Volume 31, Issue 2 -

Presented is a new method for making composition graded metal-ceramic composites using reactive interdiffusion between a metal and a complex ceramic. Composition variation in both metal and ceramic phases with distance along the direction of diffusion is achieved. The design criteria for developing such composites are discussed. The system should exhibit extensive solid solubility in both metallic and ceramic phases, a defined gradation in the stabilities of the oxides, and mobility of electrons or holes in the oxide solid solution. The complex ceramic used for making the composite should be polycrystalline with sufficient porosity to accommodate the volume expansion caused by alloy precipitation. An inert atmosphere to prevent oxidation and high processing temperature to facilitate diffusive transport are required. The process is illustrated using the reaction couples Fe-NiTiO 3 , Fe-(Mg,Co)TiO 3 and Fe-(Ni,Co)TiO 3 .

Streak defects are often present on anodized extrusions of 6xxx series aluminum alloys, increasing the fabrication cost of these products. Moreover, streaking often only becomes visible after etching and anodizing treatments, rather than in the as-extruded condition, making it difficult to identify the original causes and influencing factors of these defects. In this paper, various process variables that influence the formation of streak defects on anodized aluminium extrusions are reviewed on the basis of a literature review, industrial practice and experimental results. The influencing factors involved in various processing steps such as billet quality, extrusion process, die design and etching process are considered. Effective measures for preventing the formation of streak defects in industrial extrusion products are discussed.

The general standard reheat treatment condition to refurbishment long-term serviced turbine blades, which are made of cast nickel based superalloy, GTD-111, is usually following by solution treatment at 1438 K, 1458 K and 1478 K for 10.8 to 14.4 ks, combination with primary aging at 1328 K for 3.6 ks, and secondary aging at 1118 K for 86.4 ks. However, in practical reheat treatment process, the change of temperature during any heat treating could occur accidentally any time. To simulate this effect, the droppings of temperatures during solution treatment were chosen and carried out to temperature level of 1118 K then heating again to the solution temperature levels. The temperature droppings (according to various programs) were performed during solution treatment. From the results, it was found that effect of temperature dropping during solution treatment greatly influenced the final rejuvenated microstructures.

The single crystal nickel-based superalloys with different dendrite spacings were prepared by using various withdrawing rates, and the influence of withdrawing rates on elements segregation and creep properties of them is investigated through creep property measurements and microstructure observation. Results show that relatively bigger withdrawing rate leads to the smaller dendrite spacing and lower segregation extent of elements between the dendrite/interdendrite regions, which further causes the better creep resistance of the alloy. Dislocations climbing over the rafted γ ′ phase is deemed as the deformation mechanism of the superalloys during steady state creep. In the later stage of creep, significant amount of dislocations shear into the rafted γ ′ phase, which may promote the alternative slipping of dislocations to twist the rafted γ ′ phase. At the further latter stage of creep, the initiation and propagation of the cracks occuring up to creep fracture is the fracture mechanism of the superalloy.

Flower like cadmium sulfide/organic (CdS-or) nanostructures were synthesized via a simple reaction between CdCl 2 · 2H 2 O and thioglycolic acid using water solvent at room temperature, then CdS-or nanostructures were added to Acrylonitrile-Butadiene-Styrene (ABS) copolymer. The influence of inorganic phase on the thermal properties of ABS matrix was studied using thermogravimetry analysis and limiting oxygen index (LOI). Nanostructures and nanocomposite materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Fourier transform infrared (FT-IR) spectra. Cone calorimeter measurements showed that the heat release rate (HRR) significantly decreased in the presence of CdS-or nanostructures.

The utilization of microwave radiation as the energy source for the carbothermal reductive upgrading of a bauxite ore was investigated. The bauxite ore was mechanically mixed with carbon and reacted in a quartz crucible in a multimode cavity. The iron oxide in the bauxite ore was reduced to magnetite and/or iron and the magnetic fraction was separated using a Davis Tube Tester. Three experimental arrangements were utilized: (i) microwaving of the mixture, (ii) microwaving of the mixture plus charcoal layers under ambient conditions and (iii) microwaving of the mixture plus charcoal layers in argon. The utilization of the charcoal layers resulted in more uniform heating of the sample. The effects of irradiation time, sample mass and incident power on the mass of the magnetic fraction were determined. Both the iron and the aluminum contents of the magnetic fraction were measured and using these values, the iron removal from the bauxite ore and the alumina recovery in the non-magnetic fraction were calculated. It was shown that under mildly reducing conditions, almost half of the iron could be removed as magnetite. However, the formation of hercynite limited the iron separation as magnetite and higher iron removals could only be achieved through the formation of metallic iron under more highly reducing conditions.

In this investigation, AISI 1020 low carbon steel has been selected as the base material. The Ni based super alloy powder NiCrBSiFeC was sprayed on the base material using high velocity oxy-fuel spraying (HVOF) technique. The thickness of the coating was approximately 0.5 mm (500 μm). The coating was characterized using optical microscopy, Vickers microhardness testing, X-ray diffraction technique and scanning electron microscopy. Dry sliding wear tests were carried out at 3 m / s sliding speed under the load of 10 N for 1000 m sliding distance at various temperatures i.e., 35 ° C, 250 ° C and 350 ° C. The corrosion test was carried out in 1 M copper chloride in acetic acid solution. The polarization studies were also conducted for both base material and coating. The improvement in microhardness from 1.72 GPa (175 HV 0.05 ) to 10.54 GPa (1075 HV 0.05 ) was observed. The coatings exhibited 3–6 times improved wear resistance as compared with base material. Also, the corrosion rate was reduced by 3.5 times due to the presence of coatings.

CdS Semiconductor nanostructures were synthesized by using two different methods. Using triphenylphosphine (C 18 H 15 P) and oleylamine (C 18 H 37 N) as surfactant, CdS semiconductor nanocrystals with a size ranging from 30 to 90 nm can be synthesized by thermal decomposition of precursor [bis(thiosemicarbazide)cadmium(II)]. CdS nanoflowers were synthesized via hydrothermal decomposition of [bis(thiosemicarbazide) cadmium(II)] without any surfactant. X-ray diffraction (XRD) patterns confirm that the resulting samples were a pure hexagonal phase of CdS. The optical property test indicates that the absorption peak of the samples shifts towards short wavelength, and the blue shift phenomenon might be ascribed to the quantum effect.

Novel composite coatings consist of Al 2 O 3 micro-layers alternating with Au nano-layers have been prepared on TiAl-based alloy by magnetron sputtering. The results of high-temperature cyclic oxidation test at 900 °C for 200 h revealed that the multi-sealed α -Al 2 O 3 and Au layers effectively suppress the inward diffusion of oxygen to a low level. The formed oxide scales and composite coatings are compact and free of cracks. The thermal stress is decreased owing to the increase of thermal-expansion coefficient. And the surface scratch test exhibited that the brittle/ductile laminated structure can remarkably enhance the strength and toughness in combination with improved damage resistance of the Al 2 O 3 -Au laminated composite coatings. Consequently, the oxidation and spallation resistance of TiAl-based alloy have been improved significantly.

The paper deals with the determination of strength of laminar ceramics by mechanical tests in bending and contact modes. The bending and contact modes are simulated by the four-point bending test, and by single-cycle contact test using rollers or spheres, respectively. In general, the determination of strength of ceramic materials results from statistical methods which are usually represented by the Weibull analysis. The Weibull analysis comprises the determination of the characteristic strength σ 0 and Weibull modulus m . The characteristic strength σ 0,bend and σ 0,cont as well as the Weibull moduli m bend and m cont , which are related to the four-point bending test and the single-cycle contact test using rollers, are thus determined, respectively. The comparison of numerical results of σ 0,bend /σ 0,cont , m bend /m cont confirms the validity of the Fett's theory. Along with this verification, a microstructural analysis of strength-degrading defects which represent fraction origins is performed for both modes. The determination of the mechanical loading which causes material failure along with an analysis of parameters of cracks are also presented. The contact test using the spheres is also performed at a multi-cycle mode. The mechanical tests were applied to Al 2 O 3 -ZTA laminar ceramics ( ZTA=60% Al 2 O 3 + 40% ZrO 2 ).

The oxidation of six Cu- x Ni alloys ( x = 0.2 , 0.6, 1, 2, 3, 4 at.%) was studied at 800 °C under 1 atm O 2 . All of the binary Cu-Ni alloys underwent an internal oxidation of Ni in the presence of an external scale of Cu 2 O and CuO, in agreement with the theoretical expectations for a finite range of Ni contents. However, the behavior of internal oxidation deviates significantly from the classical behavior of internal oxidation described by Wagner, in particular for the absence of a well-defined front of internal oxidation.

The thermal stability, crystal structures, microstructure, surface chemical functional groups and molecular structures of titania slag were characterized using TG/DSC, XRD, SEM, FT-IR and Raman spectroscopy techniques, respectively. Occurrence of two phase transformation of titania slag was identified at temperatures of 851 K and 1123 K. The weight gain of samples was observed to increase with increase in the temperature. The SEM results indicated the surface morphology of the primary particles to be tighter and smoother. Raman spectrum indicated existence of vibration band of anatase TiO 2 , Ti 2 O 3 , Ti 3 O 5 in titania slag.