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Abstract In this work, the commercial SUS430 ferritic stainless steel was used as the current collector to study the fracture behaviors of the planar electrolyte-supported and anode-supported solid oxide fuel cells with the size of 10 cm × 10 cm during the thermal cycle process. The anode-supported cells (ASCs) were fabricated by tape-casting, spraying, screen-printing and co-sintering. The electrolyte-supported cells (ESCs) using fully-stabilized zirconia as material were prepared by tape-casting, multilayer lamination, screen-printing and co-sintering. The output power densities at 0.7 V (P 0.7V) of the anode-supported and electrolyte-supported cells could reach 0.60 W cm−2 and 0.43 W cm−2 at 850 °C, respectively. During the thermal cycle testing, the ESC sample was cracked, while the ASC sample had no obvious changes. The thermal expansion coefficient (TEC) of the different samples was studied, and the two cells were characterized by the XRD after the thermal cycle testing. In addition, the fracture behaviors of the two cells were discussed. The results indicated that the ASC sample had the good stability during the thermal cycle testing. The excellent anti-cracking performance of the ASC was attributable to two aspects. Firstly, the TEC of the anode support is more close to that of the SUS430 material; secondly, the phase transformation of zirconia from monoclinic phase to tetragonal phase induced by stress is favorable for contraction of the anode support layer during the cooling process. Highlights • Planar cells were fabricated by tape-casting, screen-printing and co-sintering. • The fracture behaviors of cells using SUS430 as current collector were studied. • Anode-supported cell had the good stability during the thermal cycle testing. • Anti-cracking performance was attributable to the TEC and phase transformation. [ABSTRACT FROM AUTHOR]

Friction Stir Processing (FSP) involves the use of Silicon Carbide (SiC) and Graphite (Gr) nanoparticles as reinforcements to enhance the properties of AZ91 Mg alloy composites. The relationship between FSP processing parameters and surface properties of Mg alloy composites with SiC and Gr nanoparticles is poorly understood. The present study addresses this and investigates the impact of SiC and Gr volume percentages (%vol), tool traverse speed (TTS), and tool rotational speed (TRS) on the corrosion behavior and microhardness of AZ91 alloy composites. FSP turns graphite into layered graphene, making it more corrosion-resistant and stronger through various strengthening mechanisms. Taguchi optimization yielded optimal settings in runs H7 (1500 rpm-20 mm/min-13 %vol) and H8 (1500 rpm-40 mm/min-7 %vol) for high microhardness and low corrosion rate. Conversely, runs H1 (500 rpm-20 mm/min-7 %vol) and H3 (500 rpm-60 mm/min-13 %vol) resulted in reduced microhardness and increased corrosion rate. Integrating Taguchi and Grey Relational Analysis (GRA) optimized the multi-objective enhancement of microhardness and corrosion resistance, achieving 3rd-level values for TRS, TTS, and %vol. Notably, the reinforcement percentage, followed by TRS and TTS, simultaneously improved these responses. • Fabrication of flawless AZ91 surface hybrid composites using friction stir processing. • Exploring process parameters on the microstructure, microhardness and corrosion behavior. • Strengthening mechanisms associated with microstructural changes and contributions of SiC and Gr reinforcements. • Mechanical exfoliation of few-layered graphene (FLGs) from graphite. • Taguchi-Grey Relational Analysis employed for multi-objective optimization. [ABSTRACT FROM AUTHOR]

The microstructure and sintering behavior of zirconia-based bi-phase solid solution (BPS) ceramic coating prepared by air plasma spraying have been investigated. It is found that the BPS coating is composed of cubic and tetragonal phases, which are well-adhered. During the 1200 °C thermal cycling, the densification of intersplat pores and cracks is inhibited due to the differential sintering of nano-grains and the high density of oxygen ions located in the crystal plane. The average grain diameter and Young's modulus are reduced, and the thermal conductivity is maintained at a constant level after 250 thermal cycles. The sintering resistance of BPS coating is 40 % higher than 8YSZ coating. [Display omitted] • Cubic and tetragonal phases are well-adhered in bi-phase solid solution coating. • Densification of fracture surfaces in bi-phase solid solution coating are inhibited. • Increase of Young's modulus and thermal conductivity is retarded in BPS coating. • Sintering resistance of BPS coating is 40 % higher than 8YSZ. [ABSTRACT FROM AUTHOR]

Thermal cycles have an important effect on the microstructure and properties of the components fabricated by wire-arc directed energy deposition (wire-arc DED). In this study, a Gleeble thermal-mechanical simulator was adopted to create closer-to-reality thermal cycles with the assistance of a numerical simulation model and experimental Ti-6Al-4V deposition. Step-by-step microstructure evolution, including α m , retained β, and GB α, microhardness gradual variation, and the corrosion resistance change before and after the entire thermal cycle were investigated. Therefore, combining phase orientation and high-magnification morphology, transformed and untransformed α that occurred in low- and medium-temperature thermal cycles can be distinguished. After the entire thermal cycle, α m laths coarsened from ∼1 µm to ∼1.2 µm, and the content of retained β phase became more and more. The α m formed around grain boundaries partially disappeared and was occupied by α laths from the inner grain. GB α was more continuously distributed along prior β grain boundaries due to its lower formation temperature during the subsequent thermal cycles that were occurring incomplete α→β transformation. The severe preferential orientation of α phases formed after the deposition and high-temperature thermal cycle was also alleviated through the twice low-temperature thermal cycles. Besides, the microhardness decreased from 318.78 ± 7.5 HV to 285.17 ± 5.3 HV after the high-temperature thermal cycle but eventually increased significantly to 330.5 ± 6.4 HV after experiencing the final low-temperature thermal cycle. The corrosion resistance decreased after the entire thermal cycle, indicating a performance difference between the top and bottom regions of the Ti-6Al-4 V component fabricated by wire-arc DED. • Closer-to-reality thermal cycles of Ti-6Al-4V wire-arc DED are created using Gleeble thermal-mechanical simulator. • Prior β and α phase evolution is step-by-step observed at the same zone of the same sample. • Microhardness drops after the high-temperature thermal cycle but increases after subsequent low-temperature thermal cycles. • Corrosion resistance decreases after the entire thermal cycle, indicating an ununiform corrosion performance distribution. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure formation mechanism of an AlSi10Mg alloy prepared by laser directed energy deposition (DED-LB) and its influence on the mechanical properties was fully studied. The relationships between the microstructure characteristic scale, the molten pool solidification/thermal cycle conditions, and the tensile mechanical properties were established by combining the numerical simulation, theoretical calculation, and experimental validation. The as-deposited microstructure consists of the columnar α-Al dendritic array growing epitaxially along the building direction with the primary dendritic arm spacing of 18 ± 4.5 µm, the dendritic arm cell of 3 ± 1 µm surrounded by the refined eutectic network, and the Si precipitation of 17.7 ± 0.8 nm dispersed in the α-Al dendritic trunk. The feature size of the primary dendritic arm spacing and the dendritic arm cell size can be well predicted using the Kurz-Fisher and KGT dendritic growth models. The formation and size evolution of the Si precipitation was well described by the non-isothermal aging KWN model for the first time. The as-DED-LB-processed AlSi10Mg alloy exhibits a good comprehensive mechanical property with a yield strength of 187 ± 1.5 MPa and elongation to fracture of 7.4 ± 0.5%. The boundary strengthening from the eutectic phase network, the load-bearing capacity for dislocations caused by refined dendritic arms, and the precipitation strengthening of nano-Si particles play a major role in the improvement of the tensile strength and hardening ability. As a result, a quantitative relationship of the processing–microstructure–performance has been systematically investigated and established, which explores a method for the precision control and large-scale application of DED-AlSi10Mg alloys. [Display omitted] • Experiments and simulations of directed energy deposition AlSi10Mg parts. • Validity of theoretical solidification models on the microstructure. • Linking non-isothermal aging model to precipitated phase. • Quantitative relationships of processing–microstructure–performance. [ABSTRACT FROM AUTHOR]

The additive manufacturing (AM) of eutectic high-entropy alloys (EHEAs) with seven components was simulated. The as-cast alloy comprised of primary dendritic phase and eutectic region between the FCC and Laves phase. The additive thermal cycle generated by the analytical model was used for phase-field and physical simulations. A thermomechanical simulator was used to perform the physical simulation. Scanning electron microscopy (SEM) was used to characterize the effect of AM on the thermal cycle of the test samples and the results showed that the sigma phase was formed in the primary dendritic phase. The formation of the sigma phase was correlated with thermodynamic predictions and heat treatment studies. The thermal cycle of the microstructure, which was predicted using the phase-field simulation, was correlated with the experimental results. The integrated approach that was adopted in the current study can be utilized for the accelerated exploration of alloys for additive manufacturing. • Integrated study of physical and computer simulation to identify the effect of additive manufacturing conditions in materials. • New phase formation during the additive condition for seven component EHEA. • Framework for accelerated screening new alloys for AM. [ABSTRACT FROM AUTHOR]

Al–Zn–Mg–Cu alloys are important for aerospace applications, and wire-arc additive manufacturing (WAAM) provides a way to produce large-scale metal structures. However, research on the effects of WAAM thermal cycles on the microstructure and mechanical properties of Al–Zn–Mg–Cu alloys is still lacking. In this study, quantitative thermal cycle data was obtained to investigate evolution of the microstructure, and then the mechanical behavior of the as-deposited part was investigated. Results indicated that the part mainly contained microcracks (predominantly liquation cracks), pores, and the interdendritic crystalline phase, which decreased the tensile properties. However, the grain morphology was dominated by orientations with direction of approximately 65° with respect to the deposition direction, which led to better tensile properties in the longitudinal direction than in the transverse direction. In addition, the microhardness reached the maximum (∼130 HV) after four to seven times thermal cycles, which was mainly attributed to the Guinier–Preston (GP) zone. The continuous high temperature resulted in the hardness minimum (∼104 HV), which was a significant factor in forming the η′ and coarse η phases in the part. Combined with the precipitation behavior, hardness of the whole part can be divided into two zone: unstable and stable zone. • Quantitative thermal cycle data was obtained for the first time to investigate the evolution of the microstructure and the mechanical behavior of the as-deposited part. • The effect of thermal cycles on the hardness evolution was investigated, the whole part was divided into two zone: the stable zone and the unstable zone. • Grain orientation mainly determined the anisotropy of tensile properties, and the relationship between solidification behavior and temperature field was investigated. [ABSTRACT FROM AUTHOR]

Abstract: Using a laser welding method, we have successfully welded two pieces of bulk metallic glasses based on Zr45Cu48Al7 without crystallization. No crystallization was observed and no visible defect of crack was recognized in the bead and heated-affected zone (HAZ) under the condition of welding scanning speed of 8m/min with an output laser power of 1200W. Our analysis of the temperature profile the thermal cycle (temperature history) in the bead and HAZ indicates that the temperatures in the bead and HAZ rapidly decreased to below 430°C resulted in glass formation from the melt in the bead and non-crystallization in the HAZ in the sample scanned at 8m/min. [Copyright &y& Elsevier]

For a better understanding of the transformation behaviour on NiTi, the electrical resistivity of Ni49.5Ti50.5 was precisely measured by a four-probe potentiometric method. The temperature dependence of the electrical resistivity is linear in the regions of the high- and low-temperature phases, and a drastic change in electrical resistivity is observed in the temperature range of the transformation. The transformation remains of the one-stage between the high- and low-temperature phase even with thermal cycling, although with increasing the number of thermal cycles the electrical resistivity versus temperature curve shifts to the low temperature side and the electrical resistivity increases in the single phase temperature region which is attributable to the generation of transformation-induced defects.The one-stage transformation changes to a two-stage transformation due to the appearance of an intermediate phase after an incomplete thermal cycle, and with subsequent thermal cycling the peak in the electrical resistivity is enhanced to stabilise the intermediate phase. The as-cut Ni49.5Ti50.5, of which the surface is damaged, shows a two-stage transformation, even during the first cooling after cutting, and a resistivity-peak due to such a two-stage transformation is also enhanced with thermal cycling. It is thought that the amount of defects plays important roles in the shifts of transformation temperatures and in the transfer from one-stage to the two-stage transformation, and contributes to the stability of each phase. [Copyright &y& Elsevier]

Measurements of the electrical resistivity were precisely performed on shape memory Ni50Ti50 alloy in order to reveal the irreversible behavior of the thermoelastic martensitic transformation with thermal cycling. The hump in the electrical resistivity during cooling is enhanced with increasing the number of complete thermal cycles to result in a peak, although no peak in the electrical resistivity is observed on the reverse transformation during heating. The electrical resistivity in the low-temperature phase, of which the temperature dependence is linear, increases with increasing the number of complete thermal cycles. The temperature coefficient of the electrical resistivity in the temperature region of the high-temperature phase increases with elevating the temperature. The transformation is strongly influenced by incomplete thermal cycles to result in a peak in the resistivity even on the reverse transformation after incomplete thermal cycling.It is thought that the anomalous behavior such as enhancement of a resistivity-peak, the increase in the electrical resistivity of the low-temperature phase, and the nonlinear relation between the resistivity and the temperature in the high-temperature phase are attributable to the appearance of an intermediate phase stabilized by transformation-induced defects, the accumulation of the transformation-induced defects, and the electron scattering due to the softening of a phonon mode in the high-temperature phase, respectively. It proved useful to make more accurate measurements of the electrical resistivity in order to investigate the intrinsic behavior of the transformation in NiTi. [Copyright &y& Elsevier]

For a better understanding of the transformation behavior in NiTi alloy containing silicon, the electrical resistivity and the thermal property in NiTi and NiTi(Si) were precisely measured by a four-probe potentiometric method and differential scanning calorimetry, respectively. The transformation behavior depends on the thermal cycles with the repetition of the transformation, and the thermal cycles tend to stabilize the intermediate phase during cooling because of the enhancement of a peak in the electrical resistivity. The peak in the resistivity of NiTi with increasing thermal cycles is markedly enhanced in comparison with NiTi(Si). The reverse transformation during heating remains a one-stage transformation from the low-temperature phase to the high-temperature phase in both NiTi and NiTi(Si). Although a peak in the resistivity during heating is detected in NiTi(Si), it is evaluated to be a seeming peak because the resistivity of the low-temperature phase is larger than that of the high-temperature phase near the reverse transformation temperature. The increase in the resistivity due to the transformation-induced defects is very large for the transformation of NiTi(Si), and NiTi(Si) is useful for examining the formation of defects introduced by a repetition of the transformation. It proved necessary to measure not only the electrical resistivity but also the thermal property in order to characterize the transformation behavior and the effect of the electron scattering, which are altered by an additional element. [Copyright &y& Elsevier]

In the current investigation, Al/Cu/SiC composites with different reinforcement contents were prepared for thermal applications via powder metallurgy and hot pressing technique to study the effects of reinforcement content and structure on the thermal behavior of the samples. Microstructural characterizations showed that SiC and Cu particles were uniformly distributed, and a continuous Cu network structure was formed in the Al matrix. Density measurements revealed that the samples Al/15Cu/10SiC and Al/45Cu/20SiC had the highest and lowest relative density (97% and 90%), respectively. Microhardness evaluations displayed that the composite hardness improved as the Cu and/or SiC contents increased. Besides, the coefficient of thermal expansion of the composites increased nonlinearly by elevating the temperature and it reduced with increasing the SiC content. A comparison of thermal expansion coefficient values to the Turner and Kerner models showed a slight difference (lower that 8%) only for Al/15Cu/10SiC and Al/45Cu/20SiC samples. Thermal cycles examination exhibited that as the number of cycles increased, the thermal strain of the composites increased. Furthermore, the thermal expansion coefficient of Al/45Cu/20SiC reduced to values lower than 7 ppm that indicates the significance of Cu network structure. Image 1 • Al/Cu/SiC composites were prepared for thermal applications by powder metallurgy. • SiC particles were uniformly distributed and a continuous Cu network was obtained. • A comparison of CTE values to the thermoelastic models showed a slight difference. • CTE values lower than 7 ppm indicated the efficiency of reinforcement structure. [ABSTRACT FROM AUTHOR]