Cyclic creep tests at 650°C for both 11.5CrNbTi and 15Cr0.5MoNbTi ultra pure ferritic stainless steels were conducted under the stress-controlled mode , the effect of hold time introduced at the maximum applied stress on the deformation and fracture behaviors of the ferritic stainless steels was investigated. The results show that with prolonging the hold time, the minimum cyclic creep rate increases, and the cyclic creep life and the cycle number to fracture decrease for both stainless steels. Under the same conditions, the cyclic creep resistance of the 15Cr0.5MoNbTi stainless steel is higher than that of the 11.5CrNbTi stainless steel. The cyclic creep fracture mode for two stainless steels is transgranular fracture. With prolonging the hold time, the quantity of creep voids increases and the effect of creep damage gets enhanced. The microstructures after the cyclic creep are composed of sub-grains. The deformation mechanism of cyclic creep is mainly the dislocation slip and cross slip.
Based on a cross-linked polyurethane (CPU) system composed of polyoxypropylene polyol (PPG) and diphenylmethane diisocyanate (MDI), a kind of polyether modified MQ (E-MQ) resin was added to prepare E-MQ reinforced pouring type CPU elastomer. The results show that the E-MQ resin has good compatibility with the CPU, and the prepared E-MQ resin reinforced elastomer has excellent mechanical properties. When the content of E-MQ resin is 8% (E-MQ resin accounts for the total mass fraction of the CPU) the tensile strength of polyurethane elastomer reached to 20.8 MPa, increased by 22.4% comparing to the basic CPU, tear strength is 82 KNm-1, Shore A hardness is 82 degrees.
The MIL-53(Al) was prepared by hydrothermal method from water-insoluble aluminum sources: alumina, aluminum hydroxide, boehmite. The products were characterized by SEM, XRD, N2 sorption and TGA, simultaneously compared with MIL-53(Al) prepared from aluminum nitrate. The results show that the water-insoluble aluminum sources can be good candidates for the synthesis of typical MIL-53(Al), BET surface areas of which are about 700-1000 m2/g. It’s also noticed that there is different framework flexibility of synthesized MIL-53(Al) from water-insoluble and soluble aluminum sources. The framework of MIL-53(Al) prepared from alumina mainly shows large-pore structure and less flexibility. The adsorption behavior of roxarsone on MIL-53(Al) was investigated. MIL-53(Al) prepared from alumina shows better adsorptive performance towards roxarsone. The adsorption of MIL-53(Al) from alumina fits well with secondary dynamic mode.
The paraffin/diatomite form-stable phase change materials(PA/D-PCMs) was prepared by using solvent evaporation, diatomite as carrier and paraffin as phase change materials. The microstructure and thermal properties of PA/D-PCMs were characterized by SEM、FT-IR、DSC and TGA respectively. The results show that: Leakage of melting paraffin was hindered through both the hydrogen bonding and the capillary force of the pores of diatomite, hence PA/D-PCMs put up excellent thermal stability. At the same time, secondary pores of diatomite can restrict partial paraffin crystallization, crystallinity of which would be affected. In interior of diatomite there were a few conduction channels with intercommunication, which can enhance thermal conductivity of paraffin and accelerate paraffin heat storage and release. With increase of the paraffin content phonon scattering effect would become more fierce in X, Y and Z axis thermal conduction channel of PA/D-PCMs, so thermal conductivity of PA/D-PCMs diminish, but owning higher latent heat and crystallinity. In order to ensure PA/D-PCMs structure stable and have good thermal properties simultaneously, optimal paraffin fraction in the composite is 45%.
A prerequisite for the application of carbon nanotubes (CNTs) in the industrial sectors of micro- and nano-electronics, it is essential to reduce its contact resistance with metal. Doping Au-nanoparticles can effectively reduce the contact resistance of CNTs. In this paper, a three step process was developed for doping Au-nanoparticles on CNTs, i.e. first, the CNTs are calcinated at high temperature to create defects and hydrophilic groups on their surface, then, the calcinated CNTs are dispersed ultrasonically in chloroauric acid solution to adsorb chloroauric acid, and finally, they are heated in hydrogen atmosphere at high temperature to produce Au-nanoparticles on the surface of CNTs. The produced CNTs are characterized by means of scanning electron microscopy (SEM) X-ray energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Results show that due to the Au-doping, the G-band peak of Raman spectra of the CNTs shifts to a lower frequency, which indicates that the doping is N-type. N-type dopants transfer electrons to adjacent carbon atoms and increase the electron quantity in CNTs, thereby increasing the electrical conductivity of CNTs. Subsequently, CNTs are assembled into the interval of two Au electrodes by dielectrophoresis (DEP), and the results of real-time measurement by using a precision inductance-capacitance-resistance (LCR) show that the contact resistance between the Au-doped CNTs and Au electrodes has been effectively reduced to ca. half of the original values between the bare CNTs and Au electrodes .
Effect of solution treatment temperatures on the microstructure and mechanical property of a high temperature alloy GH2787 was investigated. The results showed that the grain size of the alloy could be controlled by the solution temperature. When the solution temperature was higher than the solve temperature of γ' phase, the grain size was larger and the volume fraction of γ'- phase was low. When the solution temperature was lower than the solve temperature of γ'-phase, the grain size was smaller and the volume fraction of γ'-phase was high, and which was uniformly distributed in the alloy. η-phase precipitated when the solution temperature was around the solve temperature of γ'-phase. The Vickers hardness and the tension strength increased as the solution temperature decreased. The strengthening mechanisms of the alloy GH2787 might be ascribed to grain boundary strengthening and precipitation strengthening.
The tests of repeated low-velocity impact and compression after impact on composites laminates coated with PU were carried out, and mainly focused on the factors of damage degree ,the thickness of composites and coating which could affect the compression strength after impact of composite laminates coated with PU. Moreover the process of compression after impact acting on laminated was tested via digital image correlation (DIC) which can gather the topography of specimens during testing in time, so the damage process and damage modes of specimens with various damage degrees were analyzed. Finally, the conclusions can be acquired：The damage inflection point exists by the increasing of impact numbers, and the compression strength decreased with increasing the thickness of composite laminates. In addition, the compression strength after impact of composite laminates coated with PU increased with increasing coating thickness. As for the specific damage position of different specimens, it is related with damage degree, which is also related with compression damage process.
The wear resistance and wear mechanism of a novel light-weight Fe-24Mn-7Al-1.0C austenitic steel after water quenching (Q) and water quenching-aging (Q-A) treatments were studied by comparing with the Mn13Cr2. The impact wear tests were carried out by using MLD-10 abrasive wear testing tester under low impact energy condition (0.5 J). Results show that the wear resistance of Fe-24Mn-7Al-1.0C steel is 1.14 times higher than that of the water quenched Mn13Cr2. A large number of nano-sized (Fe, Mn)3AlC κ-carbide precipitates increase the initial hardness, strength and wear resistance of the steel after aging treatment at 550℃ for different time. The wear resistance of Fe-24Mn-7Al-1.0C steel is optimum after 1050℃ quenching and aging 1 h at 550℃, which is 1.40 times higher than that of Mn13Cr2. The worn surfaces of Mn13Cr2 consist of wide, long, uneven grooves and deep peeling pits, of which the formation may be ascribed to the repeated plastic deformation, while worn surfaces of the Fe-24Mn-7Al steel consist of tiny peeling pits and light grooves. Many stacking faults and dislocations in different directions are found on the subsurface of Mn13Cr2. Many Taylor lattices are found at the impact subsurface of Fe-24Mn-7Al steel before aging treatments. After aging treatment for 1 h at 550℃, Taylor lattices and high-density dislocations are found, but no twins and martensitic transformation appear on the worn surface.
Poly-crystal Ti with grain size larger than 12 mm was prepared through multi-stage heat treatment. Among which, the first stage of long time anneal at 860℃ could facilitate the grain growth of the original α phase, therewith reduced the total grain boundary area as a result; Meanwhile, low heating rate of 0.1℃/min in the second and low cooling rate of 0.1℃/min in the fourth stage were adopted to ensure the titanium slowly passing through the phase transformation point at 883℃ in order to restrain the number of nucleation. The orientation of hexagonal close packed (HCP) unit cell was constructed according to the Euler angle detected by electron backscatter diffraction (EBSD), and single-crystal compressive specimen was prepared for mechanical test and scanning electron microscope (SEM) observation. Slip band of 112?3112?2 type was determined, and the obvious influence of the grain orientation on mechanical behavior was analyzed by Schmid factor.
Effect of Ti addition on the pitting corrosion behavior of casting duplex stainless steel was studied by means of potentiodynamic measurement and impedance spectroscopy as well as scanning electron microscope (SEM) along with energy-dispersive spectroscopy (EDS) and X-Ray Diffractometer (XRD). It turned out that pitting corrosion occurred mainly on the austenite phase and phase boundaries because of the existence of Cr-rich zone and the precipitation of carbides in the austenite phase and at phase boundaries respectively. Pitting corrosion resistance of duplex stainless steel could be improved through the addition of Ti.
