The interfacial reaction between carbon steel and CO2-Cl-, along with the effect of HCO3- on the formation of corrosion products scale on the steel in the solution of CO2-Cl--HCO3- at room temperature were investigated via electrochemical impedance spectroscopy and potentiodynamic polarization measurement. The results show that the addition of CO2 significantly increases the dissolution rate of carbon steel, whereas affects the Cl-concentration little and that, the addition of Cl- with high concentration can inhibit the dissolution of CO2, leading to a slight decrease in the corrosion rate of carbon steel. The formation of corrosion products film on the surface of carbon steel is not obvious after adding a small amount of HCO3- in the solution, correspondingly the formation of loose corrosion products cannot inhibit the further dissolution of carbon steel; However, excessive HCO3- addition may accelerate the precipitation of fine crystallites by increasing the supersaturation of FeCO3, and thus inhibiting the corrosion process.
The effect of surface roughness of steel ring (GCr15) as a counterpart of the friction pair on the wear of bismuth bronze (CuSn10Bi3) under oil lubrication condition was investigated by MRH-3 ring-block friction and wear tester. While the friction surfaces at different wear stages were characterized by means of scanning electron microscopy (SEM) and three-dimensional profiler. The oil particle size was analyzed and the friction process of the micro-convex body was numerically simulated, and the wear mechanism of CuSn10Bi3 was revealed from the microscopic point of view by combining experiment and simulation. The results show that: The roughness of the steel ring surface has a significant effect on the wear process of bismuth bronze. When the roughness of the steel ring Ra increases from 0.01 to 0.8, the tribological performance indexes increase by about 2 times, the size of the wear debris generated in the whole process increases by 1.5 times, the time experienced in the running-in wear stage and the severe wear stage increases by 0.7 times, and the time experienced in the stable wear stage decreases by 0.4 times.
Ti-6Al-4V alloy is widely used in laser solid forming, however, low work-hardening ability and ductility limit its industrial applications. In this paper, a novel Ti-4.13Al-9.36V (%) alloy with cluster composition of 4[Al-Ti12](AlTi2)+12[Al-Ti14](V2Ti) was designed based on the cluster composition formula 12[Al-Ti12](AlTi2)+5[Al-Ti14](V2Ti) of Ti-6Al-4V. Samples of two alloys Ti-4.13Al-9.36V and Ti-6.05Al-3.94V (set as contrast alloy) were prepared by laser solid forming and followed by heat treatment. Then the microstructure and mechanical properties of the as-deposited and solution treated alloys were investigated. The results show that the microstructure of the as-deposited alloys Ti-4.13Al-9.36V and Ti-6.05Al-3.94V consists of columnar prior-β grains, which grow epitaxial from the substrate along the deposition direction. A basket-weave α-laths existed in the inner prior-β grains. The width of prior-β grains and the width of α-laths of Ti-4.13Al-9.36V alloy are ca 606 μm and 0.48 μm, in the contrast, those of Ti-6.05Al-3.94V alloy are ca 770 μm and 0.71 μm, respectively. Further, after the Ti-6.05Al-3.94V subjected to post solution treatment at 920°C for 2 h followed by water cooling, its microstructure consists of phases α'+α, and the corresponding yield strength, ultimate tensile strength and ductility to failure were ca 893 MPa, 1071 MPa and 3%, respectively. However, when the Ti-4.13Al-9.36V subjected to post solution treatment at 750°C for 2 h followed by water cooling, its microstructure consists of phases α''+α, and the related yield strength, ultimate tensile strength and ductility to failure were ca 383 MPa, 989 MPa and 17%, respectively. This may be ascribed to that the stress-induced α''-phase could significantly improve the work-hardening ability compared with α'-phase. The work-hardening ability and ductility of the Ti-alloy used for laser solid forming could be significantly improved by adjusting the microstructure with phases α''+αvia cluster-plus-glue atom model.
The highly flexible polytetrahydrofuranediol (PTMG) substrate was reacted with furfuryl glycidyl ether-2-furanethylamine (FGE-FA) to obtain the polyurethane prepolymer of tetrahydrofuran structure, and then it was reacted with bismaleimide of dienophile structure to prepare high density Diels-Alder (DA) self-healing polyurethane (PU-DA) with dynamic covalent bond. The PU-DA was characterized by FTIR, DSC and OM, and the performance of PU-DA was tested by electronic universal testing machine. The results show that the forward and reverse reaction temperatures of PU-DA are 70℃ and 132℃, respectively, after the introduction of DA dynamic covalent bond. PU-DA has good performance in remodeling, swelling solubility and multiple self-healing. Cracks of the damaged PU-DA could basically be healed by heating at 70℃ for 4 h, meanwhile, the first repair rate could 94.8%, and the third repair rate was still higher than 70%.
Self-assembled colloidal particles were prepared via electrostatic interaction between alginic acid (ALG) and lysozyme (Lys), and the effect of the mass ratio of lysozyme to alginic acid on the properties of colloidal particles was investigated in order to obtain colloidal particles at the optimal mass ratio. The size and morphology of colloidal particles were characterized by nanometer particle size analyzer and transmission electron microscope. The results show that the colloidal particles are spherical with particle size of about 143 nm. The colloidal particles can be assembled at the oil-water interface to stabilize the oil-in-water Pickering emulsion. The effects of pH value and salt concentration on the properties and the emulsifying properties of colloidal particles were investigated in detail. The results show that as the pH value increases, the colloidal particles and emulsion droplet size both gradually increase, and the emulsification performance gradually decreases; as the salt concentration increases the colloidal particles and emulsion droplet size first decreases and then increases, while the emulsification performance increases first and then decreases. The effect of pH and salt concentration on the activity of lysozyme in the emulsion was further investigated. It follows that the prepared emulsions are all active to a certain extent .
The microstructure characteristics, fracture morphology, tensile properties, impact toughness at low temperature, and strain aging behavior of X90 high-strength pipeline steel were investigated by OM, SEM, TEM, tensile test and Charpy impact test. The results show that X90 high-strength pipeline steel is rather sensitive to strain aging with a sensitive temperature of 423.15 K. After aging treatment above 423.15 K, the X90 pipeline steel loses continuous yielding and strengthening characteristics, and the tensile curve changes from the round-house-type before aging to the Lüders-type yield curve. When the aging time was fixed as tag=5 min, with the increasing aging temperature Tag , the yield strength Rp0.2, tensile strength Rm and yield ratio Rp0.2/Rm of X90 steel all show an increasing trend, and the uniform elongation UEL, fracture strain εf, total energy absorbed by low-temperature impact Ak, crack formation energy Ai and crack growth energy Ap all show a decreasing trend. The microstructure of X90 steel before and after aging treatment presents more or less the same complex structure composed of fine acicular ferrite + polygonal ferrite + lath bainite + M-A constituents. Pre-straining and aging treatment are the main inducements of the strain aging behavior of pipes. In the pipe production process, the flexible leveling method could be used to replace the rigid roll leveling method, and the multi-step progressive molding method could be used to replace the one-step spiral molding method to effectively control the pre-strain. It is noted that the temperature of the present coating process should be lowered than 423.15 K to avoid any harmful heat effect on the performance of pipes. Otherwise, one should adopt other coating process, of which the applying temperature should meet the above requirement.
Impregnating molten LiF-NaF-KF salt (46.5%-11.5%-42.0%,mole fraction, FLiNaK) into a 2D woven C/C composite was performed at 650℃ under different pressure. The mass gain, the change of density and mechanical properties of the 2D woven C/C composite after FLiNaK salt impregnation were measured. The FLiNaK salt distribution in the 2D woven C/C composite was observed by X-ray CT and SEM. The results show that the mass gain of the 2D woven C/C composite increased with the increasing impregnation pressure. FLiNaK salt distributed within open pores of the composite and fissures of fiber bundles and interlaminar fractures. The compressive strength and flexural strength of the 2D woven C/C composite increased with the increasing impregnation pressure. The coupling effect of densification induced by FLiNaK salt impregnation and residual stress formed in 2D woven C/C composite could be benefitial to the mechanical property of the C/C composite.
The effect of the addition of Mn in the range of 0.1%~0.5% (mass fraction) in molten Zn-Mn alloys at 450℃on the surface wetting behavior of X80 steel was studied by means of contact angle measurement with an improved sessile drop method and microstructure observation with SEM-EDS in terms especially of the interaction at interface molten Zn-χMn(χ=0.1~0.5) alloys/X80 steel substrate. The results show that Mn can play a positive role in the wettability between the molten Zn alloy and the steel. At 450℃, with the increasing Mn content from 0.1 to 0.5, the wetting contact angle between the molten Zn-χMn alloy and the steel decreases from 85° to 62°. The molten Zn alloy/X80 steel belongs to the reactive wetting system, correspondingly, the interface reaction may result in interface products composed of FeZn10(δ), FeZn13(ζ) and Fe3Zn10(Γ)/Fe5Zn21(Γ1) phases. Therefore, the wetting behavior is affected by the interface reaction. There is a precursor film emerged at the front of the three-phase line, which can enhance the wettability of the molten Zn alloy to X80 steel.
Three-dimensional porous multi-wall carbon nanotubes (MWNTs) sponges were prepared by chemical vapor deposition, and then which were filled with polydimethylsiloxane (PDMS). Carbon nanotubes sponges still maintain the three-dimensional structure after filled with PDMS, which provided a conductive network and mechanical framework. The uniformly filled PDMS makes the composite film stretchable and elastic. The synergistic effect between carbon nanotubes and polydimethylsiloxane resulted in high mechanical strength (3.7 MPa), stretchability (207%) and superior elasticity of MWNTs/PDMS composite films. The MWNTs/PDMS film presents the resistance change (△R/R0) of 0.9%, 1.4%, 2.3%, 3.5% and 4.6%, and gage factor change (GF) of 0.09, 0.07, 0.046, 0.044 and 0.046 when subjected to strain of 10%, 20%, 50%, 80% and 100%, respectively. The sensing performance has a good stability which cannot be influenced by stretching speed and cycle numbers. In addition, the MWNTs/PDMS composite films inherited the hydrophobicity of MWNTs sponges and PDMS.
