Advanced Materials Research Vols. 47-50

Abstract: Novel environment-friendly magnesium alloys have been developed by alkaline earth metal oxides addition without increasing cost and damaging process-ability. They can establish simultaneously ① cleaner processing routes with reduced or without SF6 gas, ② melt cleanliness in furnace and during transfer and pouring, ③ improved process abilities of casting, forming, welding and powder metallurgy such as fluidity, hot tearing susceptibility, inclusion and eutectic phase, ④ cost reduction with low-cost elements as well as by reducing or eliminating high-cost protective gas like SF6 gas, ⑤ original process abilities, ⑥ improved mechanical properties by grain refinement and internal soundness, ⑦ improved welding performance and joint properties, ⑧ safety during applications by improving oxidation and flame resistance and ⑨ improved remelting and recycling abilities. CaO, one of alkaline earth metal oxides, added Mg alloys can be well manufactured by conventional melting and casting without protective gas. This paper will discuss the effect of CaO on optimum protective gas usage, oxidation resistance and flame behavior of magnesium alloys.

Abstract: By modifying the sequences in preparation of aqueous ceramic slurries, starch was successfully employed to improve the microstructural controllability of alumina foams fabricated through protein coagulation casting technique. Open porosity was increased and the uniform distribution of microstructures was improved by the dual functions of starch as pore former and wet foam stabilizer. The viscosity of slurry was affected by the increasing amount of starch additive due to the total solid loading increase and the water uptake of starch. A well controlled pore structure will benefit multifunctional applications of these porous foams.

Abstract: This paper investigated the wetting and adhesion property of undulated a-C:H surfaces with surface morphology controlled for a reduced real area of contact. The nano-undulated a-C:H films were prepared by radio frequency plasma enhanced chemical vapor deposition (r.f. PECVD) using nanoscale Cu dots surface on a Si (100) substrate. FE-SEM, AFM analysis showed that the after repeat deposition and plasma induced damage with Ar ions, the surface was nanoscale undulated. This phenomenon changed the surface morphology of a-C:H surface. Raman spectra of film with changed morphology revealed that the plasma induced damage with Ar ions significantly suppressed the graphitization of a-C:H structure. Also, it was observed that while the untreated flat a-C:H surfaces had wetting angle starting ranged from 72° and adhesion force of 332.79 nN. Had wetting angle the undulated a-C:H surfaces, which resemble the surface morphology of a cylindrical shape, increased up to 103.6° and adhesion force decreased down to 11 nN. The measurements agree with Hertz and JKR models. The surface undulation was affected mainly by several factors: the surface morphology affinity to cylindrical shape, reduction of the real area of contact and air pockets trapped in cylindrical double asperities of the surface.

Abstract: Featured by cheap equipment, easy operation, nice controllability and low consumption, compound electroless deposit becomes an effective method to avoid failures such as high-temperature corrosion, fatigue and abrasion. Combined with the merits of nanometer material and laser treatment technology, the Ni-P nanometer Al2O3 electroless deposit after laser strengthening can get finer grains with high performances. This paper researched the technique of laser strengthening on 3Cr13 stainless steel after Ni-P-nano Al2O3 electroless plating. The experiments with low laser power and high laser power were performed. The crystallinity, phases and element distribution of coating were analyzed by X-ray Diffraction (XRD) and energy spectrometer (EDS). The microhardness and wear resistance of coating were measured as well. The results showed that composite coating heated by low laser power leads to transformation from non-crystal to crystal with high hardness. When heated by high laser power, the electroless deposit layer melted, and most of amorphous transformed to crystal. Combined with high laser power and high scanning velocity, the electroless deposit with finer grains and excellent properties was obtained. The strengthening mechanism was analyzed, and the properties including hardening and wear resistance were investigated as well.

Abstract: This study reports a novel method for the preparation of several biologically important calcium phosphate (Ca-P) phases such as hydroxyapatite (HA), dicalcium phosphate dihydrate (DCPD) and dicalcium phosphate anhydrous (DCPA). X-ray diffraction (XRD) results showed that phase pure DCPD, DCPA and HA nano-crystals could be produced in the Ca2+/PO4 3- solutions with the presence of EDTA at 120 oC, 180 oC and 210 oC, respectively. Transmission electron microscope (TEM) micrographs revealed that all the Ca-P precipitates were needle-like or rod-like. Most of the precipitates ranged from 100 ~ 200 nm in length. Selected area electron diffraction confirmed that the longitude direction of the rod-like HA precipitates were along c-axis and the flat surface was (110). Thermal gravimetric analysis of the DCPD precipitates revealed that phase transformations of DCPD to DCPA and DCPA to HA occurred at 139 oC and 195 oC, respectively, which resulted in the different Ca-P phases during hydrothermal synthesis at different temperature ranges.

Abstract: Cordierite based ceramic porous materials are very promising for filtering applications, due to their low thermal expansion coefficient, but also due to high chemical stability and good mechanical resistance. The cordierite powders were obtained through the co-precipitation method, while the porous ceramics were prepared by mixing the ceramic powder with an organic compound, which will burn during consequent thermal treatments, leading to an open pore ceramic web. Samples with different proportions of glucose were thermally treated at temperatures between 1050 and 1400oC. The samples were analyzed in what it concerns the mineralogical composition, open porosity and pores distribution, compressive strength and microstructure.

Abstract: Recent experiment [1] revealed many new characteristics of the domain patterns in a superelastic polycrystalline NiTi tube during tensile loading, such as domain wall instability and branching, dynamic topology transition of domain patterns. In this paper, we use the continuum mechanics approach and model the polycrystal as a phase-transformable continuum described by non-local nonlinear elasticity [2]. We simulate the equilibrium macroscopic domain patterns and their evolution in the tubes under tensile loading by the nonlocal Finite Element Method (FEM). It is revealed that the loading path dependence and dynamic topology transition of domain patterns are mainly due to thermodynamic metastability of the tube system. Our simulations capture all the key features of the domain patterns observed in the NiTi polycrystalline tubes.

Abstract: It is difficult for small rudder or wing with metal hollow construction to resist rain water, moisture, and salt fog, resulting in higher weight, barycenter departure, poor maneuverability, and stress due to repeating icing and evaporating. It also lead corrosion and other failures. Sealing with sealants or in situ foaming is simple and effective engineer measure. This article investigates water seepage prevention method, chooses and compares different sealants, as well as surface treatment, structures to improve adhesion performance, heat resistance, environment suitability, ageing resistance.

Abstract: A sol-gel process was used to prepare polyimide-silica hybrid films from the polyimide precursors and TEOS in N,N- dimethyl acetamide, then the hybrid film was treated with hydrofluoric acid to remove the dispersed silica particles, leaving pores with diameters between 80nm to 1µm, depending on the size of silica particles. The structure and dielectric constant of the hybrid and porous films were characterized by FTIR,SEM. The porous films displayed relatively low dielectric constant compared to the hybrid polyimide-silica films.

Abstract: The geopolymer has been prepared from fly ash, metakaolin and Quartz sand, by using the liquid sodium silicate as structural template and sodium hydroxide solution as activator. The effect of glass fiber on the properties of the geopolymer has been studied.