increased; the shear strength of solder joint increased with the increase of Bi.