Microstructural Elements Research Articles

Study on the activity, phase, thermal decomposition characteristics, microstructure, and chemical element of hardened cement powder under heating temperature of 100°C~1200°C

AbstractThe properties of thermoactivated hardened cement powder (HCP) are of great significance for the recycling and utilization of concrete waste. This paper focuses on heating activation of HCP under the temperature between 100 and 1200°C. The activity, phase changes and microstructure of thermoactivated HCP were analyzed. The results showed that HCP with heating temperature between 1000 and 1200°C showed high activity. Under the conditions of heating activation at 1200°C, water–binder ratio of 0.38 and curing time of 30 days, the compressive strength of the specimen made of HCP reached 17.56 MPa. When the heating temperature is between 700 and 1200°C, CSH gel is gradually decomposed into C2S and C3S. The chemical reaction products of cement and thermoactivated HCP are similar, both containing CaCO3, Ca(OH)2, AFt, Hydrotalcite, etc. Compared to the diffraction peaks of hydrated cement, the diffraction peaks of thermoactivated HCP are broadened and dispersed. The high Ca/Si and Al/Si ratios in the chemical reaction products of thermoactivated HCP are important reasons for the decrease in its mechanical properties.

Sleep-related epilepsies in the course of development in childhood

AbstractEpilepsy, as one of the most prevalent neurological diseases in childhood, has a strong reciprocal relationship with sleep. Sleep-associated epilepsy syndromes in childhood are mostly genetic and can be divided into (a) the group of self-limited focal epilepsies of childhood including self-limited epilepsy with autonomic seizures (SeLEAS) and self-limited epilepsy with centrotemporal spikes (SeLECTS) and (b) (non-self-limited) sleep-related hypermotor epilepsy (SHE). Sleep-accentuated (developmental and) epileptic encephalopathies (DEE/EE-SWAS, Landau–Kleffner syndrome [LKS]) are either genetic (possible transition from SeLEAS or SeLECTS) or structural, and they are characterized by continuous bilateral focal or generalized epileptic activity throughout the night with a clinical manifestation of stagnation or regression, in particular of cognition (verbal agnosia in LKS). Epilepsy syndromes with increased seizure frequency after sleep deprivation or with seizures in the transition to awakening include juvenile generalized epilepsy syndromes such as epilepsy with generalized tonic-clonic seizures alone (GTCA) or juvenile myoclonic epilepsy (JME), but also SeLECTS. Sleep is a very active process: Regeneration, reorganization, and consolidation of memory facilitate development and cognitive functioning. Epilepsy can alter sleep architecture and vice versa, which can appear as a vicious circle in epilepsies that are sleep related. Macrostructural elements of sleep such as sleep efficiency, sleep onset latency, wakefulness after sleep onset, REM and non-REM sleep fraction, as well as microstructural sleep elements such as slow-wave activity, slope of slow waves, cyclic alternating pattern (CAP), and physiological sleep figures, are important biomarkers with which to understand clinical symptoms such as cognitive stagnation and regression, to monitor treatment, but also to determine prognostic factors and will be an important tool for future studies.

Impedance Spectroscopy of Lanthanum-Doped (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 Ceramics

This study examines the effects of La3+ doping on (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3(PBZT) ceramics, which were synthesized using the conventional solid-state reaction method. X-ray diffraction analysis confirmed that the PBZT structure, including PBZT doped with La3+ at concentrations x = 1 at.% and x = 2 at.%, exhibited a rhombohedral (R3c) space group, while higher doping levels of x = 3 at.% and x = 4 at.% led to a dominant cubic (Pm-3m) phase with approximately 30% of a remnant rhombohedral component. Scanning electron microscopy (SEM, JEOL JSM-7100F TTL LV, Jeol Ltd., Tokyo, Japan) and energy dispersive X-ray spectroscopy (EDS) were utilized to investigate the structure and morphology of these ceramics. The findings indicated that the chemical composition of the ceramic samples closely corresponded to the initial stoichiometry of the ceramic powder. An increase in the amount of lanthanum results in a decrease in the average grain size of the ceramics. The electrical properties were further evaluated using complex impedance spectroscopy (IS) over a range of temperatures and frequencies, as well as temperature dependence of DC conductivity. The similarity in the changes in activation energy for DC conductivity and grain boundary conductivity, caused by lanthanum ion modification, allows for the conclusion that grain boundaries are the primary microstructural element responsible for conductivity in these materials.

Cellular solids and prestressed affine networks as models of the elastic behavior of soft biological structures.

We reviewed two microstructural models, cellular solid models and prestressed affine network models, that have been used previously in studies of elastic behavior of soft biological materials. These models provide simple and mathematically transparent equations that can be used to interpret experimental data and to obtain quantitative predictions of the elastic properties of biological structures. In both models, volumetric density and elastic properties of the microstructure are key determinants of the macroscopic elastic properties. In the prestressed network model, geometrical rearrangement of the microstructure (kinematic stiffness) is also important. As examples of application of these models, we considered the shear behavior of the cytoskeleton of adherent cells, of the collagen network of articular cartilage, and of the lung parenchymal network since their ability to resist shear is important for their normal biological and physiological functions. All three networks carry a pre-existing stress (prestress). We predicted their shear moduli using the microstructural models and compared those predictions with existing experimental data. Prestressed network models of the cytoskeleton and of the lung parenchyma provided a better correspondence to experimental data than cellular solid models. Both cellular solid and prestressed network models of the cartilage collagen network provided reasonable agreements with experimental values. These findings suggested that the kinematic stiffness and material stiffness of microstructural elements were both important determinants of the shear modulus of the cytoskeleton and of the lung parenchyma, whereas elasticity of collagen fibrils had a predominant role in the cartilage shear behavior.

Automated Workflow for Phase‐Field Simulations: Unveiling the Impact of Heat‐Treatment Parameters on Bainitic Microstructure in Steel

Bainitic steels are extensively utilized across various sectors, such as the automotive and railway industries, owing to their impressive mechanical properties, including strength, hardness, and fatigue resistance. However, the pursuit of achieving the desired optimal mechanical properties presents considerable challenges due to the intricate bainitic microstructures consisting of multiple phases. To tackle these challenges, an automated workflow is used for extracting 2D and 3D microstructural features. The proposed method allows for a detailed examination of the correlations between microstructure characteristics and the processing parameters, specifically the holding temperature during transformation. In these findings, it is revealed that as the holding temperature decreases, there is a notable reduction in microstructural element size and carbon partitioning. Some of the observations are microstructural features such as area, perimeter, and thickness of the bainitic ferrite grains under two different holding temperatures. Phase‐field simulations results show that the microstructures at lower holding temperatures have finer grains. The distributions of grain areas and perimeters are uniform, with smaller grains dominating at low and high isothermal holding temperatures. While the grain thickness measurements from simulations and experiments at high temperature are qualitatively aligned, data from low temperatures show discrepancies.

Quantifying laser irradiation-induced temperature field of particle reinforced metal matrix composites

While particle-reinforced metal matrix composites (PMMCs) are composed of particles and matrix with distinctly different thermomechanical properties, the thermal differences and coupled interactions between individual phases greatly determine the thermal characteristics of PMMCs under laser irradiation. In this work, we quantify the temperature evolution characteristics within SiCp/Al under laser irradiation by microstructural thermal finite element simulations and experimental investigation. Specifically, a 2D thermophysical FE model of laser-SiCp/Al interaction for the two-phase PMMCs material under laser irradiation is developed, which incorporates the temperature-dependent thermophysical properties of particles, matrix and interfaces, along with the considerations of the shape and distribution characteristics of particles, as well as the comprehensive thermal conditions. Furthermore, a 3D equivalent thermal FE model for experimental validation of predicted laser-induced temperature of SiCp/Al is developed, based on the derived equivalent properties. Meanwhile, an in-situ temperature measurement system is constructed for exploring temperature evolution characteristics during the on-going laser irradiation process, which validates a derivation of 1.7 % of predicted temperature by the equivalent thermal FE model. Finally, the impact of laser processing parameters on the temperature field of SiCp/Al is addressed. These findings provide valuable insights for understanding the thermal mechanisms of PMMCs under laser irradiation, and also the parameter optimization for laser processing of PMMCs.

Microstructure forming mechanism of inconel 625 alloy fabricated by laser/ultra-high (UHF) induction hybrid deposition method

To reveal the microstructure forming mechanism of laser/ultra-high frequency (UHF) induction deposition, this paper developed a microscopic phase-field (PF) model to numerically investigate dendrite growth during solidification. The macroscopic model of molten pool evolution is adopted to provide the solidification conditions for the microscopic PF model. The dendrite growth during laser deposition is simulated to evaluate the effect of UHF induction heat on the dendrite growth. Results show that because of the high temperature gradient and cooling rate, the PDAS of laser-UHF induction hybrid deposited layer is less than that of the laser deposited layer. The UHF induction heat also leads to a high flow velocity of the molten metal during laser-UHF induction hybrid deposition. The high flow velocity contributes to the decrease in PDAS by inhibiting the interdendritic enrichment of solute. During laser-UHF induction hybrid deposition, a higher solute gradient is present in the tip region of dendrite arm, leading to a faster dendrite growth rate. The UHF induction heat also increases the solute distribution coefficient during deposition, which further inhibits the element segregation. Under the action of UHF induction heat, a low interdendritic solute gradient and an evenly distributed solute can be obtained, thus helping increase interdendritic undercooling degrees and decreasing the PDAS. The simulated PDAS and solute distribution have good consistency with the experimental results. The spectral analysis of EDS line detection indicates that the laser-UHF induction hybrid deposited layer has a more refined microstructure and weaker element segregation than the laser deposited layer does.

Oxygen-rich combustion behaviors and mechanisms of a new Ni-Cr-based superalloy fabricated by selective laser melting

The mechanical and combustion behavior of a new Ni-Cr-based superalloy, fabricated by selective laser melting in an atmosphere with an oxygen concentration greater than 99.5 %, was investigated through the analysis of microstructural morphology, elements distribution and combustion kinetics. The results show that heat treatment eliminated the anisotropy of the as-built microstructures and improved the tensile strength. The studied superalloy can be ignited with a combustion threshold of about 2.5 MPa–3 MPa. The burning length and burning rate increase with the increase of pressure. The selective combustion of Al, Ti, Nb, Cr, Fe, Mo, and Cu elements occurred, resulting in the dissolution of γ′, γ", and δ precipitates and formation of holes at the grain boundaries in the heat-affected zone. The microstructures exhibit large elongated grains in the melting zone and column grains in the heat-affected zone along the heat dissipation direction. The combustion products are a mixture of oxides exhibiting dendritic structures in terms of selective combustion, density, and melting point. The findings from this study enhance our comprehension of the combustion process in nickel-based superalloys, offering valuable data and guidance for the advancement of new oxygen-rich combustion-resistant superalloys.

Thermal cycling behavior of Srx(Zr0.9Y0.05Yb0.05)O1.95+x thermal barrier coatings by suspension plasma spraying

AbstractThe thermal barrier coatings (TBCs) consisting of Srx(Zr0.9Y0.05Yb0.05)O1.95+x were prepared using the suspension plasma spraying (SPS) method. Precursor suspensions were prepared via co‐precipitation for this purpose. Detailed microstructural, phase composition, and phase content analyses were conducted on these coatings, designated as SZYY‐1 (x = 1.0), SZYY‐2 (x = 0.9), and SZYY‐3 (x = 0.8). Additionally, the coatings underwent a thermal cycling test at 1121°C for 1 h. To assess the morphology of thermally grown oxide (TGO) in a real coating, a finite element model was employed. SPS‐SZYY‐2 with columnar crystal structure was found to have the highest number of thermal cycling, up to 345 times. The thermophysical high‐temperature properties of the coating can be effectively improved through suitable second‐phase content. Microstructural and finite element analyses revealed that stress, primarily caused by the continuous growth of the Co3O4, NiO and Spinel (CNS) layer within TGO, was the predominant factor leading to coating failure. At elevated temperatures, transverse cracks formed at the interface between the bond coating and ceramic top coating due to mismatched thermal expansion and sintering effects, ultimately leading to coating degradation. Therefore, reducing the generation rate of large stresses in the coating, especially shear stresses, can effectively prevent the generation and propagation of transverse cracks and increase the thermal cycling life of TBCs.

Water-rock interfacial softening model of cemented soft rock: An experimental and numerical study

Cemented soft rock is prone to softening when exposed to water, and its mechanical properties deteriorate rapidly, which is an important reason to induce the instability and failure of engineering soft rock mass. The softening mechanism of soft rock is essentially the deterioration of microstructure caused by the change of water-rock interface. Considering the general characteristics of soft rock, the microstructural evolution characteristics and element loss over varying immersion time are then compared and analyzed. The Interfacial Cemented Bonding (ICB) structure is proposed to describe the evolution of water-rock interface. Based on the diffusion theory, the theoretical equation describing the evolution of water-rock interface is derived and compared with the experimental results. The meso-softening damage factor (MSDF) of soft rock is proposed and introduced into a numerical method to establish a strength degradation discrete element method (SD-DEM) model. The results show that the softening process of soft rock is accompanied by the shedding and suspension of particles and the dissolution of soluble substances. Besides, the softening of soft rock has obvious nonlinear dynamic characteristics. The fitting degree between the theoretical values and the experimental results is relatively high, which verifies the reliability and rationality of the dissolution-diffusion interfacial softening model. The numerical results are in good agreement with the experimental ones. This study provides a new idea for understanding the mechanism of water-induced softening characteristics and strength degradation of soft rock.

Wetting-induced collapse of loess: Tracing microstructural evolution

Loess is a silt-dominated, clastic yellow-to-yellowish brown aeolian sediment with high porosity and low density. The metastable microstructure of loess makes it highly susceptible to collapse, which plays a major role in landform evolution, geohazard development and engineering damages, particularly the widespread occurrences of settlement, deformation and cracking of civil engineering structures. Differing from the existing investigations based on pre- and post-collapse comparison, the present study is to report the microstructural changes during the collapse process and to determine how each microstructural constitutive element participates in this process. A series of laboratory tests was conducted on undisturbed loess specimens to simulate and capture snapshots of microstructure at five representative points during the entire collapse process. Results show that the loess microstructure becomes more homogeneous as the outstanding macropores are crushed into smaller (meso- and mini-pores) pores, the number of pores is dramatically increased, and the pore throats become narrower. The pore shapes have no obvious changes and remain elongated and rough-edged morphology from the point of view of statistic. Regarding solids, the pre-collapse unstable point-to-point contacts tend to transform into relatively stable edge (edge-edge or point-edge) type contacts, whilst coarse particles tend to reorient along the horizonal direction. XRD, SEM and EDS analysis indicates that these changes in the nature and distribution of pores and particles result from (1) the breakage and disintegration of moderately to highly weathered particles, (2) the disintegration of the matrix due to the swelling of clay minerals and the dissolution of calcium carbonates, (3) the consequential modifications of the microscopic forces which lead to slipping, rotation and therefore dislocation of particles, and (4) the collapse of mesoscale force chains along particles, reforming on smaller scales with larger numbers, shorter lengths and horizontal alignments.

Temperature-dependent mechanical properties and crystal plasticity parameters for additively manufactured Haynes-214 alloy: Experiments and numerical modeling

Our experimental mechanical testing data demonstrated that the additively manufactured (AM) laser powder bed fusion (L-PBF) Haynes-214 alloy exhibits non-linear mechanical properties as the temperature rises from ambient to 870 °C. Crystal plasticity (CP) simulations provide an effective approach to gaining deeper insights into microstructure-property linkages under thermomechanical loading. This method can reduce the need for costly high-temperature mechanical testing while accounting for the effects of crystallographic texture and grain morphology on the mechanical behavior of AM materials. However, calibrating a CP model is time-consuming because individual simulations are computationally expensive and hundreds (or more) of iterations over parameter sets may be required. To address this issue, we have designed a machine learning-differential evolution (ML-DE) CP framework that can accurately interpolate the tensile properties of AM L-PBF Haynes-214 alloy across a wide temperature range from ambient to 870 °C, with minimal reliance on experimental data. The framework uses electron backscatter diffraction (EBSD) measurements to generate statistically equivalent microstructural volume elements to serve as inputs to the CP modeling framework. Stress–strain curves were generated from 1000 CP simulations, which serve as the training data set for the three ML regression algorithms explored: linear, extra-trees, and multi-layer perceptron. These three regression models were independently evaluated to compare their efficiency and identify the most suitable algorithm for the given problem. Results revealed that the extra-trees ML regressor outperforms the other models in both qualitative and quantitative aspects with an R2 of 0.98. Subsequently, the differential evolution optimization approach is employed to calibrate the ML-based CP material parameters with experimental results obtained at various temperatures. Finally, temperature-dependent CP material parameters are formulated. The effectiveness and efficiency of the designed framework are validated through comparison with experimental results, demonstrating a high degree of agreement. These calibrated parametric constitutive equations enable further use of the CP model to study the deformation behavior of this alloy under a wide range of thermo-mechanical loading conditions.

Boring finance. Petroleum exploration and firm debt: Evidence from Norway

The role of financing in petroleum exploration has gained prominence due to sustainability commitments by major financing institutions. Yet the relationship between exploration and financing has been little explored and poorly understood. I create a novel data set combining detailed exploration data with financial register data on all public and private firms operating on the Norwegian Continental Shelf to analyze the relationship between debt and drilling decisions. I make use of both an over-dispersed Poisson regression model estimated by maximum likelihood and a Bayesian hierarchical negative binomial regression model where key elements of the industry microstructure are specified and explicitly modeled. I find evidence that short-term debt is associated with lower rates of drilling and more modest evidence that long-term debt has a slightly positive relationship with exploratory drilling. This evidence is consistent with a financial constraints theory of oil drilling, and supports the argument that exploration drilling is dependent on a firms access to financing.

Enhancement of the microwave absorption performance of flaky FeSiCr powder through the compounding of cobalt ferrite

FeSiCr/CoFe2O4 composites were prepared by mechanical ball milling of cobalt ferrite prepared by hydrothermal method and flaky FeSiCr alloy powder. The phase and element of the composites was observed by XRD and XPS. The microstructure and surface elements of the composites were observed by SEM and EDS. The findings from the analyses confirmed the successful synthesis of the FeSiCr/CoFe2O4 composites. The results of EMP tests indicated that the electromagnetic parameters were balanced and the impedance matching was improved. When the mass percentage of cobalt ferrite was 20 %, the impedance matching was the best, and the RLmin reached −41.04 dB at 4.8 GHz. And the maximum EAB reached 5.4 GHz. By adjusting the thickness of the absorber, the EAB can be extended to 9.5 GHz (2.6–12.05 GHz), encompassing the entire C-band and X-band. The EMA performance of the composites has been greatly improved. FeSiCr/CoFe2O4 composites may serve as potential microwave absorbing materials in the future due to the wide range of economical raw materials, strong microwave absorption capacity and extensive absorption frequency range.

Deciphering the Mortar Composition of Ancient Chinese Pagodas: A Comparative Analysis from the Tang to Ming Dynasties in Shaanxi Province

The mortar materials from the internal and external walls of ancient Chinese pagodas in Shaanxi (Luoshan Temple Pagoda (847–858 AD), Daxiang Pagoda (960–1279 AD), and Qianjin Pagoda (1609 AD)) were investigated. Qualitative and semi-quantitative techniques including scanning electronic microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and thermogravimetric analysis with differential scanning calorimetry (TGA-DSC) were employed. The physical and chemical characteristics including microstructural morphology, chemical composition, element distribution, and organic additives of the mortar samples were studied. SEM indicated that the mortar from the external wall exhibits a tightly bonded matrix, with the irregularly shaped particles, and the carbonation of the calcium carbonate in the mortars closely resembles that of aragonite crystals. The results of EDS, XRD, FTIR and TGA-DSC revealed that mortar from external wall of these ancient pagodas were air-hardened lime, and complete carbonization with no traces of calcium hydroxide, while mortars from internal wall primarily comprises local clay and lime. In addition, ATR-FTIR and iodine-starch discoloration tests confirmed that the presence of starch in the external wall of Daxiang Pagoda, whereas no organic additives were detected in the Qianjin and Luoshan Temple Pagoda.

In2O3[sbnd]Co3O4 p-n heterojunction sensors: Comparison of efficient interfaces and gas sensing enhancement mechanism through two strategies

The fabrication of heterostructure has been considered as a great potential to improve the gas sensing performances due to its flexible features at the interface. The p-n heterojunction composites with Co3O4 modified In2O3 were synthesized through physical mixing calcination process and hydrothermal method for the effectiveness comparison as gas sensors for detecting of ethanol. The morphology, microstructure, and surface element state of the heterojunction materials were investigated. Furthermore, the forbidden band width and the active oxygen species were analyzed on account of the efficient interface for the heterojunction materials. The gas response of heterojunction sensor by the physical mixing calcination method exhibits an outstanding response of 5585 towards 100 ppm of ethanol gas, which was about 10 times higher than that by two-step hydrothermal method. Moreover, it shows improved adsorption and desorption kinetics with response time of 8 s and 15 s, respectively at the operating temperature of 280 °C. It also reveals a distinct selectivity to ethanol with better reproducibility, the humidity-dependent stability and ambient retention over a period of 30 days with rendering 94 %. Combined with the in-situ infrared diffuse reflection spectrum analysis and Hall effect test from the perspective of catalytic and electrical properties, we inferred the gas sensing enhancement mechanism involved in In2O3Co3O4 p-n heterojunction with the design of proof-of-concept demonstration by surface modification, which could provide an approach to explore the effect of heterojunction interface through the variable method.

Additive manufacturing of Inconel 718/CuCrZr multi-metallic materials fabricated by laser powder bed fusion

The multi-metal structure combines the thermal stability and high-temperature resistance of Inconel 718 (IN718) with the excellent thermal conductivity of CuCrZr, making it highly valuable for applications in aero-engines. Nevertheless, it is challenging to fabricate high-strength multi-metallic interfaces due to their large thermophysical differences. In this paper, the interface between IN718 and CuCrZr was well bonded by laser powder bed melting technology and optimizing the process parameters. The effects of process parameters on the interfacial properties of the prepared IN718/CuCrZr were analyzed. The microstructure characteristics, element distribution, microhardness, tensile properties, and thermal conductivity of IN718/CuCrZr were studied. The melting behavior, interface characteristics, and formation mechanism of multi-metallic materials were discussed. The experimental results show that the volumetric energy density range of 209.88–404.76 J/mm3 is suitable for the formation of IN718/CuCrZr. The formation of interface characteristics is mainly attributed to Marangoni convection, which promotes the mixing of Ni and Cu elements, helps form a stable transition layer at the interface, and enables a natural transition between the two metal interfaces. This indicates that there is good metallurgical bonding at the IN718/CuCrZr interface. At the same time, the equiaxed grain structure and grain refinement were observed in the transition zone, which was also reflected in the longitudinal section hardness distribution of the IN718/CuCrZr interface. The tensile test results show the transverse of IN718/CuCrZr (IN718/CuCrZr (T)) and longitudinal of IN718/CuCrZr (IN718/CuCrZr (L)) exhibit different deformation mechanisms. The fracture of IN718/CuCrZr (T) occurs in the CuCrZr region, indicating that the interface is well bonded. The tensile properties of IN718/CuCrZr (L) are higher than that of CuCrZr and lower than that of IN718, and brittle fracture occurs at the interface. The tensile properties of IN718/CuCrZr (T) are dominated by CuCrZr and IN718/CuCrZr (L) is determined by both IN718 and CuCrZr. Compared with IN718, the thermal conductivity of IN718/CuCrZr multi-metallic structure is significantly improved. This will open up the possibility of multi-metallic materials additive manufacturing for the next generation of aerospace structures.

Comparing Deaf/Hard-of-Hearing Children's Oral Narratives Using Movies and Static Books.

Clinicians utilize various methods for narrative sampling, including oral assessments like story generation and retelling, often aided by visual aids. Assessing language skills in deaf/hard of hearing (DHH) children requires careful narrative technique selection. This comparative observational study investigates the narrative outcomes of story generation and retelling tasks in 21 DHH children, using both book and movie contexts. Most microstructural elements (except for the mean length of utterance) were similar across the book and movie conditions. Differences in word choice, such as the use of action verbs, were evident. Macrostructural differences between book and movie conditions were insignificant regarding story grammar elements. However, movies, being visually engaging, potentially enhance the inclusion of characters, settings, plot, and actions. This research illuminates narrative assessment considerations, emphasizing technology's role in enhancing options for assessment for DHH children.

Microstructure and finite element analysis of Mo2C-diamond/Cu composites by spark plasma sintering

Abstract Mo2C layer was generated on the diamond surface via vacuum micro-evaporating, which was used as the reinforcement particles to fabricate diamond/Cu composites by spark plasma sintering (SPS). The effect of evaporation parameters on the forming of Mo2C, and the holding time on diamond/Cu composites fabrication is studied. Combined with the experiment and finite element analysis (FEA), the holding time on diamond/Cu composites influence on the thermal conductivity (TC) of composites is further discussed. The results show that the Mo2C area on the diamond surface would gradually enlarge and cover the diamond surface evenly with the increment in evaporation time and temperature, better vacuum micro-evaporating parameters were given as 1,000°C for 60 min. The fractures in the diamond/Cu composites are mainly ductile fractures on copper and diamond falling out from the Mo2C interface. It was found that sintering time would significantly influence the dissipation property of diamond/Cu composites. A comprehensive parameter for SPS was obtained at 900°C, 80 MPa for 10 min, the relative density (RD) and TC of the composites obtained under the parameter were 96.13% and 511 W/(m K). A longer sintering time would damage the Mo2C interlayer and further decrease the bonding between copper matrix and diamond particles, which would lower the RD and TC of composites. It can be obtained from the comparison of simulation results and experimental results that the FEA result is closer to the experimental results due to the gaps with low heat conduction, and the air in the gaps is added in the simulation process.

Influence of microstructure evolution and element segregation on high temperature tensile behaviors in GH4706 alloy

This work systematically investigated the influence of microstructure evolution and element segregation on tensile properties and fracture behaviors of GH4706 superalloy under different temperatures (25 °C, 400 °C, 500 °C, 600 °C and 650 °C). The advanced methods of TEM, AES and SIMS were conducted to characterize the variation of microstructure and element distribution. Experimental results showed that the yield and tensile strength of the test alloy decreased while the corresponding elongation increased as the increment of test temperature. The dominated fracture mode was intergranular brittle fracture at the temperature of 25 °C, gradually transforming to ductile dimple fracture as the temperature increased. This phenomenon was determined to be closely related to the increment of average grain size and size of γ'/γ″ coprecipitates as temperature rose. It was worth noticing that the elongation performed abnormally low (16.3%) at the temperature of 500 °C, exhibiting intermediate temperature brittleness (ITB) phenomenon. The SIMS analysis showed that the segregation of S towards grain boundary was the most obvious at the temperature of 500 °C, which was considered as the main factor leading to ITB. In addition, the coarsening of carbides at grain boundaries and local strain non-uniformity caused by dislocations could also resulted in ITB. The main reason for maintaining good strength and plasticity at the temperature of 650 °C was contributed to the softening of γ' phases by repeated cutting of dislocations and deformation twins, reducing the hindrance to the movement of dislocations. Moreover, composite strengthening effect of P and B could improve bonding strength, stabilize grain boundaries, and effectively suppress the initiation of intergranular cracks.