Single crystal superalloy has excellent properties at elevated temperature, but it is burdened with high manufacturing costs. The repair of single crystal superalloy by welding and joining has been an important research subject in the field of single crystal superalloy. In this paper, a comprehensive overview on the development of surface defects repair technology in the field of single crystal superalloy was presented, and the effect of repair technologies (including fusion welding, brazing and transient liquid phase bonding) on the microstructure and mechanical properties of the repaired zone was summarized. The problems and limitations of the present repair technologies were analyzed. Finally, the future development direction of repair technology was also proposed.
This paper reviewed the recent progress of structural coloration of photonic crystals based on self-assembly of colloid microspheres. Firstly, photonic crystals and the corresponding structural coloration theory were simply introduced, then the different self-assembly methods of constructing photonic crystals with colloid microspheres as basic structural elements were presented. Characterization methods for the structural coloration and the stability enhancement of photonic crystals are further discussed, finally the difficulties encountered in the preparation of photonic crystals via self-assembly of colloid microspheres, and the future development direction were also mentioned.
The effect of aging temperature on austenite grain size and mechanical properties of Fe-30Mn-9Al-0.9C-0.45Mo steel were investigated by OM, SEM, XRD, EBSD and TEM. The results show that the aging treatment has a great influence on the microstructure and properties of Fe-30Mn-9Al-0.9C-0.45Mo steel. After aging treatment at 450℃ the tensile strength of the steel is 863 MPa, the elongation after fracture is 56.1%, and the strong plastic product is 48.4 GPa·%, indicating a significant improvement compared with the solid solution treated ones; After aging temperature at 500℃ the amount of the dot-shaped κ-carbide precipitates increases , the austenite grains grow significantly with the increase of ageing temperature and the yield strength and tensile strength increase. During the aging process at 550℃ DO3→B2 continuous transformation occurred, and the yield strength of the steel increased, but the plasticity decreased significantly. After tensile deformation high density dislocation wall and microstrip structure can be observed, which are plane slip characteristics.
Thin film of high entropy FeCoNiMoCr alloy was deposited on Ti substrate by magnetron sputtering method to obtain high entropy film electrode. The surface morphology, composition, phase constituent, structure and performance of the electrode were characterized by means of surface profilometer, SEM-EDS, XRD and electrochemical workstation. The results show that the electrode surface is rough, the constituent elements are evenly distributed, the film thickness is about 2.40 μm, and the film is amorphous. The electrode showed good oxygen evolution performance and good stability in the alkaline solution. Under the condition of current density of 10.0 mA/cm2, the overpotential was 360 mV, the Tafel slope was 73.45 mV/dec. Under the condition of overpotential of 360 mV, the current density was not significantly attenuated after continuous use for 24 hours. The results of cyclic voltammetry and electrochemical impedance analysis show that due to the improved intrinsic catalytic activity, the film electrode have electrocatalytic oxygen evolution performance better than that of the noble metal oxide RuO2 (over potential 409 mV, Tafel slope 94.18 mV/dec).
The quasi-static and dynamic stress-strain curves of TC2 Ti-alloy were measured by means of electronic universal testing machine and split Hopkinson pressure bar (SHPB) respectively, and the dynamic flow stress characteristics at high strain rates were investigated, meanwhile, the relevant microstructure evolution of the alloy was examined. The results show that the strain induced effect of strengthening and plasticizing for TC2 Ti-alloy is sensitive to strain rates obviously in the range of 1100- 6000 s-1, but the two effects were weakened for the strain rate above 4800 s-1. An adiabatic shear line at an angle of about 45° from the loading direction was observed in the samples by strain rate of 2500 s-1, and a shear bands may appear as the strain rate further increases, however which were not significantly widened due to the presence of the blocking zone, resulted from the slippage and agglomeration of the dispersed β particulates. The Johnson-Cook constitutive model was modified with the term of adiabatic temperature rise, then a new model was built by means of non-linear fitting. By comparison of prediction data with experimental data, it follows that the average relative error and the correlation coefficient are 2.18% and of 0.9935 respectively for the above two group data. As a result of the foregoing, the rheological behavior of TC2 Ti-alloy by high strain rate at room temperature can be described well with this improved model.
Ingots of AlSi7Mg0.4 alloys with 0.06%, 0.14% and 0.20% Zr addition respectively were fabricated with gravity casting method. The microstructure analysis of the as-cast alloys shows that (Al, Si)3(Zr, Ti) and π-Fe phases formed in these alloys. Compared with the AlSi7Mg0.4 alloys without Zr, the grain size of the alloys containing Zr is smaller. Strengthening phase (Al, Si)3(Zr, Ti) precipitated in the alloys containing Zr during the solution treatment. After T6 heat treatment, a small amount of Mg in the Fe-rich intermetallics and a little part of coarse (Al, Si)3 (Zr, Ti) phases re-dissolved into the matrix, which decreased the intermetallics sizes. The tensile strength and elongation of the alloys containing Zr are 332 MPa and 8.7%, which are 10% and 90% higher than the alloy without Zr, respectively.
A novel CsTi2NbO7@N-TiO2 core-shell hybrid material was successfully prepared by mixing CsTi2NbO7 with titanium isopropoxide and then calcining with urea in atmosphere. The prepared products were characterized by means of X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflectance absorption spectrum (UV-Vis DRS) and X-ray photoelectron spectroscopy (XPS). It was found that the N doping resulted in the shortening of the band gap of TiO2 and the red-shift of absorption edge, thus achieving the visible light response. Because of the synergistic effect of hybridization, core-shell structure, and N doping, the as-prepared CsTi2NbO7@N-TiO2 hybrid core-shell structural materials not only have strong visible absorption properties, but also exhibit enhanced photocatalytic activity for degradation of methylene blue (MB) under visible light irradiation, resulting from the improvement of carrier separation and migration efficiency due to the existence of the built-in electric field. Moreover, the reaction rate constant of CsTi2NbO7@N-TiO2 hybrid core-shell structural material is about 5.8 times that of CsTi2NbO7. Therefore, it shows good photocatalytic cycle stability.
The processes of austenite growth and microstructure transformation in the simulated coarse-grain heat-affected zone (CGHAZ) for high strength low alloy steels without and with 0.016% La addition were in-situ observed by means of high temperature laser confocal scanning microscope. The grain refinement in CGHAZ of the steel with 0.016% La was also assessed by using optical- and electron-microscopy. The results show that the complex inclusions of Al-Mg-O, (Mn, Ca)S and TiN may transform to La2O2S in CGHAZ of the steel due to the addition of 0.016% La. La2O2S had lower mismatch with α-Fe, which can effectively promote the formation of acicular ferrites. Meanwhile, many finer dispersed (Ti, Nb)(C, N) precipitates formed in 0.016% La-containing steel can effectively pin the austenite grain boundary, inhibiting the grain growth. Thus, the grains in CGHAZ of 0.016% La-containing steel became finer.
