Pre-alloyed powder of Ti-22Al-24Nb-0.5Mo (atomic fraction, %) was prepared via a two step process, i.e. electrode no crucible induction melting and then gas atomization process. Powder metallurgy (PM) Ti2AlNb alloys was prepared through a typical hot isostatic pressing (HIPing) route. Two pre-alloyed powders with average particle sizes of 70 and 200 μm respectively were prepared and adopted to prepare PM alloys tested for comparison. The results showed that the powder particle size had no significant effect on the tensile strength at room temperature, but a significant effect on the tensile strength and rupture life time at elevated temperature. It showed that the rupture lifetime of PM Ti2AlNb alloys made of the coarser powders was about 40% less than that of the finer powders.
Blended cathode materials LiCoO2/LiNi0.8Co0.15Al0.05O2(LCO/NCA) with different mass ratios of LiCoO2 to LiNi0.8Co0.15Al0.05O2 were prepared by ball milling method. The phase structure and morphology of the blended cathode materials were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical properties of the prepared cathodes were examined in half cells. It follows that after the ball milling, the crystal structure of the blended cathode materials did not change, however, the initial secondary NCA microspheres were broken into nano-sized fragments, which were then uniformly filled into the gaps between LCO microspheres, resulting in enhancement of the contact between the two cathode materials, and therewith, the density of the film prepared on cathode. For LCO:NCA = 6:4, the blended cathode material displayed the best grain-gradation effect and good electrochemical performances: namely the initial columbic efficiency of 92.4%, the capacity retention of 78% at 10 C (1 C=140 mA·g-1) referencing to that at 0.2 C, and capacity retention of 89.8% after 100 cycles at 1 C. A synergistic effect on the rate performance between the two cathode materials was obviously demonstrated.
Thick-walled macroporous silicon arrays (MSA) were fabricated on n-type monocrystalline silicon wafer with resistivity 4~5 kΩ·cm by photo-electrochemical etching in HF solutions. The surface and cross-sectional morphologies of the MSA were assessed by scanning electron microscope. The electric field distribution around the prefabricated pits were simulated by finite element method. By comparing with the simulation, the evolution of surface morphology of the prepared MSA was studied with the changing process parameters such as electrolyte, illumination, and applied voltage. During the etching process, deviations are found for the macropores despite of that there existed a restriction resulted from the prefabricated pits. This is due to the comprehensive effect of electric field distribution and etching parameters. The simulation results show that the electric field distribution on the prefabricated pits is featured by shapes along silicon orientation [100] and [110] at different values. Due to the existence of the above favorable influence factor, the etching face may tend to change from (110) to (100), in case that the illumination increases, while the surface free energy of the etching electrolyte decreases, which may be resulted from the stimulation of additives ethanol and hexadecyl trimethyl ammonium chloride (CTAC). Therefore, the increase of the applied voltage can restrain the etching deviation, which is conducive to rapidly transform the prefabricated pits into pores, hence, to promote the formation of thick-walled macroporous silicon array.
High-entropy alloy films of (CoCrFeNi)Nx were prepared by direct current magnetron sputtering. The effect of nitrogen flow ratio on the microstructure, mechanical-, electrical- and magnetic- properties of the films were investigated. The results show that all dense (CoCrFeNi)Nx films prepared with different nitrogen flow ratio all consist of simple single face-centered cubic phase with (200) preferred orientation. With the increase of nitrogen flow ratio from 0 to 30%, both the hardness and elasticity modulus increase. The max values of the hardness and elasticity modulus are 14 GPa and 212 GPa, respectively. The resistivity of (CoCrFeNi)Nx films increases with the increasing nitrogen flow ratio, while the saturation magnetization and permeability decrease. The max value of the resistivity is 138 μΩ?cm, the highest saturation magnetization is 427.43 emu/cm3, and the coercivity remains around 0.
The effect of finish rolling temperature on microstructure, precipitates, hardness of Ti-V-Mo microalloyed steel was investigated by means of Gleeble3800 thermal-mechanical simulator, OM, SEM, TEM and Vickers-hardness tester. The results show that the microstructures of Ti-V-Mo microalloyed steel, which was finish-rolled at different temperatures, consist of all polygonal ferrite, and the finish rolling temperature has a major impact on the precipitates and hardness. When the finish rolling temperature decreases from 1000oC to 800oC, the hardness increases from 400 HV to 427 HV. Meanwhile, the average grain size of ferrite in Ti-V-Mo microalloyed steel decreases gradually from 3.44 μm to 3.05 μm and the amount of (Ti, V, Mo)C particles increase monotonously, while their mean size reduces from 8.38 nm to 6.25 nm. The main factors responsible to the enhancement of hardness are the refinement of average ferrite grain size as well as the increasing amount and further refinement of nano-sized (Ti, V, Mo)C particles as the finish rolling temperature decreases. The nucleation rate of (Ti, V, Mo)C carbides in austenite decreased when the finish rolling temperature below 980oC, while more tiny particles precipitated from ferrite matrix, which promotes the increase of hardness.
The cast Mg-10Gd-3Y-0.4Zr (GW103K) alloy was solution treated at 500oC for 4 h and then aged at 225℃ for 193 h. The microstructure and corrosion performance in NaCl solution of the alloy were assessed by means of scanning electron microscope (SEM), transmission electron microscope (TEM), immersion test and scanning Kelvin probe atomic force microscope (SKPFM). The results show that the alloy shows a microstructure composed of α-Mg matrix with bulk-like Mg2(Gd, Y) phase and chain-like structure of alternatively arranged phases of (Gd,Y) solid solution and Mg2(Gd, Y), while the later two phases distributed in grains and/or at grain boundaries. The free corrosion potentials of the two phases (Gd, Y) solid solution and bulk-like Mg2(Gd, Y) are nobler than that of the α-Mg matrix, thereby the micro-galvanic coupling could form between the former phases with the α-Mg matrix. The (Gd, Y) solid solution and bulk-like Mg2(Gd, Y) acted as micro-cathodes to promote the corrosion of the surrounding matrix. It is worthy noted that even though the relative potential difference between the (Gd, Y) solid solution and the α-Mg matrix is greater, however, the interface between the (Gd, Y) solid solution and α-Mg matrix is coherent and the interfacial energy of the two phases is lower, thus they may exhibit better chemical compatibility, as a result, the (Gd, Y) solid solution phase may have little influence on the matrix corrosion.
Two kinds of diamines containing ortho-hydroxyl groups and bulky moiety, 3,3'-diamino-4,4'-dihydroxytetraphenylmethane (DDTPM) and 9,9-bis (3-amino-4-hydroxyphenyl) fluorene (BAHPF) were polymerized respectively with aromatic dianhydride 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) via a low-temperature solution polymerization, and next, two acetate-functionalized polyimides (PI) were prepared via chemical imidization, and thirdly, which were further thermally treated at 425oC in N2 atmosphere to obtain the thermally rearranged polymers. Then, the structure and property of the PIs and TR polymers were characterized by means of Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), X-ray photoelectric spectroscopy (XPS), X-ray diffraction(XRD) and gas adsorption isotherms etc. The results show that the thermal rearrangement (TR) occured partially for both of the PI(DDTPM-6FDA) and PI(BAHPF-6FDA), and the PI containing two phenyl groups show a range of thermal rearrangement temperature broader than the PI containing fluorene moieties. They show high glass transitionn temperatures (Tg) and larger interplanar crystal spacing. After the thermal treatment at 425oC, the specific surface area of TR(DDTPM-6FDA) and TR(BAHPF-6FDA) are 198 and 582 m2/g, and their pore diameters are 0.42 and 0.44 nm, respectively. They are belong to microporous materials, and the adsorption capacity for CO2 of TR(BAHPF-6FDA) is higher than that of TR(DDTPM-6FDA).
Hot compression tests of the as-forged Ti-alloy TB6 were conducted by means of thermecmaster-Z hot simulation test machine in temperature range of 950~1100oC with strain rate of 0.001~1 s-1 aiming to reveal its characters of hot compressive deformation behavior and dynamic recrystallization (DRX). Results show that the deformation activation energy of the alloy in the beta phase region is 246.7 kJ/mol; the deformation mechanism of this alloy in hot deformation is dominated by DRX, and the predominant nucleation mechanism for the growth of new grains of DRX may be ascribed to bulging nucleation. Completely dynamic recrystallization can be reached at strain rate of 0.01~0.1 s-1 and temperature below 1000oC, resulting in grain refinement of deformed microstructure. DRX grain coarsening was observed for the alloy deformed at temperatures above 1000oC and strain rates below 0.001 s-1. DRX grain size relate to Z parameter, which can be described by a function of D=6.44×102·Z -0.1628.
The copper coating was deposited on the surface of carbon steel by electroplating method, and then annealed at high temperature. The diffusion coefficient of Cu in carbon steel were calculated by the Den-Broeder method, while the influence of Cu-metalizing on the corrosion resistance of carbon steel was investigated. Results show that the inward diffusion of Cu is mainly along grain boundaries of the carbon steel, while the diffusion of Cu will inhibit the growth of grains of the steel during heat treatment. The diffusion coefficient of Cu in carbon steel limits between 1.11×10-16~3.03×10-11 cm2/s, which increases with the increasing annealing temperature and decreases with the increasing Cu-concentration of copper. The diffusion activation energy of copper Cu in the ferrite + austenite region of carbon steel is between 90~108 kJ / mol at low temperatures, and in the ferrite region of carbon steel at high temperatures is between 126~167 kJ/mol. Furthermore, a Cu-Fe gradient material on the carbon steel gennerated via Cu-inward diffusion has better corrosion resistance rather than the bare carbon steel in NaCl solution.
The deformation behavior of a new alumina-forming austenitic stainless steel (AFA) was investigated by means of isothermal hot compression test with a strain rate range of 0.01~5 s-1 at 950~1150℃, as well as OM and EBSD characterization. The hot processing map of the AFA steel was established based on dynamic material model. The influence of deformation parameters on the processability of the steel was also analyzed. Besides, the thermal deformation mechanism diagram was also constructed according to the deformation characteristics of different regions. The results show that the high temperature flow stress of the new AFA steel is significantly affected by the deformation temperature and strain rate. Serious flow instability can be observed at 950~1150℃ with strain rates of 0.18~5 s-1. Fully dynamic recrystallization occurred under the deformation conditions of 1050~1120℃ and 0.01~0.1 s-1 or 1120~1150℃ and 10-0.5~10-1.5 s-1. The recrystallized grains are fine and homogeneous with the power dissipation factor η reaching the peak value of 45%. It is proposed that the recrystallization zone should be preferentially selected and the flow instability zone should be avoided in order to establish a reasonable hot processing system.
