Al2O3/SiC composite ceramics were prepared from α-Al2O3 and SiC by a pressureless sinter method in this study. The effect of SiC contents on the mechanic properties, phase compositions and microstructure is studied. Experimental results show that the vickers hardness, wear resistance and thermal conductivity of the samples increase with the increase in the SiC content, and the hardness of the sample reaches 16.22 GPa, and thermal conductivity of the sample reaches 25.41 W/(m.K) at room temperature when the SiC content is 20 wt%(B5) and the sintering temperature is at 1 640 °C. Higher hardness means higher scour resistance, and it indicates that the B5 material is expected to be used for the solar heat absorber of third generation solar thermal generation. The results indicate the mechanism of improving mechanical properties of Al2O3/SiC composite ceramics: SiC plays a role in grain refinement that the grain of SiC inhibits the grain growth of Al2O3, while the addition of SiC changes the fracture mode from the intergranular to the intergranular-transgranular.
In order to enlarge the size of bulk metallic glasses (BMGs), two Cu36Zr48Al8Ag8 BMGs plates were successfully welded by friction stir welding (FSW) without obvious crystallization. The effect of friction stir welding on microstructure and mechanical properties of the BMGs was investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to evaluate the changes of the crystalline particles in the BMGs. Nanoindentation was applied to analyze the changes of the amorphous matrix. Micro-hardness of the stir zone before and after FSW was tested to explore changes of the mechanical properties. Results show that the original Al3Zr particles in the BMGs were refined and some cavities parallel to the rotating direction of the pin were observed in the amorphous matrix after FSW. Furthermore, micro-hardness of the stirred zone rises approximately 50 Hv compared with the as-cast sample due to structure relaxation of the amorphous matrix.
Effects of layer quantities and stacking sequences on L-shape composite manufacturing qualities in using OOA(out-of-autoclave) prepregs were studied. The mechanisms of air evacuated in 5 kinds of lay-ups were revealed by image analysis of cut surfaces and thickness measurements. Results show that air in OOA prepregs is evacuated in two ways. Most of the air is forced out of layers directly by vacuum before air accesses in prepregs closed. Very little entrapped air moves perpendicularly to outer layers under hydrostatic resin pressure. When a laminate contains less than 16 layers, voids can hardly be found in layers. When a laminate contains more than 16 layers, voids cannot be expelled completely during the window of vertical movement. As for stacking sequences, the synergetic effect of slip function and nest function determines the thickness and voids content of laminates. Results show that the average of single layer thickness of unidirectional layers is the lowest, and the average of single layer thickness of quasi-isotropic layers is the highest. The voids content of quasi isotropic is the highest, which is consistent with the theoretical analysis.
Al2O3 particles reinforced hypereutectic Al-Si composites were prepared by in situ Fe2O3/Al reaction system. The thermodynamic analysis and microstructure evolution were investigated by differential scanning calorimetry, optical microscope, scanning electronic microscopy and transmission electron microscope. Results show that the reaction between Fe2O3 and Al is spontaneous which can be separated into two steps at different temperatures. The in situ Al2O3 particles in nano size distribute on the Al matrix accompanied with long needle-shaped β Fe-rich intermetallic phase. With different content of Mn addition, β phase can be modified to α-Al15(Mn,Fe)3Si2 and δ-Al4(Fe,Mn)Si2. Both tensile strength and elongation results at room temperature and 300 °C reveal that the optimal Fe-rich intermetallic phase is finer Chinese-script and polyhedral α phase with a Mn/Fe mass ratio 0.5 for the composites. Both in situ Al2O3 particles and α-Fe phases contribute to the properties improvement of the composites
The heavyweight ultra-high performance concrete (HUHPC) was prepared with barite sand partially replaced by titanium-rich heavy slag sand (THS) at replacement proportion of 0%, 30%, 50%, 70% and 100% in this work. The results show that THS incorporation can effectively improve the mechanical properties and reduce the volume shrinkage of HUHPC. The HUHPC with 50% THS replacement reaches an apparent density of 2 890 kg/m3 (for fresh HUHPC), 28 d compressive strength of 129 MPa, 28 d flexural strength of 23 MPa, 28 d flexural toughness of 28.4, 56 d volume shrinkage of 359×10−4 and, as expected, excellent durability. Microstructural investigation demonstrates that the internal curing of pre-wetted THS promotes the hydration of the surrounding cement paste thereby strengthening the interfacial transition zone, resulting in the “hard shell” formation around aggregate to “protect” the aggregate. Additionally, the “pin structure” significantly improves the cement paste-aggregate interfacial connection. The combination of “hard shell protection” and “pin structure” remarkably improve the mechanical properties of HUHPC produced with porous THS aggregate.
The pre-soaked shale employed as an internal curing agent and CaO employed as expansion agent were incorporated into concrete to investigate their effects on the mechanical properties and autogenous deformation of early-age concrete. We have conducted the relevant tests for setting time, mechanical properties, internal relative humidity and autogenous deformation of early-age concrete with shale or/and CaO incorporation. The results indicate that the set behavior is delayed by shale addition but is accelerated with CaO. The shale addition firstly enhances and subsequently decreases the strength, but CEA addition has a weakening effect. Additionally, shale or/and CaO incorporation deteriorates the elastic modulus. The shale and CaO incorporation significantly improve the internal relative humidity of concrete. The internal curing efficacy of shale could synergistically mitigate the autogenous shrinkage, that is, could enhance the expansion of CaO and then greatly reduce the contraction, which is significantly beneficial to impede the shrinkage-introduced cracks of early-age concrete.
The physical performance of recycled asphalt was used as the main evaluation index to study the optimal range of a self-made rejuvenator. Through the penetration, viscosity and gel permeation chromatography (GPC) tests, the diffusion degree of the rejuvenator under different temperatures and time process was analyzed, and the diffusion efficiency of the rejuvenator was evaluated from the macro and micro perspective. The regeneration mechanism of the rejuvenator in the aged asphalt was also analyzed using the Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and chemical composition tests. The research results showed that the optimum rejuvenator content was about 3%. Higher temperature and longer time were beneficial to improving the permeability and diffusion of the rejuvenator. During the aging process, the light components were reduced, and more macromolecular asphaltenes were generated as well as a large number of carbonyl and sulfoxide. After diffusion and regeneration, the light components in the asphalt were supplemented, the wrinkles and gullies of the aged asphalt were almost improved to the surface state of the matrix asphalt.
In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires, a SiO2 aerogel-cement mortar coating was prepared. Based on the HC curve, a self compacting concrete cube specimens coated and uncoated with SiO2 aerogel-cement mortar (SiO2-ACM) were heated to simulate tunnel fire for 0.5, 1, 1.5, 2, 2.5, 3 and 4 h, respectively.The residual compressive strength was tested after the specimens were cooled to room temperature by natural cooling and water cooling. The results show that, the damages of specimens become more serious as fire time goes on, but the residual strength of specimens coated with SiO2-ACM is always higher than that of uncoated with SiO2-ACM. In addition, the residual strength of specimens cooled by water cooling is lower than that of natural cooling. However, for the specimens coated with SiO2-ACM, the adverse effects of water cooling are lessened. With the increase of fire time, the protective effect of SiO2-ACM is still gradually improved. Finally, a formula was established to predict the residual 150 mm cube compressive strength of specimens protected by SiO2-ACM after a simulated tunnel fire.
A molecular modified PCE-type GA was self-synthesized, and the grindability concerning grinding duration and particle size distribution of ground cement was evaluated. Setting time, flowability, hydration heat, mechanical properties and microstructure of the ground cement were also investigated. The results show that: PCE-type GA is effective in cement grinding. With 0.03% PCE-type GA added into cement clinker, the Blain surface area reaches to the highest at every ten minutes, and the volume percent of cement particles with size of (0–32 µm) reaches the highest. Excessive amount of PCE-type GA seems to impair the grinding efficiency. The grinding efficiency promotes cement fineness and hence contributes to the cement hydration degree as well as improves the mechanical properties.
A quantitative pH measuring method has been used to measure the pH of pure and blended cement mortars. The blended cement mortars incorporating supplementary cementitious materials (SCMs) such as fly ash (FA), ground granulated ballast furnace slag (GGBFS) and palm oil fuel ash (POFA) were used. Moreover, different variables affecting the pH values of CBMs such as temperature of sample solution, quantity of sample powder, dilution ratio and temporary storage of sample during pH measuring process have been studied for all cement mortars.
Hydration-heat-inhibiting materials(HIM) with polysaccharide as core material was prepared using microcapsule sustained-releasing technology, through a centrifugal spray granulation process after melting together. The preparation process parameters of HIM were selected by the semi-adiabatic temperature rise test of cement paste. TAM air microcalorimeter was used to investigate the regulation performance of HIM on the hydration of cement. The influence of HIM on the microstructure of cement was investigated by XRD, SEM, and TG-DSC.The results showed that the most suitable wall material for HIM was polyethylene wax, the optimum polyethylene wax/polysaccharide mass ratio was 1, and the most effective particle size was 0.16–0.30 mm. Polysaccharide coated by polyethylene wax released slowly, and the peak heat release rate of cement could be reduced by 55.2% after continuous regulaion. The regulation period continued to 120 h. HIM mainly decreased the C3S reaction rate, which resulted in a 39.2% peak value reduction of hydration heat release rate. However, HIM had little regulation on C3A. The hydration heat release process of cement-based materials can be designed by adjusting the dosage of HIM.
Bituminous binders have been modified by using cocamide diethanolamide. The chemical material used in this study is used for the first-time on the purpose of modification of the bitumen. In addition to the conventional bitumen tests (penetration, softening point and ductility tests), adhesion and peeling tests (Vialit, Nicholson and California tests) were carried out on the bituminous binders which are modified with different ratios of cocamide diethanolamide. According to the results of the tests, the most appropriate additive ratio has been determined. Samples containing the reference bituminous binder and the bituminous binder modified with the most appropriate cocamide diethanolamide ratio were prepared using the superpave volumetric mix design method (SuperpaveTM). In accordance with standard method of test for resistance of compacted asphalt mixtures to moisture-induced damage (AASHTO T 283), the moisture susceptibility of prepared samples has been examined. In order to observe the changes in strength due to the temperature difference, prepared samples were subjected to the freeze-thawing test in accordance with standard test method for resistance of concrete to rapid freezing and thawing (ASTM C 666).
Through the influence of the dosage of culture solution and calcium source on hardness and compressive strength of samples, the formulation of microbial cementitious materials was optimized and defined. The influence of temperature on composition, microstructure and mechanical properties of loose sand cemented by microbial cementitious material was compared and analyzed systematically. With the increase of temperature, the performance of loose sand was improved remarkably. Calcite with cementitious properties could be induced at higher temperatures, but not at lower temperatures. When the temperature was 30 °C, loose sand cemented by microbial cementitious material had more calcite and more dense structure. Moreover, hardness and compressive strength were also superior. The wind tunnel test showed that the wind erosion resistance was improved obviously and the mass loss was lower at high temperature. Engineering properties of loose sand cemented by microbial cementitious material was measured integrally. Through comparative analysis, engineering properties of loose sand were basically unchanged, and there was no negative effect on the later period use of sand.
A hyperbranched epoxy (AHEP) resin with terminal allyl groups was synthesized. The number average molecular weight of the synthesized AHEP is 1 260, the multi-dispersion coefficient is 1.88, and the branching degree is 0.9. The hyperbranched epoxy resin and bismaleimide(BMI) monomer were heated to extend the chain and then blended and cured with methyl nadic anhydride. Studies have found that when the molar ratio of AHEP: BDM is 1:2, the mechanical properties and heat resistance of the resin casting body reach the best. Among them, the impact toughness was 15.05 kg/m2, the bending strength was 101 MPa, and the heat resistance temperature index was 229.23 °C. We used AHEP to toughen bismaleimide resin in three ways simultaneously: hyperbranched structure, allyl copolymerized brackets chain and flexible side chain (epoxy group) addition. Experiments have proved that AHEP can improve the flexibility of the BMI chain and maintain its heat resistance, thereby forming a matrix with excellent mechanical properties and processing properties.
This article explores the effects of doping ferroelectric materials MgTiO3 with different proportions on the properties of polyaniline (PANI). PANI / MgTiO3 composites were prepared by in-situ composite method. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to characterize the structure of the composites. Scanning electron microscope (SEM) was used to characterize the morphology of the composites.The thermal stability of the composites was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG). Electrochemical methods (cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), and constant current charge-discharge test) were used to compare and analyze the electrochemical performance of the composites.TG-DTG analysis and electrochemical experiments all show that the thermal stability and electrochemical properties of the PANI / MgTiO3 composite with a mass ratio of 82/18 (w/w) are the best. The results indicate that there is a synergistic effect between PANI and MgTiO3, which improves the performances of the PANI when the appropriate amount of MgTiO3 is added.
High entropy alloys (HEAs) possess good mechanical properties and a wide range of industrial applications. In this paper, phase formation prediction theory, microstructure, properties and preparation methods of light-weight HEAs (LWHEAs) were reviewed. The problems and challenges faced by LWHEAs development were analyzed. The results showed that many aspects are still weak and require investigation for future advanced alloys, such as clarification of the role of entropy in phase formation and properties of HEAs, improved definition and different generations division of HEAs, close-packed hexagonal (HCP) phase structure prediction and corresponding alloy design and fabrication. Finally, some suggestions were presented in this paper including in-depth research on formation mechanism of multi-component alloy phase and strengthening of large-scale HEA preparation methods via technology compounding and 3D printing technology. Also, there is a need for more research on the in-situ preparation of HEA coatings and films, as well as developing LWHEAs with superior strength and elevated temperature resistance or ultra-low temperature resistance to meet the requirements of future engineering applications.
We demonstrate a 2205 duplex stainless steel (DSS) synthesized by aluminothermic reaction and followed two-step rolling which had a superior yield strength of 863 MPa, ultimate tensile strength of 1 103 MPa and an elongation of 21% at room temperature. The phase, grain size and distribution of the steel were characterized by optical microscope, X-ray diffraction, electron back-scatter diffraction and transmission electron microscope. The results show that the steel consists of lamellar ferrite and austenitic phase with multiple grain size distribution from nanoscale to microscale. The high strength is attributed to strengthening of high back stress arising from laminated dual-phase heterogeneous ultrafine grained structure and distribution. The high ductility originates from back-stress hardening and dislocation hardening.
The changes of the microstructure and the mechanical properties of FeCrMoCBY amorphous coatings prepared by plasma spraying after heat treatment were investigated. 300, 400, 500 and 600 °C were selected as the heat treatment temperature, and the crystallization phenomenon occurred after the heat treatment at 600 °C. The crystallization products of the coating heat-treated at 600 °C were α-Fe and Fe23(C, B)6. Heat treatment was beneficial to the microhardness and the bonding strength of the coatings. The microhardness of the coating heat-treated at 600 °C increased obviously, and the strongest bonding strength occurred in the coating heat-treated at 500 °C. The improvement of the wear resistance of the coatings could attribute to heat treatment as well, and the wear resistance of the coating heat-treated at 600 °C was the optimum, compared with the coating heat-treated at 500 °C.
A facile modification strategy is developed to promote the proliferation and osteogenic differentiation of rat bone marrow stromal cells (rBMSCs) through deposition of a bioactive calcium silicate (CS) coating on the porous surface of poly (ether-ether-ketone) (PEEK) with the assistance of poly(dopamine) (PDA). The porous structures are etched on the surface of PEEK after sulfonation treatment. A poly(dopamine) layer is coated on the porous surface of the sulfonated PEEK (SPEEK), which provides anchoring groups for the subsequent deposition of the CS layer. Results show that the CS coating on the porous surface of SPEEK significantly improve the hydrophilicity and biomineralization formation of hydroxyapatite. Compared with PEEK, SPEEK-PDA-CS displays higher bioactivity to promote the proliferation and osteogenic differentiation of rBMSCs, including the increase of ALP activity and formation of calcium nodules, the expression of osteogenic differentiation-related genes. These results are beneficial to extending clinical applications of PEEK-based implants for bone tissue repair and orthopedic surgery.