Advanced Materials Research Vols. 287-290

Abstract: The PC steel bars were cold-headed and the upset heads were not cracked in the process of the PC steel bars. The upset head of PC steel bars were analysed and tested by means of tensile test and metallographic structure examination. The results showed that the cracking has some relationship with the strength grade of the PC steel bars, and the preventive methods were also proposed to avoid similar events.

Abstract: Insider-laser coaxial powder feeding laser cladding is one kind of technique, which can be used in metal part directly manufacturing field. Compared with outsider-laser coaxial powder feeding laser cladding techniques, it has significant advantages [1]. In order to research the effect of defocus distance on the layer quality in insider-laser coaxial powder feeding laser cladding, it has taken some expriments in this paper to study the layer quality by constantly changing the defocus distance, with other laser cladding process parameters invariable. In addition, this paper measues, analysis the cladding layer’s width, height, the surface quality (including surface flatness, flat-wide ratio and flat-high ratio [2]), hardness and microstructure, then summarizes the effect of the defocus distance on the layer quality in this paper.

Abstract: SiC films were prepared by mid-frequency (MF) magnetron sputtering with graphite and poly-silicon targets on polycrystalline Al₂O₃ substrate. XPS analysis shows that the ratio of C/Si may change from 3.24 to 1.21 by adjusting the distance between target and substrate. SEM and XRD were used to investigate the surface morphology and microstructure of SiC films changing with annealing temperature. Results show that the microstructure of SiC started to be crystallized when the annealing temperature run up to 1200°C, and the film adhesion increased from 31N to 53N with the temperature changing from as-deposited to 1200 °C annealing, respectively.

Abstract: A series of Ti-Al-N films were deposited on silicon wafer and steel substrates by cathodic vacuum arc technique in N₂/Ar gas mixtures, using a compound Ti(50):Al(50) target. The chemical composition, crystalline microstructure, film deposition rate and surface morphology of the films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscope (SEM) coupled with an energy dispersive X-ray analysis system (EDX), respectively. The hardness and Young’s modulus, wear performance and corrosion behavior of the Ti-Al-N (multi-phase) films at different N₂ partial pressure were analyzed and explained on the basis of microstructure, mechanical properties and wear mechanisms.

Abstract: N-type Bi₂(Te_0.95Se_0.05)₃ thermoelectric thin films with thickness 800 nm have been deposited on glass substrates by flash evaporation method at 473 K. The structures, morphology of the thin films were characterized by X-ray diffraction and field emission scanning electron microscope, respectively. Thermoelectric properties of the thin films have been evaluated by measurements of Seebeck coefficient and electrical resistivity at 300 K. Annealing effect on Seebeck coefficient and electrical resistivity of the thin films was examined in the temperature range 373–573 K. When annealed at 473 K for 1 h, Seebeck coefficient and electrical resistivity are –180 μV/K and 2.7 mΩcm, respectively. Thermoelectric power factor is improved to 12 µW/cmK².

Abstract: With the question of Ozone Depression Potential and Global Warming Potential popping out day by day, the Freon refrigerant alternative has become one of the current research contents of refrigerant. Based on the given Freon refrigerant R22, R134a and natural refrigerant CO₂, the differences of their properties were compared, and the relevant alternative refrigerants conducted an investigation. The results show that the natural refrigerant CO₂ instead of Freon refrigerant has good application prospects; it provides basic data to develop new products, which enhance the COP of air conditioner and heat pump.

Abstract: Thin films of single-walled carbon nanotubes (SWNTs) attached to an ITO surface (SAM–ITO) self-assembled in advance from 3-aminopropyltrimethoxysilane through amide covalent bonds were prepared. The SWNTs were safely obtained via a two-step process assisted by microwave radiation, which were soluble in aqueous and organic media. However, the CV behavior of SAM–ITO in acidic aqueous systems showed unexpected oxidation signals due to redox reactions involving the defects and sidewalls of soluble functionalized SWNTs. It was found that, after a conductive polymer of polyaniline was chemically incorporated onto the surface of the SWNTs by using electropolymerization method, the CV data showed a single reversible redox couple, which indicated a more stable state.

Abstract: Pb_0.3Sr_0.7TiO₃ (PST) and 4.5 mol% Mn doped Pb_0.3Sr_0.7TiO₃ (PSTMn) thin films as well as PST/PSTMn/PST/PSTMn/PST (ML-a) and PSTMn/PST/PSTMn/PST/PSTMn (ML-b) multilayered thin films have been fabricated on Pt/Ti/SiO₂/Si substrate with sol–gel method. The structure and surface morphology of PST, PSTMn, ML-a and ML-b thin films were investigated by x-ray diffraction (XRD) and atom force microscopy (AFM). The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 100 Hz to 1M Hz and at room temperature. It was found that the surface microstructure of multilayered thin films is influenced by deposition sequence and the dielectric constant and tunability of two multilayered thin films lie between that of PST and PSTMn thin films. However, two multilayered thin films have higher the figure of merit (FOM) for lower dielectric loss. The FOM of PST and PSTMn single-component films as well as ML-a and Ml-b multilayered films are 14.2, 14.6, 16.3 and 20.2, respectively. Our results showed that multilayer structure can improve the comprehensive dielectric tunable performance of PST film.

Abstract: In order to determine thermal parameters of mass concrete, this paper utilizes homotopy technique to solve an inverse transient heat conduction problem with multi-variables. A finite element model facilitating to sensitivity analysis for non-linear direct and inverse problems is derived, and a precise algorithm of time stepping is used in the transient analysis. Numerical validation has been given with an investigation of effects of noise data and initial guess on the results.

Abstract: The defocus distance is one of the most important factors during filling laser welding with wire. Keeping defocus distances stability is the pre-condition to acquire the stable weld quality. In this paper, a QUANTA laser camera was used to measure the defocus distance, and it is compensated in real time through the numerical control system. The results reveal that the fixed defocus distances can be acquired using this system. And the experiments by using auto-controlling method of the defocus distance show that the stability of welding process can be improved greatly and the good weld quality can be easy to be obtained.