Applied Mechanics and Materials Vol. 751

Abstract: The present works concerns in evaluating thermal oxidation characteristic of composite coating on ferritic stainless steel at high temperature application. SUS430 ferritic stainless steel was used as the substrate material whereas Cr₂O₃-La₂O₃ and NiAl-La₂O₃ were used as the coating material. Thermal spray has been used as the deposition method, whereas thermal oxidation at temperature of 750°C for 24, 48 and 96 hours has been employed on the coated material in the atmosphere environment. From the weight meausurement before and after thermal oxidation, it was observed insignificant weight losses, whereas this condition is stable for all the applied oxidation period. However weight losses is more on the NiAl-La₂O₃ as compared with Cr₂O₃-La₂O₃ samples, which is due to the morphological characteristic of the former layer as observed by scanning electron microscope (SEM) characterization. From X-ray diffraction (XRD) characterization, it was observed the formation of stable layer Cr₂O₃ for Cr₂O₃-La₂O₃ coated samples, whereas formation of NiO observed for the case of NiAl-La₂O₃ sample.

Abstract: In this paper, carbon nanotubes (CNTs) were synthesized by catalytic pyrolysis of CO and CH₄ using flame pyrolysis method. The effects of using the two different carbon sources to the preparation of CNTs with all other conditions being equal were comparatively studied. The results showed that: the morphology of CNTs synthesized from different carbon source gases had certain difference. Higher yield of carbon nanotubes could be synthesized using CH₄ as carbon source than using CO. At the same time, the former had less number of tube walls and the vascular bundles arranged more neatly. Synthetizing CNTs via catalytic decomposition of CH₄ had more advantages than using CO by flame pyrolysis method.

Abstract: Based on the difficulty to accurately control temperature for torch brazing, the study is concerned with developing low-melting-point solders for brazing pure aluminum. For this purpose, Ge and Zn have been chosen to be added to Al-Si-based alloy. The melting characteristic, wetting property of solders with Al and mechanical property of the brazed joints were investigated. The results show that the addition of 10 wt. % germanium into the traditional Al-12Si (wt. %) filler metal causes its liquidus temperature to decrease by about 23 °C. An addition of 30 % zinc into such Al-Si-Ge ternary alloy will cause its liquidus temperature to drop further to 525 °C. The solders have good wettability with Al. With the increase of Zn content in the alloys, the spreading areas of solders exhibit nonlinear decrease, and there exist a very large value at the zinc content of 15%. When Al-Si-10Ge-30Zn solder was used to braze the pure aluminum, an optimized bonding strength of 116 MPa was achieved.

Abstract: The Cu/Zn-14.1Al-0.9Si/Al joints were joined by flame brazing and furnace brazing, respectively. The influence of brazing methods on the interface structure and property of Cu/Al brazed joint was investigated. It was found that the interface structure near Cu substrate of the joint with different brazing method are both Cu/diffusion layer/Al_4.2Cu_3.2Zn_0.7 layer, but the thickness of the interface layer of the joint with the flame brazing (3-4μm) is obviously thinner than that of the joint with the furnace brazing (5-10μm). The filler metal zone of the joint with flame can not find the Cu-Al IMCs. Instead, the block CuAl₂ IMC can generate in the filler metal zone of the joint with the furnace brazing. For thinner interface layer, the joint with flame brazing has higher shear strength of average 60.5MPa, which is 20.6MPa higher than that of the joint with air cooling (39.9MPa).

Abstract: In this paper, the research status and development trend of titanium alloy/stainless steel joining technology is reviewed. Characteristics and problems of titanium alloy/stainless steel jointing are analyzed. And then advantages and disadvantages of various jointing methods are compared.

Abstract: N5 single crystal was transient liquid phase (TLP) diffusion bonded under different conditions in vacuum environment using Ni-base insert metal. Scanning electron microscopy (SEM) was used to observe the microstructure of the joints. Results show that the typical TLP joint could be divided into rapidly solidified zone (RSZ), isothermally solidified zone (ISZ) and diffusion zone (DZ). The widths of RSZ decreases with the increase of holding time at any established bonding temperature, amount of bulk compounds decrease at the same time. Bonding temperature has a complex influence on TLP joint. High temperature creep rupture tests were performed, results reveal that the sample fractured in the joint interface and the fracture mechanism has been studied.

Abstract: In this work, we report polyurethane foam, sunflower husk and rice husk ash prepared via a thermal treatment process used as oil sorbents for oil spill cleanup. The oil sorbent was studied on the basis of microstructure and morphology using optical digital microscopy and scanning electron microscopy (SEM). The results of the SEM and optical microscopy studies strongly indicate that thermal treatment is a suitable method to improve structure of husk particles regarding porosity compared to virgin samples. The dependence of the sorption capacity of the sorbents on the amount of sorbent, sorption time and the thickness of the oil film, as well as the number of cycles of the sorbents were investigated.

Abstract: Background correction is an essential part in LIBS signal analysis. The interpolation method of background correction has major drawbacks. This paper introduces an interpolation method to overcome the shortcomings of linear and cubic spline interpolation methods. Finally, we compare different interpolation methods to verify the proposed interpolation method.

Abstract: The thixotropic substances can be found in different industrial sectors, such as chemical, biomedical, manufacturing and oil. These substances show a rheological time-dependent behavior, dependent of their structural level. Generally, a constitutive model for the thixotropic substances is composed by a pair of coupled equations: the constitutive equation (based on viscoelastic models) and the rate equation (that describes the structural evolution). In many works presented in the specialized literature, the shear modulus and viscosity dependencies with the structural nature are not formally considered in the dynamical principles from that the constitutive equation is originated. In the present work, a new, thermodynamically consistent, constitutive model for thixotropic substances, where such dependences are considered, is presented and some rheological tests are analyzed in a numerical simulation point of view (code developed in MATLAB). The constitutive model is based on Jeffreys’ model and the coagulation theory of Smoluchowsky.

Abstract: Structured fluids are known to be dependable of their structural level. Examples of such fluids may be found in different industries as chemical, biomedical, manufacturing, food and oil. The mathematical models to describe structured fluids are normally composed by a coupled system: one constitutive equation (based on viscoelastic models) and one kinetics equation (an equation which describes the structural level evolution in time of the material). The works found in the literature use linear viscoelastic constitutive equations which do not account the dependence of the elastic modulus with the microstructural level in their fundamental hypothesis. In this sense, the present work aims to evaluate, through numerical simulation, the effect of a new constitutive equation in rheological tests and compare its results to those of the model developed by Souza Mendes and Thompson (2013), in which those considerations are not made.