Applied Mechanics and Materials Vols. 152-154

Abstract: The hydraulic characteristics of curved channel flow are one of the most important subjects to hydraulic researchers and engineers. Among them the magnitude of circulation velocity and its calculation method is of great interests. Experimentation of generalized curved channel was carried out to explore the flow velocity parameters and circulation velocity characteristics by adopting the ADV to measure and analyze the 3D velocity datum. Theoretic formula was established for calculating the circulating velocity in the curved channel. Comparison with the results calculated from the formulas of other researchers the formula proposed in the paper is relatively quite good. The paper provides a basis to explore the hydraulic characteristics of the curved channel profoundly.

Abstract: Currently most commercial magnesium alloys are based on the Mg-Al system and it is reasonably well developed. Although the Mg-Al based alloy system has excellent castability and adequate ambient temperature mechanical properties, it shows poor creep resistance. Therefore, our group has focused on finding the way to improve the creep properties of Mg alloys. This paper presents a brief summary of the research achievements in this area recently made by AFML(Advance Functional Materials Lab in PNU, Korea). The properties of newly designed Mg alloys in our group are presented and compared with the properties of commercial A356 alloy.

Abstract: In recent years, high-efficiency and low-toxic antifouling coating are predominant in view of environmental protection and public safety. In this paper, a novel coating containing methoxysilane and acrylic resin were synthesized which have special structure to antifouling. We concluded the colonization of benthic diatoms (Nitzschia flosterium) of the novel coating, taking the antifouling coating containing AM(4.3%w\w）, HD-70 (3.4%w\w），VTMO (2.3%w\w）and Cu2O (28.5%w\w）for instance, we obtained that the colonization of Nitzschia flosterium was 4.3*104N.cm-2. A static test site was set up in Number 8-dock of Qingdao harbor, on the East Coast of China to investigate the antifouling effectiveness of the novel antifouling coating. The results of the present paper demonstrate that the novel coating enhanced the antifouling .

Abstract: Rapid solidification process was employed to make 6061 Al alloy powder. Powder size distribution was analyzed with SEM. Powder densities, i.e. apparent density and tap density, were measured. Thermal properties were measured via DSC. Surface condition and microstructures and their chemical compositions were characterized with XRD, OM, SEM/EDX. Nanoindentation was employed to obtain the hardness and Young’s modulus of the powders. The relationships among the atomization parameters, powder shapes and sizes, powder densities, thermal properties, microstructures and the mechanical properties were analyzed and rationalized.

Abstract: Multiphase flows, where two or even three fluids flow simultaneously in a pipe are becoming increasingly important in industry. In order to measure the flow rate of gas-water two phase flows accurately, the void fraction (gas volume fraction) in two phase flows must be precisely measured. The differential pressure technique has proven attractive in the measurement of volume fraction. This paper presents the theoretical and experimental study of the void fraction measurement in bubbly gas water two phase flows using differential pressure technique (the flow density meter).

Abstract: ^{Superscript text}The influence of gas nitriding on commercial pure titanium and Ti-6Al-4V (Ti64) alloy bearings by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter thin TiN coats of 0.5 to 3 µm were produced. Non-coated and coated bearings made of pure Titanium and Ti-6Al-4V alloy were tested in equal conditions and it was found that the titanium nitride layers significantly improve the rolling contact fatigue performance of titanium components. For tests up to 10⁶ cycles the wear loss of the coated samples was at least ten fold lower than that of the uncoated ones and for 7.76 x 106 cycles, the wear resistance improved almost 100-fold.

Abstract: An innovative type of one-point rolling contact fatigue (RCF) machine was developed in order to investigate crack initiation and propagation in metals. The microstructural changes and propagation of subsurface cracks during rolling contact in specimens tested by using the new device were studied by laser confocal microscope and X-ray diffraction. It was shown that this new method presents several important advantages compared to the conventional thrust type RCF machines.

Abstract: The influence of surface oxidizing using a Q-sw laser on the wear loss of titanium-4Al-6V (Ti64) alloy during rolling contact fatigue is investigated. Titanium components are widely appreciated for their superb biocompatibility, high strength to weight ratio and corrosion resistance. Due to the above mentioned advantages titanium bearings are a popular choice in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defence industries). In these rolling contact applications however issues such as fretting and wear related problems are a common occurrence as the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. In an attempt to tackle this problem, a Q-sw laser was used in this work to coat Ti64 bearings with complex titanium oxide layers in a closed chamber without any protective gas. Non-coated and coated samples were tested under water by using a thrust-type rolling contact fatigue machine. The morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and X-ray diffraction. The wear loss of the coated samples was at least fifty-fold lower than that of the non-coated bearings and a 3-fold increase in the maximum load capacity compared with TiN layers was achieved.

Abstract: Retracted article: In this paper, epitaxial growth on Ni-based single crystals was achieved by using spark deposition and laser powder deposition. Different Ni-based substrates, such as CMSX-4, TMS 138A as well as deposition materials: NiCrAl, Rene N4 and modified 4.5^th generation single crystal alloys were used. The deposited layers were analysed by laser confocal microscopy, FEG-SEM, X-ray and electron backscatter diffraction (EBSD), had very little dilution and epitaxial growth was confirmed for the deposits made using Rene N4 electrodes. The deposition time at 100 V voltage, 850 W power and 110 Hz frequency was 3min and the layer thickness varied from 0.3 to 0.5 mm. Cracks were observed in certain areas with the formation of stray grains. In order to investigate the influence of the laser processing during multiple build up, specimens with one and ten layers were manufactured. The total layer thickness on substrates was 0.3 mm and 2 mm, respectively. The processing parameters were: laser power of 500 W, laser beam diameter of 0.6 mm and the z displacement was equal to 80% of the layer height. The laser deposition also resulted in successful epitaxial growth and minimal defects (pores or cracks), however the clads presented high dilution.

Abstract: The precondition of structure integrality analysis for nozzle is temperature computation. Considering the close coupling of flow and heat transfer, thermal conditions should be treated with coupled heat transfer. The paper aimed at a typical nozzle and compared with temperatures using the universal method and the coupled method. The results show that temperature distribution laws on internal wall of two methods are similar, but not exactly the same. The radiation is the major heating form in nozzle inlet and should be considered in temperature computation. The coupled method is more reasonable and convenient to consider radiation and ablation. The coupling of flow, heat transfer，ablation and structure deformation is the development trend for future structure integrality analysis for nozzle in SRM.